1953 frank zaic year book

7/16/2019 1953 Frank Zaic Year Book

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1953

M O D E L A E R O N A U T I C

Y E A R B O O K

Edited by

Frank Za ic

MODEL AERONAUTIC PUBLICATIONS

New York



F O R E W O R D

This edition is more or less devoted to the "gathering of

the clan." It is intended to show that there are still many of

us all over the world who like the old fashioned "Model

Aeronautics"—to start from scratch and to create some

thing that has never been seen before.

In a sense, we are in a peculiar position. Our models are

not toys, nor are they full size aircraft. Yet, they give us

enough trouble to make us think that they are a worthwhile

effort for other keen minds. And with the overall model air

plane activities being classified on toy or juvenile level, it is

a problem how to attract new members to our circle.

Ii is hoped that this book will give an "adult" sense of

feeling for the hobby to the readers who may see this book

for the first time; and make them realize that "Model Aero

nautics" can be a lifelong hobby that will bring many new

adventures to that which otherwise be a "normal" life.

The make-up of this book goes back to the former Year

Books in which the contributions played a major part. The

basic idea is to provide an outlet for individual effort in

stabilizing the science of model aeronautics; and also to

assure the contributor that his material will be read by his

"peers", who may have similar interests and troubles, and can really sympathize with him.

F R A N K Z A I C .

May, 1953

I t h a c a , N . Y .

C o p y r i g h t , 1 95 3 P r i n t e d i n U . S . A .

M O D E L A E R O N A U T I C S P U B L I C A T I O N S

B o x 3 3 3 , S t a . D , N e w Y o r k 3 , N . Y .



1953 YEARBOOK

I n t h e 1 95 1 -5 2 Y e a r B o o k w e p r e s e n t e d o u r v e r s i o n o f M o d e l A e r o

d y n a m i c s . T h e b a s i c p u r p o s e w a s t o s h o w w h a t w e k n e w o r t h o u g h t w e

k n e w a b o u t t h e s u b j e c t . B y d o i n g s o w e h o p e d t h a t w e w o u l d b e c o r r e c t e d ,

o r a d d i t i o n s w o u l d b e m a d e t o w h a t w e h a d . W e a r e h a p p y t o s a y t h a t t h e

r e a d e r s c o o p e r a t e d a n d m a d e t h e i d e a w o r k . W e c a n n o w g o a h e a d a n d t e l l

y o u m o r e a b o u t t h i s s u b j e c t , k n o w i n g t h a t w e a r e o n t h e r i g h t t r a c k .

S i n c e w e a r e l i m i t e d w i t h s p a c e i n t h i s b o o k , w e w i l l o n l y p r e s e n t a

p o r t i o n o f t h e s u b j e c t i n d e t a i l . H o w e v e r , b y c o m b i n i n g t h e c o r r e c t i o n s a n ds u g g e s t i o n s s h o w n i n t h i s b o o k w i t h t h e t e x t i n t h e 1 9 5 1 - 5 2 Y e a r B o o k , t h e

r e a d e r w i l l b e a b l e t o f i n d r e a s o n a b l e a n d t r u e a n s w e r s t o a l m o s t a n y q u e s

t i o n h e m a y h a v e o n m o d e l a e r o d y n a m i c s . I t i s , o f c o u r s e , n e c e s e s s a r y t h a t

h e k n o w s w h a t h e i s l o o k i n g f o r t o r e c o g n i z e t h e s i t u a t i o n w h e n h e s e e s i t.

L O NG ITUD INA L S TA B IL ITYA f t e r a l l t h e s e y e a r s o f s t u d y i n g t h e o r y a n d p r a c t i c e o f m o d e l a i r p l a n e s

w e h a v e c o m e t o t h e c o n c l u s i o n t h a t t h e L o n g i t u d i n a l S t a b i l i t y i s t h e m a j o r

e l e m e n t i n t h e m o d e l ' s m a k e - u p . B y k n o w i n g t h e f u n c t i o n o f L o n g i t u d i n a l

S t a b i l i t y a n d i t s l i m i t s , i t i s p o s s i b l e t o k e e p t h e m o d e l f r o m g e t t i n g i n t o

o t h e r t y p e o f i n s t a b i l i t y t r o u b l e s . A c t i o n s w h i c h w e m a y h a v e be e n b l a m i n go n S p i r a l S t a b i l i t y c o u l d a c t u a l l y b e l o n g i n t h e L o n g i t u d i n a l S t a b i l i t y f i e l d .

I f a m i s a d v e n t u r e h a p p e n s w h i l e a m o d e l i s c i r c l i n g , i t d o e s n o t m e a n i t

h a p p e n e d b e c a u s e o f S p i r a l I n s t a b i l i t y . I t c o u l d b e b e c a u s e L o n g i t u d i n a l

B a l a n c e w a s d i s t u r b e d .

A m o d e l i s L o n g i t u d i n a l l y S t a b l e i f i t r e t u r n s t o i t s b a s i c t r i m a f t e r i t

i s u p s e t . F o r e x a m p l e : I f y o u t r i m o r a d j u s t a m o d e l t o g l i d e a t 6 ° , i t w i l l

b e L o n g i t u d i n a l l y S t a b l e i f i t r e t u r n s t o 6 ° g l i d e a f t e r i t w a s u p s e t t o l o w e r

o r h i g h e r a n g l e s .

T R I M M I N G O R A D J U S T I N G M O D E L SM o s t o f t h e t h i n g s t h a t a n a e r o d y n a m a c i s t d o e s o n t h e d r a w i n g b o a r d

ar e d on e on t h e f l y i n g f i e l d b y t h e m od e l b u i l d e r . T h e f i r s t f l i gh t o f a f u l l

s i z e a i r c r a f t m u s t b e a l m o s t 1 0 0 % a s s u r e d . B u t i t i s n o t s o w i t h m o d e l s .

T h e b u i l d e r f i n d s a p a t c h o f t a l l g r a s s a n d s t a r t s t o m o v e t h e w i n g b a c k a n d

f o r t h , c h a n g e i n c i d e n c e a n g l e s o r o t h e r c h a n g e s w h i c h e v e n t u a l l y d e v e l o p

o r e v o l v e a m o d e l w h i c h h a s s l o w e s t p o s s i b l e g l i d e w i t h o u t s t a l l i n g .

W e k n o w t h i s p r o c e d u r e a s " A d j u s t i n g " f o r w h i c h a n o t h e r w o r d c o u l d

b e " T r i m m i n g " . T o d e s c r i b e w h a t t h e m o d e l b u i l d e r i s d o i n g , w h i l e h e i s

a d j u s t i n g t h e m o d e l , w o u l d t a k e a t h i c k b o o k i f w e w e r e t o t a k e i n t o c o n

s i d e r a t i o n a l l o f t h e p o s s i b l e c o m b i n a t i o n s h e b r i n g s a b o u t . Y o u w i l l r e a l i z e

t h i s a f t e r y o u f i n i s h r e a d i n g t h i s c h a p t e r .



W h i l e t h e m o d e l b u i l d e r i s a d j u s t i n g o r t r i m m i n g h i s m o d e l f o r t h e

s l o w e s t s a f e g l i d e , h e i s a c t u a l l y h u n t i n g f o r a c o m b i n a t i o n b e t w e e n l i f t

a n d d r a g o f t h e m o d e l t h a t w i l l g i v e h i m t h e m a x i m u m d u r a t i o n f o r m i n i

m u m o f d r a g . T h i s c o m b i n a t i o n c a n b e f o u n d b y c a l c u l a t i o n s ; u s i n g t h e

(Ca/GD) facto. B y u s i n g t h i s t e r m a t v a r i o u s an g l e s , i t i s p o s s i b l e t o find

a t w h a t a n g l e o f a t t a c k t h e m o d e l w i l l h a v e t h e d e s i r e d g l i d e . — H o w e v e r , a s

i t s h ou l d b e ob v i ou s t o a l l o f u s , w e d o n o t k n ow t h e d r ag or l i f t v a l u e s o f

o u r m o d e l s s o t h a t w e h a v e t o u s e t h e t r i a l a n d e r r o r s y s t e m o f t e s t g l i d e s .S t i l l , i t i s i m p o r t a n t t o k n o w w h a t g o e s o n d u r i n g t h e s e t e s t g l i d e s s o w e

w i l l k n o w w h a t s o r t o f a m o d e l w e h a v e , a n d t h e n f l y i t a c c o r d i n g l y .

M o s t o f u s a c q u i r e a f e e l b y w h i c h w e k n o w w h e n t h e m o d e l i s g i v i n g

u s t h e b e s t t i m e i n a g l i d e . W e a l s o k n ow t h a t i f w e s e t t h e m od e l s o t h a t

i t w i l l f l y a t l o w e r a n g l e s , i t m a y a c t u a l l y g o g r e a t e r d i s t a n c e b u t i t w i l l

c o m e d o w n f a s t e r . S o t h a t r e d u c i n g t h e d r a g b y r e d u c i n g t h e a n g l e s d o e s

n o t h e l p a s t h e l i f t v a l u e i s a l s o r e d u c e d . — O n o t h e r h a n d , i n c r e a s i n g t h e

a n g l e s t o i n c r e a s e t h e l i f t m a y a l s o c a u s e s o m u c h d r a g t h a t t h e m o d e l w i l l

s l o w d o w n t o o m u c h a n d m a k i n g i t i m p o s s i b l e f o r t h e w i n g t o d o a n y l i f t

i n g . — S o m e w h e r e b e t w e e n t h e s e t w o e x t r e m e s t h e b e s t " d u r a t i o n g l i d e "

s e t t i n g i s f o u n d . T h e s a d p a r t i s t h a t v e r y f e w o f u s h a v e a n y i d e a s w h a tv a l u e s t h i s " d u r a t i o n g l i d e a n g l e " a c t u a l l y h a s .

" D U R A T I O N G L I D E A N G L E "F r o m t h e f e w e x p e r i m e n t s th a t w e m a d e t o d e t e r m i n e t h e " d u r a t i o n

g l i d e a n g l e " w e f o u n d i t t o b e i n t h e n e i g h b o r h o o d o f 5 ° t o 6 ° f o r t h e m o d e l s

w e w e r e u s i n g . I t m a y b e p l u s o r m i n u s o n o t h e r m o d e l s . T h e e x a c t a n g l e

d e p e n d s o n t o o m a n y f a c t o r s t o m e n t i o n h e r e . — T h e m a i n t h i n g i s t o r e a l i z e

t h a t t h e r e i s s u c h a t h i n g a s a " d u r a t i o n g l i d e a n g l e " a n d t h a t i t o c c u r s

w h e n t h e m o d e l i s a d j u s t e d s o t h a t m i n i m u m o f d r a g i s u s e d f o r m a x i m u m

d u r a t i o n , a n d t h a t f o r a v e r a g e m o d e l d e s i g n i t i s f a i r l y s a f e t o a s s u m e t h a t

i t w i l l b e i n t h e n e i g h b or h o o d o f 5 ° .

I n t h e 1 9 5 1- 52 b o o k w e w e r e w r o n g i n s a y i n g t h a t t h i s " d u r a t i o n g l i d e

a n g l e " o c c u r s j u s t b e l o w t h e s t a l l o f t h e w i n g . T h e w i n g m a y a c t u a l l y b e

c a p a b l e o f p r o d u c i n g l i f t w i t h o u t s t a l l i n g b e y o n d 1 0 ° , i f w e p r o v i d e d

e n o u g h p o w e r t o o v e r c o m e t h e d r a g p r o d u c e d a t s u c h a n g l e s a t a g i v e n

s p e e d . W e w e r e m i s l e d i n m a k i n g t h e s t a t e m e n t b y t h e f a c t t h a t d u r i n g

t h e g l i d e t e s t s t h e m o d e l w o u l d s t a l l a s s o o n a s w e a d j u s t e d i t t o g o a b i t

s l o w e r t h a n t h e s p e e d a t w h i c h t h e b e s t " d u r a i o n " g l i d e " o c c u r e d . T h e a d

j u s t m e n t s w o u l d i n c r e a s e t h e d r a g w i t h o u t i n c r e a s i n g t h e l i f t i n s a m e r a t i o .

T h i s w o u l d s e t u p a c h a i n r e a c t i o n w h i c h u s u a l l y e n d s u p i n a " m u s h " . —

S o t h a t , w h e n a ll i s s a i d a n d d o n e , w e c a n n o t d e d u c e f r o m t h i s t y p e o f t e s t

t h a t t h e w i n g a c t u a l l y s t a l l s j u s t a b i t a b o v e t h e " d u r a t i o n g l i d e " a n g l e .

F o r o ur p u r p o s e o f c la r i fy i n g t h e L O N G I T U D I N A L S T A B I L I T Y w e

w i l l a s s u m e t h a t t h e b e s t " d u r a t i o n g l i d e " a n g l e o c c u r s w h e n t h e w i n g i s

g l i d i n g a t 6 ° a n g l e a t t a c k . W e c a n n o w g o a h e a d a n d p r e s e n t a f e w e x

a m p l e s w h i c h w il l c o v e r m o s t o f t h e d e s i g n s n o w b e i n g f l o w n .

E L E M E N T S IN L ON GIT U D IN A L S T A B IL IT YW h i l e w e a r e a d j u s t i n g a m o d e l f o r t h e b e s t " d u r a t i o n g l i d e " w e m a k e

a l l s o r t s o f a d j u s t m e n t s w i t h i n c i d e n c e a n g l e s a n d C . G . l o c a t i o n s . T h e f i n a l

o u t c o m e i s t h a t t h e w i n g g l i d e s a t 6 ° a n g l e o f a t t a c k , w h i l e t h e o t h e r e l e

m e n t s ; s t a b a r e a a n d a n g l e , t a i l m o m e n t a r m a n d C . G . p o s i t i o n a r e s o a r r a n g e d o r b a l a n c e d t o e n a b l e t h e w i n g t o m a i n t a i n t h i s p o s i t i o n , o r r e t u r n

t o i t , a f t e r i t i s u p s e t f r o m t h e o u t s i d e . I n o t h e r w o r d s , t h e m o d e l h a s L o n g i

t u d i n a l S t a b i l i t y b e c a u s e i t r e t u r n s t o t h e " t r i m " a n g l e a f t e r i t i s u p s e t .



I n p r a c t i c e t h e l o c a t i o n o f t h e C . G . c a n v a r y f r o m t h e L e a d i n g E d g e t o

s e v e r a l i n c h e s b e h i n d t h e t r a i l i n g e d g e . I t a l l d e p e n d s o n t h e a c t u a l d e s i g n .

A l t h o u g h w e w i l l a d m i t t h a t C . G . a t t h e L e a d i n g E d g e i s n o t c o m m o n , a

d e s i g n c o u l d b e m a d e t o g l i d e w i t h C . G . a t t h i s l o c a t i o n . ( U n d e r p o w e r ,

s p e e d c o n t r o l m o d e l s h a v e C . G . a t t h e l e a d i n g e d g e . ) T h e l o c a t i o n o f t h e

C . G . w i l l d e p e n d m a i n l y o n th e s t a b i l i z e r a r e a , i t s a n g l e s e t t i n g a n d d i s t a n c e

f r o m t h e C . G . T h i s c a n b e b e s t u n d e r s t o o d b y r e a l i z i n g t h a t C . G . i s a p i v o t

p o i n t f o r a l l t h e f o r c e s i n v o l v e d d u r i n g t h e f l i g h t . A n d , b a s i c a l l y , t h e L o n g i -t u n d i n a l S t a b i l i t y d e p e n d s o n th e b a l a n c e b e t w e e n t h e w i n g a n d t h e s t a b i l

i z e r a b o u t t h e C . G . p i v o t . A l s o , t h e b a s i c d i f f e r e n c e b e t w e e n m o d e l d e s i g n s

i s a l m o s t e n t i r e l y b a s e d o n t h e i r d i f f e r e n c e i n t h e C . G . l o c a t i o n s . — W i t h o u t

t e l l i n g u s n o t h i n g e l s e b u t t h e C . G . l o c a t i o n w e c o u l d g i v e y o u a f a i r a p

p r o x i m a t i o n a s t o h o w y o u r m o d e l b e h a v e s i n f l i g h t , o r h o w i t s h o u l d b e h a v e .

W e w o u l d a l s o li k e t o p o i n t o u t t h a t o n e r e a s o n w h y w e h a v e s o l i t t l e

d a t a o n m o d e l d e s i g n i s t h a t t h e f u l l s i z e a i r c r a f t d e s i g n e r s s t o p w i t h C . G .

a t 3 5 % o f t h e C h o r d , w h i l e w e j u s t b e g i n a t t h i s p o i n t . T o f u l l s i z e d e s i g n

e r s , t h e 3 5 % p o i n t i s o n v e r g e o f b e i n g u n s a f e . W h i l e w e h a v e t o g o o n i n t o

t h e r e g i o n w h e r e a c h a n g e o f a n g l e s b y t h i c k n e s s o f a h a i r c o u l d m e a n

d i s a s t e r . — W h y d o w e g o b e y o n d t h e 3 5 % p o i n t ? T h a t i s a v e r y i n t e r e s t i n g

q u e s t i o n . W e w i l l g i v e y o u t h e a n s w e r i n d u e t i m e , b u t y o u m a y n o t b e a b l e

t o c o m p r e h e n d i t a t f i r s t . S o , i f y o u d o n o t f i n d t h e a n s w e r a t f i r s t r e a d i n g ,

d o n o t b l a m e u s b u t l o o k i n t o t h e m i r r o r , a n d t r y a g a i n .

S P E C I F I C A T I O N S O F E X A M P L E M O D E L SIn the examples which will follow we will use a 200 sq. in. wing which

h a s a C l a r k Y a i r f o i l . T h e s i z e o f t h e S t a b i l i z e r w i l l v a r y a s w i l l t h e l o c a t i o n

o f t h e C . G . T h e d i s t a n c e b e t w e e n t h e t r a i l i n g e d g e o f t h e w i n g a n d t h e

l e a d i n g e d g e o f t h e s t a b i l i z e r w i l l b e s a m e f o r a l l , b u t t h e M o m e n t A r m s o f

t h e w i n g a n d s t a b w i l l v a r y w i t h t h e C . G . l o c a t i o n .

T h e f o r c e v a l u e s w e r e t a k e n f r o m t h e 1 9 5 1 -5 2 Y e a r B o o k , a n d a r e s h o w n

i n g r a p h f o r m w h i c h m a y m a k e i t e a s i e r t o v i s u a l i z e t h e s i t u a t i o n t h a n t a b l e

s t y l e a s i n t h e b ook . I f you h av e t h e 1951- 53 b ook , i t m i gh t b e w e l l t o c on

s u l t i t f or d e t a i l s .

T h e w i n g f o r c e v a l u e s w e r e f o u n d b y u s i n g w i n g a r e a , l i f t c o e f f ic i e n t

a t th e p a r t i c u l a r a n g l e o f a t t a c k , a n d d i s t a n c e b e t w e e n t h e w i n g ' s " C e n t e r

o f L i f t " a n d C . G . p o s i t i o n .

T h e f o r c e v a l u e s o f t h e s t a b i l i z e r a r e f o u n d i n a m o r e c o m p l e x m a n n e r ,

b e c a u s e th e s t a b i l i z e r w o r k s i n t h e r e g i o n o f w i n g ' s d o w n w a s h a n d t u r b u

l e n t a i r p r o d u c e d b y t h e f u s e l a g e . F o r e x a m p l e : L e t u s a s s u m e t h a t w e h a v ea m o d e l w h o s e w i n g ' s i n c i d e n c e i s 3 ° a n d t h e s t a b i l i z e r i s s e t a t 0 ° . W h e n

t h i s m o d e l i s a d j u s t e d fo r b e s t " d u r a t i o n g l i d e " t h e a n g l e o f a t t a c k o n t h e

w i n g i s 6 ° , b u t o n t h e s t a b i l i z e r i t i s - 1 ° . T h i s h a p p e n s b e c a u s e t h e " d o w n -

w a s h " b e h i n d t h e w i n g i s 4 ° w h i l e t h e w i n g i s f l y i n g a t 6 °. T h i s d o w n w a s h



a n g l e c h a n g e s a s t h e w i n g ' s a n g l e o f a t t a c k c h a n g e s . F o r e x a m p l e : I f t h e

m o d e l w a s s h i f t e d t o m a k e t h e w i n g f l y a t 0 ° , t h e d o w n w a s h a n g l e w o u l d

n o w b e 2°, a n d t h e a n g l e o f a t t a c k o n t h e s t a b i l i z e r w o u l d b e — 5 ° . Y o u

c a n n o w s e e t h a t w h i l e t h e w i n g ' s a n g l e o f a t t a c k m a y h a v e c h a n g e d 6 ° , t h e

a c t u a l a n g l e o f a t t a c k o n t h e s t a b i l i z e r o n l y c h a n g e d 4°. L u c k i l y , w e m a d e

t h e n e c e s s a r y c a l c u l a t i o n s s o t h a t y o u c a n g o a h e a d a n d e n j o y y o u r s e l f .

T o r e p e a t , t h e s t a b i l i z e r ' s f o r c e v a l u e s w e r e f o u n d b y u s i n g i t s a r e a

( m i n u s i t s l o s s i n e f f i c i e n c y ) , l i f t c o f f i e c i e n t c o r r e c t e d f o r " d o w n w a s h " a n d

t h e d i s t a n c e b e t w e e n t h e s t a b ' s " C e n t e r o f L i f t " a n d C . G . p o s i t i o n .

O n t h e g r a p h s w e s h o w e d t h e D o w n w a s h A n g l e s , t h e A n g l e s o f A t t a c k

o f t h e w i n g a n d t h e L i f t C o e f f i c i e n t s , a n d t h e A n g l e s o f A t t a c k o f t h e

s t a b i l i z e r a t p a r t i c u l a r w i n g ' s a n g l e o f a t t a c k . — T h e f o r c e v a l u e s o n t h e

g r a p h s a r e t o b e u s e d o n l y f o r c o m p a r i s o n . T o o b t a i n a c t u a l f o r c e s i n

o u n c e s , i t i s n e c e s s a r y t o u s e t h e c o m p l e t e L i f t F o r m u l a , w h i c h i n c l u d e s

a i r s p e e d a n d a i r d e n s i t y f a c t o r .

C . G . L O C A T I O N SI f t h e a r e a s o f t h e w i n g a n d t h e s t a b i l i z e r , a n d t h e d i s t a n c e b e t w e e n

t h e m a r e f i x e d , t h e l o c a t i o n o f t h e C . G . w i l l b e d e t e r m i n e d b y t h e a n g u l a r

s e t t i n g o f t h e t w o s u r f a c e s . W e c a n a l s o s a y t h a t i f t h e a r e a a n d a n g l e o f

t h e w i n g , a n d t h e C . G . l o c a t i o n a r e f i x e d , t h e a r e a o f t h e s t a b i l i z e r w i l l

d e p e n d o n i t s d i s t a n c e f r o m t h e C . G . a n d t h e . a n g l e a t w h i c h i t i s s e t . I n t h e

f o l l o w i n g e x a m p l e s w e w i l l v a r y t h e l o c a t i o n o f t h e C . G . , a n d m a k e c o r

r e c t i o n s w i t h t h e s t a b i l i z e r a r e a a n d a n g u l a r p l a c e m e n t t o b r i n g a b o u t

L o n g i t u d i n a l B a l a n c e w h i c h i s s u p p o s e d t o g i v e t h e m o d e l L o n g i t u d i n a l

S t a b i l i t y .

C . G . A T 3 5 % C H O R DI f w e f i x t h e C . G . a t 3 5 % , a n d t h e n m a k e a d j u s t m e n t s t o b r i n g a b o u t t h e

6 % a n g l e o f a t t a c k f o r t h e b e s t " d u r a t i o n g l i d e , " w e w i l l f i n d t h a t th e

s t a b i l i z e r m u s t h a v e n o f o r c e , u p o r d o w n i n t h i s s i t u a t i o n . T h i s c a n b e

e x p l a i n e d b y n o t i n g t h a t w h e n C l a r k Y i s a t 6 ° , i t s C e n t e r o f P r e s s u r e o r

L i f t i s a t t h e 3 5 % s p o t . T h i s m e a n s t h a t t h e w i n g ' s l i f t i s d i r e c t l y o v e r t h e

C . G . a n d t h a t i t h a s n o f o r c e a b o u t t h e C . G . T o k e e p i t a t t h i s s e t t i n g , t h e

s t a b i l i z e r m u s t a l s o n o t h a v e a n y f o r c e a b o u t t h e C . G . B u t t o t a k e c a r e o f

p o s s i b l e u p s e t s , s o m e s o r t o f a s t a b i l i z e r i s n e e d e d t o b r i n g t h e w i n g b a c k

t o t h e " t r i m m e d " 6 ° a n g l e o f a t t a c k .

F o r o u r e x a m p l e w e a s s u m e d a 5 0 s q . i n . s t a b i l i z e r w i t h a s t r e a m l i n e d

a i r f o i l . S o t h a t i t w i l l n o t d e v e l o p l i f t w h e n t h e w i n g i s a t 6 ° , w e s e t i t a t 0 °

w h i l e t h e w i n g h a s 2 ° i n c i d e n c e . T h a t 4° d o w n w a s h w i l l g i v e t h e s t a b 0 °

a n g l e o f a t t a c k w h i l e t h e w i n g h a s 6 ° . I n o u r c a l c u l a t i o n s w e a s s u m e d t h e

s t a b t o b e 7 0 % e f fi c i e n t . — T h e f o r c e g r a p h i s s h o w n , c a l c u l a t i o n s t a k e n f r o m

the 1951-52 book .

A s y o u c a n s e e , w h e n t h e w i n g i s a t 6 " , t h e s t a b i l i z e r h a s n o l o a d , u p o rd o w n . B u t i f t h e w i n g s h o u l d b e u p s e t t o 4°, t h e s t a b i l i z e r h a s a f o r c e v a l u e

o f 9 6 u n i t s d o w n w a r d w i t h w h i c h t o b r i n g t h e w i n g b a c k t o 6 ° . A n d i f t h e

w i n g i s f o r c e d t o 8 ° , th e s t a b h a s a n u p w a r d f o r c e o f 7 0 u n i t s t o b r i n g i t

b a c k h o m e .



WING ANGLE OF ATTACK

It should be evident that when the C.G. is located at 35% point, the

L o n g i t u d i n a l S t a b i l i t y i s e x c e p t i o n a l l y g o o d . A n d i t i s s o . J u s t a s l i g h t

upset cha ng e in the wing wi l l be pro m pt ly co rrected by the ev er wa tchfu l

stab with i ts abundance of correct ive force. Why don't we use th is C.G.

lo ca t io n o n o ur m o del s? Tha t i s a n in teres t ing ques t io n !

C . G . AT 5 0 % C H O R DWh e n we mov e the C.G. to cen ter or 50% of the C ho r d we find tha t we

have a see-saw balance system. On a 5" chord wing the wing has a moment

of .75" from i ts 35% Center of Li f t or Pressure locat ion. To balance th is

force we need a counter force from the stabi l izer . To be speci f ic , the s i tua

t ion i s graphed. Note that we now use a regular a irfo i l on the stab as we

need l i f t from i t when the wing i s a t 6° "durat ion g l ide."




W h i l e e x a m i n i n g t h e g r a p h y o u w i l l n o t e t h a t t h e w i n g n o w h a s a f o r c e

a b o u t t h e C . G . a t a l l a n g l e s o f a t t a c k , a n d t h a t t h e s t a b i l i z e r h a s i t l i k e w i s e .

— A l s o n o t e t h a t t h e r e i s on l y on e a n g l e o f a t t a c k s i t u a t i o n a t w h i c h t h e s e

t w o f or c e s ar e i n b a l an c e , an d t h a t i s a t 6 ° , w h i c h i s d e t e r m i n e d w h i l e w e

a d j u s t or t r i m t h e m o d e l . N o w , i f t h e m o d e l i s u p s e t t o b r i n g t h e w i n g t o 4 ° ,

t h e b a l an c e i s u p s e t . T h e w i n g h as 10 5 f o r c e u n i t s , an d t h e s t a b i l i z e r h as 6 7.

I t i s ob v i ou s t h a t t h e w i n g w i l l t e n d t o b r i n g t h e n os e u p h i gh e r w i t h i t s

e x t r a 3 8 u n i t s . I f t h e m o d e l i s u p s e t t o h i g h e r a n g l e s , s a y 8 ° , t h e s t a b i l i z e r

n ow h as gr e a t e r f or c e t h an t h e w i n g , an d i t w i l l b r i n g t h e t a i l u p u n t i l t h e

m o d e l i s a g a i n i n b a l a n c e a t 6 ° .

W e s t i l l s e e m t o h a v e a m p l e " s t a b i l i z i n g " f o r c e i n t h e 5 0 % C . G . d e s i g n .

B u t n o t e t h a t t h e v a l u e o f t h e " c o r r e c t i n g " f o r c e s h a s d e c r e a s e d by , r o u g h l y ,

3 0 u n i t s w h e n c o m p a r e d w i t h t h e 3 5 % C . G . d e s i g n . I n c i d e n t a l l y , t h i s 5 0 %

C . G . l o c a t i o n i s u s e d a n d r e c o m m e n d e d f o r t o w l i n e g l i d e r s . W h y d o n ' t -w e

u s e i t f o r o t h e r t y p e s ? T h a t i s a n i n t e r e s t i n g q u e s t i o n !

C . G . AT 7 0 % C H O R DM o v i n g t h e C . G . f u r t h e r b a c k t o t h e 7 0 % s p o t w e f i n d t h a t w e h a d t o

u s e C l ar k Y on s t ab an d i n c r e as e i t s ar e a t o 6 6 s q . i n . W e a l s o s e t t h e w i n g

a t 3 ° a n d s t a b a t 0 ° i n c i d e n c e s e t t i n g . T h e l a y o u t s e e m s t o b e c l o s e t o w h a t

w e a r e u s i n g o n s o m e p o w e r m o d e l s . A s s u m i n g t h a t w e a d j u s t e d t h e m o d e l

t o t h e 6 ° " d u r a t i o n g l i d e , " w e f i n d t h a t t h e b a l a n c e s i t u a t i o n i s a s s h o w n

o n t h e g r a p h .

I t i s i n t e r e s t i n g t o n o t e t h a t i f t h e m o d e l w a s u p s e t t o t h e 4 ° p o s i t i o n ,

t h e w i n g h as 58 f or c e u n i t s w i t h w h i c h t o b r i n g t h e m od e l b ac k t o t h e 6 °

" s t ab l e c on d i t i on . " I f t h e m od e l i s u p s e t t o 8 ° , t h e s t ab i l i z e r h as 2 5 u n i t s

w i t h w h i c h t o r e c o v e r t h e m o d e l . — A s y o u c a n s e e , t h e r e c o v e r y f o r c e v a l u e s

a r e g e t t i n g l e s s a n d l e s s a s w e m o v e t h e C . G . b a c k w a r d t o w a r d s t h e t r a i l i n g

e d g e . W h y d o n ' t w e s t o p h e r e ? N o w , t h a t i s a n i n t e r e s t i n g q u e s t i o n !

C . G . A T 1 0 0 % C H O R DH a v i n g t h e C . G . c l o s e t o 1 0 0 % o f t h e C h o r d s h o u l d m a k e m a n y o f u s

f e e l a t h o m e a s m o s t o f t h e h i g h p o w e r g a s m o d e l s a n d l o n g f u s e l a g e W a k e -

f i e l d s h a v e t h i s p a r t i c u l a r C . G . l o c a t i o n . — I n o u r e x a m p l e w e u s e t h e l a y o u tu s e d i n p r a c t i c e : W i n g a n d s t a b s e t 0 -0 a n d 4 5 % s t a b . S o t h a t w h a t w e s a y

n o w a b o u t t h i s a r r a n g e m e n t s h o u l d c h e c k w i t h p r a c t i c e , a n d w i t h v e n

g e a n c e .




S o , s a y t h a t t h e m o d e l i s u p s e t t o 4 ° ( a s s u m i n g t h a t w e w e n t t h r o u g h

t h e t r i a l a n d e r r o r m e t h o d o f f i n d i n g t h e 6 ° " d u r a t i o n g l i d e " a n g l e ) . T h e

w i n g o n l y h a s 5 f o r c e u n i t s w i t h w h i c h t o b r i n g t h e m o d e l b a c k t o 6 ° . A n d

a n u p s e t t o 8 ° g i v e s t h e s t a b i l i z e r 1 8 u n i t s f o r c o r r e c t i o n s . — R a t h e r s m a l l ,d o n ' t y o u t h i n k ?




To m a ke i t in ter es t ing we d id a b i t o f ca l cu la t i o ns a nd fo un d a p pr o x i

m a t e v a l ue s fo r the fo r ce un i t s u se d . T h e ca l cu la t io n s were m a d e wi th

a s su m p t i o n tha t the m o del we ig hs 8 o z . Ro ug h l y , o ne Fo rc e Un i t equa l s

.04 in. oz. So , in the 3 5 % C. G. ex am pl e, th e st ab il iz er ha s 96 un it s or 3.84

in. oz. force with which to bring the wing back to 6°; but on the 100% C.G.,

the wing only has 5 units or .2 in. oz. force to bring the model back to 6°.

Ro ug h ly , the co rrect iv e fo rce o n the 3 5 % C.G. m o de l i s 2 0 t im es g rea ter

tha n o n the 1 0 0 % C.G. Which o ne wo u ld y o u sa y ha s bet ter Lo ng i tud ina l

S t a b i l i t y ?

P O W E R F L Y I N G A N D C . G . L O C A T I O NRo ug h ca l cu l a t i o ns sho w tha t i f o ur ex a m pl e m o de l s wer e g l i d in g a t

about 12 .5 m.p .h . they would l i f t around 8 oz . , which i s a normal weight

for a 200 sq. in. model . By applying power so that the speed has been in

creased to about 18 m.p.h . the l i f t o f the models would be increased to 16

ozs . i f they are held in the "durat ion g l ide" angle o f a t tack of 6° .

Now, i f a model , which weighs 8 oz . , develops 16 ozs . o f l i f t , somethingwi l l happen. And that something i s a loop whose d iameter i s such that the

Centri fugal Force wi l l be equal to the excess l i f t . Don't ask us to go into

deta i l s . The main th ing to remember i s that i f the model develops more l i f t

tha n i ts we igh t , i t s te nde nc y wi l l be to loop . Th e loop i tse l f ma y ta ke a l l

so r t s o f sha pes a nd s i zes , l a rg e , sm a l l , ho r i zo nta l , v er t i ca l o r he l i ca l . The

model may never actual ly complete a loop but f ly in a curve path of some

s o r t .

To re duc e the l o o p in g t end enc i es under po wer , a l o g i ca l s t e p wo u ld be

to reduce the l i f t o f the model to lower va lues . For example: I f we could

re du ce the win g' s an gl e o f a t ta ck to 0° , whi le the mod el i s f l y ing at 18 m.p.h. ,

the new l i f t would be about 8 ozs . instead of 16 ozs . which occurs at 6° . Thene xt qu es t i on i s : Ho w can we ma ke the w i n g f l y a t 0° wh en the mode l i s

tr immed to f ly a t 6°?

On the 3 5 % C. G. gr ap h we can see that i f the wi ng i s br ou gh t to 0° , the

stabil izer wil l try to bring it back with a force of 250 units or 10 in. oz.

Al l that i s ne ed ed to ma ke the wi ng f ly a t 0° i s to pr od uc e a counte r-s tab

force of 250 uni ts . Downthrust or thrust above the C.G. could do i t . From

ex p er ie nce , th i s m a y m ea n a do w nth rus t o f 1 0 to 2 0 de g re es .

On the .100% C. G. gr ap h we note that i f th e w i n g is br ou gh t to 0°, the

wing has only 15 force units or .6 in. oz. which is trying to bring it back to

6 ° . I t i s o bv io us tha t pra ct i ca l ly no do wnthrust i s requ ired , a nd a ctua l ly

none i s used in pract ice .

T he 7 0 % lo ca t io n req u ir es so m e do w nt hr us t a s the fo rce wh ich i s t r y in g

to bring the wing back to 6° has 100 units or 4 in. /oz. As you may have had

ex p er i en ce in th i s ty pe , y o u kno w tha t so m e d o w nt hr us t i s neede d . No w

y o u kno w why . T he do wn thr ust i s s i m pl y br in g i ng the wi ng do wn to l o wer

an gl es so tha t i t wi l l not l i f t more than i s nee de d.

