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IiOT~S ~.A lL"..TIOiiAL ADYISOR7 C01EUTTE3 FOR A::::mO:rAUTICS ~

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CASE FILE COpy

1::0 . ? 85

WHrD-'l'u:m:i::L IN7ESTIGATlo:r O? :?USELAG:::.:; STA:3ILITY IN

YAW 1.7ITH VARIOUS AR3.AEGE::IE1JTS O~ FIHS

By li e ?a~e ilo~~ard , Jr . Lan~ley Mernerial Aero~autical Labera~ory

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i7ashine;ton l,jovenoer ],940

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https://ntrs.nasa.gov/search.jsp?R=19930081581 2018-06-08T23:04:04+00:00Z

NATI ONAL ADVISORY COK~I~T~E ?Oa A3RO~AUTIC S

TECHNICAL NOTE EO. 785

iVIND-TU~~NEL I UVES'lIGATIO - OF FUS~LAGE Sr::ABILITY I:r

'!AW WITH VARIOUS ARRANGE MENTS OF FINS

SUMrf. ARY

An investi~ation was sade in the 7 - by l a - foot wind tu~nel to determ i ne the e ffects of dorsal -type f i ns and of various arran~eme~ts of fins o~ the aerodyna mi c char­act e ristics of a streamline circular fusela~e . Co mpa r a­tive plots of the aero dynamic characteristics of t~e fuse­la~e alone and the fusel a~e with various fin arran~em ents ar e ~iven to s~ow the ir effects on coefficie~ts of yawin~

moment, dra~ , and l ate r al f orc e . Resu l ts are a lso ~ iven

for one case in which a rear fin on a circular fusela~e was faired with m o de li ~~ clay to obta i n a fus8la~e shap e with the same s i de ele vat ion a s the fuseln~e with the un­faired fin but wi th an elliptical cross se c tion ov e r t~e

rearward p ortion of the fusela~e .

The resul t s indicated t~at f i n area to tne rear of t~e center of ~ravit y of th e fusela~e was beneficial i n red~c­in~ the Da~nitude of the unstable yawi n~ m o m~nts a t lar~e an~les of yaw ; whereas, fin area forward of the center of ~ravity was harmful . The do r sal - type fin was more e ffec­tive for increasin~ the yaw i n~ sta~il it y of th e fusela~e than was a smoothl y fa ir ed rearward porti on with the same side elevation as the fusela~e wit h the unfaired dorsal ­typo fin . The minimum dra~ coe f ficient and th e slope of the curve of yawin~ - moDent co e ff ici ent of th o fusela~e at zero yaw ~er a unaffected by t ~e addition of the fins , with­in the experim e ntal accura c y of th e tests.

I ~ ':i:EODT]CT I ON

Tho ~ re ator p ortion of the fixed vertical tail sur­faces of a ircraf t is requir ed to counte r act t~e directional instability of conventional fusela~c s~apes . Methods h~vc therefore b oe n su~~estod of r educin~ the maximum v a lue of the unstable fusela~e moment to permit a reduction of tho vertical tail. One method , which has b e en onployed on com­ma rcinl air craft, is the addit ion of a narrow strip of fin

2 N.ACA Techu i cc..1 _'J o~e ~Jo '. 785

are:l , refer r ed to n,s a IIdorsn.I " :!' i u' , 3..l o nA; tho top c e n t er l i ne of the fuse l a~e nhead of tho usual vert i c~l t a i l sur­f~ce . Anothe r notho d i s t~e sn~pin~ of the r e~ r of tbe fuse l ~~e int o a we d~e , effect ively n,dd i n~ fin a r ea at the top ~n~ the bottom . A thi r d method recently su~~ ested i s the add i t i on of a sha rp- ei~e protube r~n c e alon~ the 7ert i ­cal center l i ne of the forward ~orti o r. of the fuse l a~e . I t wns t~ou~ht thn. t such a prot~be r~nce , by dis tu rb i n~ the fl o w ove r the do"n-\': i r..d sid.e of the ;rar.ed. f1:_ sel n.~e , mi~ht decr eas e the ma~ni t~de of the no~at i 7e pressure in th~t rep';ion for ard of th e center of ~ravity and t hereby reduce the unstable mo nen t .