S U M M A R Y O N C . G . L O C A T I O N SWe no w kno w tha t the 3 5 % C.G . l o ca t io n wi l l g i v e m a x i m u m Lo ng i

tud i na l S ta b i l i t y wi t h sm a l l es t s ta b i l i zer . Bu t i t w i l l a l so requ ire ex ce pt io n

a l ly l a rg e do wnthrust to m a ke i t u sa b le fo r po wer f l y ing . Co nsequent ly , th i spo s i t i o n i s u sed a lm o st ex c lus iv e ly by g l iders such a s A/2 No rd ics . I t i s

espec ia l ly use fu l fo r th i s des ig n a s the ru les inc lude to ta l a rea s o f wing

a nd s ta b in the requ irem ent . So tha t sm a l l s ta b i l i zer wi l l m ea n la rg er wing

where the area wi l l do most good.—



We also now know that the 100% C.G. is also the most touchy in sense

that the layout has ve ry l i t t le p lu s or mi nu s sta bi l iy fact or s . Th i s ma ke s

a djus t ing v ery to uchy . But i t ha s the a dv a nta g e tha t no m a t ter ho w h ig h

the power may be, the 100% C.G. design can be easi ly made to cl imb without

lo o p ing o r t i g h t sp i ra l l ing cha ra cter i s t i c s .

The other two locat ions , 50% and 70%, are a good compromise: 50%

for g l iders , and 70% for power models which are not extra h igh powered

and which can use downthrust .



S o f a r w e h a v e a s s u m e d t h a t t h e f l i g h t o r g l i d e p a t h i s s t r a i g h t a h e a d .

I n t h i s t y p e o f f l i g h t i t i s e a s y t o i m a g i n e h o w t h e L o n g i t u d i n a l S t a b i l i t y

w o r k s . H o w e v e r , a s t r a i g h t p a t h i n m o d e l f l y i n g i s r a r e . C i r c l i n g o f s o m e

s o r t i s t h e r u l e . A n d s o w e r e a c h t h e " C i r c u l a r A i r f l o w " p a r t o f t h e m o d e l ' s

flight.

F r a n k l y , i f y o u r i d e a s a b o u t t h e L o n g i t u d i n a l S t a b i l i t y o r B a l a n c e a r e

v a g u e , i t w o u l d b e b e s t t o g o b a c k t o t h e b e g i n n i n g o f t h e b o o k a n d s t a r t

a l l o v e r a g a i n , a n d s t u d y t h e s u b j e c t u n t i l y o u k n o w w h a t w e a r e t r y i n g t o

s h o w . I t i s s i m p l y i m p o s s i b l e t o u n d e r s t a n d t h e p a r t t h a t " C i r c u l a r A i r f l o w "

p l a y s i n f l i g h t u n l e s s o n e h a s a c l e a r p i c t u r e o f L o n g i t u d i n a l S t a b i l i t y .

W h i l e a m o d e l i s c i r c l i n g , t h e a n g l e s o n t h e w i n g a n d t a i l c h a n g e s o t h a t

t h e i n i t i a l " t r i m " a n g l e i s n o l o n g e r i n p o w e r . W i t h o u t y o u d o i n g a t h i n g ,

t h e s t a b i l i z e r m a y a c q u i r e f e w d e g r e e s o f g r e a t e r a n g l e o f a t t a c k w h i l e t h e

m o d e l i s f l y i n g i n a c i r c u l a r p a t h . B y k n o w i n g j u s t w h a t h a p p e n s , i t i s p o s

s i b l e t o t a k e a d v a n t a g e o f t h i s s i t u a t i o n . B u t i f y o u a r e i n d a r k .

W e a r e a t l o s s h o w t o e x p l a i n t h e d e v e l o p m e n t o f t h e " C i r c u l a r A i r f l o w . "S o , s u p p o s e w e a s s u m e t h a t w e h a v e a o n e f o o t l o n g p i e c e o f i r o n r o d . T o

t h e r o d e n d s w e a t t a c h 1 0 f t . s t r i n g s . W e g r a s p t h e e n d o f t h e s t r i n g s t o

g e t h e r a n d b e g i n t o w h i r l t h e r o d a r o u n d i n a 2 0 f t . d i a m e t e r c i r c l e . D i a -

g r a m a t i c a l l y t h e s i t u a t i o n w i l l b e a s s h o w n . — T h e c e n t e r o f t h e r o d w i l l

f o l l o w t h e 2 0 d i a . c i r c l e , w h i l e t h e r o d e n d s w i l l e x t e n d b e y on d t h e 2 0 f t .

c i r c l e , a n d f o r m a l a r g e r d i a m e t e r c i r c l e .



The next step is to imagine two air molecules, one on the 20 ft . diameter

orbit and the other on the larger orbit . As the rod is swung around it is

easy to imagine that the center of the rod and the t ips just skim by the two

m o l e c u l e s . A n d n o t h i n g h a p p e n s .

Now, let us p lace a th ird molecule between the two circles . What hap

pens now? As the rod reaches the #3 molecule the point o f impact wi l l be

on the "upper" surface of the rod. As the rod cont inues around, the #3molecule wi l l aga in inpinge on the rod, but th is t ime on the " lower" surface.

Fo rg et t ing a bo ut the res tra in ing fo rces o f the two end s tr ing s , wh ich

way do you think that the rod would rotate if the two "impacts" were

powerful enough to make the rod pivot about the C.G.? To us i t looks l ike

c o u n t e r c l o c k w i s e .

By doing a b i t o f ca lculat ion we can a lso determine at what angle the

# 3 m o lecu le "a t ta cked" the ro d . To s im pl i fy the s i tua t io n l e t u s a ssum e

that the attack occurred at the t ip of the rod so that we wil l have an evenone foot value. Well , i t just so happens that one foot in a 20 ft . diameter

circle takes up 6° o f the c ircumference's 360° . This would reso lve into 3°

for each side of the rod.

To bri ng the prob le m clos er to home, let us su pp os e th at we ha d a wi ng

on each end of the rod, set at 0° to the rod and each other. It can also be

see n that , i f we forg et about the dow nwa sh fr om the fr ont wi ng an d C P .

loc at i ons , the two would be in ba lanc e. The n we beg in to whirl th is com

binat ion around so that the wings are vert ica l . A look from the top i s shown

on the d iagram.—Is i t asking too much to make you bel ieve that the front

wi ng no w ha s a 3° neg at iv e angl e of atta ck wh il e the re ar on e ha s a 3° po si

t i v e a ng le o f a t ta ck?

If we were to remove the strings from the ends of the rod and tie them

to the center or C.G. o f the rod, which way would the combinat ion rotate?

To us i t looks l ike counter c lockwise .



S o , b y a c t u a l l y m a k i n g n o p h y s i c a l c h a n g e s , e x c e p t t o m a k e t h e m o d e l

f l y f a s t e n o u g h t o g e n e r a t e e n o u g h l i f t t o c a u s e a 2 0 ft . l o o p , w e b r o u g h t

t h e an g l e o f a t t ac k f r om 6 ° t o 0 ° . W e n ow ge t i n t o e v e r w i d e n i n g ar e a o f

e x p l a n a t i o n a s t o w h a t h a p p e n s a s t h e a n g l e o f a t t a c k i s d e c r e a s e d , a n dw i t h i t , a d e c r e a s e o f l i f t w h i c h or i g i n a l l y s t ar t e d or c a u s e d t h e 2 0 f t . l oo p . -

W e l l , t h e o u t c o m e d e p e n d s o n t h e p o w e r , i f i t i s g r e a t e n o u g h t o m a k e t h e

w i n g d e v e l op 16 oz . a t 0 ° an g l e o f a t t ac k , t h e l oop w i l l b e b a l an c e d a t

20 ft . Dia. -

A c t u a l l y , t h i s i s n o p l a c e t o w o r r y a b o u t m i n u t a e . T h e b a s i c p u r p o s e f o r

a l l t h i s t a l k i s t o m ak e as m an y o f you s e e t h e ac t i on o f " C i r c u l ar A i r f l ow "

s o t h a t i t w i l l b e e as i e r t o u n d e r s t an d w h at goe s on . A t p r e s e n t w e ar e

t r y i n g t o s h o w h o w th e c u r v e d f l ig h t p a t h c a n c h a n g e t h e " L o n g i t u d i n a l

B a l a n c e . " T h i s c o n d i t i o n c a n b e v e r y h a n d y i n p r o v i d i n g a n a u t o m a t i c s y s

t e m fo r c h a n g i n g t h e b a l a n c e f o r g l i d e a n d p o w e r . I f y o u g r a s p t h e b a s i c

i d e a y o u w i l l s i t b a c k a n d s a y , " W h a t d o y o u k n o w ? " A n d y o u w i l l a l s or e a l i z e t h a t m od e l s h av e b e e n f l y i n g d e s p i t e a l l w e d i d or d o t o k e e p t h e m

f r o m f l y i n g .

L e t u s n o w c h a n g e t h e w h i r l , f r o m h o r i z o n t a l t o v e r t i c a l , t o r e p r e s e n t

l o o p i n g . T h i s g i v e s u s a m o r e f a m i l i a r c o n d i t i o n i n w h i c h t h e L o n g i t u d i n a l

S t a b i l i t y p l a y s a p a r t . I n a s t r a i g h t f l i g h t o u r t a n d e m a r r a n g e m e n t m a y b e

i n a b a l an c e d c o n d i t i o n , b u t i n a l o op i t i s ob v i o u s l y n o l o n g e r i n b a l a n c e .

T h e a n g l e o f a t t a c k h a s d e c r e a s e d i n f r o n t a n d i n c r e a s e d i n t h e r e a r . T h e

a n g u l a r d i f f e r e n c e b e t w e e n t h e t w o w i n g s h a s i n c r e a s e d b y 6 ° . I f y o u f o l

l o w e d t h e l o g i c s o f a r , w e c a n m o v e t o p r a c t i c a l p r o b l e m s .

T h e C . G . l oc a t i on w h i c h w i l l s h ow t h e e f f e c t o f t h e " c i r c u l a r a i r f l o w "

m o s t c l e a r l y i s t h e 3 5 % . — H e r e t h e C . G . i s a t t h e w i n g ' s C P . s o t h a t w h a t

e v e r a n g u l a r c h a n g e s w i l l c o m e a b o u t d u e t o l o o p i n g w i l l b e s h o w n d i r e c t l y

on t h e s t ab i l i z e r . S a y t h a t t h e m od e l i s i n a 2 0 f t . d i a . l oop , an d t h a t t h e

d i s t a n c e f r o m t h e w i n g ' s C P . a n d s t a b i l i z e r ' s C P . i s o n e f o o t , a n d t h a t t h e

s t a b i l i z e r i s p l a c e d o u t s i d e o f t h e d o w n w a s h . I n a s t r a i g h t g l i d e t h e w i n g

w ou l d b e a t 6 ° an g l e o f a t t ac k an d s t ab a t 0 ° . B u t i f w e p l ac e t h i s l ay - ou t

in a 20 f t . d ia . loop, the 6° "angular change in one foot" wi l l ac t on the

s t a b i l i z e r s o t h a t i t w i l l b r i n g t h e w i n g t o 0 ° a n g l e o f a t t a c k .



T o f i n d o u t h o w m u c h o f p o s i t i v e a n g u l a r a i r f l o w i s n e e d e d t o b r i n g t h e

3 5 % C . G . d e s i g n f r o m 6 ° t o 0 ° w e p l a c e t h e w i n g a t 0 ° t o t h e b a s e l i n e , a n d

t h e s t a b i l i z e r a t — 2 . ° . T h e d o w n w a s h i s 2 ° w h i c h m a k e s t h e s t a b i l i z e r a c t

a t — 4 ° . N o r m a l l y , t h i s w o u l d s w i n g t h e n o s e u p w a r d b a c k t o 6 ° . B u t i f w e

p r o d u c e d 4 ° o f p o s i t i v e a n g u l a r a i r f l o w , t h e s t a b w o u l d b e a t 0 ° a t w h i c h i t

w i l l n o t p r o d u c e a n y u p o r d o w n f o r c e . . S o , t o b a l a n c e t h e 3 5 % C . G . d e s i g n ,w h i l e t h e w i n g i s a t 0 ° , w e n e e d a c u r v e d p a t h t h a t w i l l p r o d u c e 4 ° p o s i t i v e

a n g l e o n t h e s t a b .

T h e p r o b l e m , i n b r i n g i n g t h e w i n g f r o m 6 ° " d u r a t i o n g l i d e " t o 0 ° " p o w e r

f l i g h t " a n g l e w h e n t h e C . G . i s a t 7 0 % , i s a b i t m o r e c o m p l i c a t e d o r c o n f u s e d .

— I t i s o b v i o u s t h a t w h e n t h e w i n g i s a t 0 ° t h e t w o s u r f a c e s m u s t b e i n

b a l a n c e . T h e g r a p h s i m p l i f i e s t h e s i t u a t i o n . B y d r a w i n g a h o r i z o n t a l l i n e

f r o m t h e w i n g ' s 0 ° p o s i t i o n a c r o s s t h e s t a b c u r v e w e c a n s e e a t w h a t a n g l e

t h e s t a b w i l l p r o d u c e s a m e f o r c e a s th e w i n g . I t i s a b o u t — 3 . 4 ° . — T h e n e x t

s t e p i s t o b r i n g a b o u t " C i r c u l a r A i r f l o w " c o n d i t i o n w h i c h w i l l b r i n g t h e

s t a b t o — 3 . 4 ° . A f l i g h t c u r v e t h a t w i l l p r o d u c e a b o u t V/ 2° o f a n g u l a r c h a n g e

w i l l d o t h e t r i c k .

H o w d i d w e d e t e r m i n e t h i s a n g l e ? W e l l , p l a c e t h e w i n g a t 0 ° t o t h e b a s e

l i n e , a n d t h e s t a b i l i z e r a t — 3 ° . T h i s i s t h e p h y s i c a l s e t - u p . N o w p l a c e 2 °

d o w n w a s h i n t h e p i c t u r e . T h e s t a b i l i z e r i s n o w o p e r a t i n g a t — 5 ° a t w h i c h

i t s f o r c e v a l u e i s o n l y 4 2 u n i t s i n c o n t r a s t t o w i n g ' s 1 40 u n i t s . — T o m a k e

t h e s t a b i l i z e r d e v e l o p 1 4 0 u n i t s w e h a v e t o " i n c r e a s e " i t s a n g l e t o — . 3 . 4 ° .

T o d o t h i s w e n e e d a p o s i t i v e a n g u l a r a i r f l o w o f 1 . 6 °. A n d t h i s p o s i t i v e

a n g u l a r a i r f l o w o f 1 .6 ° c a n o n l y b e p r o d u c e d b y a c u r v e d f l i g h t . ( O r , i f y o u

l i k e , b y d e f l e c t e d p r o p w a s h . )

H e r e i s w h e r e f u n b e g i n s , b e c a u s e i t i s u n d e r t h i s a r r a n g e m e n t t h a t t h e

" C i r c u l a r A i r f l o w " b e c o m e s a m a t t e r o f d o l l a r s a n d c e n t s . A n d i t i s u n d e r

t h i s 1 0 0 % C . G . c o n d i t i o n t h a t t h e " C i r c u l a r A i r f l o w " t h e o r y w o r k s t o p e r

f e c t i o n . Y o u c a n s e e i t i n a c t i o n . S o — .

T o b r i n g t h e w i n g t o 0 ° a n g l e o f a t t a c k , w e s e e b y t h e g r a p h t h a t t h e

s t a b i l i z e r s h o u l d h a v e — 1 . 8 ° a n g l e o f a t t a c k . H o w m u c h o f a c u r v e d f l i g h tp a t h i s n e e d e d t o b r i n g a b o u t a b a l a n c e d c o n d i t i o n b e t w e e n t h e w i n g a n d

s t a b ? A g a i n , p l a c e t h e w i n g a t 0 ° a n d s t a b a t 0 ° a n d t h e n a d d t h e 2 ° d o w n -

w a s h . T h i s p l a c e s t h e s t a b a t — 2 ° w h i c h g i v e s i t 2 4 5 f o r c e u n i t s a g a i n s t

w i n g ' s 2 6 0 u n i t s . I f n o t h i n g i s d o n e , t h e w i n g w i l l t e n d t o b r i n g t h e m o d e l

C I R C U L A R A I R F L O W A N D 7 0 % C . G .

C I R C U L A R A I R F L O W A N D 1 0 0 % C . G .



b a c k t o 6 ° . B u t i f w e p r o d u c e a . 2 ° p o s i t i v e a n g u l a r a i r fl o w w e " i n c r e a s e "

t h e s t a b a n g l e f r o m — 2 ° t o — 1 . 8 ° a t w h i c h i t s f o r c e v a l u e e q u a l s w i n g ' s . —

S o , j u s t b y p l a c i n g t h e m o d e l i n a c u r v e p a t h t h a t p r o d u c e s . 2 ° o f p o s i t i v e

a n g l e , w e a r e a b l e t o b r i n g t h e 1 0 0 % m o d e l f r o m 6 ° t o 0 ° .

L O O P S D I A M E T E R S F O R B A L A N C E

B y u s i n g t h e f o r m u l a w h i c h g i v e s a n g u l a r c h a n g e d u e t o c i r c l i n g a n da s s u m i n g 1 . 5 f t . m o m e n t a r m s f o r o u r e x a m p l e s , w e f i n d t h a t t h e 4 ° n e e d e d

f o r t h e 3 5 % C . G . e x a m p l e w i l l b e d e v e l o p e d i n a 4 5 f t . d i a . l o o p . T h e 7 0 %

C . G . r e q u i r e s a 1 2 0 f t . d i a . l o o p . A n d t h e . 2 ° c h a n g e r e q u i r e d i n t h e 1 0 0 %

C . G . m o d e l i s p r o d u c e d i n a 9 0 0 f t . d i a . l o o p . I t s h o u l d b e o b v i o u s t h a t t h e s e

c u r v e s c a n b e o b t a i n e d b y h e l i c a l c l i m b . T h e l o o p s i m p l i f i e s t h e e x p l a n a t i o n .

S U M M A R YW e h a v e s h o w n t h a t t h e C . G . p o s i t i o n d e t e r m i n e s t h e v a l u e o f t h e L o n g i

t u d i n a l S t a b i l i t y , a n d a l s o d e t e r m i n e s t h e t y p e o f f l i g h t t h e m o d e l w i l l m a k e

u n d e r p o w e r . A l s o , w e a d j u s t t h e m o d e l s t o h a v e b e s t " d u r a t i o n g l i d e " a n g l e .

T h i s a n g l e i s i n t h e n e i g h b o r h o o d o f 5 ° . B u t w h i l e t h e m o d e l i s u n d e rp o w e r , t h e a n g l e o f a t t a c k o n t h e w i n g m u s t b e r e d u c e d s o t h a t t h e w i n g

w i l l n o t l i f t m o r e t h a n i s n e e d e d . T h i s c a n b e d o n e b y u s i n g d o w n t h r u s t ,

d e f l e c t e d p r o p w a s h o r l e t t i n g t h e " n a t u r a l " d e s i g n o f t h e m o d e l d e v e l o p

i t s o w n f l i g h t p a t h w h i c h i s a l m o s t i n v a r i a b l y o f c u r v e t y p e .

Some formulas in the 1951-52 YEAR BOOK were home-made.A request to L.Licher for check resulted in the followingcorrect ions:

N o w y o u c a n s e e w h y s u c h m o d e l s c a n c l i m b w i t h o u t l o o p i n g , s p i r a l l i n g

o r g e n e r a l l y c o r k s c r e w u p w a r d . J u s t a s l i g h t c u r v i n g p a t h i s n e e d e d t o k i l l

e x c e s s i v e l i f t . O f c o u r s e , t h e r e i s a p e n a l t y a t t a c h e d t o t h i s ; i t ' s " e t e r n a l

v i g i l a n c e " a s y o u c a n s e e i n t h e 1 9 5 1 - 5 2 B o o k .

PAGE 17

The an gl e 90 ° is in quest ion . It should be 57 .3 °



TILTED STAB FOR CIRCLING

F r a n k B e t h w a i t e b r o u g h t t o o u r a t t e n t i o n t h e l a c k o f i n f o r m a t i o n o n t h e

a c t i o n o f t h e t i l t e d s t a b i l i z e r . P l e a s e r e a d h i s l e t t e r b e f o r e g o i n g o n s o t h a t

y o u w i l l h a v e a n i d e a o f t h e p r o b l e m s i n v o l v e d .

T h e b a s i c p u r p o s e o f t h e t i l t e d s t a b i l i z e r i s t o p r o v i d e a t u r n i n g t e n d e n c y d u r i n g g l i d e w i t h o u t e f f e c t i n g t h e p o w e r s e t t i n g : A n a u t o m a t i c t u r n

a d j u s t e r t h a t w i l l v a r y i n o u r f a v o r w h e n s p e e d i s c h a n g e d .

A s w e h a v e s e e n , t o r e t a i n l o n g i t u d i n a l s t a b i l i t y a b o u t t h e C . G . , b o t h

s u r f a c e s m u s t h a v e s i m i l a r m o m e n t f o r c e s . I n a g l i d e t h i s m a y t a k e p l a c e

w h i l e t h e w i n g i s a t 6 ° a n g l e o f a t t a c k . T h e t u r n i n g f o r c e o f t h e t i l t e d

s t a b i l i z e r d e p e n d s o n t h e s i d e c o m p o n e n t o f i t s l i f t . O n a 3 5 % C . G . m o d e l ,

t h e s i d e c o m p o n e n t i s z e r o s i n c e t h e s t a b i l i z e r i s n o t r e q u i r e d t o c o n t r i b u t e

an y f o r c e w h i l e t h e w i n g i s a t 6 ° . B u t on t h e 10 0 % C . G . m o d e l , t h e l i f t o f

t h e s t a b i l i z e r i s c o n s i d e r a b l e s o t h a t t h e s i d e f o r c e w o u l d n a t u r a l l y b e p r o

p o r t i o n a l , d e p e n d i n g o n t h e t i l t a n g l e .

W h e n w e a p p l y p o w e r t o i n c r e a s e s p e e d b y , t h e l i f t d o u b l e s . I f t h e

m o d e l i s k e p t a t 6 ° t r i m , t h e s i d e f o r c e o f t h e t i l t e d s t a b w ou l d s t i l l b e z e r o

on t h e 35 % C . G . , b u t i t w o u l d b e d o u b l e d on t h e 10 0 % . ( I f t h e r u d d e r h a d a

t u r n s e t , i t s f o r c e w o u l d a l s o b e d o u b l e d . )

S i n c e e x c e s s i v e l if t t e n d s t o p r o d u c e l o o p i n g i n w h i c h t h e m o d e l t e n d s

t o r e d u c e i t s a n g l e o f a t t a c k , t h e r e i s a c h a n g e i n t h e t r i m o r b a l a n c i n g s i t u

a t i o n . — S e e g r a p h s . — T h e 3 5 % C . G . m o d e l n o w r e q u i r e s c o n s i d e r a b l e " u p

l o a d " o n t h e s t a b i l i z e r t o k e e p t h e w i n g , s a y , a t 0 ° . S o t h a t a n y t i l t i n g t h a t

w e m a y h a v e g i v e n t h e s t a b i l i z e r w i l l n o w b e v e r y s t r o n g i n c o n t r a s t , t o i t s

" n o f o r c e " i n t h e g l i d e . T h e s t a b i l i z e r o n t h e 1 0 0 % C . G . n e e d s a v e r y s l i g h t

e d g e o n t h e w i n g t o k e e p i t a t 0 ° . S o t h a t i t s a c t u a l f o r c e v a l u e m a y b e s a m e

as i t w as u n d e r 6 ° c on d i t i on . T h at i s , i f i t s n e w ov e r - a l l l i f t i s s i m i l ar t o

g l i d e v a l u e .

T h e a b o v e s i t u a t i o n s h o w s t h a t t h e v a l u e o f t h e t i l t e d s t a b i l i z e r d e p e n d s

o n t h e C . G . l o c a t i o n . R o u g h l y , i t c a n b e s a i d t h a t t h e " f o r c e " v a l u e v a r i e s

f r o m m a x i m u m w i t h C . G . a t 3 5 % t o w a r d s m i n i m u m a s t h e C . G . m o v e s b a c k

w a r d . A s f a r a s a c t u a l u s e f u l n e s s t o u s i s c o n c e r n e d , t h e v a l u e w i l l b e j u s t

t h e o p p o s i t e . W e c a n u s e i t b e s t w h e n t h e C . G . i s i n t h e 1 0 0 % n e i g h b o r

h o o d : W e c a n m a k e g l i d e t u r n a d j u s t m e n t s b y t i l t i n g t h e s t a b i l i z e r , k n o w

i n g t h a t t h e y w i l l n o t i n c r e a s e i n f o r c e d u r i n g p o w e r r u n . B u t w i t h C . G . a t

3 5 % , s t a b t i l t i n g i s l i k e r u d d e r s e t t i n g , i t w i l l v a r y w i t h s p e e d .

" P ow e r f l i gh t p a t t e r n i s a g o o d i n d i c a t or o f h o w m u c h t i l t t o u s e . A l o n gc u r v e d p a t h s h ow s t h a t ov e r a l l l i f t i s n o t e xc e s s i v e , s o t h a t yo u c an u s e a s

m u c h t i l t a s y o u m a y n e e d f o r a g l i d e t u r n . B u t i f t h e f l i g h t h a s t i g h t s p i r a l

c h a r a c t e r i s t i c s , u s e ti l t s p a r i n g l y , a n d i n c o m b i n a t i o n w i t h o t h e r a i d s , s u c h

a s s i d e t h r u s t .

C O N C L U S I O N O F T H E O R YT h i s i s a b o u t a l l w e c a n s a y i n t h i s b o o k . T h e 19 5 1 -5 2 Y e a r B o o k c a n

c a r r y y o u o n f r o m h e r e . W e w i l l s e e w h a t i s n e e d e d d u r i n g t h e c o m i n g

y e a r , a n d i n c l u d e i t i n t h e f u t u r e y e a r b o o k s — Y o u r c o m m e n t s a n d s u g g e s

t i o n s w i l l d e c i d e t h e t o p i c .



J O H N W O R T H — R A D I O C O N T R O L —Ex per ience ha s sho wn tha t success fu l r - c pra ct i ce d i f f ers f ro m the un

success fu l l a rg e ly in a cco rda nce wi th the a m o unt o f a t t en t io n pa id to de

ta i l s . The f iner po in t s o f m o de l des ig n , co ns truct io n a nd f ly ing , p lus ra d io

e q u i p m e n t a d j u s t m e n t a n d o p e r a t i o n , a r e u s u a l l y r e q u i r e d f o r s u c c e s s y e t

the deg re e of sk i l l involved i s ap pa re nt ly not so impo rt an t . I t has o f ten

been noted that some beginners start r ight o f f without trouble whi le o thers

can't seem to get away from it .

Go o d pra ct i ce do es no t requ ire sk i l l ed wo rkm a nsh ip but i t do es ca l l fo r

g o o d ha b i t s a nd fea tur es o f co ns tr uct io n . T he m o st bea ut i fu l ly - bu i l t m e ch

a n i sm ca n be fu l l o f bug s a nd po o r des ig n f ea tures wh i l e a co m pa ra t iv e ly

s lo ppy a f fa i r m a y perfo rm perfec t ly . The po in t , then , i s tha t there a re r ig h t

and wrong ways of do ing th ings and some educat ion may be in order to

ra i se the s ta nda rd o f perfo rm a nce .

Study of the s i tuat ion has conf irmed that there i s a need to publ ic ize

the deta i l s o f good pract ice as a guide to better resul ts . The fo l lowing in

fo rm a t io n ha s been s i f t ed f ro m d i scuss io n , o bserv a t io ns , a nd co rrespo ndence

to present a co ndensed cro ss - sec t io n o f tho ug hts co ncern ing co ntro l sy s temins ta l la t ion s , for i t i s in th is phase of the f ie l d tha t a t te nt io n ap pe ar s to be

m o st needed .

A free ly p iv o te d co ntro l su rf a ce i s v er y im po r ta nt to the perf o r m a n ce

o f a re l i a b le co ntro l sy s tem . Wha tev er the m etho d o f p iv o t ing used , the

surface should be free to f lop easi ly from one extreme to the other when

the a c tua to r l inka g e i s d i sco nnected . I t i s ev en prefera b le fo r the co ntro l

surfa ce in s ta l la t io n to be m o re s lo ppy tha n t ig h t , a l tho ug h the m o re s lo p

the greater i s the loss o f ef fect ive contro l .

Free m o v em ent o f the surfa ce sho u ld no t depend upo n lubr ica t io n fo r

sm o o th o pera t io n . In o ther wo rd s , a su rf a c e tha t do es no t m o v e f ree l y wi t h

o ut lubr ica t io n sho u ld be rewo rked unt i l i t do es . Ca ses ha v e been seenwhere a drop of o i l loosened up a contro l surface, but in the heat and dust

o f su m m e r f ly ing lo ss o f lubr ic a t io n re su l ted in the o r i g in a l b i nd in g co n

d i t io n . Lubr ica t ing a f ree ly p iv o ted surfa ce i s g o o d to he lp o u t the a c tua to r ,

but it should not be used as a cure.

Lu br ic a t io n ca n a l so be the ca use o f t ro ub l e i f do n e ca re l es s ly . A dr o p

of o i l on ex po se d ba ls a nex t to the p ivot ed sur fa ce ca n swe l l the wo od and

c a u s e i n t e r f e r e n c e w i t h m o v e m e n t — e x a c t l y t h e o p p o s i t e r e s u l t f r o m t h a t

in tended Lubr ica t io n do es ha v e a n im po rta nt purpo se o ther tha n tha t o f

reduc ing f r i c t io n a s i t he lps to prev ent co rro s io n a nd ev entua l s t i ck ing i f

music wire or steel f i t t ings are used in the contro l system.

Af ter be ing a ssured tha t the co ntro l surfa ce p iv o t s f ree ly wi tho ut the

l inage hooked up, care should be taken to see that the connect ion of the

l i nk a g e do es no t in tr o duc e b ind ing . I f the l i nk a g e m u st be sp ru ng o r

twisted to make the hookup, i t should be reworked unt i l th is i s not neces

sa ry . The l inka g e sho u ld co nnect na tura l ly wi th no fo rce be ing ex erted to

m a t e the co nne ct in g f i t t ing s . Af t er the co nn ect io n i s m a d e , the l i nka g e

should be moved from one extreme to the other severa l t imes to see whether

the tota l act ion i s fre e from bin din g .

Ma ny contr o l l ink age s whic h chec k out ok ay wi th the mod el in a hor i

zonta l posi t ion do not operate a t a l l when the model i s held vert ica l . This

i s a n im po r ta nt co ns ide ra t io n bec a use we need po s i t i v e co ntro l m o st whenthe m o del i s in th i s da ng ero us a t t i tude . Pa rt i cu la r ly wi th push-pu l l l ink

a g es a nd pu l s ing sy s tem s i s th i s im po rta nt . Th i s s im ple t es t ca n be v ery

rev ea l ing . Alo ng wi th th i s check o f the a c t io n in v a r io us a t t i tudes , a wea k



set o f batteries should be tr ied . I f the contro l system wi l l operate horizon

ta l ly with weak batteries and i t works as wel l in a dangerous att i tude the

chances are that the system wi l l be rel iable under a l l condit ions . A contro l

sy s tem tha t o pera tes wi th wea k ba t ter i es no m a t ter wha t the a t t i tude o f

the model i s what to s tr ive for .

A g o o d check o n co ntro l sy s tem respo nse sho u ld be m a de by ra p id ly

switching the actuator on and off . The contro l system should fo l low snap-

p i ly wi tho ut l a g o r sk ip . A s lug g i sh a c t io n wi l l sho w up im m edia te ly under

this test and i s usual ly caused by too much mass that must be moved or too

m uch fr i c t io n in the sy s tem .

Fo r esca pem ent sy s tem s , the s i ze o f the rubber requ ired to o pera te the

system may be a good guide to performance. A model up to s ix feet in span

sh oul d not re qui re mo r e than 1 /8" f la t rub ber for com ple te ly re l ia ble and

sna ppy co ntro l sy s tem a ct io n i f the sy s tem i s pro per ly des ig ned a nd bu i l t .

Inc ide nta l ly , a n esca pm e nt de s i g n which uses a ba l l -bea r ing ty p e wa s her to

reduce the fr ict ion caused by the loading of the wound rubber wi l l usual ly

o pera te bet ter to dr iv e l a rg e o r hea v y co ntro l sy s tem s . The sm a l l es t o f the

co m m erc ia l ly a v a i la b le esca pm ents ha v e been used to o pera te co ntro l sy s t em s in l a rg e sh ips such a s the Super-Bucca neer , bu t i t ta kes a t t en t io n to

the f iner points o f construct ion to do the job properly .

Th e rubber sho u ld a l s o unw ind unt i l i t ha ng s s la c k wi th ha rd ly a ny

twi s t l e f t . Th i s i s po s i t i v e pro o f tha t the co ntro l sy s tem requ ires l i t t l e

po wer fo r o pera t io n . Ma ny t im es co ntro l sy s tem tro ub le i s cured by us ing

heavi er rubbe r, up to 3 / 16 " or f la t , but th is us ual ly le ads to tr oub le s

later on. The problem is that the heavier rubber resul ts in the escapment

pawl taking more of a beat ing under the increased torque and pretty soon

bea ts i t se l f o u t o f a d jus tm ent . Al so , the increa sed to rque puts m o re pres

sure on the pawl in s ignal o f f posi t ion so that more actuator battery power

i s requ ired to pu l l in the esca pem ent a rm a ture . Th i s in turn resu l t s in the

need for fresh batteries for rel iable operat ion or more vo l tage. I f the bat

t er i es g e t wea ker , the o pera t io n beco m es erra t i c . I f to o m uch v o l ta g e i s

used in i t ia l ly , the current dra in goes up so that battery l i fe i s shortened.

Al l these th ings add up to eventual trouble that can be avoided completely

by m o re ca re in the beg inn ing .

In the des ig n o f co ntro l l inka g e , co ns idera t io n sho u ld be g iv en to the

mass to be moved. For instance, i f e i ther a torque rod or a push-pul l rod

can be used there is a lot in favor of the torque rod. The relative motion

involved in a torque rod insta l la t ion i s smal l s ince the rod pivots on an

a x i s a lo ng i t s l eng th . The push-pu l l ro d , ho wev er , m ust be sho v ed ba ck a nd

forth and th is may require as much power or more from the actuator than

is required to move the contro l surface i tse l f .

One of the common pract ices noted in contro l l inkages i s the use of

smal l d iameter music wire for push rods or torque rods. I f the wire i s being

pu sh ed or twis ted , i t s f lex i b i l i t y can res ul t in con sid er abl e lost mot ion tha t

never gets to the contro l surface. What i s needed i s a materia l with a

rea so na b ly l a rg e cro ss sec t io n but l i g h t in we ig ht .

W he r e -032" or .040" wi re mi gh t be us ed , i t ma y be bet ter to use 1/8´

sq . ba lsa with wire f i t t ings on the ends. The balsa i s suff ic ient ly s t i f f—if

se l ec ted f ro m g o o d c lo se g ra ined s to ck—so tha t i t res i s t s twi s t s a nd bend

ing yet i s l ight enough so that the power of the actuator i s not expendedin dr iv in g the cont ro l l i nk ag e. Fo r la rg e mo de ls , 3 /16 " sq . ba ls a , 1 /16" o .d .

a luminum tubing , or l /8" dowel may be used. Whatever i s used, the main

idea is to get al l the motion and power of the actuator to the control sur

face with as l i t t le loss as poss ib le in the connecing l inkage.



Where a s l id ing y o ke i s u sed o v er a n esca pem ent p in , b ind ing m a y o ccur

at some point in the yoke—usual ly a t the end of the loop—if the contact

edges of the yoke are not paral le l and free s l id ing a long the fu l l d istance of

pin travel . If music wire is used for the yoke and if the end of the loop is

so ldered the jo int must be a good one, preferably bound with l ight wire , as

a co ld so lder jo in t m a y brea k lo o se dur ing reg u la r po und ing o f e sca pem ent

o pera t io n a nd ca use the esca pem ent to ja m o r a t l ea s t resu l t in s lo ppy

operat ion due to the opened yoke.

Ca ses ha v e been no ted where the m o del f l i e s under perfec t co ntro l under

po wer but m isses s ig na l s in the g l ide . Th i s ca n be ca used by a sy s tem which

wo rk s oka y under the inf luence of engin e v i br at io n but not wi th ou t it . T h e

explanat ion i s that the v ibrat ion keeps the system loosened up so that parts

do not b in d, but in the comp ar at iv e smo ot hn es s o f the g l id e the f i t t ing s

se t t l e in to g um m y o r s t i cky a c t io n .



C L A U D E — M c C U L L O U G H — T H E A N V I L C H O R U S —O n e o f t h e m o s t i n t r i g u i n g a s p e c t s o f r a d i o c o n t r o l f l y i n g i s t h a t i t h a s

n o t y e t r e a c h e d t h e p o i n t w h e r e a l l t h e r u l e s h a v e b e e n l a i d d o w n a n d a

f o r m a l i z e d s t y l e o f d e s i g n d e v e l o p e d , a s h a s b e e n t h e c a s e w i t h f r e e f l i g h t

g a s a n d U - c o n t r o l s p e e d f o r e x a m p l e . W i t h s o m a n y a v e n u e s o f t h o u g h t

a v a i l a b l e f o r e x p l o r a t i o n , i t i s t o b e h o p e d t h a t s o m e t i m e w i l l e l a p s e b e f o r e

r - c f l y i n g w i l l b e i n an y d a n g e r o f g e t t i n g i n t o a r u t an d gr ow l e s s i n t e r

e s t i n g f r o m t o o m u c h " s a m e n e s s " .

M o s t o f t h e i d e a s r - c e r s b e g a n w i t h w e r e i n h e r i t e d f r o m f r e e f l i g h t , i n

d e e d e a r l y a t t e m p t s ( a n d m a n y s i n c e ) a t r e m o t e c o n t r o l w e r e f a r m o r e f r e e

f l i g h t t h a n r a d i o d i r e c t e d — t h e u s u a l c o u r s e b e i n g t o f i r s t t e s t, a d j u s t a n d

f l y t h e a i r p l a n e w i t h o u t a n y e q u i p m e n t a n d t h e n a d d i t a s a s o r t o f e x t r a

t h u m b t h a t p e r m i t t e d a c e r t a i n d e g r e e o f m a n e u v e r i n g . N o w t h a t a l i t t le

c o n f i d e n c e h a s b e e n d e v e l o p e d i n t h e r e l i a b i l i t y o f t h e r a d i o se t s , c o n s i d e r

a b l e s t r i d e s h a v e b e e n m a d e t o w a r d d e v e l o p i n g d e s i g n p r a c t i c e s t h a t c o n

s i d e r c o n t r o l t h e p r i m a r y r a t h e r t h a n s e c o n d a r y f a c t o r . W i t h e x c e s s i v e d i

h e d r a l p r o v e n t o h a v e b e e n a s a c r e d c o w a n d s o m e t h i n g b e s i d e d e e p u n d e r -

c a m b e r e d a i r f o i l s n o w f l y i n g , o n e w o n d e r s i f p e r h a p s m o r e o f t h e n o r m s o f

c u r r e n t f l y i n g t e c h n i q u e a r e n o t p r o f i t a b l y s u s c e p t i b l e t o a m e n d m e n t .

S e v e r a l c a s e s o f e s c a p e m e n t s k i p p i n g , w h i c h o c c u r r e d o n l y w i t h t h e

e n g i n e r u n n i n g — s o m e t i m e s o n l y a f t e r t h e m o d e l w a s l a u n c h e d — w e r e

t r a c e d t o v i b r a t i o n c a u s e d b y a g i v e n e n g i n e a n d p r o p c o m b i n a t i o n . C h a n g

i n g t h e p r o p t o a d i f f e r e n t m a k e , p i t c h o r d i a m e t e r p r o d u c e d d i f f e r e n t v i b r a

t i o n c h a r a c t e r i s t i c s w h i c h e l i mi n a t e d t h e s k i p p i n g .

S k i p p i n g ca n a l s o b e c a u s e d b y i m p r o p e r r e l a y a d j u s t m e n t o r m o u n t i n g .

S o m e r e l a y s a r e m o r e s e n s i t i v e t o v i b r a t i o n t h a n o t h e r s . T h e S i g m a 4 F o r

5 F r e l a y s a r e a l m o s t i m m u n e t o v i b r a t i o n w h e n c o r r e c t l y a d j u s t e d a n d u s u

a l l y m a y b e m o u n t e d s o l i d l y i n a m o d e l o r o n a s i m p l e r u b b e r p a d d i n g .

O t h e r s , s u c h a s t h e K u r m a n o r s i m i l a r t y p e s w i t h o u t a p i v o t e d a r m a t u r e o r

r u g g e d c o n t a c t s u p p o r t s m u s t b e s u s p e n d e d l o o s e l y f r o m r u b b e r b a n d s o r

o t h e r w i s e p r o v i d e d a d e q u a t e i s o l a t i o n f r o m v i b r a t i o n e f f e ct s .

T o d i f f e r e n t i a t e b e t w e e n s k i p p i n g c a u s e d b y r e l a y o r e n g i n e v i b r a t i o n ,

t h e r e l a y a r m a t u r e m a y b e h e l d b y h a n d i n t h e " o n " p o s i t i o n w h i l e t h e e n

g i n e s p e e d i s v a r i e d . I f t h e e s c a p e m e n t s k i p s , t h e t r o u b l e i s p r o b a b l y n o t

w i t h t h e r e l a y b u t w i t h t h e e n g i n e / p r o p s e t u p o r t h e e s c a p e m e n t a d j u s t

m e n t . U s u a l l y t h e c u r e r e q u i r e s o n l y t h e c h a n g i n g o f t h e t y p e p r o p u s e d .

I n t h o s e r a r e c a s e s w h e r e t h e s k i p p i n g o c c u r s o n l y a f t e r l a u n c h i n g o f t h em o d e l t h e t r o u b l e m a y b e a b i t m o r e d i f f i c u l t t o t r a c e b u t c h a n g i n g t h e p r o p

w i l l g e n e r a l l y s o l v e t h e p r o b l e m .

I f h o l d i n g t h e a r m a t u r e " o n" c u r e s t h e s k i p p i n g , t h e n i m p r o p e r r e l a y

m o u n t i n g o r a d j u s t m e n t i s p r o b a b l y t h e c a u s e . I n g e n e r a l , t h e b e s t r e l a y

a d j u s t m e n t i s a c o m p r o m i s e b e t w e e n t h e m o s t s p r i n g t e n s i o n p o s s i b l e a n d

t h e c l o s e s t c o n t a c t s p a c i n g w h i c h w i l l p r o v i d e p u l l - i n a t j u s t u n d e r t h e

n o r m a l m a x i m u m c u r r e n t a v a i l a b l e . I f r e l a y a c t i o n i s s n a p p y a n d p o s i t i v e

w h e n n o t u n d e r v i b r a t i o n t h e c h a n c e s a r e t h a t t h e a d j u s t m e n t i s o .k ., b u t

t h e m o u n t i n g m u s t b e m a d e l e s s st i f f s o a s t o b e t t e r a b s o r b t h e v i b r a t i o n .

T h e r e a r e n o c u t a n d d r y r u l e s o f g o o d p r a c t i c e — t h e s u b j e c t i s b r o a d

e n o u g h t o r e q u i r e a b o o k i n i t s e l f — b u t t h e i n f o r m a t i o n p r e s e n t e d o f f e r s ab a c k g r o u n d t o p r o v i d e a s t e e r i n t h e p r o p e r d i r e c t i o n . J u s t a s a c h a i n i s

o n l y a s s t r o n g a s i t s w e a k e s t l i n k , s o i s t h e p e r f o r m a n c e o f a n r - c m o d e l

d e p e n d e n t u p o n t h e a t t e n t i o n g i v e n t o t h e s m a l l e s t d e t a i l s . I f t h e e n d

r e s u l t i s a p r o d u c t o f a c c u m u l a t e d g o o d f e a t u r e s , t h e c h a n c e s a r e t h a t s u c

c e s s f u l r - c f l y i n g w i l l b e a c h i e v e d a n d m a i n t a i n e d .



After a season of f ly ing a ship that was somewhat h igher powered and

considerably heavier than the average R-C, i t i s my opinion that the de

v e lo pm ent o f the idea l ra d io sh ip—rug g ed , sm o o th f l y ing a nd wi th a l l -

wea ther perfo rm a nce—l ies in the d i rec t io n o f the a pp l i ca t io n o f wha t Dick

Schum a cher ha s ca l l ed "Brute Fo rce . ' . '

Th e "W iz a r d" in i t s o r ig i na l fo r m g a i ned a cer ta i n deg r ee o f fa m e (o rin fa m y ! ) a s the o n ly ra d io co ntro l l ed pa y lo a d sh ip a t the ' 5 2 Na t io na l s .

Rushed to f ina l co m ple t io n the week befo re the Na ts , the hurr i ed ins ta l la

t i o n o f the m a ny m ec ha n i sm s a nd ba t t er i es requ i red fo r a 3 -co ntro l a i r p la ne

played havoc with the C.G. posi t ion , gett ing i t so far back that severa l to ta l

fa i l ur e tes t f l i ght s pr ov ed with ou t dou bt that there wa s only one th in g to

d o — w e i g h t t h e n o s e .

S i nc e the sh ip had a sh or t no se th is re qu ir ed some doing , but than ks to

C. O. Wr ig ht —w ho be l i ev e s in co m i ng to a co ntes t equipped —a lead weight

weighing 1 lb. 11 ounces was turned up. It was my intention to cut off part

of i t to try , s ince the wh ol e amo un t se em ed to be an expe rim ent that cou ld

o n ly resu l t in a rea l ly sensa t io na l ba sh . But dec id ing tha t despera te s i tua t io ns ca l l fo r despera te m ea sures , the en t i re chunk wa s p la ced in the no se .

The plane was heavy to beg in with and now weighed in at 11% lbs .

on 7 sq. ft . of wing area—a wing loading of 27 ounces per sq. ft .

S i nc e the only fr ee on- the -a ir t ime ava i l abl e for te st ing wa s whe n the

reg u la r a f t erno o n Ca l i fo rn ia hurr i ca ne wa s b lo wing , the wo rs t wa s ex

pec ted . Bu t wi th the fe el in g tha t i t wo ul d be best to get i t over with , the

At wo o d .4 9 wa s cr a nk ed a n d wi t h J a c k Wi l l i a m s hea v ing , up the f l y ing

anvi l went to turn in about as successful and smooth a test f l ight as could

be a sked fo r , cu lm ina t ing in a perfec t l a nd ing o n the runwa y .

Whi l e such i l l - co ns idered inno v a t io ns a s a 5 -whee l l a nd ing g ea r , ba d lypla ce d, prov ed to be a goo d deal o f a ha nd ic ap in the compet i t ion , s t i l l the

a ir p la ne pe rf o r m ed v er y cr ed i ta b ly fo r i t s f i r s t 3 0 m inu tes o f f l y ing l i f e ,

part icularly in the wind, which had very l i t t le ef fect on i t .

After the Nats" , modif icat ions and further test and contest f l ights were

made and the ship has evolved to Mark II as shown in the three view.

Cha ng es inc luded a l eng thened a nd re - sha ped no se , two whee l l a nd ing g ea r

wi th ta i l whee l a nd increa sed rudder a rea . The lo ng er no se wa s m a in ly to

permit moving equipment forward so as to "get the lead out ." But much to

our sur pr is e the a i rp la ne pr ov ed to have bee n a mu ch smoother, a l l rou nd

sh ip at the hea vie st we ig ht tha n aft er l i ght en in g . So back in with a pay -

lo a d! Sm o o ther turns , no bo unc ing o n reco v ery a nd no wind co u ld beturned up that could keep i t from complet ing a quarter mi le cross country ,

at t imes when no other job could do it . A small , 4 oz. weight is placed in

the no se fo r espec ia l ly h ig h wind co nd i t io ns .

One th ing that was not iceable was that nei ther the c l imb or g l ide seemed

to be affected to any degree by increasing the weight . The g l ide in any case

wa s a lm o st to o g o o d fo r m a ki ng a ppr o a ch es to spo t l a nd in g s ; f l a t a nd f lo a t

ing , a lm o st unbe l i ev a b le co ns ider ing the wing lo a d ing . The co ntro l re

sponse was so good and the stabi l i ty seemed so ample, that one of the main

changes planned for the ship is to increase the power plant to a .65 to give

m o re reserv e ca pa c i ty fo r ta keo f f s a nd c l im bing to a l i tude , m a k ing use

of the motor control to keep it at the alt itude you want it . It is feltthat the ship wil l be able to f ly in any weather in which a contest can be

he ld . Th e pa y lo a d i s be ing m a d e use fu l by ins ta l l in g so m e hea vier ba t t er i e s

a nd a new m o re re l i a b le e l ev a to r m echa n i sm .



T o f u r t h e r t e s t t h e f l y i n g a n d m a n e u v e r i n g a b i l i t y o f h i g h w i n g a n d

p o w e r l o a d i n g s a l o n g w i t h s e v e r a l o t h e r f e a t u r e s , a n e w s h i p i s n o w

a ' b u i l d i n g . T h i s h a s h o p e f u l l y b e e n c h r i s t e n e d " A c r o b a t " a n d i s s h o w n i n

t h r e e - v i e w . I t i s a 3 - c o n t r o l 5 f o o t e r w i t h p r o p o r t i o n a l p u l s e r u d d e r , s e

q u e n c e e l e v a t o r a n d m o t o r s p e e d a n d s h u t o f f c o n t r o l . I t i s t h o u g h t t h a t t h i s

i s n o t o n l y a n o p t i m u m s i z e b u t a l s o t h e s m a l l e s t p r a c t i c a l o n e f o r t h i s

n u m b e r o f c o n t r o l s . T h e m a i n d e s i g n f e a t u r e s a r e l o w a s p e c t r a t i o ( 5 t o 1 )a n d a s h o r t m o m e n t a r m , s e l e c t e d w i t h a n e y e t o w a r d m a n e u v e r a b i l i t y

r a t h e r t h a n s t a b i l i t y , a n d t e n d i n g t o c o n f i rm E . L . R o c k w o o d ' s c o m m e n t

t h a t I w a s d r i f t i n g d e s i g n w i s e t o " U - c o n t r o l s t u n t j o b s . "

T h e s h i p h a s a n a m p l e r u d d e r , p a r t i c u l a r l y n e c e s s a r y o n s h o r t m o m e n t

a r m s h i p s b u t a l s o a n a i d i n a v o i d i n g " w a n d e r i t i s " o n a c r o s s - c o u n t r y , e v e r y

g u s t o f w i n d b r i n g i n g a n e w f l i g h t p a t h . U s i n g p r o p o r t i o n a l p u l s e , s u c h a n

a i r p l a n e c a n b e f l o w n i n a p e r f e c t l y s t r a i g h t l i n e c r o s s c o u n t r y i n a c r o s s

w i n d , s i m p l y b y s e t t i n g t h e s t i c k f o r t h e c o r r e c t c r a b b i n g a n g l e .

T h i s s m a l l , h i g h p o w e r e d , h e a v i l y l e a d e d s h i p w i l l b e f l o w n a g a i n s t t h e

l a r g e e t c . e t c . W i z a r d t o d e t e r m i n e w h i c h i s t h e m o s t s u c c e s s f u l s i z e f o r

c o n t e s t w o r k . I t i s p r o b a b l y a f o r e g o n e c o n c l u s i o n t h a t t h e s m a l l e r s h i p

c a n n o t b e q u i t e a s h e a v y i n w i n g l o a d i n g a s t h e l a r g e s h i p f o r e q u i v a l e n t

r e a c t i o n s , i f M r . R e y n o l d s a n d h i s n u m b e r b e r i g h t .

P l e a s e d o n ' t m i s u n d e r s t a n d m e o n t h i s w e i g h t q u e s t i o n . I a m n o t a d

v o c a t i n g t h a t e v e r y b o d y c a r r y a l e a d w e i g h t j u s t t o b e p a c k i n g it . B u t w h a t

I a m s a y i n g i s t h a t p e r h a p s t h e p o p u l a r t r e n d t o a l i g h t w i n g l o a d i n g , l o w

p o w e r a i r p l a n e i s n o t t h e b e s t w a y t o t h e i d e a l R - C d e s i g n . P a r t i c u l a r l y

l i g h t w e i g h t a t t h e e x p e n s e o f r a d i o r e l i a b i l i t y o r s t r u c t u r a l s t r e n g t h , j u s t

t o k e e p d o w n i m p a c t f o r c e s o r f l a t t e n t h e g l i d e .

I h i n k i t i s t h r o w i n g i n t h e t o w e l f o r m o d e l e r s t o d e c i d e t h a t s t r u c t u r e s

c a n n o t b e b u i l t o f b a l s a t o r e a l l y t a k e t h e p u n i s h m e n d e a l t o u t b y h e a v i e rw e i g h t a n d f a s t f l y i n g . S e n s i b l e w o o d s e l e c t i o n , g e n e r o u s s p a r d e p t h ( a n

r - c w i n g s h o u l d b e a b l e t o s u p p o r t t w i c e t h e w e i g h t o f t h e s h i p w h e n h e l d

b y t h e t i p s ! ) , l i b e r a l p l a n k i n g a n d f r e e f l i g h t k n o c k - o f f a t t a c h m e n t o f t h e

p a r t s p l u s a r r a n g e m e n t o f e q u i p m e n t t o a b s o r b s h o c k , c a n p r o d u c e a s h i p

t h a t w i l l t a k e a n y a v e r a g e " p r a n g " , w i t h o u t d a m a g e .

A t t h e D e s M o i n e s m e e t m y e l e c t r o n i c p u l s e r b e g a n k i c k i n g u p i t s h e e l s ,

s p i n n i n g m y s h i p i n f r o m a h i g h a l t i t u d e u n d e r p o w e r , n o t o n c e , b u t three

t i m e s . E a c h t i m e t h e o n l y r e p a i r s w e r e a n e w p r o p , s t r a i g h t e n i n g t h e 1 . g .

a n d r e p l a c i n g r u b b e r b a n d s . T h i s i s a p r e t t y d r a s t i c w a y o f t e s t i n g o u t a

s t r u c t u r e , b u t i t d o e s s h o w t h e b a l s a d e s e r v e s i t s r e p u t a t i o n f o r h a v i n g t h e

h i g h e s t s t r e n g t h t o w e i g h t r a t i o o f a n y w o o d .

T h e o b j e c t i o n m a y w e l l b e r a i s e d t h a t t h e l i g h t e r a i r p l a n e s h o u l d b e

m o r e m a n e u v e r a b i e . M y t h o u g h t i s t h a t a s f a r a s m a n e u v e r a b i l i t y i s c o n

c e r n e d , g i v e n p l e n t y o f p o w e r , 2 5 o u n c e l o a d i n g s d o n o t a p p e a r h e a v y

e n o u g h t o a d v e r s e l y a f f e c t m a n e u v e r i n g a n d d o s m o o t h o u t t h e m o r e s e d a t e

f l y i n g c o n s i d e r a b l y .

B u t r e g a r d l e s s o f t h e p r o a n d co n o f i t , t h e i n e v i t a b l e m a r c h o f p r o g r e s s

w i l l s o o n m a k e t h e l i g h t e r l o w - p o w e r e d s h i p s t h e t r a i n e r f o r t h e n o v i c e

a n d h e a v i e r h i g h e r p o w e r e d s h i p s a m u s t f o r c o n t e s t w o r k . F o r i t s e e m s

q u i t e e v i d e n t t h a t th e d a y o f a s c e n d a n c y o f t h e r u d d e r o n l y a i r p l a n e i s

c o m i n g t o a n e nd . A l e x S c h n e i d e r a n d th e S a n F r a n c i s c o M u s t a n g s a r e

f l y i n g p r o o f t h a t m u l t i p l e c o n t r o l w i l l n o w b e n e c e s s a r y .

P l a c i n g t h e e q u i p m e n t n e e d e d f o r t h i s t y p e o f o p e r a t i o n in a l i g h t a i r

p l a n e w i l l p r o d u c e r e s u l t s o f a m o s t p o s i t i v e n a t u r e . T h e f i r s t t i m e t h e s h i p

h i t s a n o b s t r u c t i o n , i t w i l l s t o p a n d t h e b a t t e r i e s a n d r a d i o w i l l k e e p r i g h t

o n g o i n g !



J . K . Q U E R M A N N — N O T E S O N V 2 A D E S I G N —S o m e i d e a o f h o w t h e d e s i g n c a m e t o b e m a y b e o f s o m e i n t e r e s t . T h e

l a y o u t i s b a s e d o n m y c o n c e p t s o f s t a b i l i t y a n d t h e a b i l i t y t o t r i m f o r b o t h

t h e h i g h p o w e r c l i m b a n d f o r a g l i d e . T h e s i z e , a i r f o i l a n d g e n e r a l s t r e a m

l i n i n g a r e , o f c o u r s e , a l l a i m e d a t h i g h p e r f o r m a n c e .

1 . F o r l o n g i t u d i n a l s t a b i l i t y a n d c o n t r o l a m o d e l s h o u l d h a v e t h ef o l l o w i n g : S t Jtt

a ) A l a r g e t a i l v o l u m e c o e f f i ci e n t , S i v c • T h i s p r o v i d e s p l e n t y o f

d a m p i n g ( Z a i c c i r c u l a r f l o w c o n c e p t ) a n d m a k e s a r e a r c e n t e r o f g r a v i t y

l o c a t i o n n e c e s s a r y . T h e d a m p i n g i n p i t c h m a k e s t h e e x a c t lo c a t i o n o f t h e

c e n t e r o f g r a v i t y l e s s c r i t i c a l , d a m p s o s c i l l a t i o n s , a n d g e n e r a l l y t a k e s u p

t h e s l a c k c a u s e d b y o t h e r e r r o r s . T h e r e a r c e n t e r o f g r a v i t y h e l p s t h e l a t e r a l

s t a b i l i t y i n d i r e c t l y . O n t h e d e b i t s i d e , t h e l a r g e t a i l c o s t s d r a g . T h e s m a l l

a m o u n t o f l i f t i t c a n p r o d u c e w h e n t h e c e n t e r o f g r a v i t y i s l o c a t e d f o r

p r o p e r s t a b i l i t y d o e s n ' t b e g i n t o p a y f o r t h e d r a g . I b e l i e v e t h e s t a b i l i t y i s

w o r t h t h e p r i c e .

b ) T h e c e n t e r o f g r a v i t y m u s t b e f a r a f t f o r e a s y a d j u s t m e n t o f p o w e r

o n a s w e l l a s p o w e r o ff f l i g h t , ( a g l i d e r c a n h a v e a f o r w a r d c e n t e r o f g r a v

i t y ) . T h e c e n t e r o f g r a v i t y s h o u l d b e s l i g h t l y a h e a d o f t h e a e r o d y n a m i c

c e n t e r d u r i n g t h e g l i d e a n d o n o r e v e n b e h i n d d u r i n g t h e c l i m b . D u r i n g a

s t e e p c l i m b t h e m o d e l i s m o r e o f a h e l i c o p t e r t h a n a c o n v e n t i o n a l a i r p l a n e .

F o r t h e h e l i c o p t e r t h e c e n t e r o f g r a v i t y s h o u l d b e b e l o w t h e a e r o d y n a m i c

c e n t e r o f t h e s i d e f o r c e s , i n t h i s c a s e l i f t .

c ) A n u n r e s t r i c t e d p r o p e l l e r s l i p s t r e a m w h i c h p a s s e s o v e r o r v e r y c l o s e

t o t h e h o r i z o n t a l t a i l . T h e e f f e c t o f t h e s l i p s t r e a m o n t h e t a i l i s t h e b i g i t e m

i n c h a n g i n g t h e t r i m f r o m p o w e r off t o p o w e r o n f l ig h t . D o w n t h r u s t c h a n g e s

t h e d i r e c t i o n o f t h e f l o w a t t h e t a i l a s w e l l a s a d d i n g s o m e d o w n l o a d a t t h e

n o s e . T h e m o m e n t c a u s e d b y t h e u p l o a d a t t h e t a i l a l o n g d i s t a n c e f r o m t h e

C . G . i s m o r e p o w e r f u l i n t r i m m i n g t o a l o w e r l i f t c o e f f i c i e n t , i . e . p r e v e n t i n g

l o o p s . A p y l o n w h i c h p u t s t h e w i n g a b o v e t h e p r o p e l l e r s e e m s a b o u t r i g h t .

H i g h e r p y l o n s p r o b a b l y d o n ' t h e l p m u c h .

d ) S o m e d o w n t h r u s t m e a s u r e d r e l a t i v e t o t h e n o r m a l f l i g h t p a t h i n t h e

g l i d e . N e c e s s a r y t o c h a n g e t h e t r i m .

A s a p a s s i n g n o t e i t m i g h t b e p o i n t e d o u t t h a t w h i l e t h e r e a r C . G . l o c a

t i o n i s n e e d e d , i t i s e a s y t o g e t i n t o r e a l t r o u b l e b y p u t t i n g t h e C . G . t o o f a r

b a c k . F o r t h e b e g i n n e r a g o o d w a y t o a v o i d o v e r s h o o t i n g i s t o p u t t h e C . G .

a l i t t l e f a r t h e r f o r w a r d t h a n t h e e x p e r t s . U s e a m o d e r a t e a m o u n t o f d o w n

t h r u s t a n d t h e n s t a r t f l i g h t t e s t s . T r i m f o r t h e g l i d e t h e n t r y p o w e r . I f t h em o d e l d i v e s u n d e r p o w e r o r s h o w s o n l y s l i g h t l o o p i n g t e n d e n c i e s a c h a n g e

i n t h r u s t a d j u s t m e n t i s i n o r d e r . H o w e v e r , i f i t s h o w s v i o l e n t l o o p i n g t e n

d e n c i e s m o v e t h e c e n t e r o f g r a v i t y b a c k a n d r e t r i m f o r t h e g l i d e ( b y c h a n g

i n g t h e t a i l i n c i d e n c e ) . A s t h e c e n t e r o f g r a v i t y i s m o v e d b a c k t h e l o o p i n g

t e n d e n c y s h o u l d d i s a p p e a r . I f y o u w a n t t o s e e h o w f a r o u t t h e w i n d o w y o u

c a n l e a n , t a k e o u t s o m e o f t h e i n t i a l d o w n t h r u s t a n d t r y a g a i n .

2 . F o r l a t e r a l s t a b i l i t y a n d t r i m :

a ) P l e n t y o f d i h e d r a l . D i h e d r a l i s l i k e m o n e y i n t h e b a n k . I t i s d i f f i cu l t

t o h a v e t o o m u c h a s f a r a s s t a b i l i t y i s c o n c e r n e d . T h e m o r e d i h e d r a l t h e l e s s

f u s s y y o u h a v e t o b e w i t h s o m e o f t h e o t h e r i t e m s . T h e r e i s a p r i c e . T h e

u s e f u l l i f t i n g w i n g a r e a d e c r e a s e s . N o t m u c h i s l o s t f o r m o d e r a t e a n g l e s t h o .

b ) A s m a l l v e r t i c a l t a i l . M y m o d e l h a s n o v e r t i c a l t a i l a s s u c h , b u t t h e

d r o o p e d o u t e r p a n e l s a c t a s a v e r t i c a l t a i l . T h e e f f e c t i v e a r e a i s t h e t o t a l

a r e a o f t h e p a n e l s t i m e s t h e s i n e s q u a r e d o f t h e d i h e d r a l a n g l e o r a b o u t %



o f th e p r o j e c t e d a r e a . T h e r e is a f a i r l y w i d e r a n g e o f s a t i s f a c t o r y ta i l s i z e s

f o r w i n g s w i t h p l e n t y o f d i h e d r a l , p a r t i c u l a r l y fo r t h e g l i d e . F o r t h e c l i m b

t h e t a i l m u s t b e s m a l l s o t h e c e n t e r o f g r a v i t y i s v e r y c l o s e t o or b e h i n d t h e

a e r o d y n a m i c c e n t e r o f t h e s i d e f o r c e s . T h e h e l i c o p t e r c o n c e p t m u s t b e k e p t

i n m i n d . A m od e l w h os e t a i l i s t oo s m al l w i l l d u t c h r o l l or i n e x t r e m e c as e s ,

s p i n — n o t a s p i r a l d r i v e , b u t a c l a s s i c a l s p i n w i t h t h e s u r f a c e s s t a l l e d . M y

m o d e l , e v e n w i t h t h e a p p a r e n t l a c k o f t a i l h a s n e v e r s h o w n a n y h i n t o f d u t c h r o l l .

c ) M o d e r a t e a s p e c t r a t i o . A l o w a s p e c t r a t i o i s g e n e r a l l y g o o d fo r s t a b i l

i t y , b u t b e g i n s t o c o s t i n t e r m s o f p e r f o r m a n c e . A m o d e r a t e a s p e c t r a t i o

a r o u n d 7 s e e m s a g o o d c o m p r o m i s e .

d ) P o s i t i v e d i h e d r a l a h e a d o f t h e c e n t e r o f g r a v i t y , n e g a t i v e d i h e d r a l

b e h i n d t h e c e n t e r o f g r a v i t y . T h i s p r o v i d e s a f a v o r a b l e r o l l i n g m o m e n t d u e

t o y a w i n g v e l o c i t y . ( S o r t o f a c i r c u l a r a i r f l o w i n y a w ) . I f t h e a n g l e o f y a w

i s t a k e n as z e r o a t t h e c e n t e r o f gr av i t y , t h e n t h e t u r n p r o d u c e s a s i d e f l ow

i n o n e d i r e c t i o n a h e a d o f t h e C . G . a n d i n t h e o p p o s i t e d i r e c t i o n b e h i n d i t .

W i t h t h e p o s i t i v e d i h e d r a l o f t h e w i n g a h e a d o f t h e C . G . , a n d t h e n e g a t i v e

o f t h e t a i l b e h i n d , t h e r o l l i n g m o m e n t c a u s e d b y t h e t u r n t e n d s t o c a u s e t h e

m od e l t o r o l l ou t o f t h e t u r n .

e ) O n t h i s p a r t i c u l a r m o d e l w i t h n o v e r t i c a l t a i l f o r t h e s l i p s t r e a m t o

a c t o n , s i d e t h r u s t i s n o t v e r y e f f e c t i v e . T h e s l i p s t r e a m t w i s t a c t i n g o n t h e

p y l o n t e n d s t o c a u s e a r i g h t t u r n . W i h a l o w v e r t i c a l t a i l t h e t w i s t a l s o

c a u s e s a r i g h t t u r n . T o a v o i d t h i s d i f f i c u lt y t h e t a i l d r o o p i s s t a r t e d b e y o n d

t h e n o r m a l s l i p s t r e a m . T h e m o d e l c l i m b s r i g h t , g l i d e s l e f t .

3 . T h e s i z e m a y b e o f s o m e i n t e r e s t s i n c e t h e m o d e l i s l a r g e r t h a n m o s t

y<l A m o d e l s . T h e i d e a i s s i m p l y t h i s : T h e m o d e l s h o u l d b e a s l a r g e a s p o s

s i b l e , y e t i t s h o u l d w e i g h n o m o r e t h a n t h e a b s o l u t e m i n i m u m . W i t h a f u l l

t a n k o f f u e l m y m o d e l b a r e l y t i p s 5 o z . F o r t h e c r a f t s m a n w h o c a n m a k et h e m l a r g e r a n d s t i l l s t r o n g e n o u g h I r e c o m m e n d l a r g e r w i n g s . T h e l o g i c

i s s i m p l e . T h e r a t e o f c l i m b d e p e n d s m o s t l y o n th e w e i g h t a n d e n g i n e

p o w e r . D r a g i s a s e c o n d a r y f a c t o r . S i n c e t h e r e i s l i t t l e t o l o s e i n c l i m b a n d

m u c h t o g a i n i n t h e g l i d e m a k e t h e m b i g , b u t l i g h t . T h e r e i s a p r i c e . F i r s t

t h e s t r u c t u r e i s w e a k e r . S e c o n d , i t i s m o r e d i f f i c ul t t o t r i m p r o p e r l y f o r b o t h

p o w e r o n a n d p o w e r of f f l i g h t . T h e r e a s o n i s t h a t t h e f o r c e s d u e t o t h e

e n g i n e a r e r e l a t i v e l y s m a l l e r c o m p a r e d t o t h o s e d u e t o t h e s u r f a c e s . I t

b e c o m e s m o r e n e c e s s a r y t o p l a c e t h e c e n t e r o f g r a v i t y p r o p e r l y t h a n i n t h e

s m a l l e r a i r p l a n e w i t h t h e s a m e e n g i n e .

4 . T h e a i r f o i l . T h e b l u n t t r a i l i n g e d g e m a y s t a r t l e y o u . T h e a i r f o i l i s

s i m i l a r t o a n N A C A 45 0 9 w i t h a t h i n n e d d o w n l e a d i n g e d g e a n d a t h i c k e n e d t r a i l i n g e d g e . T h e a i r f o i l w a s d e s i g n e d t o h a v e l o w d r a g a t a l i f t c o

e f f i c i e n t o f 0 . 8 . G l i d e t e s t s on o t h e r w i n gs s h ow e d t h i s t o b e t h e n or m al

g l i d i n g C L . T h e l o w e r s u r f a c e i s d e s i g n e d f o r a l a m i n a r b o u n d a r y l a y e r —

a t le a s t t h e p r e s s u r e g r a d i e n t i s f a v o r a b l e f o r o n e . T h e b l u n t t r a i l i n g e d g e

t e n d t o i n c r e a s e t h e m a x i m u m l i f t c o e f f i c i e n t a n d t a k e s i n t o a c c o u n t t h e

f a c t t h a t a t t h e lo w R e y n o l d s n u m b e r s t h e f l o w h a s p r o b a b l y s t a r t e d t o

s e p a r a t e s l i g h t l y a t t h e t r a i l i n g e d g e o n m o s t a i r f o i l s . T h u s t h e d r a g i s

p r o b a b l y s m a l l . T h e s m a l l s t r u c t u r a l m e m b e r a t t h e t r a i l i n g e d g e h e l p s k e e p

t h e w e i g h t d o w n .

5 . T h e l a n d i n g g e a r i s a l m o s t a n a f t e r t h o u g h t . I t i s s h o w n o n t h e

d r a w i n g a s i t i s . I t w o r k s , b u t I w o u l d r e c o m m e n d m o v i n g i t a b o u t 1 "f u r t h e r f o r w a r d .

6 . T h e e x h a u s t d e f l e ct o r o n t h e f a i r i n g b e h i n d t h e e n g i n e k e e p s m o s t

o f t h e g o o f r o m s p l a s h i n g o n t h e w i n g .



—(Mar. 1953)—S o r r y I h a v e n ' t b e e n a b l e t o w r i t e e a r l i e r . Y o u r l e t t e r g o t h e r e w h i l e I

w a s i n t h e m i d d l e o f a r u s h p r o j e c t a t C V A . S e e . i f t h e s e a n s w e r s s a t i s f y

y o u .

1 . P e r f o r m a n c e o f t h e m o d e l : I a m r e l u c t a n t t o m a k e s p e c i f i c p e r f o r m

a n c e c l a i m s w i t h o u t e x t e n s i v e t e s t s t o d e t e r m i n e a n a c c u r a t e f i g u r e . M o s t

p u b l i s h e d f i g u r e s s m e l l l i k e f i s h s t o r i e s a n y w a y . I c a n s a y t h a t i t w i l l o u t

g l i d e an y 1 / 2 A I h a v e e v e r s e e n a n d t h e c l i m b i s g oo d .2 . C e n t e r o f g r a v i t y a h e a d o f a e r o d y n a m i c c e n t e r : T h e d i s t a n c e b e t w e e n

t h e c e n t e r o f g r a v i t y a n d t h e a e r o d y n a m i c c e n t e r i s a m e a s u r e o f t h e s t a t i c

s t a b i l i t y o r t h e r e s t o r i n g f o r c e f o l l o w i n g a d i s t u r b a n c e f r o m a t r i m m e d



c o n d i t i o n . Y o u a r e p r o b a b l y u s e d t o t h i n k i n g i n t e r m s o f t h e c e n t e r o f

p r e s s u r e . W h e n a m o d e l i s f l y i n g a l o n g t r i m m e d , t h e r e i s n o p i t c h i n g m o

m e n t , h e n c e , t h e r e s u l t a n t f o r c e p a s s e s t h r u t h e c e n t e r o f g r a v i t y , i . e . t h e

c e n t e r o f p r e s s u r e l i e s a t t h e C . G . T h e A e r o d y n a m i c C e n t e r i s a s l i g h t l y

d i f f e r e n t a n i m a l . I f t h e t r i m m e d m o d e l i s d i s t u r b e d , f o r e x a m p l e b y a g u s t ,

t h e t o t a l l i f t w i l l b e c h a n g e d . T h e c e n t e r o f p r e s s u r e o f t h e a d d i t i o n a l l o a d

i s t h e a e r o d y n a m i c c e n t e r . K e e p i n m i n d t h a t i t h a s n o d i r e c t c o n n e c t i o n

w i t h t h e o v e r a l l c e n t e r o f p r e s s u r e l o c a t i o n e i t h e r b e f o r e o r a f t e r t h e d i s

t u r b a n c e ; o n l y t h e i n c r e m e n t a l l o a d . I f t h e c h a n g e i n l o a d p r o d u c e s a m o

m e n t t e n d i n g t o r o t a t e t h e m o d e l b a c k t o t h e t r i m m e d a n g l e o f a t t a c k , t h e n

t h e a e r o d y n a m i c c e n t e r i s b e h i n d t h e c e n t e r o f g r a v i t y . A n u p g u s t w i l l

p r o d u c e a n a d d i t i o n a l l o a d w h i c h p r o d u c e s a d i v i n g m o m e n t , b u t o n l y u n t i l

t r i m i s r e s t o r e d . A d o w n g u s t p r o d u c e s a m o m e n t a r y n o s e u p m o m e n t .