These meth o ds are pr i ~arily inten de d to r e~u C e the max i num v~lue or the ~usela~ e yawi n~ moment, which occur s at mode r ately lar~e anp'; l es of yaw where v e rt i cal tail sur ­faces of conventional 2spect ratio$ are nor~all~ stalled . Ar..y reducti on of slope of the YRwi n~ -r oment curve i n the vicinity of zero yaw is i~cidental . ~one of t~e ~ethods is expe cted apprec i ably to increase the dra~ of the fuse ­la~e for ~he uny~wed condi t i on of th e a irpl~ne .

In the reported invest i ~ation two fusela~e shapes we r e tested i n co~binat i on with f i n area at var~ous l o ca ­tions or.. the fusela~e t o pr ov e the effect i veness of each of the thr ee methods .

_,.1ODELS

~he two fuse l a~e shapes used in th i s investi~at i on are sho wn in fi "'; Hes :!. and. 2 . One 0-: these fuselages i s a b o dy o f r e v o l ut i on tha t was pre7iously used f or the wi n g ­fusela~e i nvesti~ati on re~o r ted in r efe r en c e 1 . Tho othe r shape was obta i ned by fa i r i n~ the rearwa r d po r t io n of the fusela~e with model i n~ cla~ as shown in fi~ures 2 , 3 , and 4 . The fuse l ases 7ill here i nafte r be referred to as " fuse l age A " and "fusela.«;e B . "

The fin ar ran~enents use d a re a~s o shown in f i ~ures 1 and 2. All fins ex c ept one of 1/32- ir..ch - diamete r wir e were ~ade of 1/32 - inch sh oe t brass cut to conform to the i'use ­l a~e shane . I n th i s r eno r t the constant - widt h fins (f i g . 1) reill :bO call ed. ty po i , the tail - t:'pe f i n (:fi~ . 2) \,"ill be Cal l ed type 2 . The f i ns were ~olde red to the heads o f flat - head uo o d screws , i rn~odded i n t~ c fuso l a~e , wh i ch he l d the fins snu~l y asa i ns t t~e fusela~e to pro v ent a i r loak­a~e und.e r them .

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NACA 2ec~ni cal ~o te ~o . 785 3

Th e type 1 finE were rrado in four ~idthB, 0 . 0312, 0.172, 0 . ~44. and 0 . 688 inch , rhich e re eQual to 0 . 4 5, 2 . 5 , 5 . 0 , ~nd 1 0 . 0 percent , respect ive ly , of the maxi m~m f use ­l a~e di a~e t e r . The f in s we r e cut in sections so thn t they CQuld b e attached to the fusel~~e i n v~rious combinations. The fins attached to the forward p ortion of the fu se l a~e

are deBi ~ natod for wa rd f ins and those at tach e d to the re~r­ward p ortion of the body ar e dos i ~nated rear~Rrd fi r s . The action of these rear~Brd f ins, a l thou~h they a re dis ­p os e d sy~metri call: above and be low the fus e l a~ e, Gh cu l d b e sicil ~r to that of the do=s a l - type fin use ~ on severa l pre sen t-day trans~o rts .

Th e typo 2 fin was ma de to be attached to th e re n r­w~rd p ortion of fus e l a~e A. Thi fin h as ~ width Bt the trnilin~ ed~e 50 pc rcen ~ of the fusol a ?e di ~~c ter and is f a ired i nt o th e top and th e b o ttom contours of fuscla~e A a~ a station 70 p8rcen t f ro m ~ho fls o l a~e no se .

TESTS

The t os ts were ma de i n the NACA 7 - by l 0 - foot wind tun­nel , which is descr ibed ~ n ref e r en c es 2 and 3 . The t ests we~e ma de at a dynam ic press-lre of l6 . ~7 pounds pa r squa re foot , vhi ch c o rres~ o n~s to a ve locit y of a bout 80 mil es per hour under s t anda~d se a - le v el conditions and to a tes t Reynolds number of a bout 6 1 8 . 000 bp-scd on t~e cube root of the fuscla~e volu~e ( 0 . 846 ft) .