3 . D i f f e r e n c e b e t w e e n s k i d a n d y a w : T o c l e a r u p t h e s i d e s l i p , ( s k i d )

y a w c o n f u s i o n , l e t ' s l o o k f o r a m i n u t e a t t h e s i n k i n g s p e e d , a n g l e o f a t t a c k ,

a i r p l a n e a t t i t u d e s i t u a t i o n . I t m a y b e e a s i e r t o s e e . T o s t a r t w i t h a s s u m e a

s y m m e r i c a l m o d e l c o n s t r a i n e d s o t h a t i t s h o r i z o n t a l a x i s r e m a i n s p a r a l l e l

t o t h e g r o u n d . F i r e i t f r o m a c a t a p u l t i n t h i s p o s i t i o n . S i n c e i t i s s y m m e t r i

c a l i t h a s n o l i ft . H e n c e , i t w i l l s t a r t d o w n w a r d , d e v e l o p n g a s i n k i n g s p e e d

a s i t g o e s . A t t h e s a m e t i m e , t h e r e s u l t a n t w i n d i s n o l o n g e r a l o n g t h e a x i s

( m o d e l s t i l l c o n s t r a i n e d t o h a v e i t s a x i s p a r a l l e l t o t h e g r o u n d ) . Y o u w i l lr e c o g n i z e t h e g e n e r a t i o n o f a n a n g l e o f a t t a c k — t h e a n g l e b e t w e e n t h e c e n

t e r l i n e o f t h e m o d e l a n d t h e r e s u l t a n t w i n d . I n t h i s c a s e , s i n k i n g s p e e d a n d

a n g l e o f a t t a c k a r e t w o w a y s o f s a y i n g t h e s a m e t h i n g . I t i s n o t a l w a y s s o ,

o f c o u r s e . L e v e l f l i g h t , f o r e x a m p l e , r e q u i r e s a n a n g l e o f a t t a c k w i t h o u t a



s i n k i n g s p e e d . T h e g e n e r a l c a s e o f a m o d e l g l i d i n g c a n b e d e s c r i b e d b y t h e

s i n k i n g s p e e d a n d o n e a n g l e o r t w o a n g l e s , t h e a n g l e o f a t t a c k ( a n g l e b e

t w e e n t h e c e n t e r l i n e a n d t h e w i n d ) a n d t h e a t t i t u d e r e l a t i v e t o t h e g r o u n d

( a n g l e b e t w e e n t h e c e n t e r l i n e a n d t h e h o r i z o n t a l ) .

T h e s a m e s o r t o f a s i t u a t i o n e x i s t s i n t h e d i r e c t i o n a l c a s e . C o n s t r a i n a

m o d e l t o k e e p i t s c e n t e r l i n e p o i n t i n g a l o n g a c o m p a s s d i r e c t i o n , s a y d u e

N o r t h . C a t a p u l t i t i n t h i s d i r e c t i o n . N o w p u l l i t s i d e w i s e , b u t l e a v e t h e

c e n t e r l i n e o n t h e " no r th h e a d i n g . T h e m o d e l i s o b v i o u s l y s k i d d i n g . E q u a l l y

o b v i o u s i s t h e f a t t t h a t t h e r e i s a n a n g l e b e t w e e n t h e c e n t e r l i n e a n d t h er e s u l t a n t w i n d . T h e s i t u a t i o n i s e n t i r e l y a n a l o g o u s t o t h e s y m m e t r i c a l

m o d e l w i t h t h e s i n k i n g s p e e d . S i n c e m o s t a i r p l a n e s a r e s y m m e t r i c a l a b o u t

t h e v e r t i c a l p l a n e , y a w a n d s i d e s l i p a r e t h e s a m e t h i n g i n a d i f f e r e n t l a n -



g u a g e . I t d o e s n o t h a v e t o b e s o , h o w e v e r , f o r i f t h e m o d e l w e r e f l y i n g

l e v e l r o t a t e d 90 ° t o b e on i t s s i d e ( a d i f f i c u l t f e a t I ad m i t b u t f or i l l u s t r a

t i o n o n l y ) t h e r e w o u l d b e a y a w a n g l e b u t n o s i d e s l i p .

4 . T o r q u e a n d s l i p s t r e a m . I d o n ' t s h a r e y o u r c o n c e r n o v e r t o r q u e . T h i s

i s o n e o f t h e m o s t o v e r r a t e d f o r c e s i n t h e b u s i n e s s . Y o u c o n t e n d t h a t a

m o d e l u n d e r p o w e r i s i n a l e f t s k i d . N o t n e c e s s a r i l y ! M a y b e i t i s , a n d m a y b e

i t i s n o t . I t c e r t a i n l y v a r i e s f r o m p l a n e t o p l a n e , a l t h o t h e o d d s m a y f a v o r

a l e f t s k i d i n l e v e l f l i g h t . A c t u a l l y , t h e q u e s t i o n i s a c a d e m i c . A s f a r a s

stability i s c on c e r n e d i t d oe s n ' t m ak e an y r e a l d i f f e r e n c e . I t i s a m at t e r o f

t r i m o n l y . I n o t h e r w o r d s a s l o n g a s I c a n f i n d a r o l l i n g m o m e n t t o b a l a n c e

t h e e n g i n e t o r q u e w i t h o u t s t a l l i n g a n y s u r f a c e I a m i n b u s i n e s s . W h a t a r e

s o m e o f t h e p o s s i b i l i t i e s ?



(1 ) S id es l i p (o r y a w) . Ro l l in g m o m en t i s pro duce d by the d ihe dra l .

(2) Cir c l i ng f l i g h t (y a w in g v e l o c i ty ) . Th e ro l l ing m o m e nt i s pr o d uc ed by

the outs ide wing travel ing faster than the ins ide wing and by the act ion

of d ihed ral ahe ad of or beh ind the center of gra vi t y .

(3 ) Rol l ing veloci ty . Keep in mind that a model which i s c l imbing or d iv

ing a lways has a ro l l ing veloci ty i f there i s any steady turn. Consider a

" st ra ig ht up cl im b to cl i nch the poin t.

(4 ) Ai lerons '—or w ar p s in the win g .

Take a look at that last force to see why some models don't have a left

s ide s l ip . Suppose we consider power on f l ight as the normal state o f a f fa irs ,



a n d l e t ' s a s s u m e t h a t w e h a v e a d e v i c e fo r m e a s u r i n g t h e s i d e s l i p . N o w

d u r i n g t h e f i r s t f e w f l i g h t s w e a d j u s t t h e a i l e r o n s ( w i n g w a r p s ) , r u d d e r ,

a n d s i d e t h r u s t s o t h a t t h e r e i s z e r o s i d e s l i p a n d t h e f l i g h t i s s t r a i g h t . S i n c e

i t i s e a s y t o o v e r p o w e r t h e t o r q u e w i t h a i l e r o n s , w e c o u l d j u s t a s e a s i l y

h a v e t r i m m e d f o r a r i g h t s i d e s l i p . W i l l i t g l i d e ? S u r e ! I t m a y h a v e a c i r c l e

a n d i t m a y h a v e s o m e s i d e s l i p , b u t i t w i l l g l i d e a n d v e r y n i c e l y . Y o u k n o w

a s w e l l a s I d o t h a t e v e r y b o d y h a s s o m e w a r p s n o m a t t e r h o w w e l l h e

b u i l d s . C h a n c e s a r e t h a t t h e s e a r e m o r e i m p o r t a n t t h a n t h e t o r q u e ; a t l e a s tt h e t o r q u e t h a t r e m a i n s a f t e r t h e f l o w i s s r a i g h t e n e d o u t b y a l l t h e v a r i o u s

s u r f a c e s , p y l o n , w i n g , h o r i z o n t a l t a i l , v e r t i c a l t a i l , a n d f r i c t i o n o n t h e

f u s e l a g e .



T h e e f f e ct o f t h e s l i p s t r e a m t w i s t o n y a w i n g m o m e n t s i s p r o b a b l y m o r e

i m p o r t a n t . T h e v e r t i c a l t a i l i s a l o n g w a y f r o m t h e c e n t e r o f g r a v i t y . A

s m a l l f o r c e p r o d u c e s a l a r g e m o m e n t . N o t e t h a t w i t h a r e a s o n a b l e a m o u n t

o f d o w n t h r u s t t h e b o t t o m p a r t o f t h e s l i p s t r e a m c a n a c t e v e n o n a v e r t i c a l

t a i l a b o v e t h e f u s e l a g e . T h e f o r c e o n t h e t a i l i s t h e n i n t h e o p p o s i t e d i r e c

t i o n f r o m t h a t o n t h e p y l o n , b u t t h e m o m e n t s a r e i n t h e s a m e d i r e c t i o n .

A s I r e a d m o d e l p u b l i c a t i o n s I a m f o r c e d t o c o n c l u d e t h a t t h e t h i n gm o s t n e e d e d i s a c l e a r u n d e r s t a n d i n g o f t h e f u n d a m e n t a l d i f f e r e n c e b e t w e e n

s t a b i l i t y a n d t r i m . T h i n k a b o u t t h a t f o r a w h i l e .



P A R N E L L S C H O E N K Y — P A A C L I P P E R C A R G O D E S I G N N O T E S —I n m a n y m o d e l c a t e g o r i e s , a w e l l - d e s i g n e d a n d s t r u c t u r a l l y - e x c e l l e n t

m o d e l h a s l i t t l e , c h a n c e t o p r o v e i t s w o r t h a g a i n s t t h e f i e l d o f s t a n d a r d i z e d

d e s i g n s w i t h h o t e n g i n e s — f o r t h e r m a l s a r e i n d e e d b l i n d a n d t h e y s w e e p a l l

m a n n e r o f d e b r i s i n t o t h e c l o u d s . H a p p i l y , t h e C l i p p e r C a r g o i s n o t a m o n g

t h e s e u n f o r t u n a t e e v e n t s ; t h o u g h i t g o e s w i t h o u t s a y i n g t h a t a C l i p p e r

C a r g o m u s t h a v e a p o w e r f u l e n g i n e , t h e e l e m e n t s o f l u c k t a k e a b a c k s e a t t o

t h e s k i l l s o f t h e d e s i g n e r a n d t h e c r a f t s m a n .

A C l i p p e r C a r g o m o d e l s h o u l d b e b u i l t o f l i g h t , c a r e f u l l y s e l e c t e d w o o d

i n o r d e r t o k e e p t h e d e a d w e i g h t d o w n , f o r o n l y p a y l o a d m e a n s p o i n t s !

L i g h t c o n s t r u c t i o n d o e s n o t m e a n f l i m s y c o n s t r u c t i o n i f t h e b u i l d e r p u t s

t h e b a l s a , c e m e n t , a n d w i r e w h e r e t h e l o a d s a r e t h e g r e a t e s t ( a s i s s o w e l l -

i l l u s t r a t e d b y t h e m o d e r n W a k e f i e l d a n d i n d o o r m o d e l s ) a n d , f u r t h e r , i f t h e

s h i p i s d e s i g n e d t o b e n d , t w i s t , o r t o s h e d p a r t s w h e r e i t i s i m p r a c t i c a l f r o m

a w e i g h t s t a n d p o i n t t o b u i l d i n t h e s t r e n g t h a n d r i g i d i t y n e c e s s a r y t o a b

s o r b s h o c k s h e a d o n . T h e a e r o d y n a m i c d e s i g n o f th e C l i p p e r m u s t g i v e g o o d

t ak e - o f f s i n b o t h w i n d an d c a l m , an d t h e r a t e o f c l i m b an d t h e s t ab i l i t y a t

h i g h a n g l e s o f a t t a c k m u s t a l s o b e s u f f i c i e n t t o e n a b l e t h e C l i p p e r t o l i f t 1 5

t o 2 0 o u n c e s o f l e a d o r o t h e r p a y l o a d t o a h e i g h t f r o m w h i c h t h e m o d e l m a y

g l i d e f o r a b o u t 2 5 s e c o n d s b e f o r e l a n d i n g — a l l t h i s w i t h i n t h e s t r u c t u r a l

l i m i t a t i o n s n e c e s s a r y t o. p r o d u c e b o t h a l i g h t m o d e l a n d a r u g g e d m o d e l

c a p a b l e o f m e e t i n g t h e u n d a m a g e d l a n d i n g r e q u i r e m e n t s .

T h e " P a c i f i c C l i p p e r " p r e s e n t j u s t o n e s o l u t i o n t o t h i s i n t r i g u i n g d e

s i g n p r o b l e m , i n t h e f o r m o f a f a i r y c o n v e n t i o n a l a n d r e a l i s t i c m o d e l .

T h e r e a r e o t h e r a v e n u e s o f a p p r o a c h w h i c h t h e m o d e l e r m a y d e s i r e t o

i n v e s t i g a t e , p a r t i c u l a r l y t h e B u r n e l l t y p e o f c r a f t a n d t h e p u r e f l y i n g w i n g s

— o f w h i c h t h e B r o g g i n i " C a r g o w i n g " i s a n e x c e l l e n t e x a m p l e .I t m a y b e s a i d t h a t t h e " P a c i f i c C l i p p e r " w a s d e s i g n e d a r o u n d t h e w i n g

an d t h e l a n d i n g ge a r . T h e 37 5 s q . i n . w i n g i s s u i t e d t o a m o d e l o f 2 0 t o 2 5

o z . o v e r - a l l w e i g h t a n d h a s b e e n p r o v e n s u ff i c i e n t l y r u g g e d b y p l e n t y o f

r o u g h l a n d i n g s . T h e p a p e r s h e a r w e b u s e d t o c o m p l e t e t h e " D " s p a r w o r k s

f i n e — a n d i t s a v e s b o t h t i m e a n d b a l s a . A t w o - w h e e l l a n d i n g g e a r w h i c h i s

p l a c e d f a r e n o u g h f o r w a r d t o p r o t e c t t h e f u s e l a g e i n s t e e p l a n d i n g s i s i n

t h e w o r s t p o s s i b l e p o s i t i o n s o f a r a s p r e v e n t i n g g r o u n d l o o p s i s c o n c e r n e d .

H e n c e t h e u s e o f t h e t r i c y c l e g e a r — w h i c h a l s o o f f e r s t h e d i s t i n c t a d v a n

t a g e o f p e r m i t t i n g t h e t a k e - o f f a n g l e o f a t t a c k t o b e a d j u s t e d f o r f l i g h t s

o f f o f s h o r t r u n w a y s a n d f o r t h o s e s i t u a t i o n s w h e r e t h e C l i p p e r C a r g o ' s

b e s t f r i e n d , t h e w i n d , f a i l s t o s h o w u p . T h e s t a b i l i z e r i s p l a c e ' d h i g h a n dd i h e d r a l e d i n o r d e r t o p r o t e c t i t i n l a n d i n g s a n d a l s o i n a n e f f o r t t o m i n i

m i z e t h e t r i c k y e f f e c t s o f t h e t u r b u l e n t w i n g w a k e .

H e a v i l y l o a d e d a s t h e y a r e , C l i p p e r s s t i l l f l y f a s t e n o u g h f o r d r a g t o b e

i m p o r t a n t , a n d t h i s m o d e l w a s m a d e a s " c l e a n " a s p o s s i b l e . S p e a k i n g o f d r a g ,

t h e C l i p p e r b u i l d e r w h o d e s i g n s h i s o w n s h o u l d a v o i d t h e s u p e r h i g h - l i f t

a i r f o i l s e c t i o n s u n l e s s h e r e a l l y k n o w s h i s a e r o d y n a m i c s , f o r t h e d r a g o f

s u c h s e c t i on s i s l i k e l y t o b e h i gh ; t h e d an ge r i n t h i s i s t h a t t h e t o t a l d r ag

m ay b e s o gr e a t a s t o s l ow t h e m od e l d ow n t o w h e r e p r op s o f 3 t o 4 i n c h

p i t c h m a y b e p a r t i a l l y s t a l l e d o u t . T h e e n g i n e f o r y o u r " P a c i f i c C l i p p e r "

m u s t s w i n g a 6 - 3 or 5y 2 - 4 p r o p a t 13 ,500 R P M or b e t t e r t o p u t yo u i n t h e

r a c e . F o r t h e n e w e r e n g i n e s , r a t e d a t 1 8 t o 2 0, 00 0 R P M , e n l a r g e t h e w i n ga r e a t o 4 5 0 - 4 6 5 s q . i n . , f i n a n d s t a b , p r o p o r t i o n a t e l y , a n d i n c r e a s e n o s e g e a r

w i r e gau ge t o . 0 50 . "



G . R . N O L I N — A D J U S T I N G F O R C L I M B —A m od e l c an b e m a d e s p i r a l l y s t ab l e i f i t i s p r o p o r t i o n e d s o t h a t i t f l i es

i n a n a t u r a l p o w e r c i r c l e w h i c h i s s l i g h t l y s m a l l e r t h a n t h e d e s i r e d c i r c l e .

T h e d e s i r e d c i r c l e s h o u l d b e o b t a i n e d b y s e t t i n g t h e r u d d e r t a b a g a i n s t t h e

n a t u r a l p o w e r c i r c l e . T h a t i s, t h e m o d e l c l i m b s r i g h t w i t h l e f t r u d d e r , o r

v i c e - v e r s a . T h i s s e t - u p i s b a s e d o n t h e b e l i e f t h a t t h e f o r c e e x e r t e d b y t h e

r u d d e r t a b v a r i e s d i r e c t l y w i t h t h e a i r s p e e d , a n d t h a t t h e n a t u r a l t u r n i n g

f o r c e r e m a i n s n e a r l y c o n s t a n t w h e n t h e a i r s p e e d i n c r e a s e s .

F o r e x a m p l e : A m o d e l w h i c h fl ie s u n d e r p o w e r i n a " n a t u r a l " c i r c l e o f

r a d i u s " A " i s f o r c e d i n t o c i r c l e " B " b y t h e u s e o f l e f t r u d d e r . T h e m o d e l

w i l l t h e n c l i m b s t e e p e r , a n d a t l o w e r a i r s p e e d ( C i r c u l a r A i r f l o w T h e o r y ) .

I t c a n n o t a p p r o a c h c i r c l e " A " w i t h o u t a n i n c r e a s e i n a i r s p e e d , a n d a c o r

r e s p o n d i n g i n c r e a s e i n r u d d e r t a b l o a d . T h e a d d e d r u d d e r t a b l o a d w i l l

t h e n c o r r e c t t h e m o d e l t o w a r d c i r c l e " B " .

I n t h e e v e n t t h a t t h e m od e l m ov e s i n t o an e v e n l ar ge r c i r c l e " C " t h e

a i r s p e e d w i l l d i m i n i s h d u e t o t h e i n c r e a s e d a n g l e o f c l i m b ( C i r c u l a r A i r

f l o w a g a i n ) . T h e r u d d e r t a b w i l l t h e n h a v e l e s s f o r c e w i t h w h i c h t o o p p o s et h e n a t u r a l t u r n i n g f o r c e . T h e n a t u r a l p o w e r t u r n w i l l t h e n c o r r e c t t h e

m o d e l t o w a r d s c i r c l e " B " . T h u s w e n o w h a v e b o t h m a x i m u m a n d m i n i m u m

l i m i t s on t h e s i z e o f t h e p ow e r c i r c l e .

W h e n p u t i n t o p r a c t i c a l t e s t t h e s e t - u p w i l l o f t e n s e e m u n s a t i s f a c t o r y

b e c a u s e o f t h e f a c t t h a t t h e m o d e l w i l l i n m a n y c a s e s t r a v e l b a c k a n d f o r t h

b e t w e e n t h e c i r c u l a r l i m i t s . I n o t h e r w o r d s , a m o d e l w h e n l a u n c h e d i n t o a

b r e e z e w i l l a t t e m p t t o f l y c i r c l e " C " . A n e x c e s s i v e c o r r e c t i o n t o w a r d c i r c l e

" B " w i l l r e s u l t , a n d t h e m o d e l w i l l p a s s t h r o u g h c i r c l e " B " a n d a p p r o a c h

c i r c l e " A " . A n e x c e s s i v e c o r r e c t i o n t o w a r d s c i r c l e " C " w i l l f o l l o w w i t h t h e

m o d e l a g a i n p a s s i n g t h r o u g h c i r c le " B " a n d a p p r o a c h i n g " C " . E t c . E t c .

( S e e d i a g r a m . )



W h e n t h i s d i f f i c u l t y i s e n c o u n t e r e d i t i s e a s i l y c o r r e c t e d b y d e c r e a s i n g

t h e n a t u r a l t u r n o f t h e m o d e l s o t h a t t h e o p p o s i n g r u d d e r t a b d e f l e c t i o n c a n

b e s a f e l y d e c r e a s e d . T h e r u d d e r t a b l o a d w i l l t h e n v a r y a t a l e s s e r r a t e

w h e n t h e a i r s p e e d v a r i e s , a n d t h e o s c i l l a t i o n b e t w e e n c i r c u l a r l i m i t s w i l l

d i m i n i s h o r d i s a p p e a r .I f a m o d e l h a s l i t t l e n a t u r a l t u r n ( t h a t i s , r e q u i r e s r i g h t r u d d e r t o t u r n

r i g h t ) , a v a r i a t i o n i n t h e t h r u s t l i n e w i l l u s u a l l y c o r r e c t t h e d i f f i c u l t y .

H o w e v e r , e n l a r g i n g a p o w e r t u r n w h i c h i s t o o t i g h t b y a d d i n g s i d e t h r u s t

d o e s n o t a p p e a r t o b e s a t i s f a c t o r y i n p r a c t i c e .

G e n e r a l l y s p e a k i n g , e n l a r g i n g t h e f i n w i l l i n c r e a s e t h e l e f t t u r n i n g

f o r c e s o f a m o d e l , a n d d e c r e a s i n g t h e f i n w i l l i m p r o v e t h e r i g h t t u r n i n g

a b i l i t y . I t s h o u l d b e n o t e d t h a t b e c a u s e o f f u n d a m e n t a l s p i r a l s t a b i l i t y c o n

s i d e r a t i o n s a n i n c r e a s e i n f i n a r e a m o m e n t i s o f t e n u n d e s i r a b l e .

I h a v e f o u n d t h a t t h e r i g h t t u r n i n g c a p a b i l i t i e s c a n b e d e c r e a s e d b y

m o v i n g t h e f i n f o r w a r d , a n d i n c r e a s e d b y m o v i n g t h e f i n r e a r w a r d w h i l e

m a i n t a i n i n g a m i n i m u m f i n m o m e n t v a l u e ( A r e a x D i s t a n c e f r o m C . G . )

Note: W h e n u s i n g t h i s a p p r o a c h t o t h e s p i r a l p r o b l e m t h e g l i d e c i r c l e a d

j u s t m e n t s m u s t b e m a d e b y t i l t i n g t h e s t a b i l i ze r ' .

F r a n k H e e b a n d I h a v e b e e n r u n n i n g s o m e i n t e r e s t i n g t e s t s o n p r o p

w a s h t h e o r y . W e h u n g a p i e c e o f t h r e a d i n t h e s l i p s t r e a m a n d n o t e d t h a t

i t b l e w s t r a i g h t b a c k a n d v i b r a t e d r a p i d l y . H a d a n i d e a t h a t t h e a i r b e t w e e n

t h e b l a d e s w a s c o m i n g t h r u t h e p r o p q u i t e s t r a i g h t , b u t t h e a i r f r o m t h e

b l a d e s t h e m s e l v e s w a s m o v i n g a t a n a n g l e .

W e " s t o p p e d " t h e b l a d e w i t h a s t r o b o s c o p e a n d t h e s t r i n g n o l o n g e r

v i b r a t e d , b u t h u n g b a c k a t t h e e x p e c t e d a n g l e — a p p r o x . 20 ° . H i g h e r p i t c h

i n c r e a s e d t h e a n g l e , a n d t h e a n g l e g r a d u a l l y d i m i n i s h e d a s t h e d i s t a n c ef r o m t h e p r o p i n c r e a s e d .



S A L T A I B I — F L O A T S —I p e r s o n a l l y l i k e t w o E d o t y p e f l o a t s b e s t b u t h a v e f o u n d o u t i n t h e p a s t

f i v e y e a r s o f f l y i n g R O W t h a t i t j u s t d o e s n o t p a y off, t h e d r a g a n d w e i g h t

s e e m t o h a n d i c a p t h e m o d e l t o o m u c h . B u t f o r f l y i n g - f o r - f u n I t h i n k t h e y

a r e t o p s . I l i k e t o w a t c h t h e l o n g r u n w h i c h i s s o r e a l i s t i c , a n d a l s o t h e r e a l

a p p e a r a n c e o f t h e m o d e l i n th e a i r . I u s u a l l y s e t E d o f lo a t s s o t h a t t h e t o p

o f t h e f l o a t , w h i c h i s s t r a i g h t , i s a p p r o x i m a t e l y y 4" p o s i t i v e t o t h e w i n g ,n o t t o t h e t h r u s t l i n e o r c e n t e r l i n e o f t h e f u s e l a g e , b u t t o t h e a n g l e o f t h e

w i n g . T h e s e f l o a t s m u s t b e f i x e d v e r y r i g i d . I u s u a l l y m a k e t h e l a n d i n g g e a r

a s s h o r t a s p o s s i b l e s o t h a t t h e p l a n n i n g a c t i o n o n t h e w a t e r w i l l b e b e t t e r .

A l l o w a b o u t 2 " c l e a r a n c e f r o m p r o p t o t h e t o p o f t h e f l o a t .

T h e f l o a t m u s t b e v e r y r i g i d . I t s h o u l d b e " X d " w i t h l i g h t w i r e a n d

s o l d e r e d . T h e r e a r f l o a t s u p p o r t i s a l s o s o l d e r e d t o t h e r e a r s p r e a d e r b a r

a n d f a s t e n e d t o t h e f u s e l a g e w i t h s m a l l r u b b e r b a n d s a r o u n d a s m a l l h o o k .

T h e m a i n l a n d i n g g e a r i s p u l l e d t o g e t h e r a n d t h e n s l i d i n t o b r a s s t u b i n g

i n t h e f l o a t : N o f a s t e n i n g n e c e s s a r y a s t h e s p r e a d i n g a c t i o n o f t h e g e a r w i l l

h o l d w i r e i n t u b i n g . I t i s b e s t t o c e m e n t s m a l l h a r d w o o d w e d g e s i n p l a c e

w h e r e r e a r f l o a t s u p p o r t i s f a s t e n e d t o t h e b o d y s o t h a t t h e s u p p o r t w i l l n o t

s l i d e b a c k o r f o r w a r d . I f t h i s h a p p e n s , i t w i l l c h a n g e a n g l e o f a t t a c k o f t h e

float.

C O N T E S T T Y P E F L O A T S — I a m e n c l o s i n g f u l l s iz e l ay o ut o f t h e

f l o a t s I u s e d a t th e 1 9 51 N a t s . H a d t h e m o n a n . 09 9 A r d e n p o w e r e d Z e n i t h



model whose weight was 11 oz. with f loats, and had an area of 365 sq. in. It

p la ced seco nd . There i s no in terna l co ns truct io n , jus t s ides a nd co v er ing .

Sides are cut from 3 /32 soft ba lsa , and covered a lso with soft 3 /32 . Brass

tub ing wa s wr ap pe d and cem ent ed to a ba l sa and ceme nted in the

flo at. A 1/ 16 wi re pi ec e is ce me nt ed to the si de of the flo at. It is fix fed to

the lan din g gear , whi ch i s s l ip pe d into the br as s tubi ng , with rubber band s.

The models these days are so h ighly overpowered that with the s led

typ e f lo ats the y req uir e prac t i ca l l y no take-off ru n; as soon as they are

released they just jump off the wetar, especial ly i f there is a 5 to 10 m.p.h.

bre eze . T h i s is not "my idea of a sea pl an e, rath er, i t 's an ex cu se to ent er a

good flying model in a seaplane event. I tried flying a seaplane for four

ye ar s, an d then saw the fu ti l i ty of i t and buil t a pai r of sle d ty pe float s

for my Zenith .



J O E B I L G R I — R U B B E R M O T O R —As for rubber; I don't have any specia l treatment but a f ter I make up a

motor I wash i t wel l wi th co ld water, dry i t out thoroughly and saturate

i t wel l wi th Castor Oi l , and then prewind i t , s tart ing with about 50%, then

60%, 70% , 80 % an d finish ou t wi th ab out 90% of ca pa ci ty wi nd s. I f igur e

that capaci ty for 16 strands of Dunlop i s about 20 turns per inch, for over

that the rubber tears apart fast . After i t i s prewound I wash some of the

excess oil off, dry it out and put it away until I am ready to use it. On hot

days I also use lots of excess oi l on the motors for I would rather have an

oi ly model than a busted one.

I usual ly s tretch the motor out between 3 to 3y 2 t im es i t so r ig ina l l eng tha nd put in a ppro x im a te ly 7 5 % befo re co m ing in .



D I C K B A X T E R — E N D P L A T E S — R U B B E R T E S T S —T h e w e a t h e r o u g h t t o b e p r e t t y a w f u l i n I t h a c a b y n o w s o I w i l l t e l l

t h a t I w e n t f l y i n g S u n d a y m o r n i n g — d e a d c a l m — 7 5 ° a n d h a d a f i n e t i m e

f l y i n g m y W a k e f i e l d . T h e o n l y s o r e s p o t i s t h a t t h e o r y le t m e d o w n i n t h e

p u b l i c e y e .

W h e n y o u g e t m y W a k e f i e l d p l a n s y o u w i l l d i s c o v e r t h e t i p p l a t e s o n

t h e p r o p . I a l w a y s w o n d e r e d w h a t w o u l d h a v e h a p p e n e d , s o — I m a d e s i xf l i g h t s , t h r e e w i t h t i p p l a t e s a n d t h r e e w i t h i d e n t i c a l p r o p m i n u s t i p p l a t e s .

S a m e n u m b e r o f t u r n s — p r o p s w e r e a l t e r n a t e d o n c o n s e c u t i v e f l i g h t s .

M o t o r a b o u t 2 / 3 w o u n d . S u r e p r o v e d n o t h i n g t h a t t i m e e x c e p t t h a t t h e

p l a t e s d i d n o t d o a n y d a m a g e m a y b e ! ( P h o o i e o n S c i e n c e ! )



A s f o r t r u e c o n f e s s i o n s — t r y t h i s : A t M I T a n d o u t h e r e i n C a l i f o r n i a

I ' v e s p e n t a f e w e v e n i n g s t r y i n g t o f i n d o u t w h i c h r u b b e r i s b e s t f o r W a k e -

f i e l d s . T h e c r i t e r i o n I p i c k e d w a s m a x i m u m u s e f u l e n e r g y s t o r a g e p e r u n i t

w e i g h t . T h i s y o u g e t b y i n t e g r a t i n g t h e l o a d - s t r e t c h c u r v e , ( ( o b t a i n e d a s

t h e r u b b e r r e l a x e s ) a n d d i v i d i n g b y t h e w e i g h t o f th e s a m p l e . H . P a r u -

c h e n i a n , W . R o b e r t s a n d H . J e x d i d a s m u c h o f w o r k a s I d i d a n d h e r e i s

h ow w e w e n t ab ou t i t .

S a m p l e s w e r e st r e t c h e d h o r i z o n t a l l y , u s i n g e x p e n s i v e s p r i n g s c a l e — n o tc o m p l e t e l y a c c u r a t e — b u t e a s y . L o a d w a s o b s e r v e d a t v a r i o u s l e n g t h s a n d

w o r k d o n e b y t h e r u b b e r i n c o n t r a c t i n g w a s m e a s u r e d b y t h e ( g r a p h i c a l )

i n t e g r a t i o n m e n t i o n e d a b o v e . W e i g h t o f t h e s a m p l e s w a s a c c u r a t e t o 1 % .

T h e r e l a x i n g a n d s t r e t c h i n g w a s d o n e s l o w l y — a b o u t 5 m i n u t e s p e r c y c l e

w i t h a 1 0 t o 1 5 m i n . r e s t b e t w e e n r u n s . S e v e r a l r u n s w e r e t a k e n o n e a c h



sample and first few were thrown out to take care of the break-in period.

The results are qualitatively that T-56 is worst of the present crop.

Pirell i 's best and Dunlop Type 6010 is second. Numbers are about as

follows: T-56 2,^00 Dunl 6p 2 , 7 0 0 Pirel li 3,000 (£c(, Memory)

Note that if the energy in the rubber could be converted entirely to alti

tude a piece of rubber (Pirelli) could shoot itself up to 3000 ft.

These results quoted above are not the exact values we obtained. I can't

give you those because I let the data get away from me. But they are Ith in k wit hin 100 lb. ft ./ lb . of what we go t on several t es ts ran at wid el y

different t imes .

My que st io n: W h y can't U . S . Rub be r Co. sell rubb er as goo d as the

European—20% more turns goes a long way up.



E . D . S L O B O D — T O F R E E W H E E L O R F O L D —I d o n o t w i s h t o e n t e r t h e f r e e - w h e e l v s . f o l d e r d e b a t e w h i c h i s o f t e n

c a r r i e d o n b y p e o p l e w h o h a v e n o t u s e d b o t h e n o u g h t o k n o w w h a t t h e y a r e

t a l k i n g a b o u t , b u t i n s t e a d w o u l d l i k e t o l i s t w h a t I t h i n k a r e t h e a d v a n t a g e s

a n d d i s a d v a n t a g e s o f b o t h .

1 — T h e f i rs t c o n s i d e r a t i o n i s d r a g . O f c o u r s e t h e f o l d e r o f f e r s l e s s r e s i s t a n c e . C a n t h e r e b e a n y d o u b t a b o u t t h a t . W e d o n o t k n o w h o w m u c h ,

b u t a s h i p w i t h f r e e - w h e e l f l i e s s l o w e r t h a n t h e s a m e s h i p w i t h a f o l d e r , a n d

t h e r e c a n o n l y b e o n e r e a s o n f o r t h a t . ( H e r e , h o w e v e r , w e m a y h a v e a b l e s s

i n g 'in d i s g u i s e , b e c a u s e i f t h e r e i s n o t a g r e a t d i f f e r e n c e i n s i n k i n g s p e e d ,

t h e s l o w e r s h i p i s m o r e t h e r m a l s u s c e p t i b l e . ) N o o n e k n o w s j u s t h o w m u c h

a d d i t i o n a l d r a g a f r e e - w h e e l e r o f f e r s , b u t t h e r e s u l t s o f t h e W a k e f i e l d f i n a l s

t h e s e p a s t f e w y e a r s s e e m t o i n d i c a t e t h a t t h e f r e e w h e e l e r i s n o t r e a d y f o r

t h e a s h - c a n .

2. Free wheeler may be b u i l t - lighter-

3 — T h e r e a r e n o . h i n g e s t o b e n d o r lo o s e n , h e n c e t h e b l a d e s w i l l r e m a i n

a t t h e a n g l e c a r v e d .

4 — T a k e - o f f r e l e a s e i s s i m p l e r a s t h e o p p o s i t e b l a d e d o e s n o t d a n g l e

p r e c a r i o u s l y w i t h i n f o u l i n g d i s t a n c e o f t h e f u s e l a g e .



5 — T h e f r e e - w h e e l e r c a n n o t f o l d i m p r o p e r l y , r e s u l t i n g i n e i t h e r a t o o

w i d e g l i d e c i r c l e o r s p i n .

6 — W h e n p r o p e r l y t e n s i o n e d , m u c h m o r e s l a c k c a n b e u s e d w i t h a f r e e -

w h e e l e r e q u i p p e d w i t h o u t f e a r o f s t a l l s d u e t o t h e f o r m a t i o n o f k n o t s .

( I s a f e l y f l e w a s h i p t h a t u s e d a 4 3" m ot or w i t h on l y 2 3" b e t w e e n h ook s f or

s e v e r a l s e a s o n s . )

7 — T h e f r e e - w h e e l e r d a m p e n s o u t s l i g h t l o n g i t u d i n a l o u t o f t r i m s t a l l

t e n d e n c i e s . ( T h i s i s a n o b s e r v e d c h a r a c t e r i s t i c — I c a n n o t e x p l a i n w h y ) .

8 — T h e a r g u m e n t t h a t f r e e w h e e l r s a r e p r o n e t o b r e a k a g e i s n o t a v a l i d

o n e . I f t h e u p p e r c o r n e r o f t h e i n s e r t e d p o r t i o n o f t h e n o s e p l u g i s r o u n d e d ,

t h e n o s e p l u g w i l l t i p f o r w a r d w h e n t h e p r o p t i p s t r i k e s t h e g r o u n d t h e r e b y

a b s o r b i n g t h e s h o c k .



9—If the model s tr ikes ground under power, one i s just as apt to break

as the other. I f th is sh oul d hap pe n to ty pe use d in Sout he rn Cal i f or ni a the

break wi l l a lmost invariably occur at the hub where p lywood plates end.

Field repairs can be made in 30 minutes by using Y 8 ha rd ba l sa sheet sp l in t .

10—The free-wheeler i s eas ier to make as there are no hinges to foo l

with and no worries about gett ing the best fo ld posi t ion .

11—When winding a free wheeler equipped ship , only the rubber i s

wound and the prop is not given a free ride.

Whi le on the s ub je ct o f pr op s I mig ht add that we have bee n up an d

down the sca le and have found no s imple rule for determining what d ia

meter, b lade area and pi tch a prop should have. Only through experience

can these factors be arranged efficiently, and at that, i t 's a "first guess."



PETE BUSKELL—AIRFOIL TEST FLIGHTS—Yo ur que ry o n Do n But l e r ' s A/ 2 , N A C A 6 40 9 i s the o n ly sec t io n which

has bee n th or ou gh ly test ed on th is mod el to date , but a wi ng to the sa me

sect ion as on "Sl ick St ick" i s in the course of test ing .

T he lo ng A / 2 wa s dev e l o ped fro m a m e d i um co u p le d 1 / ta i lp la ne

A/2 designed by Don, the orig inal o f which had a Goldberg G5 wing , asthis sect ion had proved good on gas models o f s imi lar weight .

Performance was about 3 min. from 300 f t . l ine which did not sat i s fy

Don. So he fo l lo wed with a me di um th ic kne ss Da vi s ver s i on whi ch had s i m

i lar pe rf or ma nc e, and then a N A C A 6409 ver s io n, whi ch y ie lde d 3 min.

45 sec.

Around the same t ime I decided to carry out a few tests on sect ions

that were c la imed the tops , and f igured that a rubber model o f around 36"

span would be the best indicator, the reasoning being that the wing i s used

on cl imb as wel l as g l ide, and an improved sect ion would make quite a

di f ference to to ta l t ime.

I was using such a model a t the t ime, so bui l t the fo l lowing wings for i t :

N A C A 6 40 9, D a v i s ( M e d . T h i c k . ) J a k o w s k y ( R o n W a r r i n g ' s P e t ) , f iv e o f

the m o s t su i ta b le Ben ed ek Sec t io ns wh ich the Sw ed es c la im ed we re the

goods, and the "Sl ick St ick" sect ion , which i s a French curve and ruler

e f fo r t f ro m o ne o f Do n ' s ea r l i er l i g h tweig ht des ig ns .



T h e B e n e d e k s g a v e t i m e s b e t w e e n 2 m i n . 3 0 s e c . a n d 2 m i n . 5 0 s e c .

S t a b i l i t y n o t b e i n g v e r y b r i g h t , i n f a c t t h e b e s t o f t h e m h a d t o b e r i g g e d

a t 5 ° t o g e t t h e g l i d e a n d t h i s m a d e t h i n g s v e r y t o u c h y .

T h e D a v i s c a m e o u t a r o u n d 3 m i n . m a r k , s t a b i l i t y g o o d . J a k o w s k y a n d

N A C A l e v el p e g g e d a t 3 m i n . 1 5 s e c . S t a b i l i t y g o o d fo r N A C A a n d e x c e l

l e nt f o r J o k o w s k y . F l i g h t c h a r a c t e r i s t i c s w e r e e n t i r e l y d i f f e r e n t h o w e v e r ,

t h e J o k o w s k y looks m u c h i n f e r i o r t o t h e N A C A .

W a y o u t i n f r o n t c a m e D o n ' s F r e n c h c u r v e a n d r u l e r s e c t i o n , g i v i n g

a r o u n d 4 m i n . 1 0 s e c , a n d a s i f t h e i m p r o v e d l i f t f i g u r e s w e r e n o t e n o u g h ,t h e s t a b i l i t y w a s n o t h i n g s h o r t o f a m a z i n g .

I c h e c k e d b y b u i l d i n g a w i n g f o r m y W a k e f i e l d a n d g o t t h e s a m e r e

s u l t s . S o b u i l t " S l i c k S t i c k " w i t h i t b u t f o u n d s t a b i l i t y o f s a m e h i g h o r d e r ,

b u t t h e g l i d e t h e s a m e a s f o r N A C A . H o w e v e r , t h e g l i d e i s q u i t e f a s t s o

I t h i n k t h i c k e n i n g th e s e c t i o n m a y i m p r o v e t h i n g s .



M A X H A C K L I N G E R — A R T I F I C I A L T U R B U L E N C E —T h e R e y n o l d s N u m b e r o f o u r A / 2 m o d e l s v a r i e s f r o m 6 0, 0 00 t o 4 5 ,0 00 ,

t h e e f f e c t i v e o n e o f t h e r u b b e r p o w e r e d m o d e l s i s s o m e w h a t , b u t o n l y

s l i g h t l y , s m a l l e r . A t t h e s e R N n u m b e r s o u r t h i n , c a m b e r e d a i r f o i l s a r e

t h r o u g h o u t " o v e r c r i t i c a l " , b u t t h e y s t a l l a t r a t h e r a s m a l l a n g l e o f a t t a c k

a n d t h i s t h e s o o n e r , t h e s m a l l e r R N a n d t h e g r e a t e r t h e c a m b e r a r e . T h i s

d e v e l op m e n t i s n o t , a s w e m i gh t t h i n k , l i n e ar , b u t s q u ar e or e v e n c u b i c . I f t h e s t a l l o c c u r s s o e a r l y t h a t t h e n o r m a l c a 3 m a x i m u m i s n o l o n g e r r e a c h e d

a t a l l , ( g r a p h ) a r t i f i c i a l t u r b u l e n c e m u s t b e a p p l i e d t o o b t a i n t h e b e s t

a c h i e v e m e n t . I t s a p p l i c a t i o n i s o f t e n s u i t a b l e e v e n w i t h h i g h e r R N n u m

b e r s f o r t h e p u r p o s e o f i m p r o v i n g t h e l o n g i t u d i n a l s t a b i l i t y , b e c a u s e t h e r e

b y t h e C a - C w c u r v e ( P o l a r ) b e c o m e s m u c h r o u n d e r . W e k n o w f r o m p r a c t i c e

t h a t a i r f o i l s , i n c a s e o f V y ( s i n k i n g s p e e d ) b e i n g s m a l l , h a v e a g r e a t e r c a m

b e r ( f o p s - 8 % ) . T h e l a t t e r , h o w e v e r , i n v o l v e s v e r y b a d s t a b i l i t y , a n d i n

s u c h c a s e s a n a r t i c i c i a l m e a n s o f t u r b u l e n c e i s o f t e n t h e o n l y , w e l c o m e

T E S C U E .

T h e r e h a v e b e e n t e s t e d t h e m o s t v a r i e d t y p e s o f a r t i f i c i a l t u r b u l e n c e :

A r o u g h s u r f a c e o f t h e a i r f o i l i n t h e u p p e r t h i r d i n f l u e n c e s t h e m a r g i n a lz o n e ( g r e u z s c h i d e s ) , i t i s t r u e , b u t i t a l s o r e s u l t s i n m o s t c a s e , i n d i s a g r e e

a b l e s t a l l i n g p h e n o m e n a . A t u r b u l e n c e - s t r i p o n t h e u p p e r s i d e s h o r t l y b e

h i n d t h e n o s e ( c a . 1 / 16 s q . ) i s f r e q u e n t l y u s e d b e c a u s e i t i s e a s y t o m o u n t .

I t s e f f e c t i s s i m i l ar b u t s l i gh t l y i n f e r i or t o t h a t o f a t h i n w i r e i n f r on t o f

n o s e . T h e e f f e c t o f t h e e l a s t i c o f t u r b u l e n c e , h o w e v e r , i s s t r o n g e r t h a n a l l

t h e s e m e a n s . T h e d i s t a n c e f r o m t h e n o s e , t h e a n g l e f o r m e d w i t h t h e f r o n t -

t a n g e n t a n d t h e f r e q u e n c y ( a s f i x e d b y t h e t e n s i o n a n d b y d i s t a n c e o f t h e

h o l d i n g w i r e ) a r e u n f o r t u n a t e l y u n k n o w n f a c t s t h a t w i l l h a v e t o b e d e t e r

m i n e d f r o m t i m e t o t i m e b y e x p e r i m e n t s . S u c h e x p e r i m e n t s a r e v e r y e a s y ,

i f y o u p r i c k t h r o u g h t h e s i l k - r o u n d s p u n r u b b e r ( w e c a l l i t h e a t - r u b b e r )

a n d t h e n i n t o t h e n o s e o f t h e w i n g w i t h l o n g p i n s . A n a p p r o x i m a t e v a l u e

f o r s i m i l a r a i r f o i l s i s g i v e n b y t h e d r a w i n g o f t h e 2 n d w i n n e r m o d e l a t

G r a z , w h i c h c o n t a i n s s p e c i f i c v a l u e s . ( I t s f r e q u e n c y c o r r e s p o n d i n g t o t h a t

o f t h e b a s s C ) . T h e e f f e c t o f t h i s " t u r b u l e n c e - r u b b e r " i s o f t e n a m a z i n g ,

e s p e c i a l l y w i t h t h i c k , r o u n d n o s e d a i r f o i l s . T h e c o n n e c t i o n b e t w e e n t h e

v i b r a t i o n o f t h e m a r g i n a l z o n e a n d t h e v i b r a t i o n o f t h e t u r b u l a t o r i s o f

v i t a l i m p o r t a n c e a n d m u s t n o t b e o v e r l o o k e d .

S U M M A R Y — T h e a p p l i c a t i o n o f a n a r ti fi c i a l m e a n s o f t u r b u l e n c e n e e d

n o t a l w a y s r e s u l t i n a n i m p r o v e m e n t o f t h e a c h i e v e m e n t . I n a n y c a s e , h o w

e v e r , t h e l o n g i t u d i n a l s t a b i l i t y g e t s b e t t e r , a n d , t h e r e b y , t h e f l i g h t m o r e

q u i e t a t R N o f 55 , 0 0 0 . T h e b e s t r e s u l t s s o f ar h av e b e e n p r od u c e d b y an

e l a s t i c t i g h t e n e d i n f r o n t o f t h e n o s e o f t h e w i n g , w h o s e p o s i t i o n a n d

t e n s i o n c a n e a s i l y b e d e t e r m i n e d b y e x p e r i m e n t s . I f y o u c a n g e t a q u i e t

f l i g h t a n d r e a c h t h e a n g l e f o r t h e b e s t V y ( s i n k i n g s p e e d ) w i t h o u t s u c h a

" w i r e e n t a n g l e m e n t , " y o u r m o d e l w i l l g l i d e a l i t t l e l o n g e r a s a w i r e i n a n y

c a s e r e s u l t s i n a d d i t i o n a l d r a g . B u t o u r b e s t a i r f o i l s w i t h t h e n e e d e d g r e a t

a s p e c t r a t i o a r e w i t h o u t a r t i f i c i a l t u r b u l e n c e v e r y d i f f i c u l t .



C AR L H E R M E S — S T RE SS ED S K IN W I N G S

W h i l e t h e w r i t e r c a n s e e n o w o r t h w h i l e a e r o d y n a m i c o r s t r u c t u r a l a d

v a n t a g e s i n s h e e t b a l s a w i n g s a s a p p l i e d t o f r e e - f l i g h t o r r a d i o - c o n t r o l l e d

m o d e l s , t h e y d o h a v e t h e d i s t i n c t a d v a n t a g e o f b e i n g e x t r e m e l y e a s y t o p u t

t o g e t h e r . T h e s e w i n g s h a v e b e e n u s e d s u c c e s s f u l l y o v e r t h e p a s t f i v e y e a r s

o n a l l t y p e s o f m o d e l s . T h e m e t h o d d e s c r i b e d , w h i l e e x t r e m e l y s i m p l e ,

i n v o l v e s a f e w fi n e p o i n t s t h a t a r e w o r t h y o f c o n s i d e r a t i o n .

T h e p l a n f o r m c a n b e m o s t a n y t h i n g c o n s i d e r e d p l e a s i n g . C u r v e d o u tl i n e s b e c o m e s l i g h t l y m o r e i n v o l v e d , h o w e v e r , s i n c e a " c u t f r o m s h e e t " o r

l a m i n a t e d t r a i l i n g e d g e i s u s u a l l y r e q u i r e d . T h e a i r f o i l se l e c t i o n i s c r i t i c a l

f r o m a s t r u c t u r a l s t a n d p o n t . S i n c e t h e s h e e t b e c o m e s t h e s p a n i n a w i n g o f

t h i s t yp e , t h e m or e c am b e r t h a t i s ap p l i e d t o t h e s h e e t i t s e l f t h < - b e t t e r o f f



y o u a r e f r o m a s t r e n g t h a n d r i g i d i t y s t a n d p o i n t . M o s t a i r f o i l s h a v e a s uf fi

c i e n t a m o u n t o f u p p e r s u r f a c e c a m b e r n e a r t h e l e a d i n g e d g e b u t o n m a n y

t h e u p p e r c a m b e r n e a r t h e t r a i l i n g e d g e i s v e r y n e a r l y a s t r a i g h t l i n e . W i t h

t h i s t y p e t h e s h e e t d o e s n o t h a v e a c h a n c e t o d o m u c h g o o d i n t h e a f t a r e a

a n d u s u a l l y r e s u l t s i n w a r p e d o r b o w e d t r a i l i n g e d g e s .

T h e t y p e o f w o o d s e l e c t e d i s n o t t o o c r i t i c a l e x c e p t f r o m a w e i g h t s t a n d

p o i n t . Q u a r t e r g r a i n e d m a t e r i a l i s n o t r e c o m m e n d e d s i n c e i t i s h a r d e r t o

b e n d a n d h a s n o p a r t i c u l a r a d v a n t a g e s . S e e c h a r t f o r s i z e s a n d d e n s i t i e s .



T h e a n g l e d l e a d i n g e d g e i s s i m p l e s t s i n c e i t i n v o l v e s n o p r e - s h a p i n g .

T h e e x a c t d i m e n s i o n s w i l l d e p e n d o n th e a i r f o i l , t h e s i z e s g i v e n b e i n g o n l y

a p p r o x i m a t e . T h e g e n e r a l i d e a i s a s s h o w n b e l o w :

On the y 2 A w i n g s n o t r a i l i n g e d g e i s r e q u i r e d , j u s t b e v e l t h e s h e e t . T h e

c e n t e r s e c t i o n w i l n e e d t o b e r e e n f o r c e d t o t a k e t h e e l a s t i c , h o w e v e r .

O n t h e l a r g e r w i n g s , t r y t o d e s i g n s o t h a t s t a n d a r d t r a i l i n g e d g e s t o c k

m ay b e u s e d . I f you w an t t o b e f an c y an e x t r a p i e c e o f T . E . s t oc k m ay b e

us ed to f inish i t off . •



D i b e d r a l j o i n t s a r e h a n d l e d i n t h e u s u a l m a n n e r w i t h h e a v y l e a d i n g a n d

t r a i l i n g e d g e g u s s e t s .

T h e r i b a t t h e d i b e d r a l b r e a k s h o u l d o n t h e l a r g e r w i n g s ( 4 0 0 s i a n d u p )

b e t w i c e t h e n o r m a l r i b t h i c k n e s s s i n c e i t t a k e s q u i t e a l o a d . W e a l s o d o u b l e

s h e e t t h e a r e a f o r o n e r i b s p a c e o n e i t h e r s i d e o f t h e b r e a k , l i k e w i s e t h e

b o t t o m s u r f a c e i n t h i s a r e a . A n a r r o w p i e c e o f n y l o n o r c r i n o l i n e i s t h e n

c e m e n t e d a l l a r o u n d t h e s e a m . N e e d l e s s t o s a y , a l l t h e s e j o i n t s s h o u l d b e



T h e f o l l o w i n g i s t h e a s s e m b l y p r o c e d u r e :

1 . G l u e s h e e t s t o g e t h e r t a k i n g p a i n s t o s e e t h a t t h e s e a m s a r e c l o s e d .

2 . L a y o u t w i n g p l a n o n t h e s h e e t w i t h a s o f t p e n c i l . D r a w i n r i b l o c a t i o n s .

( N o f u l l s i z e p l a n s a r e r e q u i r e d w i t h t h i s m e t h o d ) . B e s u r e t o l a y o u t

t h e c h o r d w i s e " fl at p a t t e r n " d i m e n s i o n s . T h i s c a n , b e s t b e d o n e b y b e n d

i n g a t h i n s t r i p o f w o o d o v e r t h e t o p o f t h e m e t a i l r i b t e m p l a t e a n d

m a r k i n g t h e t r u e l e n g t h .

3 . C u t ou t s h e e t .

4 . C u t r i b s u s i n g t e m p l a t e .

5 . R e m o v e a n y " p e r m a n e n t s e t " f r o m t h e l e a d i n g a n d t r a i l i n g e d g e s b y

s t e a m i n g . C e m e n t t o s h e e t a n d w a t c h c a r e f u l l y w h i l e d r y i n g f o r a n y

" b o w s " w h i c h m i g h t c r e e p i n .



C u t r i b s a t r e a r t o p r o p e r l e n g t h a n d c e m e n t i n p l a c e . T r i m b o t t o m o f

r i b s a s n e c e s s a r y a f t e r c e m e n t i n g .

C e m e n t p a n e l s t o g e t h e r with p r o p e r d i b e d r a l . Important': B e f o r e a d d i n g

g u s s e t s c h e c k t o s e e t h a t w i n g h a s d e s i r e d w a s h - o u t . T o a d j u s t , c r a c k

e i t h e r l e a d i n g o r t r a i l i n g e d g e j o i n t ( n o t b o t h ) a n d t r i m j o i n t o r a d d

s m a l l b a l s a w e d g e s u n t i l w i n g p a n e l s a r e a s y o u w a n t t h e m a n d t h e n

r e c e m e n t .

N 6 w a d d g u s s e t s , r i b s , a n d e x t r a s h e e t a t t h e j o i n t .



JO S E PH B O Y L E — I N D O O R G L ID E R S —We g enera l ly f l ew indo o r g l iders ev ery Sunda y m o rn ing a nd fo und tha t

our average t ime was increased by about 5 seconds every week. After each

sess ion we would discuss the f l ights and in a general way decide on a change

or ch an ge s we cou ld mak e for the next wee k f ly ing .

We would bui ld three or four g l iders a l ike as to weight and a irfo i l .

Out of each week's output o f g l iders , one or perhaps two would show prom

ise . The others , for some unknown bui l t - in error would s imply not perform

wel l . These we just threw away and concentrated on the best ones .

Usua l ly , a bo ut 1 0 seco nds co u ld be a dded to a g o o d g l ider ' s perfo rm a nce

by ca refu l a d jus tm ents a nd perha ps s l i g h t m o di f i ca t io n here a nd there . Oneof the tr ic ks wh ic h I d is cov er ed was that a t ig hte r c ircle cou ld be obta in ed

wi tho ut a p pa re nt l o ss o f t im e o r l a unch in g co ntro l by s im ply redu c in g the

rudder area . This was an advantage to us as we were f ly ing in a long but

n a r r o w b a l l o o n h a n g e r ,



W h e n I s t a r t e d t o f l y g l i d e r s i n t h i s h a n g e r I d o p e d m y g l i d e r s j u s t a s

1 h a d d o n e f o r o u t d o o r g l i d e r s . G e n e r a l l y , i n o r d e r t o f l y a g l i d e r m o r e t h a n

o n e w e e k a n e w r u d d e r a n d s t a b i l i z e r h a d t o b e m a d e d u e t o t h e d o p e w a r p

i n g t h e v e r y t h i n s e c t i o n s , a n d t h e y a l s o q u i c k l y b e c a m e b r i t t l e . L a c q u e r

a n d g l i d e r p o l i s h w e r e t r i e d n e x t w i t h b e t t e r r e s u l t s b u t s t i ll a l i t t l e w a r p -

a g e o c c u r r e d . S o I t r i e d s e v e r a l g l i d e r s w i t h n o f i n i sh a t a l l . T h i s w a s r a t h e r

u n u s u a l b u t i t k e p t t h e s u r f a c e s f r o m w a r p i n g . T h e m o d e l w a s s a n d e d v e r y

t h o r o u g h l y w i t h 6-0 s a n d p a p e r b e f o r e e a c h s e s s i o n o f f l y i n g . O c c a s i o n a l l yI r u b b e d t h e m od e l w i t h a p i e c e o f w ax p ap e r , b u t i t d i d n o t s e e m t o m ak e

a n y d i f f e r e n c e . I st i l l h a v e a t h r e e y e a r o l d m o d e l o n w h i c h t h e w i n g , s t a b



a n d r u d d e r a r e s t i l l s t r a i g h t a n d w a r p f r e e . I b e l i e v e t h a t t h e i n c r e a s e i n

d r a g i s m o r e t h a n o f f s e t b y t h e w a r p f r e e s u r f a c e s t h a t a r e s o i m p o r t a n t t o

e ff ic ie n t g l i d i n g m o d e l . — ( S i n c e g l i d e r s m o v e a t s u c h s l o w s p e e d a f t e r t h e

i n i t i a l l a u n c h , t h e d r a g m a y n o t b e m o s t i m p o r t a n t i t e m . )

I n g e n e r a l w e f o u n d l o w d i h e d r a l a n d f a i r l y l o n g t a i l m o m e n t a r m a

m u s t . A l m o s t e v e r y o n e a t t h e " B r a i n b u s t e r s " u s e d f a i r l y s m a l l s t a b i l i z e r

a n d r u d d e r w i t h s h o r t n o s e m o m e n t a r m . F u s e l a g e s w e r e u s u a l l y V/4 t i m e sl o n g e r t h a n t h e s p a n o f t h e w i n g . S t a b i l i z e r h a d a b o u t 1 5 % o f t h e w i n g a r e a

a n d t h e r u d d e r a p p r o x i m a t e l y 5 % . M y w i n g s w e r e m a d e f r o m l i g h t 3 / 6 x 4 "

s t o c k , w e r e u n d e r c a m b e r e d a b o u t 1 / 1 6 a n d h a d a b l u n t l e a d i n g e d g e .



A L A N C . B R O W N — G L I D E R T O W —P l e a s e f i n d e n c l o s e d t h e p l a n s o f m y A / 2 S a i l p l a n e .

I t h a s s e v e r a l p o i n t s o f i n t e r e s t . F i r s t o f a l l , t h e w i n g a n d t h e t a i l s e c

t i o n s a r e S i g u r d I s a a c s o n ' s t u r b u l e n t fl o w a i r f o i l s . A s t h e y a r e o n l y e f f e c t i v e

a b o v e a c e r t a i n c r i t i c a l R e y n o l d ' s N u m b e r , t h e t h i c k n e s s / c h o r d r a t i o i s

r e d u c e d a t t h e t i p s , t o p r e v e n t l a m i n a r b r e a k a w a y a n d h e n c e t i p s t a l l i n g .

T h i s h a s b e e n p r o v e d q u i t e e f f e c t i ve , a n d s o a f a i r l y s m a l l d i h e d r a l c a n b e

s a f e l y u s e d .O f f s e t t o w h o o k s s e e m t o b e o f t e n u s e d i n A m e r i c a , b u t t h e s e a r e n o t

t h e a n s w e r f o r t h i s r e a s o n : A t t h e b e g i n n i n g o f t h e t o w t h e p o s i t i o n i s a s

s h o w n . T o w h o o k o n r i g h t h a n d s i d e o f f u s e l a g e c o u n t e r a c t s r i g h t r u d d e r



se t t ing . When the p la ne i s g e t t ing to wa rds o v erhea d , the t ens io n o n the l ine

tends to ro l l the a ircraft in the same way as the rudder i s turning , and the

a ircr a f t ' s turn i s g en era l ly a g g r a v a t ed so m u ch tha t i t i s im p o ss ib l e to g e t

overhead launch, the turn pull ing it off the l ine of tow right into a spiral

launc h at a tow l ine an gl e o f ab ou t 60° .

Regarding your wedged rudder, I have decided to go over to the sys

tem mysel f now. Previously I had used t the tow hook operated auto rudder

because i t g ives a s l ight amount of extra contro l in that you can s lacken

off or t ighten the l ine to a certain extent on the tow, and so put the rudder

where you want i t . However, I have decided that the l imitat ions of th is

method on gusty weather or on the point o f release when you are wait ing

for a the rmal far out we ig he d the s l ig ht contro l ad va nt ag e.



W A LTE R E R B A C H — T H E P A L M G R E N F O R M U L A S —A r v i d P a l m g r e n h a s w o r k e d o ut a s e t o f u s e f u l f o r m u l a s f o r r u b b e r

p o w e r e d m o d e l p o w e r p l a n t s b u t u n f o r t u n a t e l y t h e y a r e i n m e t r i c u n i t s a n d

b a s e d o n b l a c k r u b b e r c h a r a c t e r i s t i c s . F o r m o r e r e a d y u s e w e h a v e c o n v e r t e d

t h e m t o E n g l i s h u n i t s a n d g r a p h e d s e v e r a l o f t h e m . H e r e w i t h t h i s i n f o r m a

t i o n i s p r e s e n t e d t o g e t h e r w i t h s u g g e s t i o n s a n d i l l u s t r a t i o n s f o r i t s u s a g e .

A s y o u w i l l s e e f r o m o u r e x a m p l e s l a t e r o n t h e b l a c k r u b b e r i s a v e r y s m a l l

h a n d i c a p , i n f a c t s e e m s t o c a n c e l i t s e l f o u t . T h e r e s u l t s a r e s t i l l , a s P a l m -g r e n s t a t e d , " a p p r o x i m a t e l y v a l i d fo r s i n g l e s k e i n r u b b e r p o w e r e d m o d e l

a i r p l a n e s o f s t a n d a r d d e s i g n , " a n d c e r t a i n l y w o r t h t h e l i t t l e e f f o r t t o u s e

t h e f o r m u l a s .

T h e e a s i e s t w a y t o s h o w t h e w o r t h o f t h i s m a t e r i a l i s t h r o u g h a n i l l u s t r a t i o n . L e t u s d e s i g n t h e p o w e r p l a n t fo r a t y p i c a l o u t d o o r m o d e l h a v i n g a

4 0 i n . s p an w i n g o f 2 0 0 s q . i n c h e s ar e a w i t h an ov e r a l l w e i gh t o f 8 ou n c e s .

F o r m u l a ( 1 ) o r t h e s p a n p o w e r l o a d i n g g r a p h s h o w t h a t 3 0 s t r a n d s o f y 8

s h o u l d b e t h e t o p p o w e r u s e d . F o r m u l a s ( 9 ) o r ( 1 0 ) o r t h e o u t d o o r p r o p



Su re ly th is i s a c lo se eno ug h chec k. ( T o be mos t sc ient i f ic the met hod s

should have been combined. By using the answer from method one and

a ssum ing a su i ta b le pro p d ia m eter , we ca n so lv e the pro p rps fo rm ula ba ck

wa rds to f ind the needed b la de wid th . Try ing th i s fo r o dd o d ia m eters g iv es

a 5% in. blade width for a 12 in. prop and a 1% in. blade width for a 20 in.

pro p , bo th a wkwa rd but rea so na b le fo r 3 0 s t ra nds o f

As a f ina l s t ep we can co mp ut e the ap pr ox im at el y , a t mea nto rque o r cru i s ing co nd i t io ns . The thrus t wi th 1 5 % pro pe l l er s l ip i s

F = 1.3 -4- IS - 10 = 1.3 x l l 5 - 10 = l . l o z s .

(Note: P a l m g r e n a h s in h is orig inal thrust formula but in

a l l o f m y ca l cu la t io ns th i s g iv es a ppa rent ly erro neo us resu l t s ;

co m ing c lo ser in m y o p in i o n to a c t ua l i ty . The L / d ca l cu la t io n us in g

g iv es 3 .1 wh ic h cer ta in ly see m s lo w. )

Wh i l e the res t o f the fo rm ul as , tho se for a l t i tu de , mo to r ru n an d f l ight

t im e a re perfec t ly s t ra ig ht fo rwa rd a nd no t needed fo r the des ig n they

p i tch g r a p h g iv e the a p pr o p r i a t e p i t ch to wh ic h the pro p sho u l d be ca rv ed .

Fo r a h ig h c l im bing sh ip the m in im um p i tch ind ica ted , IS^fa ' n -> should be

used . Fo r m o re sa t i s fa c to ry a l l a ro und perfo rm a nce the m ea n p i t ch (wh ich

is a lways 1% t imes the minimum) of 23 l / 2 in. should be used. A check of the

bet ter Am erica n o utdo o r sh ips fo r wh ich we ha v e in fo rm a t io n sho ws tha t

the m ea n p i t ch g ra ph c lo se ly represents o ur pra ct i se .

N ow th er e ar e two wa y s in wh ic h we can proce ed and thes e two w ay sshould check each other. Method One: We have a formula (No. 8 ) te l l ing

us how far the model wi l l f ly each second under cruis ing condit ions and

so by using the propel ler va lue for mean torque, we can ca lculate the neces

s a r y p r o p r p s . M e t h o d T w o : F o r m u l a ( 6 ) g i v e s p r o p r p s d i r e c t l y a n d b y

dec id i ng upo n su i ta b le pro pe l l er d im e ns i o ns we ca n use it .



O f n i n e r e c o r d i n d o o r s t i c k s w h i c h w e f e l t h a d d o n e a b o u t a l l t h a t c o u l d

b e e x p e c t e d o f t h e m s i x h a d c o e f f i c i e n t s w i t h i n

F R A N K B E T H W A I T E — T H E R M A L R U D D E R —( R e : A / 2 S a i l p l a n e i n t h e 1 95 2 Y e a r B o o k . ) T u r n w a s b y a s p r i n g - l o a d e d

r u d d e r t a b . D o n o t t h i n k I m e a n a u t o m a t i c r u d d e r , s h e h a d t h a t t o o , o f

c o u r s e . B u t t h e t a b w a s b i a s e d t o t h e " t u r n " p o s i t i o n b y t h e t o r s i o n o f a n

u n s t r e t c h e d r u b b e r b e n d , t w i s t e d s l i g h t l y . M e t h o d w a s t o p u t a t u r n o r t w o

i n t h e b e n d , a n d h a n d g l i d e t h e m o d e l . T h e t a b w o u l d b l o w s t r a i g h t a s s h e

f l e w . S o , p u t a n o t h e r t u r n i n , a n d a n o t h e r , u n t i l t h e t a b j u s t h o l d s a g a i n s t

t h e t u r n " s t o p " a t n o r m a l s p e e d . T h i s w a y I o b t a i n e d v e r y t i g h t c i r c l e s

w i t h a b i g " 8 4" m o d e l , an d ye t w h e n s h e h i t t u r b u l e n c e an d t r i e d t o s p i r a l ,

t h e r u d d e r j u s t b l e w s t r a i gh t a s s oo n as s p e e d b u i l t u p a k n ot or t w o , an ds h e s i m p l y z o o m e d , a n d t u r n e d a g a i n o f t h e t o p o f i t. I t a l l w o r k e d v e r y

w e l l , an d t i m e s w as ar ou n d 2 30 - 2 4 0 s e e s o f f 30 0 f e e t i n c a l m a i r . — I d o n o t

r a t e i t a s a g o o d m o d e l n o w . R e a s o n s : S i n k i n g s p e e d s h o u l d b e l o w e r , p e n e

t r a t i o n a n d b u o y a n c y i n r o u g h a i r s h o u l d b e b e t t e r , a n d h u n t i n g c i r c l e

s h o u l d b e l a r g e r .

A L A T E R S A I L P L A N E — I t s c h ie f v i r t ue s a r e i ts a b il i t y t o h u nt t he r-

m a l s i n v e r y w i d e c i r c l e s , a n d t i g h t e n i t s c i r c l e i n s t a n t l y a n y t u r b u l e n c e i s

e n c o u n t e r e d . I t t o o k a l o n g t i m e t o d e v e l o p t h i s . P r i n c i p a l l y , a v e r y s m a l l

r u d d e r i s c o m b i n e d w i t h s l i g h t t i l t i n t h e s t a b i l i z e r , t h e w h o l e b e i n g o n a

m o d e l w i t h l a r g e r a d i u s o f g y r a t i o n . ( T h a t i s, t h e w e i g h t i s n o t c o n c e n t r a t e d ,

b u t i s w e l l s p r e a d o u t i n t h e e n d s ) a n d a s m a l l i s h s t a b i l i z e r i s o p e r a t e d a ta t a s m a l l w i n g - t a i l d i f f e r e n c e a n d a f a r - b a c k C . G . p o s i t i o n ( r e l a t i v e l y ) . T h e

t a i l m o m e n t a r m i s l o n g e n o u g h t o t a k e c a r e c f a n y s t a b i l i t y t r o u b l e s t h a t

w o u l d n o r m a l l y b e e x p e c t e d w i t h t h i s s o r t o i s e t - u p . I n fl i g h t, t h e w h o l e

a f f a i r w o r k s l i k e t h i s :

s h o u l d b e s t u d i e d c a r e f u l l y fo r a n u n d e r s t a n d i n g o f th e b a s i c f a c t o r s w h i c h

a f f e c t t h e p e r f o r m a n c e a n d d e a d a i r e n d u r a n c e .

F o r i n d o o r m o d e l s t h e p r o c e d u r e o u t l i n e d a b o v e c a n a l s o b e c a r r i e d

t h r o u g h , u s i n g t h e m a x i m u m p i t c h p r o p f o r m u l a . T h e m a x i m u m f l i g h t t i m e

f o r i n d o o r s t i c k j o b s i s g i v e n v e r y c l o s e l y b y t h e f r e e w h e e l i n g p r o p

f o r m u l a



T h e s l i gh t t i l t t o t h e t a i l d o e s n o t e f f e c t t h e t ow a t a l l . A f t e r r e l e a s e i n

c a l m a i r , t h e au t o r u d d e r d e f l e c t s t h e t ab a t r i f l e — ab ou t an e i gh t h o f an i n c h

— a n d a v e r y w i d e l e f t c i r c l e r e s u l t s o f a b o u t 1 50 a n d 2 0 0 y a r d s d i a m e t e r .

A s s o o n a s a n y t u r b u l e n c e s h o w s u p , h o w e v e r , t h e n o s e r u n s h i g h e r , b u t t h e

l a r g e r i n e r t i a p r e v e n t s " n o s e l i g h t " s t a l l i n g , a n d t h e e x t r a l o a d o n t h e t a i l ,

w h i c h p r o m p t l y t i g h t e n s t h e t u r n , a l s o c h e c k s a n y s t a l l . T h e w h o l e e f f e c t i s

u n c a n n y . S h e ' s h u n t e d l i k e t h i s i n f r o n t o f b i g c r o w d s a n d h a d t h e m s p e e c h

l e s s . F i r s t t i m e t h r o u g h m a y n o t b e q u i t e c e n t r e , b u t i t t u r n s h e r e n o u g h

t o c o n n e c t m o r e q u i c k l y n e x t t i m e , a n d i t ' s n o t l o n g b e f o r e s h e ' s i n a n d

a w a y . T h e p r o b a b i l i t y o f h o o k i n g o n e i s o b v i o u s l y m u c h h i g h e r t h a n t h a t o f

t h e f i x e d r a d i u s m o d e l . D i a m e t e r i n t u r u b u l e n c e , b y t h e w a y , w o u l d b e

ab ou t 4 0 t o 50 yd s .