No pre liminary t e sts wer 8 ~ade to dete r mine tho tare forces and the moments caus ed by the ~~del - Bupport f i ttin~~

because ~t was believed that the rolat! v e me rit of the var­ious arrar~eDen ts would bo unaffectod ~y the val~s of tar e .

Th e t es ts ~~ re made at zt ro an~ 1 8 of attack and at an­~los of yaw , ~ , ran~ing fra n - 1 0 0 to 60 0 •

RESULTS AKD ~ISCUSS ION

The results of th e te~ts are ~ i vcn i n t~8 for m of UACA standard co eff icien t s of forcos a~d D o~ ents with r e ­spe ct to the wind axes that int e r se ct a t the conter- of ­~ravit: location previously used in r e f e r e nce 1 and shoun in fi~ure 1 .

Tho coe ff ici en ts use d a r e based on the volum e of fus e ­la~e A in acco rda nce ~ith the p oc edure of r e ference 4 , an d are defined as follows :

4 NACA Technical Note No . 785

where

q dynamic pressure (16 . 37 Ib/sq ft)

V volume of fusel~~e A (0.606 cu ft)

The effect of t h e rearwa rd fins on the aerodynamic characteristics of fusela~e A is shown in fi~ure 5 . The curves of yawin~-mogent coeffici ent s how that, with the 0 . 172 - inch fin added to the rearward porti on of the fuse­la~e , t~e maximum value of th e unstable yaw i n~ momen t is reduced by more tb an half . Increasing the fin hei~ht p ro ­~re ss ively decreased the naximum un s table ;yawin~ mo men t and the trim an~le . The effectiveness of increasin~ the fin hei~ht , h owever, became pro~ressively smaller with hei~ht . The type 2 f i n was o n ly sli~htly more effect i ve than the 0 . 172-inch type 1 fin althou~h its ai ea - momont is nearly equal to that of the 0 . 344 - inch type I fin . This' result , couplod with th o fact that the effectiveness of the t ype 1 fins was n o t pr oportional to the fin hei~ht, appears t o indicate that the effect i veness of these fins primarily depends on the len~th or the sharp ed~es and t h eir spoi li n~ effect depends on the type of fl ow ove r the rear portion of the fuselage . This conclusion appea rs to be substantiateQ by the dra~ curves , w~ich sho w that the increase in drag at lar~ e an~les of yaw i s also les s for the type 2 fin than the 0 . 344 - inch t ype 1 fin.

The slope of the curve of the yawin~ -moment coeffi ­ci en t at small anlY,les of yaw is appreciably re duced ·bY th e rearward I ~ns. As expected , however, the re ~uct ion is small . The effe ct of the fins on the dra~ a t zero yaw (normal-fli~ht c ondition) was not me asurable .

In order to check further on the relative effects of the sharp ed~es and the i n c r eased area back of the center

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I ~

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J

NA CA Tec~nical ~ote ~o . 785 5

of ~ravity . the un fa ir ed type 2 fin on fuse l a~e A has been compared with fuse l a~e B in fi~ur e 6 . Fus e l a~e B , as pre vio us l y me ntion e d , has t he same side are a as fuse ­l a~e A p lus the type 2 f in and was deriv e d by fairin~ the t ype 2 fin in to t h e fuse l a,e t a il wi t h m o de lin ~ clay to el i mi na t e th e s~arp Gd~os . F i ~ure 6 s hows that, a1 -thou~ h both tho typ e 2 fin and fusG l a~e B we re loss u n ­stable than fu se l a~o A , the i mp rovemen t o btained f ro m fusela~c B was l oss tha n h a lf t ha t o btained from t he type 2 I ln . It is the r efore a~par ont tha t the sha r p ed~os of the unfair o d f i n ve r e advanta~o ous in reduci n~ tho u~­stabl e yawin~ -m o melt co eff ic ien ts of the fusela~e shapes .