A C T I O N D U R I N G C I R C L I N G — Y o u a s k s pe c i f i ca l l y a b o ut t h at p o w e r

j o b o f m i n e . T o u n d e r s t a n d t h a t o n e I w i l l h a v e t o s t a r t a l o n g w a y f u r t h e r

b a c k . — F i r s t , t u r n i n g a n d s p i r a l s t a b i l i t y . A n y t u r n , i n d u c e d b y r u d d e r (o r

a i l e r o n ) w o r k s l i k e t h i s : ( A s s u m e t h e m o d e l t o b e l e v e l a n d t h e r u d d e r t h e n

d e f l e c t e d ) . T h e d e f l e c t e d r u d d e r c r a b s t h e s h i p a l i t t l e , d i h e d r a l t h e n r o l l s

t h e m o d e l b e c a u s e " a i r g e t s u n d e r t h e a d v a n c e d t i p , " t h e l i f t f o r c e o f t h eb a n k e d w i n g t h e n h a s a h o r i z o n t a l c o m p o n e n t , a n d t h i s i s t h e f o r c e w h i c h

a c t u a l l y t u r n s t h e m o d e l . A l s o , a s t h e t u r n d e v e l o p s , t h e m o d e l t e n d s t o

s l i p i n a l i t t l e , s u c h t h a t d i h e d r a l i s n o w t e n d i n g t o r o l l i t l e v e l a g a i n .

T h e t u r n w i l l s t a b i l i z e a t t h a t p o i n t w h e r e t h e o v e r b a n k i n g t e n d e n c y

( b e c a u s e t h e o u t e r w i n g i s t r a v e l l i n g f a s t e r t h a n t h e i n n e r , a n d t h e r e f o r e

l i f t i n g m o r e ) a n d t h e t e n d e n c y o f t h e n o s e t o s l i p d o w n , ( b e c a u s e t h e s i d e

s l i p i s r e s i s t e d l a r g e l y b y t h e r u d d e r a t t h e b a c k ) ; a r e e x a c t l y c o u n t e r

b a l a n c e d b y t h e t e n d e n c y o f t h e m o d e l t o r u n s t r a i g h t a n d r e s i s t t u r n i n g

( b e c a u s e i t h a s v e r t i c a l s u r f a c e s , a c t u a l o r e f f e c t i v e , b o t h f o r e a n d a f t ) a n d

t h e t e n d e n c y o f t h e d i h e d r a l l e d w i n g s , s l i p p i n g , t o r o l l t h e m o d e l l e v e l . T h e

a c t i o n i s c o m p l e x . Y o u r " C i r c u l a r A i r f l o w " w i l l p r e d i c t t h e l i f t c o e ff i c i e n ta t w h i c h t h e m o d e l w i l l f i n a l l y t r i m , a n d t h i s m a y b e a s p i r a l d i v e .

H o w e v e r , t h e i m p o r t a n t f a c t i s t h i s — a m o d e l m a y b e t r i m m e d p e r f e c t l y

s a f e l y t o a s l o w , g l i d i n g t u r n . L e t t h e s p e e d b u i l d u p , f o r a n y r e a s o n w h a t

s o e v e r , a n d t h e a n g l e o f b a n k i n c r e a s e s — i t m u s t t h e n c o m e t o a p o i n t w h e r e

t h e d e f l e c t e d r u d d e r d r i v e s t h e n o s e d o w n , a n d y o u a r e a w a y i n a s p i r a l d i v e .

T h i s i s f u n d a m e n t a l . T h u s , f o r a n y m o d e l w h i c h m a y a t s o m e s t a g e b e

t r a v e l l i n g v e r y f a s t , t u r n b y r u d d e r i s p o t e n t i a l l y d a n g e r o u s , a n d i s t h e r e

f o r e t o b e a v o i d e d .

I t i s c l e a r t h a t s o m e m e t h o d o f t u r n i n g o t h e r t h a n a p o s i t i v e l y d e f l e c t e d

r u d d e r i s r e q u i r e d . T h e w e i g h t e d " d r a g - f l a p " u s e d o u t n e a r t h e w i n g t i p ,

b l o w s s t r a i g h t a t h i g h s p e e d , i s q u i t e s a t i s f a c t o r y . A v e r y l i g h t l y s p r i n g -

l o a d e d r u d d e r t a b , w h i c h j u s t h o l d s i t s d e f l e c t i o n a t d e s i g n g l i d e s p e e d , a n d

w i l l b l o w s t r a i g h t t h e r e a f t e r , i s a n o t h e r v e r y s a t i s f a c t o r y m e t h o d . O r o n e

c a n u s e a t i l t e d t a i l . T h e r e a s o n w h y a t i l t e d t a i l i s s a f e i s n o t g e n e r a l l y a p

p r e c i a t e d , an d I h av e n e v e r s e e n i t i n p r i n t , s o h e r e i t i s .

T h e t u r n , o f c o u r s e , a r i s e s f r o m t h e h o r i z o n t a l c o m p o n e n t o f t h e t a i l ' s

l i f t f o r c e ( a n a f t C . G . p o s i t i o n a n d p o s i t i v e t a i l l o a d , a r e f u n d a m e n t a l t o

t h e t i l t e d t a i l m e t h o d ) . N o w , a s s p e e d b u i l d s u p f o r a n y r e a s o n a t a l l , t h e

w i n g a n g l e o f a t t a c k d e c r e a s e s . T h e r e i s a l w a y s s o m e w i n g - t a i l a n g u l a r

d i f f e r e n c e , w i t h t h e t a i l a l i t t l e l e s s p o s i t i v e t h a n t h e w i n g . T h u s , a s t h e

w i n g a n g l e o f a t t a c k d e c r e a s e s , t h e t a i l a n g l e o f a t t a c k t e n d s t o a p p r o a c h

z e r o , o r m o r e s p e c i f i c a l l y , t h e n o - l i f t a n g l e . O n c e t h e r e i s n o l i f t f r o m t h e

t a i l , t h e r e i s n o t h i n g , n o li f t , n o s i d e f o r c e , s o t h e t u r n s t o p s . A n a l y z e d

r i g h t o u t , t h i s m e a n s t h a t a n y m o d e l t r i m m e d w i t h a t i l t e d t a i l w i l l h a v e

o n e d e f i n i t e s p e e d , a n d r a d i u s o f t u r n , a t w h i c h i t w i l l b e s t a b l e . F a s t e r o r



s l o w e r s p i r a l l i n g o r o t h e r w i s e u p s e t , i t w i l l a l w a y s r e v e r t t o t h i s f l i g h t

p a t h . F o r t h i s r e a s o n I p r e f e r i t .

S P I R A L P O W E R C L I M B — N o w f or t he p o w e r s i d e o f t he p i c t u r e .

A t h i g h t h r u s t - w e i g h t r a t i o s i t i s a l m o s t i m p o s s i b l e t o p r e v e n t a m o d e l f r o m

l o o p i n g ( u s i n g n o r m a l t r i m m e t h o d s ) , a n d s o w h a t m u s t b e d o n e i s t oa r r a n g e t h a t t h e m o d e l r o l l s i n p h a s e w i t h i ts l o o p , t h u s p r o d u c i n g a n

u p w a r d h e li x . C l e a r l y , t h e g r e a t e r t h e r a d i u s o f lo o p , t h e g r e a t e r w i l l b e

t h e t i m e i n w h i c h t o a r r a n g e t h e m o d e l r o l l s . A n d a l e f t h a n d t u r n , w i t h a

r e a l l y f a s t m o t o r , p r o d u c e s a u s e f u l n o s e - u p g y r o m o m e n t .

T o c o m b i n e a l l t h i s , t h e m o d e l i n q u e s t i o n i n t e r c e p t s t h e l o w e r , l e f t -

g o i n g s w i r l o f th e p r o p - w a s h , a n d t h e l o w m o u n t e d w i n g le t s t h e u p p e r

s w i r l g o o v e r u n c h e c k e d . N e t r e s u l t i s t o d r i v e t h e n o s e l e f t .

A t l o w s p e e d s , p r o p w a s h ( b l a s t a n d s p i n ) i s a t a m a x i m u m h e n c e t h e

l e f t - t u r n i n g e f fe c t i s c o n s i d e r a b l e — a s i s a l s o , t h e r e f o r e , t h e g y r o f o r c e

l i f t i n g t h e n o s e u p . A s s p e e d b u i l d s u p t h e p r o p w a s h b e c o m e s r e l a t i v e l y

l e s s e f f e c t i v e , h e n c e t h e t u r n o p e n s o u t a n d t h e n o s e - u p f o r c e d e c r e a s e s .

T h e e f f e ct i s f o r t h e m o d e l t o a c c e l e r a t e i n a n o p e n i n g s p i r a l o r h e l i x . I t

s e t t l e s a f t e r f o u r o r f i v e s e c o n d s i n t o a f l i g h t p a t h i n c l i n e d u p w a r d a b o u t

5 0 -6 0° b a n k e d l e f t a b o u t 4 5 ° , a n d t r a v e l l i n g e x t r e m e l y f a s t . O n c e t h e m o t o r

c u t s , i t u s u a l l y d o e s a h a l f a l o o p , a n d r o l l s o f f t h e t o p i n t o i t s r i g h t - h a n d

g l i d e t u r n . I f a t a n y t i m e t h e s p e e d b u i l d s , i t t e n d s s i m p l y t o r u n s t r a i g h t

a n d l o o p — b o t h , i n t e r c e p t e d p r o p - w a s h a n d t i l t e d t a i l , a s m e t h o d s o f t u r n

t e n d t o z e r o a t s p e e d , an d a l l t h a t i s l e f t i s l oop , b e i t v e r t i c a l , ob l i q u e or

h o r i z o n t a l . H e n c e t h e m o d e l t e n d s t o b e s a f e , i f s e n s i b l y h a n d l e d .

I t t o o k m e a l i t t l e w h i l e t o u n d e r s t a n d t h e p r i n c i p l e o f t h e o p e n i n g

s p i r a l a f t e r l a u n c h i n g . A s m e n t i o n e d i n t h a t A e r o m o d e l l e r a r t i c l e , a l a u n c h ,w i n g s l e v el a n d n o s e u p , t e n d s t o s e t t l e i n t o a f i n a l h e l i x t h e a x i s o f w h i c h

i s i n c l i n e d s o m e 3 0 - 4 0 ° f r o m t h e v e r t i c a l . A l a u n c h t o t h e N o r t h , f o r e x

a m p l e , w o u l d r e s u l t i n t h e m o d e l c l i m b i n g a w a y , r o l l i n g a r o u n d a h e l i x

i n c l i n e d a b o u t t h e S . W . h o r i z o n . F i n a l l y , I r e a l i z e d t h e m e t h o d a n d n o w

a l a u n c h , f u s e l a g e l e v e l a n d b a n k e d s t e e p l y r i g h t w i l l r e s u l t i n t h e h e l i x

g o i n g s t r a i g h t o v e r h e a d . R a t i o s , o f c o u r s e , a r e i m p r o v e d .

I t h i n k t h a t i s a b o u t a l l . T h e m o d e l d i d w o r k a s p l a n n e d a n d i t s p e r

f o r m a n c e r e a l l y w a s t e r r i f i c — r a t i o s a b o u t 2 0 -2 2 w e r e t h e b e s t I c a n e s t i

m a t e . I w a s h e d i t o u t c o m p l e t e l y o n e c a l m e v e n i n g . T h o u g h t l e s s l y I

c h a n g e d t h e b r a n d o f p r o p . T h e p o s t m o r t e m d i s c l o s e d t h a t t h e o l d h e a d

h a d b r o a d e r , t h i c k e r , h i g h e r p i t c h t i p s t h a n t h e n e w o n e o f t h e s a m e n o m i n a l d i m e n s i o n s . A s a r e s u l t I l o s t s o m e o f t h e t u r n , an d t h e s h i p d i d on e

l o o p t o a n i n c o m p l e t e r o l l — t h e p h a s i n g h a d b e e n a l t e r e d . S h e e r c a r e l e s s n e s s .

T h e l o w e r f o r w a r d f i n w o r k s , b u t d e f i n i t e l y . A p y l o n j o b , d e a d t r u e a n d

s t r a i g h t , t e n d s t o g o r i g h t , o f c o u r s e . A s t h e r e l a t i v e p o s i t i o n o f t h e p r o p -

w a s h i n g i s s h i f t e d , t h e t e n d e n c y t o t u r n s h i f t s t h r o u g h z e r o t o a l e f t

t e n d e n c y .

I h a v e d e m o n s t r a t e d t h i s o n a m o d e l w i t h a m o v e a b l e m o t o r . Y o u n o t e

t h e C . G . p o s i t i o n a n d a n g u l a r d i f f e r e n c e . A c t u a l l y , I s t a r t e d o u t w i t h C . G .

a t a b o u t 9 0 % a n d a s m a l l a n g u l a r d i f f e r e n c e . B u t , a l t h o u g h t h e s h i p w a s

s t a b l e i n t h e g l i d e , i t h a d s o h u g e a r a d i u s o f r e c o v e r y a f t e r a d e a d s t a l l

t h a t i t f r i g h t e n e d m e . S o t h e w i n g w e n t b a c k a n d s o m e m o r e a n g l e w e n tw i t h i t. C e r t a i n l y t h e l o o p w a s n o w t i g h t e r , b u t s t i l l o p e n e n o u g h t o b e

e a s y a n d s a f e . A d j u s t m e n t s w e r e n o t t o u c h y . B u t . l o o k i n g b a c k o n i t, I n o w

r e a l i z e t h a t t h e f i r s t f e w s e c o n d s d u r i n g w h i c h i t w a s t u r n i n g t i g h t l y ,

a c c e l e r a t i n g a n d e s t a b l i s h i n g i t s p r o p e r h e l i x w e r e p r e t t y c r i t i c a l , s o l e l y

b e c a u s e o f t h e t e r r i f i c p o w e r a n d t h e t i g h t t u r n s . A s s p e e d b u i l t , e v e r y t h i n g

o p e n e d o u t , a n d t h e s h i p p e r f e c t l y d o c i l e .



HANK COLE—DEAR FRANK—(Oct. 1951)—

Noted your interest in the Ci r s ta b i l i ty t erm . Th i s i s the ro l l ing m o m ent

resu l t ing f ro m ro ta t io na l v e lo c i ty in co ef f i c i en t fo rm . The m o st pro m inent

part o f th is term arose from the fact that the rotat ion causes the outbroad

t ip to travel faster than the inboard t ip . S ince th is generates more l i f t on

the outboard t ip than the inboard one, the resul t i s a ro l l ing moment into

the turn. This i s the major ef fect contribut ing to spira l instabi l i ty and as

you can see indicates that h igh aspect rat io jobs are more suscepible to

spi ra l d ive s than low as pe ct ones . I am sur e you are a l re ad y fa mil ia r wi th

the effect, but not in the terminology I use. The above effect can be counter

acted by cathedral in the ta i l , a large subrudder, or by moving the center

of gravi ty back. The long job Wakef ie ld of mine uses a combinat ion of large

sub rudder and rearward locat ion of C.G. Incidenta l ly , the above ef fect has

a stabi l iz ing inf luence in turns by reducing the angle o f bank i f the turn

t ightens which tends to ra ise the nose as the turn t ightens . This i s es

pec ia l ly des i ra b le fo r wind so a r ing .

By the way, model design may be carried out in the same way as full

sca le des ign. I could s i t down and in about two months of fu l l t ime workco u ld fo r in s ta nce des ig n the o p t im um Wa kef i e ld . Th i s i s ju s t to g iv e y o u

an idea of how much work would be involved. The procedure of opt imizing

is far from s imple . I d id carry i t through for an indoor model once and

came up with a des ign which has consistent ly done over 20 min. For i ts

we ig ht , the jo b o utperfo rm s a ny th ing I 'v e seen indo o rs . But , a s y o u wel l

know, in indoor work, l ight weight contributes to performance as wel l as

e f f ic i ency . Al th o u g h the a c tua l des ig n pr o ce dur e i s m uc h to o co m pl i c a te d

to ca rr y thr o ug h fo r pra ct i ca l purp o se s , I u su a l l y rpa ke ro ug h pre l i m in a ry

des ig n ca l c u la t i o ns o n end ura n ce , by es t im a t i ng pa r a s i t e a nd ind uce d dr a g

and avai lable l i f t coeff ic ients . From this you can ca lculate , the

whi ch i s pr opo rt ion al to end ura nc e. I t was on th is ba si s that I de s i gn ed my

lo ng jo b. R ou g h ca lcu lat ion s pr ove d that th is layout wo ul d have a 15%

edge in endurance over the convent ional layout and about a 5% edge over

the canard layout .

— J a n . 1 9 5 2 —

Never seem to set t le down to wri te th is th ing on spira l s tabi l i ty . Went

on a long skiing trip the f irst part of this month and the latter part of

December. Have to get in condit ion because I am racing th is year. I guess



t h i s c o m p e t i t i o n b u s i n e s s g e t s i n y o u r b l o o d a f t e r a w h i l e . A n y w a y , I

t h o u g h t i t w a s a b o u t t i m e t o s e n d y o u s o m e m o r e d e t a i l s o n t h e i d e a s I

m e n t i o n e d . T h i s w o r k o n s p i r a l s t a b i l i t y h a s b e e n d o n e b y m a n y i n t h e f u l l -

s c a l e f i e l d , b u t , a s y o u s a y , n o b o d y h a s a c t u a l l y m a d e a c o m p r e h e n s i v e s t u d y

i n r e g a r d s t o m o d e l s . T h e r e a s o n i s q u i t e o b v i o u s . T h e e q u a t i o n s o f m o t i o n

a r e m u c h t o o d if f i cu l t t o u n d e r s t a n d u n l e s s o n e i s w e l l t r a i n e d i n a e r o

d y n a m i c s a n d m a t h e m a t i c s . I f y o u e v e r h a v e t h e t i m e , i t m i g h t b e w o r t h

y o u r w h i l e t o g o t h r o u g h s o m e o f t h e e a r l y B r i t i s h R e s e a r c h M e m o r a n d u m s ,p a r t i c u l a r l y t h e w o r k o f G l a u e r t . A l s o Z i m m e r m a n ' s N A C A r e p o r t s .

S i n c e t h e w o r k w o u l d b e m u c h t o o l e n g t h y t o p r e s e n t i n i t s e n t i r e t y ,

I w i l l g i v e y o u o n l y t h e m a i n p o i n t s w h i c h I h a v e f o u n d i n t h i s w o r k . T h e

s p i r a l s t a b i l i t y o n l y w i l l b e c o n s i d e r e d h e r e , a n d s h o u l d n o t b e c o n f u s e d

w i t h D u t c h r o l l . T h e f i r s t r e q u i r e m e n t f o r s p i r a l s t a b i l i t y i s s t a t i c d i r e c

t i o n a l s t a b i l i t y . T h i s m e r e l y m e a n s t h a t t h e n e u t r a l p o i n t i n y a w m u s t b e

a f t o f t h e c e n t e r o f g r a v i t y . I f t h i s c o n d i t i o n i s s a t i s f i e d , t h e n s p i r a l s t a b i l

i t y i s s a t i s f i e d i f

Always Pos. Usua lly Po s. Angle of climb usu ally ne glec ted

Hence we se that Spiral Stability depends on

Rollins' Moment due to sideslip K (increases withincrease in dihedral^

Yawing Moment due to Yawing velocity ( Increaseswith rudder area and side area and fuselage length)

Rolling Moment due to yawing velocity (increases withAspect Rat io , forward movement of C.G., incr ea se in ,wins in cidenc e, r a i s i n g of si d e ar ea above fc af t o f C.G.,

Yawins Moment due to sideslip (static Stability termincrease with rudder area and tail length)

T h a t ' s t h e s i t u a t i o n . N o w l e t ' s s e e w h a t w e c a n d o a b o u t i t f r o m t h e d e s i g n

s t a n d p o i n t . F i r s t l e t u s c o n s i d e r t h e t e r m s a n d . W e s e e t h a t m o s t

o f t h e t h i n g s w h i c h i n c r e a s e o n e i n c r e a s e t h e o t h e r e x c e p t f o r o n e t h i n g .

T h e d a m p i n g i n y a w , t h a t i s , m a y a l s o b e i n c r e a s e d b y i n c r e a s i n g

s i d e a r e a a n d f u s e l a g e l e n g t h . S i n c e i s o n t h e p o s i t i v e s i d e , w e s e e t h a t

t h e s e t h i n g s c o n t r i b u t e t o s p i r a l s t a b i l i t y . T h i s a g r e e s w e l l w i t h e x p e r i e n c e .

M o d e l s w i t h l a r g e f u s e l a g e s s e e m t o b e m o r e i n s e n s i t i v e t o s p i r a l d i v e s

t h a n t h e p e n c i l b o m b e r s a n d s t r e a m l i n e d j o b s . T h i s d a m p i n g t e r m i s t h e

r e a s o n . I f m a y b e e a s i l y s e e n t h a t i n c r e a s i n g t h e r u d d e r a r e a o r t a il l e n g t h

w i l l n o t i n c r e a s e t h e s p i r a l s t a b i l i t y b e c a u s e b o t h a n d a r e i n c r e a s e d .

W e s e e t h a t l a r g e d i h e d r a l i s o n t h e p o s i t i v e s i d e a n d i n c r e a s e s s p i r a l

s t a b i l i t y . N o w o n d e r s u c h l a r g e d i h e d r a l s a r e i n e v i d e n c e o n h i g h - p o w e r e d

g a s m o d e l s . D i h e d r a l i s n o c u r e - a l l t h o u g h , f o r i f i t i s c a r r i e d i n t o e x c e s s

a n o t h e r i n s t a b i l i t y a r i s e s , n a m e l y D u t c h R o l l . T h e a n s w e r t o s p i r a l s t a b i l i t y ,

t h e n , l i e s i n t h e r e m a i n i n g t e r m

T h i s t e r m c a n b y c a r e f u l d e s i g n b e m a d e e q u a l t o z e r o , a n d , w h e n

t h i s i s d o n e , s p i r a l s t a b i l i t y i s a s s u r e d . . T o b e m o r e

s p e c i f i c , I w i l l e x p l a i n t h i s t e r m c a r e f u l l y . T h i s i s t h e r o l l i n g m o m e n t w h i c h



1 — L a r g e s i d e a r e a . 2 — S m a l l w i n g i n c i d e n c e .3 — L a r g e w i n g d i h e d r a l , n e g a t i v e s t a b d i h e d r a l .

4 — R e a r w a r d p o s i t i o n o f C e n t e r o f G r a v i t y .5 — P y l o n a n d s u b r u d d e r s . 6 — Low A s p e c t r a t i o .

B y t h e w a y , F r a n k , y o u c a n s e e w h e r e m y l o n g j o b g e t s i t s e x c e p t i o n a l

s p i r a l s t a b i l i t y . T h e l o n g f u s e l a g e g i v e s h i g h r o t a r y d a m p i n g . L o w

i n c i d e n c e g i v e s p r o d u c t o f i n e r t i a t e r m s w h i c h r o l l a w a y f r o m t u r n . P y l o n

a n d s u b r u d d e r a l s o c o n t r i b u t e . C . G . i s 2 i n . a f t o f t r a i l i n g e d g e g i v i n g

f a v o r a b l e d i h e d r a l e f f e c t . N o w o n d e r t h e j o b c a n c l i m b a n d g l i d e i n s u c h

t i g h t c i r c l e s .

W e l l , F r a n k , r o u g h l y t h e r e ' s y o u r s p i r a l s t a b i l i t y . H o p e I ' v e c l e a r e d u p

a f e w p o i n t s , a n d l e t m e k n o w i f y o u h a v e a n y q u e s t i o n s . A m i n c l u d i n g

s o m e s k e t c h e s t o i l l u s t r a t e t h e i d e a s . T h e r e a r e a n u m b e r o f e f f e c t s w h i c h

I h a v e n o t i n c l u d e d ( i . e . s l i p s t e a m , s i d e w a s h , e t c . ) , b u t i f c a r e f u l a t t e n t i o n

i s p a i d t o t h e a b o v e d e s i g n f e a t u r e s s p i r a l s t a b i l i t y i s a s s u r e d .

a r i s e s d u e t o t h e r o t a t i o n a l v e l o c i t y ( a n g u l a r v e l o c i t y ) i n y a w . T h e m o s t

p o w e r f u l e f f e c t i n m o s t m o d e l s a r i s e s f r o m t h i s y a w i n g v e l o c i t y c a u s i n g

t h e o u t e r w i n g t i p t o t r a v e l f a s t e r t h a n t h e i n n e r w i n g t i p , t h u s c a u s i n g t h e

m o d e l t o r o l l "in to t h e t u r n an d go i n t o a s p i r a l d i v e . W e n o t e i m m e d i a t e l y

t h a t a l o w a s p e c t r a t i o w i n g w o u l d k e e p t h i s e f f e c t t o a m i n i m u m , a n d t h i s

t o o a g r e e s w e l l w i t h e x p e r i e n c e . H o w e v e r , f o r p e r f o r m a n c e r e a s o n s , l o w

a s p e c t r a t i o w i n g s a r e n o t d e s i r a b l e s o w e m u s t s e e k o t h e r m e a n s t o c o u n

t e r a c t t h i s e f f e c t . O n e t h i n g w h i c h h e l p s i s t o r e d u c e t h e i n c i d e n c e o f t h e

w i n g . T h i s i n c l i n e s t h e p r i n c i p a l l o n g i t u d i n a l a x i s o f t h e a i r p l a n e t o t h e

a i r s t r e a m w i t h t h e r e s u l t t h a t t h e c r o s s p r o d u c t s o f i n e r t i a o p p o s e t h e r o l l

i n t o t h e t u r n . A n o t h e r , b u t s m a l l e r e f f e c t i s t o l o w e r t h e a r e a b e h i n d t h e

c e n t e r o f g r a v i t y a n d t o r a i s e t h e a r e a f o r w a r d o f t h e c e n t e r o f g r a v i t y .

H e r e a g a i n t h e o r y a g r e e s w i t h p r a c t i c e f o r th e b e n e f i c i a l e f f e c t s o f p y l o n

a n d s u b r u d d e r s i s w e l l k n o w n . I t s h o u l d b e m e n t i o n e d t h a t t h e f a r t h e r

t h e s e a r e a s a r e f r o m t h e c e n t e r o f g r a v i t y , t h e m o r e e f f e c t i v e t h e y a r e .

H e n c e , i f t h e C G i s m o v e d b a c k t h e p y l o n b e c o m e s m o r e e f f e c t i v e i n i m

p r o v i n g s p i r a l s t a b i l i t y . H o w e v e r , r e a r w a r d m o v e m e n t o f t h e C . G . r e q u i r e s

a l a r g e r s t a b i l i z e r t o m a i n t a i n l o n g i t u d i n a l s t a b i l i t y ( o r l o n g e r m o m . a r m . )

T h e r e a r e o t h e r a n d m o r e e f f e c ti v e m e a n s o f i n c r e a s i n g s p i r a l s t a b i l i t y .

N e g a t i v e d i h e d r a l i n t h e s t a b , i s v e r y e ff e c t i v e . I n a c a n a r d , t h e s a m e t h i n g

i s a c c o m p l i s h e d b y d i h e d r a l i n t h e f o r w a r d t a i l , a m u s t b e c a u s e o f t h e p o o r

s p i r a l s t a b i l i t y o f c a n a r d s . W e c a n a l s o s e e t h a t r e a r w a r d m o v e m e n t o f t h e

C . G . c a u s e s t h e w i n g d i h e d r a l t o h a v e a b e n e f i c i a l e f f e c t o n c o n v e n t i o n a l

t y p e s .

T h e t e r m s i n T a n s h o u l d b e m e n t i o n e d . T h e s e a r i s e f r o m t h e f l i g h t p a t h

a n g l e a n d a r e i n g e n e r a l s m a l l . I n g e n e r a l , t h e y s h o w t h a t a m o d e l i s m o r e

s p i r a l l y u n s t a b l e i n a c l i m b t h a n i n a d i v e . H a v e y o u e v e r n o t i c e d t h a t s o m e

m o d e l s s e e m t o b e g o i n g i n t o a s p i r a l d i v e f r o m t h e c l i m b , b u t w h e n t h e y

g e t t h e n o s e d o w n t o l e v e l f l i g h t t h e y m a i n t a i n a l t i t u d e j u s t b u z z i n g a r o u n di n a c i r c l e . T h i s h a p p e n s b e c a u s e t h e s p i r a l s t a b i l i t y i n c r e a s e s a s t h e n o s e

d r o p s . T h e r e a r e a l o t o f m o d e l s i n t h i s c a t e g o r y . J u s t g o t o a c o n t e s t s o m e

t i m e a n d y o u w i l l s e e a h a l f d o z e n m o d e l s t h a t g o r o u n d a n d r o u n d a t

u - c o n t r o l s p e e d w i t h o u t g a i n i n g a l t i t u d e , b u t w h i c h d o n o t s p i r a l i n .

I w i l l n o w s u m m a r i z e t h e d e s i r a b l e f e a t u r e s t o o b t a i n s p i r a l s t a b i l i t y :



A s f a r a s I k n o w f r o m i n f o r m a t i o n a c c u m u l a t e d f r o m m a n y d i f f e r e n t

s o u r c e s an d m y ow n e x p e r i m e n t s t h e 3" f a n m a d e o f .0 40 t o .0 51 2 4 S O

A l u m i n u m A l l o y i s a b o u t t h e b e s t s i z e f o r 1 / 2 A m o t o r s o f " G o o d T o r q u e . "

I u s e D i e s e l s f o r m o s t o f m y j o b s n o w , a s I c a n g e t f u e l i n g r e d i e n t s e a s i l y

a n d c h e a p l y , a n d n o b a t t e r i e s t o l u g a r o u n d , a s p e e d r a n g e a l m o s t e q u a l t oi g n i t i o n e n g i n e s , t o p s p e e d s e q u a l t o G l o - P l u g s a n d m o r e p o w e r p e r d i s

p l a c e m e n t t h a n e i t h e r , i n s m a l l s i z e s . ( U p t o . 20 c u . i n . ) G l o P l u g E n g i n e s

s e e m t o b e b e t t e r a t h i g h e r d i s p l a c e m e n t s .

G e t t i n g b a c k t o t h e f a n ! A 3 0 ° P i t c h A n g l e a t t h e t i p o f t h e b l a d e i s

a p p r o x i m a t e . Y o u m a y c h a n g e i t u p o r d o w n d e p e n d i n g o n r e v s , o b t a i n e d .

R e v s , n e c e s s a r i l y m u s t b e h i gh . 16, 00 0 w i t h fi n e r p i t c h w o u l d b e m o r e ef fi c i e n t t h a n 1 2 , 0 0 0 w i t h h i g h e r p i t c h . M y f o o l i n g a b o u t h a s n o t b e e n d o n e

w i t h a n y t h i n g i n m i n d e x c e p t s p o r t , s o I h a v e n o f i g u r e s o n t h r u s t o r e f f i

c i e n c y o r d u c t e d f a n s .

A r t i c l e s b y P h i l S m i t h o f E n g l a n d i n " M o d e l A i r c r a f t " a n d A « r o -

m o d e l l e r " a n d b y T o m P u r c e l l i f " M o d e l A i r p l a n e N e w s " h a v e m o r » - « #

l e s s l e d ' me t o :

A p p a r e n t l y , I n l e t A r e a m u s t b e l a r g e r t h a n t h e E x i t A r e a . A n d t h e

E x i t A r e a a t l e a s t l / 2 t h e F a n A r e a ( N o t D i a . ) .

I N L E T

. 5 f o r 10 ,0 0 0 r e v s , u p t o . 8 f or 16 , 00 0 r e v s . m i n . T r y t o k e e p w e i g h t u n d e r

1 1 o z s . o r 8 o z . / S q . F t . w i n g . M a x i m u m c l e a r a n c e o f f a n i n d u c t : 1 / 1 6" f o r

e f f i c i e n c y . L e s s i f p o s s i b l e . C a r v e d b l o c k s i s n o t v e r y s t r o n g b u t l i g h t a n d

s i m p l e t o m a k e . L a m i n a t e d p a p e r I t r i e d w a s h e a v y a n d t e n d e d t o l o s e s h a p e .B u i l d u p h e x a g o n t u b e u s e d b y P h i l S m i t h ; l i g h t b u t n o t s o e ff i c ie n t a s a

d u c t . T o o m u c h c l e a r a n c e . C a r v e d b l o c k O . K . i f n o s e i s n o t o p e n .

R . I . " H a n k " M A C K E N Z I E — G E N O N D U C T E D F A N S —



B I L L H E N D E R S O N — J E T I C O P T E R D E S I G N —O p i n i o n v a r i e s a s t o t h e v a r i o u s s i z e s a n d w e i g h t s e t c . t h a t a r e m o s t

s u i t a b l e f o r e a c h s i z e o f m o t o r b u t t h e t a b l e b e l o w g i v e s a g e n e r a l i d e a o f

t h e m a j o r i t y o p i n i o n .

I t i s o b v i o u s w i t h t h i s f o r m o f m o d e l l i n g a s w i t h e v e r y o t h e r , t h a t

p o w e r / w e i g h t r a t i o i s i m p o r t a n t a n d w i t h f i x e d p o w e r m o t o r s , w e i g h t m u s t

b e c ut d o w n a s m u c h a s p o s s i b l e t o g e t a b e t t e r c o n t e s t p e r f o r m a n c e .

T h e S p a n L o a d i n g i s t a k e n s o i t i s p r o p o r t i o n a l t o t h e d i s c l o a d i n g a n di s i n f i g u r e s m o r e e a s i l y c o m p r e h e n d e d . — T h e R o t o r C e n t e r S e c t i o n i s u s u

a l l y a b o u t 2 8 - 3 5 % o f t h e R o t o r D i a m e t e r . — T h e P i t c h A n g l e v a r i e s f r o m

m od e l t o m od e l b u t ge n e r a l l y u s e 15° on " 50 " an d " 10 0 " m od e l s , an d 12 ° on

" 20 0" t o " 3 5 0" m o d e l s . — T h e " d e l t a 3 " ( f u l l - s i z e p a r l a n c e f o r t h e s y s t e m o f

s k e w h i n g e s y s t e m f o r p r o d u c i n g a u t o - r o t a t i o n a n g l e c a n v a r y b e t w e e n 30 °

a n d 3 5 ° .

T h e r o t o r c e n t r e s e c t i o n c a n b e m a d e f r o m p l y w i t h h i n g e s m o u n t e d i n

b l o c k s a t e n d s a t a p p r o x i m a t e p i t c h a n g l e . T h i s i s e a s i e r t h a n b u i l d i n g i t

u p b u t i t i s h e av i e r .

S h o u l d a n y o n e b e a s t i c k l e r f o r h e l i c a l p i t c h t h e y c a n b u i l d t h e o u t e r

r o t o r b a l d e s o n a p i t c h a n g l e j i g , b u t g e n e r a l l y fl a t o n e s s e t a t t h e a p p r o x i

m a t e a n g l e b y t h e h i n g e s o n t h e c e n t r e s e c t i o n w i l l b e q u i t e e f f e c t i v e .



These m o del s wi l l a scend fa i r ly qu ick ly a nd sho u ld descend o n a uto -

rotat ion much more s lowly , in fact in good thermal condit ions they should

be a b le to so a r s l i g h t ly a nd thus g rea t ly enha nce the i r perfo rm a nce .

Ba l l ra ces a re no t necessa ry in the hea d bea r ing s but a re s t ro ng ly rec

ommended on "200" and "350" models , they being much more fr ict ion free

t h a n a n o r d i n a r y j o u r n a l b e a r i n g .

The hinges used are universa l on a l l s izes o f jet icopters and so far noo ther sa t i s fa c to ry o ne ha s been tho ug ht o f , bu t so m e im pro v em ents co u ld

possib ly be made to lock hinge wire in p lace and yet a l low i t to be taken

o ut fo r ea se o f t ra nspo rta t io n .



B RUC E L E S T E R— J E T E X P O W E R—M y f i r s t " J e t e x " d e s i g n s f o r t h e " 1 0 0 " u n i t w e r e r e a l l y i n t h e f a s t m o v i n g

" D y n a m i c - s o a r i n g " c l a s s w i t h a s l i t t l e a s 3 4 s q . i n s . o f w i n g a r e a . W i t h t h e

i n f o r m a t i o n f r o m t h e s e " h o t " l i t t l e j o b s t h e " M e t e o r " w a s e v e n t u a l l y d e v e l

o p e d b y c a r e f u l w i n g d e s i g n a n d r o c k e t m o t o r s e t t i n g , w i t h o v e r d o u b l e

t h e w i n g a r e a o f t h e o r i g i n a l s a n d s t i l l s a c r i f i c i n g n o t h i n g o f m y n e a r

v e r t i c a l c l i m b .

S i n c e t h e g r e a t e r p a r t o f t h e d u r a t i o n o f f l i g h t i s m a d e i n t h e g l i d e , t h e

g l i d e i s t h e r e f o r e e s t a b l i s h e d fi rs t, a n d a u t o m a t i c a l l y t h e c e n t e r o f g r a v i y .

A s I h a d n o d e s i r e t o a d d b a l l a s t t o t h e n o s e w h e n t h e " d e a d " m o t o r i s

e v e r p r e s e n t i n t h e g l i d e , I f o u n d i t b e s t t o f i x t h e m o t o r o n r a t h e r t e m

p o r a r i l y w i t h r u b b e r b a n d s s o t h a t i t c o u l d b e m o v e d a v e r y s l i g h t d i s t a n c e

f o r e a n d a f t i n a n e f f o r t t o f in d w h e r e t h e m o d e l s h o w e d s i g n s o f " p l a n i n g "

o n a s l i t t le w i n g i n c i d e n c e a s p o s s i b l e .

T h i s I e v e n t u a l l y f o u n d w a s b e s t a c c o m p l i s h e d b y c o m p l e t i n g a l l c o m

p o n e n t p a r t s , c o v e r i n g a n d d o p i n g t h e m t o f i n a l s t a t e , c o m p l e t i n g t h e t a i l

a s s e m b l y , m a k i n g s u r e t h e s t a b i s s e t a t Z e r o d e g r e e s i n c i d e n c e , a n d t h a tt h e r u d d e r i s o n w i t h n o t u r n .

S t e p b y s t e p h e r e a r e t h e f i n a l p o i n t s o f a d j u s t m e n t . T h e g l i d e i s e s t a b

l i s h e d f i r s t .

W i t h t h e " 1 0 0 " m o t o r a n d m o t o r a t t a c h m e n t c l i p l i g h t l y l a s h e d o n i n t h e

d e s i r e d p o s i t i o n , a n d w i t h n o r e s p e c t a t t h i s t i m e f o r o f fs e t o r d o w n t h r u s t

o f a n y k i n d , t h e m o t o r i s c l i p p e d o n without a c h ar ge i n i t , an d t h e w i n g i s

n e x t r i g g e d o n . T h e q u i c k e s t w a y t o d o t h i s i s t o s p o t g l u e t h e t r a i l i n g e d g e

o f t h e w i n g d o w n o n t o t h e b o o m a t t h e c o r r e c t f o r e a n d a f t l o c a t i o n , b u t

u s e a b a l s a w e d g e a n d a l a r g e p i n f o r t h e f r o n t f i x i n g . S e v e r a l s h o u l d e r

l e v e l g l i d e s s h o u l d n o w b e m a d e a ll t h e t i m e v a r y i n g t h e f r o n t w i n g i n c i

d e n c e f i x i n g u p a n d d ow n a d e gr e e or s o a t a t i m e u n t i l a s p o t c an b e f o u n dw h e r e t h e m o d e l s e t t l e s a w a y i n a s t r a i g h t f o r w a r d p l a n i n g t y p e o f s i n k .

O n c e t u r n i s a p p l i e d y o u w i l l h a v e t h e n a p e r f e c t w i n d y w e a t h e r s e t - u p .

T h e " M e t e o r " h a s w o n s e v e r a l t i m e s i n w i n d w h e n m o s t o t h e r m o d e l s h a d

d i s i n t e g r a t e d o n t h e r u n w a y d u e t o p o o r a e r o d y n a m i c s e t - u p .

O n c e s a t i s f i e d w i t h t h e s i n k t h e n a p p l y g l u e a b o v e a n d b e l o w t h e w e d g e ,

a n d m a k e t h i s s e t t i n g s e c u r e f o r a l l t i m e . Y o u w i l l f i n d y o u c a n d e p e n d o n

i t , an d i f i t i s c o r r e c t yo u w i l l n e v e r h a v e t o v a r y i t . T h e m o t o r c l i p c an n ow

b e t a k e n o f f , a n d t h e r e a r s c r e w - n a i l h o l e e l o n g a t e d s i d e w a y s s o t h a t " r i g h t -

t h r u s t " c a n b e a p p l i e d t o t h e r o c k e t . B e f o r e r e - m o u n t i n g i s a t t t e m p t e d a n

o t h e r a n g u l a r w e d g e s h o u l d b e m a d e t h a t w i l l s t r a d d l e t h e r e a r h o l d - d o w n

s c r e w , a l l o w i n g t h e e q u i v a l e n t o f " D o w n - t h r u s t " o n a " r u b b e r - p o w e r e d "

m o d e l t o b e e a s i l y v a r i e d , a n d s e t t i n g m a d e s e c u r e d u r i n g a c t u a l p r e l i m

i n a r y f l i g h t t e s t s . A l l r u b b e r - p o w e r e d " f a n s " k n o w t h e v a l u e o f a p p l y i n g

" d o w n t h r u s t " t o h o l d t h e n o s e d o w n d u r i n g p o w e r b u r s t w h i c h o n t h e

" 10 0 " u n i t i s n e ar t h e e n d o f t h e m o t o r - r u n an d t h e m o d e l h a s g o t u p t o

u l t i m a t e v e l o c i t y i n v e r s e l y a l l o w i n g t h e u n i t t o d e l i v e r i t ' s b e s t o u t p u t .

S t a r t t e s t i n g o v e r t a ll g r a s s w i t h q u a r t e r - s i z e p e l l e t s , w a t c h f o r s i g n s o f

l o o p i n g , s w i n g i n g t o h a l f - s i z e d o n e s a s s o o n a s p o s s i b l e l e s t y o u m i s i n t e r

p r e t t h e s y m p t o m o n a q u a r t e r - p e l l e t , a s i t g i v e s y o u p r e c i o u s l i t t l e t i m e t o

d e c i d e a t b e s t , y e t e n o u g h t o g e t a n i d e a o f w h a t t h e m o d e l i s g o i n g t o d o .

S i n c e t h e g l i d e a n d t h e c e n t e r o f g r a v i t y h a v e a l r e a d y b e e n d e c i d e d ,y o u r n e x t s t e p i s t o p e r f e c t y o u r f i n a l " a i r p a t t e r n " o r ' t h e r m a l c i r c l e . "

K e e p a p p l y i n g r i g h t t h r u s t u n t i l y o u c a n a p p l y a f i n e a m o u n t o f l e f t r u d d e r

t o g e t a b o u t a 2 0 0' l e f t . c i r c l e . T o t h e " R u b b e r - p o w e r e d f a n t h a t m e a n s



" r i g h t c l i m b , l e f t g l i d e . " C o u p l e d w i t h t h e l o n g m o m e n t a r m o f t h e m o d e l

a n d t h e n i c e t a p e r - o f f o f p o w e r o n t h e " J e t e x " m o t o r , y o u w i l l p r o b a b l y b e

s u r p r i s e d a t t h e q u i c k r e s p o n s e , a n d r i g h t a b o u t t h e n i f a b o u n c i n g "t h e r

m a l " i s u n d e r yo u , you ar e a w a y f o r a 6 or 7 m i n u t e f l i gh t or ou t - o f - s i g h t a s

I h a v e h a d h a p p e n t o m e m a n y , m a n y t i m e s . R i g h t a b o u t n o w y o u w i l l b et h i n k i n g a b o u t d e t h e r m a l i z e r s , a n d b e l i e v e m e t h e y a r e n e c e s s a r y , a " p o p " -

u p o n e w o u l d b e b e s t d u e t o t h e l i g h t w e i g h t i n v o l v e d , b u t b e f o r e p u t t i n g i t

on t r y t o p e r f e c t you r m od e l f i r s t , t h e n ad d i t l a t e r . I r e a l i z e t h i s i s r i s k y

i n g o o d w e a t h e r b u t o n e h a s t o t a k e t h a t c h a n c e . T h i s i s t h e w a y a l l m y

w i n n i n g m o d e l s h a v e b e e n t r i m m e d , a n d i n t h a t p r e c i s e o r d e r .

N o w a f e w o t h e r p o i n t e r s .

F i r s t t h a t o f c o l o u r — I u s e y e l l o w o n a l l u p p e r s u r f a c e s , r e d o n a l l u n d e r

s u r f a c e s , a n d b l a c k o n s i d e s o f f u s e l a g e s a s i t h a s t e n s y o u r c h a n c e s o f p i c k

i n g i t u p on gr as or i n t h e a i r w h e n i t b e c om e s s m al l i n t h e s k y .

I h a v e h a d m o s t s u p e r i o r r e s u l t s o u t o f a l l - b a l s a m o d e l s r a t h e r t h a n t h eb u i l t - u p v a r i e t y , a n d e a s e o f h a n d l i n g i n c o m p e t i t i o n m e a n s a l o t , a n d w i t h

" a l l - b a l s a " y o u c a n m a k e a q u i c k , e a s y r e p a i r a n d d o a f a s t b a c k - i n t o - t h e - a i r

c o m e b a c k i n r e c o r d s t y l e .

A v o i d t h i c k a i r f o i l s i f y o u w a n t t o g e t h i g h p e r f o r m a n c e a n d s t i l l d e

s i g n m o d e l s o f a g o o d r e l a t i v e s i z e . I n a l l " J e t " p l a n e s u s i n g t h e " r e a c t i o n "

p r i n c i p l e f o r p r o p u l s i o n , t h e " d r a g " f a c t o r i s o n e o f t h e g r e a t e s t p e r

f o r m a n c e k i l l e r s e v e n f u l l - s c a l e d e s i g n e r s h a v e t o c o n t e n d w i t h . T h e r e i s

a c o m p r o m i s e p o i n t , a n d , a f t e r c h a n g i n g a r o u n d i n c i d e n c e s , a i r f o i l s , n o s e

a n d t a i l m o m e n t s , r o c k e t s e t t i n g s e t c . o n o v e r a d o z e n o f s u c c e s s f u l m o d e l s ,

t h e " M e t e o r " h a s p a i d o f f i n r e l i a b i l i t y a n d i n " a i r s e c o n d s , " a n d a f t e r a l l

t h a t ' s w h a t c o u n t s .



S. B . PFEfFFER—DEAR FRANK—

Your ideas on "Circular Airf low" look O.K. , a l though I d id not get

thro ug h a l l the a pp l i ca t io ns y o u m a de o f i t . One po in t tha t y o u d i sco v ered

wa s that sh ip s wi th good lon gi tu di nal s tabi l i ty don't sp i n in as eas y as ones

with less s tabi l i ty . This i s def in i te ly true and can be proved from a more

o r t h o d o x a p p r o a c h .

Yo u r m et ho d o f pre se nt i ng y o ur m a ter ia l i s m o st d i s t urb in g to a pe rs o n

tra ined in a ero dy na m ics . The resu l t o f th i s i s tha t m a ny techn ica l peo p le

may dismiss your ideas as erroneous unless they take the t ime to ferret out

the ba s i c idea s .

My per so n a l f ee l in g i s tha t y o u co u ld do ev ery bo dy m o re g o o d a nd

m a k e f a s t e r p r o g r e s s i f y o u w o u l d a c q u a i n t y o u r s e l f w i t h t h e s t a n d a r d

m e t h o d o f a p p r o a c h i n g i n c o m p r e s s i b l e f l o w a e r o d y n a m i c s . I t i s n o t c o m p l i

cate d ! And i t pro vi de s an eas y wa y to gr as p theo rie s once you ge t i t . A l s o

sh ow s wha t to do re se ar ch on. Ma in ly pol ars ( C l vs Cp ) by g l id e te st s i s

m y s u g g e s t i o n .

Yo u r wo r k o n t r im , fo r ex a m pl e , a c t ua l l y bro ug h t o u t ho w the C.G .s h i f t e d a f t ( f o r a g i v e n m o d e l ) ac t u a l l y d e c r e a s e d S T A B I L I T Y a n d t h e r e

by l ea d to v a r io us t ro ub le . Ho wev er , y o u nev er m ent io ned i t a s s ta b i l i ty ,

a nd co nsequent ly l o s t so m e ins ig h t in to the pro b lem .

I hope you do not feel o f fende d by my cri t i c i s m. Th e va lu e of yo ur bo ok

a n d the e f fo r t y o u ha v e ex p end ed o n i t ju s t i fy so m e s t ra ig ht f r o m the

sho u lder rem a rks in o rder to po ss ib ly im pro v e i t .

Inc ide nta ly , F r e d Yo ung er , who m y o u m a y kno w, a nd I , f e e l in g the

b a s i c n e e d f o r f u n d a m e n t a l i n f o r m a t i o n a t m o d e l R e y n o l d s N u m b e r s , s t a r t e d

an a irfo i l g l ide test program. We only f in ished the work at R.N. 14 ,000

wh ic h i s onl y of use to indoo r mod el s . F r e d i s a mem be r of the L o w S p e e d

Aero . Resea rch Asso c . so pub l i shed i t a s o ne o f the i r reprt s . I t m ig ht be

useful to you in indicat ing the type and amount of data that can be found

f r o m g l i d e t e s t i n g . U n f o r t u n a t e l y F r e d m o v e d b a c k t o B o s t o n s o o u r g l i d e

tes t pr o g ra m a t the R . N. o f the Wa kef i e ld m o de l s wa s o n ly ju s t s ta r t ed . As

wel l a s t es t ing the a i r fo i l we ca l cu la ted the theo ret i ca l pressure d i s t r ibu

t io n a nd l i s t ened to the bo und a r y la y er by s t e thes co pe to det erm ine ch a n g e s

f r o m l a m i n a r t o t u r b u l e n t ( w h i c h i s T H E t h i n g ) .

At the ty pi ca l R. N. o f a Wakef i e ld wi ng i t i s touc h and go wi th es ta b

l i sh ing suff ic ient turbulence to develop the fu l l potent ia l o f the a irfo i l .

Our s te thesco pe f ind ing s checked o ut presence o f the turbu lence a nd wha t

caused i t ( i . e . , i t came not only from the a irfo i l shape but str inger bumps

fr o m the Cle v e l a nd ty pe co ns tru ct i o n were v ery e f f ec t iv e in pr o d uc in g i t ) .

The s i tuat ion on a irfo i l s i s very c loudy. Our tests showed that most o f

the resea rc hes a re o f f the bea m . Th in g s l ike ba l sa co v ered L . E . (o r sm o o th

—y o u wa nt ro ug h) , ca m ber ex cept io na l ly fa r fo rwa rd a nd espec ia l ly l a m

inar f low shapes are poor for minimum sink.

Inc ide nta l ly y o u sho u ld rea d (o r y o u pro ba b ly ha v e ) Sc hm i tz ' s bo o k

on a irfo i l s a t low R.N. I t i s very good on the nature of what i s happening .

Schmitz only spent about a year gett ing the turbulence out o f h is tunnel

so don't be mis lead by taking anything f r o m t h e N A C A t u n n e l s a s b e i n g

wha t they a re sa id to be a t the R .N. they sa y . Turbu lence fa c to rs a re a v a i l

abl e for a l l ma jo r tu nn el s bu t the tun nel s wer e never inten ded to g ive re su l t sat R .N . eve n clos e to 45,000 so the y ar e al l too tu rb ul en t . fo r the se R . N .

It i s ver y po ss ib le tha t whe n the N A C A l i s ts a tes t for 50 ,000 R. N. i t mi gh t

ta ke a fr ee f l ight mo de l f lying at a R. N. of 100,000 to get com po ra bl e re s ul ts .

Yo u m ig ht ha v e a cha t wi th them o n e f f ec t iv e R .N. v ersus ca l cu la ted R.N.



C U R T I S J A N K E — D E A R F R A N K — ( D e c . 1 9 5 2 ) —Y o u h a v e , p e r h a p s , i n a w a y s o l v e d w i t h o u t t r y i n g a p r o b l e m t h a t m o s t

p e o p l e d o n ' t r e a l l y k n o w e x i s t s , s o t h a t t h e y m a k e a l a b o r i o u s c i r c l e t o g e t

b a c k t o w h e r e t h e y s t a r t e d . A l o t o f m o n e y i s d e s i r a b l e o n l y a s a m e a n s t o

a n e n d , b u t w h a t e n d ? T o g e t t h e t h i n g s y o u w a n t , b u t w h a t d o y o u w a n t ?

L e i s u r e ? — y o u ca n h a v e t h a t w i t h o u t m o n e y , a n d t h e v e r y e ff o r t n e e d e d t og e t m o n e y d e s t r o y s i t. E n j o y m e n t ? — w h a t c o n s t i t u t e s e n j o y m e n t ? — y a c h t s ,

C a d i l l a c s , b u c k e t s o f c h a m p a g n e ? — n o t f o r m e . I t ' s a v e r y a n c i e n t r a t - r a c e ,

a n d t h e " A m e r i c a n w a y o f l i f e " i n s o m e o f i t s f a c e t s i s m e r e l y a n e x a g

g e r a t e d e x a m p l e o f o n e o f t h e s y m p t o m s o f o n e o f t h e m a n y t h i n g s w r o n g

w i t h t h e w h o l e w o r l d . N o d o u b t y o u ' d f e e l p r o u d e r i n t h e e y e s o f o t h e r s i f

y o u r b o o k s m a d e y o u a m i l l i o n , b u t w h a t w o u l d y o u d o w i t h t h e m i l l i o n ?

P r o b a b l y j u s t w h a t y o u ' r e d o i n g n o w . M a y b e y o u ' d L I K E t o h a v e a p i a n o

a n d a h o u s e , b u t t h e s u m t o t a l o f y o u r h a p p i n e s s w o u l d n ' t b e i n c r e a s e d a s

m u c h a s y o u m i g h t t h i n k . P l e a s u r e i n p o s s e s s i o n s a n d e v e n t a l e n t s o r d e

v e l o p e d a b i l i t i e s s o o n w e a r s o f f . Y o u ' r e d o i n g n i c e l y a s y o u a r e , i t ' s a s you

s a y ; t h e a c t o f m a k i n g m o n e y i t s e lf i s o f t e n t h e c h a i n t h a t y o u w a n t e d t o

b e r i d o f i n t h e f i r s t p l ac e . I ' v e b e e n t h i n k i n g ov e r t h i s d e a l m ys e l f , a s k i n gm y s e l f q u e s t i o n s ( i n D i a n e t i c s w e c a l l i t s t r a i g h t - w i r i n g y o u r s e l f ) . I f I

h a d a l i t t l e m o r e m o n e y o n h a n d , I m i g h t b u y a n e w b a s s f i d d l e — w h y ? — t o

m a k e i t e a s i e r o n m y s e l f t o p l a y w h i l e I ' m e a r n i n g m o r e m o n e y — h e y , t h a t ' s

w h e r e w e c a m e i n ! A n y w a y , m a y b e I c a n b u i l d o n e — I ' v e b e e n t h i n k i n g o f

i t . I t ' d b e o u t o f s e c o n d g r a d e b a l s a , p l a n k e d o v e r r i b s a n d s t r i n g e r s , w i t h

a c r o s s - g r a i n l a m i n a t e d l a y e r f o r g r e a t e r s t r e n g t h , a n d i f i t w a s s u c c e s s f u l

I ' d g e t a b i g c h a r g e o u t o f i t — m o r e t h a n i f I ' d b o u g h t o n e . W e l l , a n y w a y ,

I c ou l d s t i l l u s e s o m e c as h t o go d o w n t o P h o e n i x f o r a w h i l e t o p i c k u p on

t h e l a t e s t D i a n e t i c t e c h n i q u e s a n d g e t a f u r t h e r b o o s t o n t h e w a y t o b e i n g

" c l e ar " . O n t h e o t h e r h a n d , t h e r e ' s n o go od r e as on w h y I c an ' t d o i t m y s e l f

a t h o m e a n d m a y b e l e a r n a f e w t h i n g s i n t h e p r o c e s s t h a t n o o n e e l s e k n o w sa b o u t y e t . H m m m — w e l l , a n y w a y , I ' d l i k e t o g e t t o a f e w i n d o o r m e e t s ,

w h i c h w o u l d t a k e m o n e y a n d t i m e — b u t t h e n I d o n ' t f e e l t o o a m b i t i o u s

a b o u t b u i l d i n g a n y t h i n g a n y w a y .

I t a l l b o i l s d o w n t o t h i s — p e o p l e w a n t m o n e y f o r w h a t t h e y t h i n k o f a s

v a r i o u s r e a s o n s , b u t t h e r e a s o n s a r e a l l t h e s a m e — p l e a s u r e o f s o m e s o r t o r

a n o t h e r . A n d s t r a n g e a s i t m a y s e e m t o y o u , t h e O N L Y p l e a s u r e i s t h a t o f

c r e a t i o n — a l l o t h e r s a r e p h o n y , w i t h o u t e x c e p t i o n — t h i s i s o n e o f t h e m a n y

d i s c o v e r i e s o f D i a n e t i c s , b y t h e w a y . T h i s i s h a r d t o b e l i e v e , b e c a u s e t h e r e

a r e s o m a n y o b s c u r i n g f a c t o r s , b u t i t h a s b e e n p r o v e d , a t l e a s t s u b j e c t i v e l y ,

ov e r an d ov e r . S o yo u ar e , r i gh t n ow , j u s t ab ou t a s w e l l o f f a s m on e y c an

e v e r m a k e yo u , e v e r y t i m e you t u r n ou t a b o ok or b u i l d a s h i p o f n e w d e s i g n

o r a n y o f y o u r o t h e r a c t i v i t i e s . S o d o n ' t w o r r y a b o u t y o u r a p p a r e n t l a c k o f

f i n a n c i a l s u c c e s s u n l e s s a t t h e p o i n t o f a c t u a l d e p r i v a t i o n o f s o m e s o r t .

Y o u r c o m p u t a t i o n c o n c e r n i n g s l a n t i n g y o u r b o o k s a t t h e a d u l t s i s O . K .

a s f a r a s i t g o e s , b u t r e m e m b e r t h a t t h e s e a d u l t s a r e a v a n i s h i n g b r e e d , b e i n g

t h e y o u n g f e l l o w s o f f i f t e e n o r s o y e a r s b a c k , w h o s e n u m b e r s a r e n o t b e i n g

r e p l e n i s h e d f r o m t h e r a n k s o f t h e p r e s e n t y o u n g s t e r s . A n d I d o n 't k n o w

w h a t c a n b e d o n e a b o u t i t. E v e r y t h i n g y o u s a y a b o u t t h e k i t - b u i l d e r s i s t r u e ,

a n d m o r e . A b o u t t h e o n l y r a y o f l i g h t i n t h e d a r k n e s s i s t h i s ; t h e a c t i v i t y

i s v e r y m u c h e x p a n d e d o v e r t h e e r a t h a t p r o d u c e d u s , s o i f e v e n a r e l a t i v e l y

s m a l l p e r c e n t a g e o f t h e g r e a t e r n u m b e r o f p a r t i c i p a n t s i n t h e s p o r t ca n b e

p e r s u a d e d t o a m o r e s e r i o u s v i e w , t h e u l t i m a t e r e s u l t w i l l n o t b e a s o r t o f

c o l l a p s e , w h i c h i s w h a t i t s o m e t i m e s l o o k s l i k e n o w . A f t e r a l l , e v e n t h o u g h

t h e s p o r t h a s b e e n c o m m e r c i a l i z e d a l m o s t t o t h e p o i n t o f r u i n , t h e r e c o u l d n ' t

h a v e b e e n a b a s i c c h a n g e i n t h e h u m a n r a c e . I d o u b t t h a t o u r g e n e r a t i o n i s



' Steel 1

so much cleverer or nobler than the present one—we were merely forced to

develop our own resources and some of us decided that we preferred i t that

w a y .

Frankly , because I 've lost the ambit ion or whatever i t i s that I used to

have, I don't look forward to spending a lo t o f t ime and energy bui ld ing

something that can be lost or smashed as eas i ly as can an outdoor rubber

j o b , s o t ha t I m y s e l f m i g h t be c o m e a k i t - c ha uf f e ur , e x c e p t f o r t h e s e f a c t s :

There are no good rubber k i ts , i f there were I 'd st i l l th ink they weren' t

good enough, the t ime and energy saved probaly wouldn't be great enough

to make a big difference anyway, I don't l ike being just one of the crowd,

I have ideas of my own not shared by the probable designer of the kit , and

f inal ly I have too gre at a con tem pt for other guy 's de s i gn s to lowe r my se l f

to bui ld their s i l ly th ings . But under the present set -up you can' t b lame



t h e k i d s t o o m u c h . I n a t h e r m a l y o u d o n ' t N E E D ' t o s q u e e z e o u t t h e l a s t

p o s s i b l e b i t o f s u p e r l a t i v e p e r f o r m a n c e — a r o t t e n k i t - j o b h a s n e a r l y a s g o o d

a c h a n c e a s t h e f i n e s t o r i g i n a l , a n d i s s o m u c h e a s i e r i n m a n y w a y s , b e c a u s e

y o u ' v e n o t h a d t o p u t t e r a r o u n d c h a n g i n g t h i n g s t o g e t o u t t h e b u g s . I g u e s s

t h e o n l y t h i n g t o d o i s t o g o o n a s y o u h a v e , a n d d o n ' t w o r r y a b o u t c r u s a d e s .

I h o p e d r o p p i n g t h e p r i c e m a k e s a d i f f e r e n c e , b u t i t 's n o t t o o l i k e l y — t h e

f e l l o w s wh o wa n t i t w i l l buy i t a t $2 .00 , a n d t h e o n e s w h o d o n ' t wo n ' t bu y

i t a t $ 1 .0 0 . E n j o y y o u r s e l f , a n d d o n ' t w o r r y , i t ' s N O T l a t e r t h a n y o u t h i n k ,i t ' s m u c h e a r l i e r .

I d o n ' t h a v e G l a s s ' s a d d r e s s — s e n d i t t o m e o n e o f t h e s e d a y s . I d o n ' t

d o u b t t h a t h e ' d e n j o y h e a r i n g a b o u t m y t r i b u l a t i o n s w i t h f i l m . I m a y h a v e

g o n e f a r t h e r t h a n h e d i d i n s o m e w a y s b e c a u s e t h e r e w e r e n ' t a s m a n y t h i n g s

t o t r y i n h i s d a y , b u t o n t h e o t h e r h a n d I d o n o t h a v e t h e m e t h o d i c a l , s c i e n

t i f i c a p p r o a c h , s o t h a t h e p r o b a b l y f o u n d o u t t h i n g s t h a t I d i d n ' t . Y o u r p r e

wa r f i l m wa s g o o d — I c a n m ix s t uf f l ik e i t o r be t t e r a t w i l l , but i t ' s n o

l o n g e r g o o d e n o u g h . T h e s t u f f y o u m i x e d f o r A n d r e w s , o n t h e o t h e r h a n d ,

I ' v e n e v e r b e e n a b l e t o d u p l i c a t e . M a y b e I c a n f i nd o u t m o r e a b o u t i t f r o m

t h e n a m e . P r i c e i s n o l o n g e r a f a c t o r , b y t h e w a y — a g o o d f i l m w i t h t h e r i g h t

p r o p e r t i e s w i l l f e t c h a n y p r i c e w i t h i n r e a s o n , b e c a u s e i n d o o r b u i l d e r s w h os t u c k i t o u t t h i s l o n g h a d t o b e f a n a t i c s . Y o u s h o u l d s e e s o m e o f t h e m d r o o l

o v e r E r b a c h ' s i n d o o r s t o c k ! — t h e y ' d t r a d e t h e i r f a v o r i t e w i v e s f o r i t ! S o m e

o f t h e w e s t c o a s t g l i d e r b o y s w h o w a n t w h a t t h e y w a n t a r e w i l l i n g t o p a y i n

c r e d i b l e p r i c e s f o r it . H o w e v e r , E r b a c h i s n' t g e t t i n g r i c h o n i t a n y m o r e

t h a n y o u d i d — I ' m m e r e l y m e n t i o n i n g t h a t t h e r e ' s n o n e e d t o c u t t h e q u a l i t y

o f f i l m s o l u t i o n t o g e t d o w n t o a p r i c e .

T h e r e ' s n o m y s t e r y a b o u t t h e w a t e r - p r o o f d o p e I m e n t i o n e d — i f y o u e v e r

g o i n t o t h e b u s i n e s s I 'l l l e t y o u k n o w h o w t o m i x i t y o u r s e l f . I f y o u m a k e

a n y m o n e y o n i t y o u c a n p a y m e a s m a l l r o y a l t y o n i t ; i t m i g h t a m o u n t t o

a s m u c h a s $ 1 . 25 p e r a n n u m . I d o u b t t h a t it ' s p a t e n t a b l e o r c o p y r i g h t a b l e

o r a n y t h i n g e l s e .

O u t s i d e o f s t u f f l i k e t h a t , I f i n d m y s e l f n o t t o o a m b i t i o u s a b o u t m o d e l s .

N o t o n l y d o I l a c k a m b i t i o n , b u t I d o n ' t k n o w W H A T t o b u i l d , f o r i n d o o r

s t i c k s , a n d e v e n t h e n I ' m s h a k y — I c a n b u i l d ' e m l i g h t , b u t t h e r u b b e r

q u a l i t y w o r r i e s m e , a s w e l l a s w h a t t o b u i l d f o r w h a t c o n d i t i o n s . A s f o r

i n d o o r c a b i n , I ' m c o m p l e t e l y a t s e a . W a k e f i e l d s t u m p s m e b e c a u s e , i n a d d i

t i o n t o t h e c r a f t s m a n s h i p a p p a r e n t l y n e c e s s a r y — g e a r s , r e t r a c t i b l e l a n d i n g

g e a r , a n d w h a t h a v e y o u , I ' v e n e v e r h a d e i t h e r t h e b r u t e s t r e n g t h o r t h e

t e c h n i q u e t o w i n d t o c a p a c i t y a b i g m o t o r — e i t h e r t h e y b r e a k o r m y a r m

d o e s , a n d t o c o m p e t e y o u n e e d e v e r y l a s t s e c o n d y o u c a n g e t . T h e n t h e r e ' s

a n o t h e r t h i n g — i n i n d o o r e v e n t s — w h a t i f w i s h i n g o u t o f t h e r a f t e r s o r i n t o

s t a y i n g u p a n o t h e r e x t r a m i n u t e a c t u a l l y w o r k e d ? — i t ' d t a k e t he k i c k o u t o f t h i n g s — a n d s t r a n g e a s i t m a y s o u n d t o y o u , i t ' s n o t a t a l l i m p o s s i b l e t o d o

j u s t t h a t w h e n y o u ' v e r e c o v e r e d t h e u s e o f c e r t a i n p o w e r s s o m e t i m e s c o n

s i d e r e d p s y c h i c ( t h e y a i n ' t ) a n d w h i c h a l l D i a n e t i c i s t s a r e w o r k i n g t o w a r d .

—(March 1953)—T h e f a m i l y h e r e i s i n t h e t h r o e s o f f i l l i n g o u t t h e w h o l e d a m n t o w n ' s

i n c o m e t a x r e t u r n s , s o I s e l d o m h a v e t h e t i m e o r a m b i t i o n f o r w r i t i n g , b u t

y o u r l e t t e r p r o b a b l y n e e d s a n a n s w e r s o m e t i m e t h i s y e a r , s o I ' m d o i n g i t

n o w .

T h a t b r i n g s m e t o t h e l e t t e r o f m i n e y o u w a n t t o p r i n t . I t ' s O . K . b y m e ,t h o u g h I' d h a v e p r e f e r r e d t o m a k e i t m o r e i m p r e s s i v e i n t h e w a y o f s y n t a x

i f I ' d k n o w n . I h o p e I h a v e n ' t g i v e n t h e w r o n g i m p r e s s i o n . I d o n ' t c o n s i d e r

m o d e l s a c h i l d i s h t o y t h a t I ' v e o u t g r o w n — t h e y ' r e m e r e l y t o y s t h a t I n o w



c o n s i d e r d o n o t r e t u r n a s u f f i c i e n t a m o u n t o f p l e a s u r e f o r t h e e f f o r t e x

p e n d e d , a n d I n o w p r e f e r t o s p e n d m o r e o f m y t i m e w i t h t o y s t h a t g i v e m e

b e t t e r o d d s . A c t u a l l y , I n e v e r d i d g e t r e a l p l e a s u r e f r o m s t a y i n g u p s e v e r a l

n i g h t s i n a r o w , d r i v i n g 3 0 0 m i l e s d o w n t o a m e e t , r u n n i n g a r o u n d l i k e a n

i d i o t a l l d a y , t h e n d r i v i n g b a c k 3 00 m i l e s t h e s a m e n i g h t c h e w i n g c a f f e i n e

p i l l s a l l t h e w a y . L o o k i n g b a c k , I n o w r e a l i z e t h a t s o m e h i n g w a s d r i v i n g

m e t o d o t h i n g s t h a t w e r e n ' t w o r t h i t . I t ' s n o t t h a t I c o n s i d e r m o d e l s b e

n e a t h m e a s a m a t u r e h u m a n — I t h i n k i t ' s j u s t a s s i l l y t o g o t w o t h o u s a n d

m i l e s t o w a t c h a R o s e B o w l g a m e , o r t o s l o s h a r o u n d i n f r e e z i n g s w a m p s

b e f or e d aw n i n or d e r t o ge t a c h an c e t o s h oo t a t a d u c k , or an y o f t h e o t h e r

r i d i c u l o u s t h i n g s t h a t a r e k n o w n a s s , p or t o r p l e a s u r e . S o I d o n ' t i n t e n d t o

g i v e u p m o d e l s e n t i r e l y , j u s t r e f u s e t o k n o c k m y s e l f o u t o v e r t h e m , u n l e s s

i t ' s f o r a t e n t h o u s a n d d o l l a r f i r s t p r i z e o r s o m e t h i n g o f t h e s o r t . I t ' s n o t



L E E R E N A U D — D E A R F R A N K — ( D e c , 1 9 5 2 ) —G l a d t o r e a d t h a t y o u l i k e d t h e W a k e f i e l d s o m u c h . I d o n ' t k n o w i f y o u

r e a l i z e d i t , b u t t h i s a i r p l a n e i s a c t u a l l y d e s i g n e d . E v e r y t h i n g t h e r e i s m y

i d e a o f t h e b e s t t h e o r y , c o m b i n e d w i t h m y o w n e x p e r i e n c e . S o m e o f t h e

t h i n g s a r e n o t a e r o d y n a m i c a l l y p e r f e c t , b u t i t i s a l l p r a c t i c a l . . T h i s is ar e f i n e m e n t o f s e v e r a l d i f f e r e n t d e s i g n s a n d I c o n s i d e r i t t o b e t h e b e s t

W a k e f i e l d t h a t c a n b e b u i l t . I t h i n k t h a t s o m e o n e w h o r e a l l y k n e w h o w t o

a d j u s t a n d f l y r u b b e r c o u l d e a s i l y w i n i n S w e d e n w i t h t h i s m o d e l .

I f o u n d t h a t 1 / 2 0 " C " s t o c k f o r t h e f u s e l a g e s i d e s s p l i t s t o o e a s i l y o n

l a n d i n g . W h e n t h e m o d e l h i t s t h e g r o u n d t h e r u b b e r t e n d s t o g o o u t t h r o u g h

t h e s i d e s a n d c a n r e a l l y d o a j o b . A t t h e b e g i n n i n g o f t h e s e a s o n I w a s

u s i n g 1 / 3 2 " C " cu t s i d e s a n d b u i l d i n g a i r p l a n e s w h i c h w e i g h e d f r o m 2 %

t o 3 o z . w i t h o u t r u b b e r . H o w e v e r t h e s e p l a n e s j u s t w e r e n o t s t r o n g e n o u g h

f o r p r o l o n g e d f l y i n g . E v e r y f l i g h t m e a n s a r e p a i r s o m e w h e r e . T h e m o r n i n g

o f t h e W a k e f i e l d e l i m i n a t i o n s I w a s t e s t i n g m y s p a r e m o d e l . T h i s g l i d e d i n

f o r a p e r f e c t l y n o r m a l l a n d i n g a n d s e e m e d p e r f e c t l y a l l r i g h t . W h e n Iw a l k e d o v e r a n d p i c k e d i t u p , h o w e v e r , th e f u s e l a g e c o l l a p s e d i n m y h a n d s .

F o u n d " A " s t o c k r e s i s t e d s p l i t b e t t e r a n d h a d m o r e t h a n a d e q u a t e s t r e n g t h .

T h e o n l y f i n i s h o n t h e s h e e t i s t w o c o a t s o f d o p e r u b b e d i n w i t h t h e

f i n g e r s b o t h i n s i d e a n d o u t b e f o r e a s s e m b l y . I h a v e d i s c o v e r e d a t r i c k o f

t h a t I ' m a t i r e d o l d m an , e i t h e r ; a t t h i r t y s e v e n I f e e l a s w e l l or b e t t e r t h an

I r e m e m b e r e v e r h a v i n g f e l t , a n d I i n t e n d t o i m p r o v e .

I d o h a v e an i d e a f or t h e b oo k , h o w e v e r . I h av e n ' t t r i e d i t b u t w i l l u s e i t

o n m y n e x t o u t d o o r r u b b e r j o b . Y o u m a y h a v e n o t i c e d h o w , w h e n s t r a p p i n g

a w i n g t o t h e f u s e l a g e i n t h e a b s e n c e o f f a n c y w i n g m o u n t s , t h e r u b b e r h a s

a t e n d e n c y t o d i s t o r t t h e l o n g e r o n s . T h i s b o t h e r s m e . S o w h y n o t u s e a n

L s e c t i o n ? O . K . , b u t i t' s w o r k . T h e n t h e r e ' s a n o t h e r t h i n g . I K N O W y o u ' v en o t i c e d h o w i t 's a l m o s t i m p o s s i b l e t o p r e v e n t d i s t o r t i o n w h e n g l u i n g t h e

t w o s i d e s o f a f u s e l a g e t o g e t h e r — n o m a t t e r h o w c a r e f u l l y y o u ' v e s e l e c t e d

t h e w o o d t h e l o n g e r o n s d o n 't m a t c h p e r f e c t l y i n s t i f f n e s s . S o t r y t h i s —

b u i l d i t a s f o u r s i d e s , t h e n g l u e t h e m t o g e t h e r , a s y o u w o u l d a s h e e t s i d e d

j o b . F o r t h e s a m e w e i g h t a s y 8 s q . u s e 1 / 8 b y I ' l l u s e t r u s s c o n s t r u c t i o n ,

a s i t i s i m p o s s i b l e f o r t h e s i d e t o d i s t o r t w h e n p i c k e d of f t h e b o a r d w h e n i t

i s u s e d . T h e c r o s s p i e c e s m u s t b e t r i m m e d t o l e a v e a s p a c e a t t h e e d g e o f

t h e l o n g e r o n s e q u i v a l e n t t o t h e w i d t h o f t h e b r a c e s t h e m s e l v e s s o t h e y d o n 't

i n t e r f e r e w i t h e a c h o t h e r w h e n j o i n i n g t h e s i d e s . N e e d l e s s t o s a y , t h i s w o n ' t

b e v e r y p r a c t i c a l o n a n y t h i n g b u t s y m m e t r i c a l , s q u a r e f u s e l a g e s . O t h e r

t y p e s c o u l d b e u s e d , b u t w o u l d r e q u i r e r a t h e r e x p e r t d r a f t s m a n s h i p b e c a u s e

o f d i f f e r e n t p r o j e c t i o n r a t i o s o f m o r e d e e p l y c u r v e d t o p s a n d b o t t o m s .

Y o u ' l l h a v e t o b e c a r e f u l t h a t y o u d o n ' t h a v e a l l t h e b r a c e s r u n n i n g i n o n e

d i r e c t i o n , t o o , w i t h a n y d e s i g n . I 'l l e n c l o s e a r o u g h s k e t c h .



m a k i n g t h e d o p e w a t e r p r o o f w i t h o n l y l i g h t c o a t s , s o t h a t t h i s i s a d e q u a t e

p r o t e c t i o n . I s u b s c r i b e t o t h e t h e o r y t h a t a " l i t t l e e x t r a w e i g h t i s w o r t h

w h i l e — t o o m a n y o f t h e l i g h m o d e l s a r e n e v e r a d j u s e d b e c a u s e o f s t r u c t u r a l

f a i l u r e s o r h a n d l i n g d i f f i c u l t i e s . .

I w a s p l e a s e d t o r e a d y o u r c o m m e n t s o n t h e o v e r a l l p i c t u r e o f t h e m o d e l

a v i a t i o n . I t r e a l l y i s t o o b a d t h a t s u c h a c o n d i t i o n p r e v a i l s , b u t I m u s t a g r e e

w i t h y o u c o m p l e t e l y . N o n e o f t h e k i d s e v e r t h i n k o f d e s i g n i n g t h e i r o w nm o d e l s . I t i s t oo e a s y f or t h e m t o b u y a k i t . I n f a c t I v e r y s e l d om s e e a

m o d e l w h i c h w a s b u i l t f r o m m a g a z i n e p l a n s — t o o m u c h w o r k t o c u t o u t

r i b s , e t c . K i t s a r e g o o d i n t h a t t h e y e n s u r e a r e a s o n a b l e c h a n c e o f s u c c e s s ,

w h e r e a n o r i g i n a l m a y b e a c o m p l e t e f l o p ( I k n o w ) . I t h i n k t h a t a g r e a t d e a l

o f t h e f a u l t l i e s w i t h t h e m a g a z i n e s . T h e y n e v e r h a v e a n a r t i c l e w h i c h p r e

s e n t s g o o d d e s i g n f u n d a m e n t a l s a n d t h e o r i e s . T h i s i s w h y I t h i n k y o u a r e

t h e o n l y h o p e . A s l o n g a s o n e f e l l o w b o t h e r s t o e x p l a i n t h i n g s a n d t o p r e

s e n t n e w i d e a s , o r i g i n a l i t y w i l l n e v e r b e d e a d . I f t h e g e n e r a l m o d e l e r r e

j e c t s y o u r n e w b o o k a s b e i n g o v e r h i s h e a d , I d o n ' t k n o w w h e r e t h e a n s w e r

l i e s .

P AR NE LL S C H O E N K Y — D E A R F R A N K — ( N o v. 1 9 52 )—I t w a s c e r t a i n l y n i c e t o h e a r f r o m y o u a g a i n , a n d p a r t i c u l a r l y t o h e a r

t h a t y o u a r e p l a n n i n g t o c o n t i n u e y o u r s e r i e s . I s u p p o s e t h a t i t i s d if f ic u lt

f o r u s t o r e a l i z e h o w m u c h c h a n g e t h e r e h a s b e e n i n t h e h a b i t s a n d a t t i t -

t u d e s o f t h e A m e r i c a n m o d e l b u i l d e r s i n c e t h e t h i r t i e s . I n m y o w n m i n d I

s e e n o t on l y t h e e f f e c t s o f t h e W ar an d i t s i n t e r r u p t i on o f t h e n or ar r i l b i g -

b r o t h e r ' - t e a c h e s - l i t t l e - b r o t h e r i n d o c t r i n a t i o n p r o c e s s , b u t a l s o t h e a d v e n t o f

t h e l a r g e , w e l l - o r g a n i z e d b u s i n e s s i n t e r e s t s w h i c h h a v e f u n c t i o n e d t o d i v e r t

t h e b e g i n n i n g m o d e l e r s ' t h o u g h t s a w a y f r o m t h e g r a d u a l p r o c e s s o f l e a r n i n g

a n d c r e a t i n g a n d t o w a r d s t h e f l a s h y r e a d y - b i l t s a n d t h e m o r e p r o f i t a b l e l i n e s .

A b o u t a l l t h a t w e o f t h e " g o o d o l d d a y s " c a n d o a t p r e s e n t , I ' m a f r a i d ,

i s k e e p t h e f l a m e g o i n g w h i l e w e f e e l a b o u t f o r t h e b e s t a p p r o a c h t o t h e

m o d e r n m o d e l e r . I ' m h o p i n g t h a t , m u c h a s h a l f - A e n g i n e s a n d W a k e f i e l d

s w e p t f r e e f l i g h t m o d e l i n g b a c k i n t o t h e p i c t u r e , s o m e n e w f a c t o r o r s i t u a

t i o n w i l l a r i s e t h a t w i l l e n c o u r a g e s e v e r a l t h o u s a n d m o d e l e r s t o d e l v e i n t o

d e s i g n .

I r e a l l y s h o u l d n ' t p r e s u m e t o b e t e l l i n g y o u w h a t a n y s i g n i f i c a n t c r o s s -

s e c t i o n o f a e r o e n g i n e e r s a n d f o r m e r m o d e l - b u i l d e r s t h i n k a b o u t t h e f e x t

a n d c a l c u l a t i o n s i n y o u r b o o k , b e c a u s e I h a v e n ! t b e e n ab l e t o f i n d m an y h e r e

a t M c D o n n e l l w h o s t i l l c a r e a b o u t m o d e l s . B i l l N e t z e b a n d h a s b e e n d e v o u r

i n g t h e m a t e r i a l i n y o u r b o o k — a n d a p p l y i n g t h e m e t h o d s t o c h e c k i n g h i sp a s t m o d e l s a n d t o d e s i g n i n g s o m e n e w s t u n t m o d e l s . I f t h e n e w c r e a t i o n s

p e r f o r m w e l l , h e 'l l h a v e a p r e t t y g o o d i d e a w h y . B i l l i s a n E l e c t r i c a l a n d

m a k e s n o p r e n t e n s i o n s o f k n o w i n g i t a l l a b o u t a e r o d y n a m i c s , s o h e c a n

r e f e r t o a m o d e l e n c y c l o p e d i a w i t h n o l o s s i n p r i d e .

I t ' s m y f e e l i n g t h a t s om e o f t h e ae r o d e gr e e b oys c an ' t ge t ov e r t h e f e e l

i n g t h a t t h e y h a v e m a s t e r e d s o m e c l a s s r o o m c o u r s e s i n t h e f u n d a m e n t a l s o f

f u l l - s c a l e d e s i g n a n d t h e r e f o r e a r e q u a l i f i e d t o d e s i g n a n d t o e v a l u a t e t h e .

s m a l l , s l o w - s p e e d , i n h e r e n t l y s t a b l e a i r c r a f t w h i c h w e c a l l " m o d e l s . " S e v

e r a l h a v e p o i n t e d o u t t o m e t h e f r a g m e n t a r y r e f e r e n c e s t o c i r c u l a r a i r f l o w ,

e t c . , w h i c h c a n b e f o u n d i n a e r o d y n a m i c s t e x t s — w i t h t h e u s u a l r e m a r k

" t h a t s t u f f i s n ' t n e w . " O f c o u r s e , t h e i m p o r t a n t t h i n g i s t h a t w h i l e c i r c u l a ra i r f l o w m a y b e o n l y o f a c a d e m i c i n t e r e s t t o d e s i g n e r s o f f u l l - s c a l e c r a f t i t

a p p e a r s t o b e o f g r e a t i m p o r t a n c e t o t h e "s c i e n c e " o f m o d e l d e s i g n — a n < i

t h a t n o w h e r e e l s e i n m o d e l l i t e r a t u r e i s t h e r e a v a i l a b l e a t r e a t i s e o n t h e

s u b j e c t .



W e k n o w t h a t i n a s c i e n c e a s l a c k i n g i n a c c u r a t e d a t a a n d a s p o o r l y i n

t e g r a t e d a s i s o u r " M i c r o a e r o n a u t i c s , " e m p i r i c a l r e l a t i o n s h i p s m u s t b e a c

c e p t e d a n d u s e d i n g r e a t n u m b e r s ; h e r e , t h e n , i s t h e c a t c h — t h e f e l l o w s

a d e p t a t m a t h e m a t i c s a n d u s e d t o m o r e e x a c t f o r m u l a s t e n d t o s h y a w a y

f r o m e m p i r i c i s m s . W h e r e w e e x p e c t t o p o s t u l a t e , t h e n e x p e r i m e n t , a n d

t h e n r e p e a t t h e p r o c e s s t o l e a r n m o r e a b o u t o u r f i e l d , s o m e o f t h e e n g i n e e r s

w a n t t o t a k e u p w h a t c a n b e c o v e r e d b y c l e a r - c u t e q u a t i o n s a n d t o n e g l e c t

t h e r e s t . T h e f e w e x - m o d e l e r s w h o s e q u a l i f i c a t i o n s a s a e r o d y n a m i c i s t s I

r e a l l y r e s p e c t a r e j u s t t o o b u s y t o d e v o t e e n o u g h t i m e t o m o d e l i n g t o g i v e

u s t h e b e n e f i t o f t h e i r e x p e r i e n c e b y c h e c k i n g e x p e r i m e n t s a n d c a l c u l a t i o n s

t o w e e d o u t e r r o r s a n d t o s u g g e s t f u r t h e r l i n e s o f e n d e a v o r . I m u s t c o n

c l u d e t h a t f o r a w h i l e w e m u s t d e p e n d u p o n t h o s e e n g i n e e r s w h o s e p r i m a r y

i n t e r e s t ( a n d e g o d r i v e ) a r e f i x e d u p o n m o d e l a i r c r a f t f o r t h e w o r k t h a t

l i e s a h e a d .

Y o u s e e m t o h a v e t h e r i g h t i d e a b y y o u r p r e s c r i p t i o n f o r " l e s s e n i n g t h e

d o s e , i n c r e a s i n g t h e f l a v o r i n g , a n d s t r e t c h i n g o u t t h e c u r e ! " E v e n t h o u g h

$ 2 . 50 i s e as i e r t o c om e b y t od ay t h an w as a d o l l ar i n 1937 , t h e r e ar e j u s t an

a w f u l l o t o f m o d e l e r s w h o p a s s u p t h a t b o o k b e c a u s e i t s o u n d s e x p e n s i v e

a n d t h e y a r e n ' t c o n d i t i o n e d t o l o o k i n g f o r w a r d t o i t — o r e v e n t o r e f e r i n g

t o A N Y b o o k o n t h e s u b j e c t . T o " t a l k s e n s e t o t h e A m e r i c a n m o d e l e r " y o u

w i l l f i r s t h a v e t o d r e s s u p t h e p a c k a g e a n d t o n e d o w n y o u r a p p r o a c h u n t i l

yo u c an s e l l l ar ge n u m b e r s o f t h e b o ok s t o t h e e a ge r 16 - ye ar o l d an d t o t h os e

w h o ' v e b e e n d i v e r t e d i n i t i a l l y t o w a r d s c o n t r o l - l i n e .

I k n o w t h a t t h e y o u n g s t e r s a r o u n d h e r e w h o n e e d t h e Y e a r b o o k s m o s t

a r e s i m p l y n o t a w a r e e i t h e r o f t h e i r v a l u e — o r p o s s i b l y o f H O W t o u s e

t h e m . I w o u l d c o n c u r w i t h s o m e o f t h e c o m m e n t s y o u h a v e r e c e i v e d t o t h e

e f f e c t t h a t a f e w p a r a g r a p h s o f c l e a r d i r e c t i o n s a b o u t e a c h p l a n o r t y p e o f

m o d e l p r e s e n t e d w i l l g o f a r t o b r i d g e t h e g a p s f o r t h e n o v i c e . Y o u k n o w ,

t h e r e d o e s n ' t s e e m t o b e a n y t h i n g o n t h e d e a l e r s ' s h e l v e s i n t h e w a y o f a

" H o w t o d o i t " b oo k , an d I h av e b e e n w o n d e r i n g i f i t w o u l d n o t h e l p t h e

c i r c u l a t i o n o f t h e Y e a r b o o k s t o d e v o t e s uf f ic i e n t s p a c e t o f u n d a m e n t a l s t o

h i t a t t h a t m a r k e t . . . w i t h o u r t e c h n i c a l m a t e r i a l a n d a d v a n c e d d e s i g n s

g o i n g a l o n g o n t h e s a m e b u s .

( I f y o u a r e s t i l l w i t h m e a f t e r a l l o f t h a t w o r d a g e , y o u m u s t b e p a t i e n t

i n d e e d . I t m u s t b e t h a t I a m a s s t a r v e d a s t h e r e s t f o r a n o p p o r t u n i t y t o

t a l k w i t h a n y o n e a b o u t m o d e l s a s s o m e t h i n g w o r t h y i n t h e m s e l v e s . . . I' ll

s i gn o f f f or t on i gh t an d w r i t e s om e m or e as s oon as I h av e t h e t i m e . . . )

, — ^ ' 1 4 J a n u a r y 1 95 3S e v er a l m o n t h s h a v e s l i p p e d b y . . . w e ' r e s t i l l w o r k i n g 4 8 t o 54 h o u r s

p e r we elt f a t M c D o n n e l l . \ . I ' v e b e e n u s i n g t h e f e w h o u r s w h e n I f e e l b e t t e r

t o w o r k o n . m y r a d i o c o u r s e ( l o o k i n g t o R / C i n 1 9 5 3 ) a n d t o s e t i n o r d e r m y

h u n d r e d s o f c o l o r s l i d e s o f t h e N a t s , e t c . , w h i c h I h a v e t o m o u n t b y h a n d . . .

i t m a y b e t h a t I ' v e . f a i l e d y o u o n t h i s t r i p w i t h m y t a r d i n e s s — t h o u g h I

s u r e l y h o p e n o t . M a d e a n o t h e r c h e c k w i t h t h e d e s i g n e r s a m o n g t h e T h e r m a -

l e e r s , t o d a y ; N e |z /e ba n 'd ' s l a t e s t e x p e r i m e n t i n t h e C - L s t u n t f i e l d ( d e s i g n e d

w i t h \ h e a i d ' p f , y' 51 -5 2 Y e a r b o o k ) i s n 't r e a d y fo r u n v e i l i n g ( n e e d s r e b u i l d

i n g ! ) i . ^ D j W g ^ M o i J a n i s s t i l l f l y i n g - h i s 1 9 5 1 - 5 2 d e s i g n s a n d c o u l d n ' t c o m e

u p w i t h a n y c o n t r i b u t i o n s t fi a t h e f e l t w e r e s i g n i f i c a n t . J o h n C o c h r a n e i s

s t i l P c o o p e d u p i n h i s t i n y a p a r t m e n t w i t h n o s p a c e t o l a y o u t b a l s a o r d r a w i n g p a p e r . E a r l i e r t h i s f a l l I t h o u g h t I h a d a h o t o u t d o o r h e l i c o p t e r i n t h e

w o r k s , b u t i t t w i s t e d ' ou t o f $ h ap e s o b a d l y as I w o u n d i t u p f or t h e f i r s t

t i m e t h a t I d i d n ' t d a r e l a u n c h i t — n e e d s a c o m p l e t e s t r u c t u r a l o v e r h a u l , d e -

s i g n w i s e , a n d t h e n — F r a n k E h l i n g m i g h t h a v e s o m e c o m p e t i t i o n .



L L O Y D L I C H E R — D E A R F R A N K — ( D e c . 1 9 5 2 ) —En cl o s ed o n sep a ra te pa g es a re the co m m ent s y o u a s ke d fo r re g a rd in g

so m e fo rm ula s f ro m the bo o ks .

I 'm sorry to hear that sa les are so poor. I t can be mighty s ickening and

d i sco ura g ing in a wa y a nd seem s to s t em fro m y o ur v ery wo rds , the y o ung er

minds have been led astray by the Pied Piper of Kits . About a l l I have to go

on here in thi s "mo de rn era" is wh at I see ab ou t me here in the B os t on ar ea ,

and that 's not much. There i s l i t t le or no free-f l ight work, even in the sum

m er . Ab o u t a l l the d i e - ha rd s ha v e bo und to g e ther in the N E W G , Ne w E n g

lan d Wak ef ie ld Gr ou p, an d only two of us ar e und er 21 (no t me ) . A n d

everyone doesn' t bui ld Wakef ie lds by any means, but i t sort o f g ives a

p u r p o s e t o t h e o r g a n i z a t i o n .

When I go in one of the few hobby shops around here I 'm a lways struck

by the decrea s ing em pha s i s be ing put o n the a i rp la ne l ine , pa rt i cu la r ly the

free-f l ight jobs , hardly any ki ts and they don't even bother keeping a varied

stock of wood on hand for orig inal sh ips . I guess l iv ings are made off

ra i l ro a ds a nd to y s , sh ips , e t c .But yet I can' t help reta in the feel ing that there's a powerful , la tent

un de rc ur re nt o f free- f l ight potent ia l , no dou bt br ou gh t on by my edu cat ion

a nd und er s t a nd in g o f the theo ry a nd pra ct i ce a nd k no w ing tha t a t l ea s t y o u

are try ing to pract ica l ly hand i t to the k ids on a p latter . I t ' s l ike rel ig ion

I think, you can lead 'em to it and have them read on it but some sort of

fa i t h i s ne ce ss ar y , fa i th in what other, exp er ie nc ed , pe opl e te l l you yo u

need and how to get i t . Maybe a Bi l ly Graham technique, ha? Somehow we

have to se l l the idea aft er we ours elv es un de rs ta nd and have fa i t h whi ch

we no doubt have now. The best way i s by pract ic ing what we preach and

set t in g g o o d ex a m p le s—w hic h m ea n s use o f a nd cre d i t g iv en fo r the idea s

y o u ha v e so g ra c io us ly co m pi l ed to co nv ince the skept i cs a nd sho w the"know-i t -a l l s" what conf idence we have in what we are say ing and doing .

C A R L H E R M E S — D E A R F R A N K — ( N o v . 1 9 5 2 ) —I feel ashamed in not having wri t ten as soon as I received the books.

In fact every time I used the book I would be reminded of the fact that I

owed a let ter ,but somehow i t just kept putt ing off .

The book is, I bel ieve, the best yet. I st i l l , after al l these months, go back

and f ind th ings I hadn't not iced before—more of that la ter .

I took the extra f ive copies and distr ibuted them where I thought i t

would do the most good. Each one of the persons I gave them to promised

fa i thful ly to wri te and g ive you their comments but I have a hunch none

of them did . One copy went to J i m St ew ar t o f Gr an d Pr ai r ie wh o has a

co py of ev er y one of the others . J i m is one of tho se fe l l ow s wh o has a

g a r a g e f u l l o f a i r p l a n e s , s a i l p l a n e s , W e s t e r n e r s , V^As, giant Gools, rubber

etc .—but only free-f l ight . He has every book and magazine that has been

publ ished in th is country and England s ince 1936 or so . He i s the co l lector

ty pe—ha s do zens o f eng ines inc lud ing Eng l i sh d i ese l s . He i s no t to o co n

cerned with the whys and wherefores o f model behaviour except to a very

l im i ted deg ree—th ing s l ike do wnthrust , b ig o r l i t t l e rudders o n the sa i l

p lane etc . He loves to ta lk models , run contests , form clubs and the l ike .

He has re ad the new bo ok from cover to cover. He l i ke d mo st ly the coll ection of plans. He couldn't see how all the rest couid be applied. It was nice

to know but couldn't be used to win contests . He did f ind i t very interest

ing , howe ver, and we have had sever a l go od dis cu ss io ns s in ce . J i m is the

C. O. W r i g h t type of mo de l bui l der i f you kno w wh at I me an.



Th e se co nd co p y we nt to K e n Que rm a n who i s a n a er o dy na m ic i s t here

a t Cha nce Vo ig ht . Yo u m ig ht kno w h i s bro ther Dick o f the Pro p Sp inners .

K e n i s a f e l l o w I en j o y ta lk ing to —keen ly in tere s ted in l o w spe ed a ero

dynamics and has done qui te a b i t o f research on the subject o f a irfo i l s . He

st i l l feel s ther e i s mu ch to be done and has so me pre tt y go od reas on s for

bel iev ing that way. I am going to try and ta lk h im into wri t ing for the next

book. If he won't I wil l write down what he says and send it on. He and Ih a v e h a d b i g d i s c u s s i o n s a b o u t C h e e s e m a n ' s a i r f o i l s — h e s a y s " m a y b e " . W e

ha v e a l s o a r g u ed o v er J i m Ho r to n ' s cha n g ea b le t r i m idea . T h e o n ly th i ng

concluded was that i f a free-wheeler can do 4 l / 2 m inutes , a fo lder sho u ld

do 51/2 or 6. We don't know exactly how, but there is a way.

He rb K o t h e ( P A A L o a d Wi nne r 1 94 8 -1 9 51 ) g o t the th i r d co py . He rb

st i l l has the "old feel ing" toward models that you seem to lose as you get

o n in y e a r s . Wh a t I m ea n— m o de l s to h im a re the m o s t im po rta nt th in g in

l i f e . I rem em be r I f e l t tha t wa y m a n y y ea rs a g o . Wha t a wo n der fu l wo r l d

tha t wa s—so s im ple—no th ing to wo rry a bo ut ex cept whether to use the

R A F - 3 2 o r t h e E I F F E L 4 00 . H i g h S c h o o l w a s t h e o n l y d i s t r a c t i o n ( n o t

ev en g i r l s ! ) wh i ch d idn ' t bo ther m e to o m uch . I rem e m ber I pu rp o s e l y to o ka su mm er jo b on a mi lk tr uc k so I coul d sp en d the da ys bu i l d i ng an d f ly ing .

It seems as you get o lder you reluctant ly admit to yoursel f that the models

m ust ta ke seco nd p la ce to th ing s l ike co l l eg e , m a rr ia g e , ea rn ing a l i v ing e tc .

I a lways fe l t that i f I could work up as much enthusiasm for a job as I

cou ld for mod e ls I sho ul d not do so bad ly . I t see ms you only have so mu ch

"e nt hu si as m" to sp en d each day . I know now that i t mus t be us ed at wo rk —

the models can only be to th ink about . I do a lso know that just before the

Wa kef i e ld e l im ina t io ns ea ch y ea r the jo b su f fers co ns idera b ly . I rem em ber

so m e th in g I rea d in Mo de l Aer o na ut i c s ( I th i nk tha t wa s i t s na m e ) , the

l i t t le magazine you put out once or twice . I t was, I bel ieve, in answer to a

l e t t er f ro m J o e He rw a t a nd i t wa s a lo ng thes e sa m e l ines . Wh en I f i r st rea di t I thought "What a s i l ly th ing to say!" but as the years went on I rea l ized

ho w r ig ht y o u were .

T h e f o u r t h c o p y w e n t t o W i t M c C o r m i c k w h o w o r k s i n D e v e l o p m e n t

h e r e ( h e a c t u a l l y designs a i rp la ne s ) . Wi t i s l ike m e , m a r r i ed e tc . bu t m a n

ages to turn out a Wakef ie ld each year.

The f i f th copy went to Dick Swenson who i s an o ld free f l ighter now

fly i ng sp ee d only . He has som e nice spee d de si gn s I can se nd i f you are

interested . Dick ta lked to you at L. A. last summer. I asked him to get you

to sto p by T e x a s but he to l d me la te r about you r f l y i ng .

About the book i tse l f—I l iked the text very much. Just about a l l o f i tsee m ed to m a ke sense be s i de s pro v id in g so m e g o o d m enta l ex erc i se . I sus

pect however that there are too few people who are rea l ly interested . The

reason I say this is that of al l the good model builders I have known I can

count the ones who would be interested in the "whys" on one hand. After

a l l , k n o w i n g exactly what i s happening during f l ight i s a s tudy in i tse l f , a

very interest ing one to me I wi l l admit , but not too many other people , I

fear . F o r ins ta nc e— th e goo d conte st f l i er kn ow s that the mor e he can "load

up" the stab the lower the s inking speed wi l l be . He a lso knows that th is

tends to "f la t ten out" the power c l imb, which i s good. He also kno ws tha t

this i s a touchy s i tuat ion and too much wi l l resul t in a d ive from which

there i s no reco v ery . Th i s he kno ws a nd he co pes wi th the s i tua t io n us ing

1/16 sheet, y 8 squares , c lay , etc . He usual ly does not know what the inci

den ce s ar e an d doesn' t car e par t ic ula rl y . I don' t mea n to bel i t t l e th is gu y

b e c a u s e h e k n o w s plenty. He warps wings , t i l t s ta i l s to get the ef fect he

wa n ts . He i s m a in ly in t ere s te d in dev e lo p ing co ns i s t en t l y g o o d f l i ers —he



knows this is the way to do it . Now the other type, of which there are so

few, usual ly never wins contests—always seems to be "test f ly ing ." This

guy gets h is k ick out o f watching the stab correct ing for a sudden gust or

the l ike. He has a pretty good idea what the angle of attacks are at al l t imes,

kn ow s wha t to exp ect befor e each laun ch. I fr an kl y bel ie ve that there i s a

lo t o f perso na l sa t i s fa c t io n to be ha d thro ug h the ty pe o f ex per im enta t io n ,

but there just are not enough people interested today . Maybe the book wi l ls tart something . I hope so . I wi l l say , Frank, that I enjoyed the text im

mensely and intend to read i t many more t imes.

I bel ieve the art ic les on how to do speci f ic th ings nave more interest to

the a v e ra g e bu i lder . By these I m ea n , Mur ph y ' s g e a rs , Sh um a ch er ' s R / C

which wa s v ery g o o d , J o e Bo y le , J im Ho rto n .

I must admit I f ind the plans the most interesting of al l . I don't care too

much for the "out l ine" type. The deta i l s are the a l l important part o f each

drawing as far as I am concerned. I can realize the trouble you must have

ha d coll ec ti ng wh at you did and I th ou gh t it wa s wel l wo rt h it. I wil l rea ll y

try to help from this end but most of the older guys are just plain lazy.

Bu i l d i ng the mode l i s about a l l they can do . Dr aw in g ske tc hes se em s to be

too much. I can understand th is when your free t ime i s s tr ict ly l imited .

I feel one reason why the books are se l l ing s lowly , or a t least s lower

th an in 1938, is tha t the hobb y has. ad va nc ed to the po in t wh er e we se em to

have al l the answers. In 1938 the big problem was to get the thing to move

through the air properly and come down in one piece. I feel that the use of

de th er mal iz er s ma rk ed the end of an era , so to spe ak . We a l l kno w ho w to

make a model s tay up 10 minutes under the present rules . The best "re

tr ievers" seem to end up as the experts . In 1938 we a l l dreamed of des igning

the one "super" model which would run off with a l l the contests . Each

person paid attent ion to a irfo i l s , s treamlining , f in ishes in the hope that h is

model would be "it". I don't think we realized it at the t ime, but none

rea l ly be l i ev ed tha t such a th ing wa s po ss ib l e . Me a nw hi l e we pro c ee ded to

have the t ime of our l ives bui ld ing and f ly ing a lways with th is theoret ica l

goal in mind. Of course Carl Goldberg came a long and did i t wi th an ugly

l i t t le model that put a l l the Shereshow type beaut ies to shame when i t came

to flying. I feel this sort of shocked us al l out of our l i tt le wonderful dream

world with the resul t that many dropped out never to return. The 1939

Nats was the end of model building as the '38 Book pictured it . I don't

bel ieve th is "golden era" wi l l ever return. We have mastered the thermal .

Maybe a rule change would help . I bel ieve the Bri t i sh have the idea on

Wa ke f i e l ds . Wi th the t im e up a ro u nd f iv e m in ut es they a re co ns i der ingl im i t ing rubber we ig ht , e t c .

Ma ny o f the o ld bo y s ha v e turned to R / C . Pe rh a p s co n cen tra t in g o n tha t

phase would help . Most o f these fe l lows wi l l buy anything on the subject

an d who know s, they mi gh t be p l eas ant ly su rp ri s ed ! The r e i s a lo t to be

d o n e he r e . R / C s o a r i n g h a s t r e m e n d o u s p o s s i b i l i t i e s .

Frank, I hope you have been able to f igure out what I 've been try ing to

say through a l l th is . I 've been wri t ing during lunch hours and sometimes I

g uess i t s eem s ra ther d i sco nt inuo us .

Louise was g lad to hear about the house—says i t i s a trend in the r ight

d irec t io n . Actua l ly there i s a l o t to th i s m a rr ia g e bus iness . Our l i t t l e bo y ,

Bi l l , i s thr ee now and I f ind mysel f re l iv i ng my boy hoo d to a cert a in ext ent

—wo uldn ' t t ra de i t fo r a ny th ing .

We both hope to get up to see you next summer when we visit the folks

in Co nnect i cu t .



O F F I C I A L R E S U L T S

1952 WORLD CHAMPIONSHIP COMPETITIONS

WAKEFIELD CUP J u l y II Norkopping, Sweden

1 s t A. Bl omg re n Sweden 810 sec. 2nd J. N i l b o r n Sweden 78 9 sec.

SWEDISH CUP Aug. 15-16 Graz, A u s t r i a

1s t B.G uni c Yu gos la v . 8 4 8 .8 s 2nd M.Ha ck l i ng er Ger 8 10 . 4 s

ENGINE POWER F.F. Sept . 13-14 Dubendorf , S wi t z er l and

1s t B.Whee ler Gr .B r . 8 07 .6 s 2nd H. La uc hl i S wi ss . 74 5 . 8 s

ENGINE POWER Control Li ne B r u s s e l l s , Belgium

Speed C l a s s I ( 2. 5 c c ) Speed C l a s s III (10 c c )

1 s t W ri gh t G r . B r . 1 58 . 6 9 km/ h 1 s t B a t t i s t e l l a I t a . 2 3 3 . 7 6 6 M1

2nd Ser ens en Den. 155 . 84 4f c / h

2na Davenport G r . B r . 225 . 00

Speed Cl as s II (5.0 c c ) Ac ro ba ti cs1s t . Dr . Mi l l e t Fr . 198 .395 k/h 1s t Ridsway G r . B r . 632 p t s .

2nd Wright Gr . B r . 193. 64 8 K/b 2nd J an se em s B e l . 597 p t s .

NOTE: Wake f i e ld , Towline G l i d e r s and Fr ee F l i g h t En gi ne Power

f l i g h t s a r e t imed to 5 min. max. Dur at i on t o t a l i s for

"Three F l i g h t s " . Speed g iv en i s an av er ag e of two ru ns .

F.A.I. RULES FOR INTERNATIONAL

MODEL AIRCRAFT COMPETITION

Wakefield Cup — Rubber PowerTotal surface area between 263.5 and 294.5 sq. in. Minimum

fuselage cross section area 10 sq. in. Minimum total weight 8.113

oz. Rise off Ground. Max. Rubber 2.8 lo z.

Swedish Cup — Towline GlidersTotal surface area between 495.3 and 526.3 sq. in. Minimum

fuselage cross sectiori=Total Area/100. Minimum weight 14.5 oz.

Maximum towline 100 meters?

Engine Power Free FlightMaxi mum engine displ acement 2.5 c c . (0.15 cu. in.) Minimum

weight 200 grams per cu.cm. of engine displacement. Minimum

surface loading 12 grams per sq. dcm. (2.75 oz. per 100 sq. in.)

Fuselage cross section=Total Area/80. Rise off Ground.

NOTES: Total area includes wing and stabilizer. Area is as

sumed to be effective area or "look down," interruptions in the

surface to count as area. Flights limited to five minutes. The final

score to be average of three flights.



I.

C O N T R I B U T I O N S

Our ba si c need is for experi ment al .material which may prove or disprovecer tain notions. In the 1951-52 YEAR BOOK we presented many new ideas

on MODEL AERODYNAMICS whi ch need c he cki ng on the f i e l d by the ac t i v e

f l y e r s . ^ P l a n s and report s of experimental models are always welcomed.

Our or ig in al drawing si ze is 9 i n . x 14 in .- -Y ou can send fu l l siz e

drawing of small models, but large models should be drawn to 1/4 (Engl is h)

or 1/5 (metric) sc al e. Always try to incl ude f u l l si ze a i r f o i l so that

we may draw it full size on our drawings. Be sure to include C.G. position

as well as inc ide nce angl es . Al l t hese thines wi ll help the theory boys

in their work.-—All correspondence will eventually be answered.

MODEL AE RONAU TIC ENC YCL OPE DIA *3 ?? Sp ir i t was wi l l in ? but the purse

was weak af ter the 1951-52 book was publ ished. ; Perhaps this ed i ti on wi l l

be more suc ce ss fu l in the f ina nc ia l f i e l d and provide the ex tr a money to

print fi. We wi l l le t you know. It w i l l be published someday as it has

worthwhile inf ormat ion . , _



P. S. Thanks to a l l who he lp ed . —T he cartoo n below is the l a s tone we have from Fred Col bu s. He used to draw them on bottom of h i s pre-w ar l e t t e r s . Anyone know where he is now?

Dear Friends:As you may have realized by now, this book is intended

to be ci rc ul at ed among fr ie nd s; and i t s readers and co nt ri bu to rsco ns t i tu te an informal in te rn at io na l c lub. So tha t i f por t ion s of book seem st ra ng e for a " t e x t book", remember th a t in fo rm al it y isthe keynote of this club.

Frankly, this book was prepared under very discouraging conditions; almost l ike those that call for another f l ight r ighta f t e r coming down in a t a i l s p i n . — T h e 1951-52 YEAR BOOK r eq u i re dabout about $4,000.00 of cash ou tl ay. So far very l i t t l e of t h i scas h h a s found i t s way. home. (Wish you. would t e l l you r fr i end sabou t t he 1951-52 book in ca se the y do not have i t . )

On ot he r hand, we were encouraged to keep on by the l e t t e r swe r ec eiv ed from r eader s who s a i d , "Now I know why--------------?

With th i s ed it io n we ar e going back to our pre- war p r i c e of $1. 00 per book. However, t h e law of economics l im i t ed us to 129

p ag es .. We doubled up some p la n s to make up for t h i s . .

In the near future we expect a more stringent application of the economic law to our personal requirements so that there maynot be as many plans in the future books as we would like to see.

Would l i k e to he ar from you . Let us know what you ar e doi ngto advance model aer odyna mics .. Your opinio ns and su gge sti ons w i l lbe appreciated.

1953 frank zaic year book

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