FU3ela~e A wi th the t ype 2 fin had th e lar~est values of lat e r a l - fo rce coeffi c ient at la r ~e an~les of yaw, fusela~e B ~ad snaller values , and fus81e~e A a lo ne had t~e s mallest values . I nasmu ch as a lar~e l a t­e r al f orc e is de s ira ble fo r s t a ili t~ wh e n s i des li 2~ i n~, fuse l a~e A with the type 2 fi n wou ld als o be bett e r than fU3ela~e B fo r this manouv e r . T ~e values of dra~ coef ­ficient at lar~e an~l e s of yaw decroased in the sam e or der as the va l uos of l ate r al - force co eff ici en t . The minimum dra~ coefficient a t z ero yaw was u naffectod by fus o la~e shapo or type 2 fin , wi thin the expe ri menta l accu r acy of th e tests, in sp it e of th e f act tha t tho d ra~ coeffic i en t s in overy case we r e based on th o vo lume o f fusola~o A.

The llns mounted for~ard (fi~ . 7) ~r oved to be harn­ful to sta ~tlity in yaw . The an ticipated s p 0i l er a ctio n d id not occur and t hese fo r war d fins a r e therefore unde ­s irable . The late r a l - force and dra~ coef f i cients i ~c r ease

wit h the an~ l e of yaw and th e fin widt h .

The compa r a t i ve p lots ( fi~ . 8 ) for f i ns co u nte d i n both forwa r d a n d rearward locations show t h at these a r­ran~ement s are i n ever~ case less desirable than the c o m­parable ar ran~ em ents wi th the r earward fin alon e (fi ~ . 5 ) f ro m con Rid e r at ion of stabili ty in yaw . The late r al ­force and t~ e dr a~ coef : icient s f o r t he c om b i nati o n forward - an d-r ea r wa rd location increase with i n creases i n the a~~le of yaw and th e f i n a r ea and are ~re~ter than for com pa rable arran~ements 0: fo r war d o r recrward f i ns a lo ne .

A comp~r i son o f th e se v e r e l locatio ~s of t~9 ~ i ns

wit h a \v:!. d t !:J. 0 f O. 344 i n c h ( :- i ~ . 9 ) s t_ 0 W s t:1 11. to: 11 ye o m­binatio ns witl t he rearwQrd fin decre~se t h e unE~~ble yaTI i n~ -Do~ent coeffic i en t of th e fusel a~ e at ler~e nn~ l es

6 ~ACA Tachn i cal Note No . 785

of yaw . The dra~ and the la t e r al - for c e c oeff i cien t s a t l a r .r::;e anl';les o.f /a\v . h owe v e r. i ncrease i n propo rtio n t o an i nc r e~se i n the f i n area . The . dra~ a nd t~e stabilit y i n yaw at small an~les of yaw ~r e only sl i ~h t ly affe c ted by the v a rio uG l oca tions o f the O. 344- inch f i r. on fusela~e A.

CO:if C:;:'US I O~iS

1 . Th e rea rwa~d f in s were ve r y effect i ve i n decreas ­~n~ the u n s t a b le yawi n~ momen t of t ~e fusela~e at the la r~e an~ l es o f yaw ~

2 . The benef i c i a l effects of the forwa r d - and- rearwaT d c o mb i nat io n o f fins and of the fin cOF.pletely ~ round the fuse l a~e we r e due to the presen c e of the fin area beh i nd the c ente r of ~ r avi ty 6f the ~odel .

3 . The sha r p f i n ed~es were found def i nite l y benef i ­c i a l at l a r~e ang l es of yaw .

4 . The mi n i rr.um dra~ c o eff i c i ent an d the slope of t h e cu rve of the yaw i ng - momen t c oefficient of the.fuse l a~e at zer o yaw we r e unaffected b y the addit io n ~f th e f i ns , wi thin t he experimental accuracy of the tests .

Lan~ l ey Mem o r i al Aeronautica l Lab o ratory . Nat io na l Advi so r y Commi t ee fo r Aer o naut i cs ,

Lan~l e y F i e ld , Va . , Oc tober 22 , 1940 .

J

NACA Tec~nical Note Jo . 785 7

REFERE NCE S

1 . Bamber, M. J ., and House, R . 0 .: Wi nd - Tunn el Investi ­~ation of Effe c t of Ya w on Lateral - Stab i lity Char ­a cteri st ics . II - Rectan~ul ar N. A . C . A . 2 3 0 12 Win~ with a Circula r Fu i e l a~ e and a ? i n . T . N. No . 7 30 , NACA,1939 .

2 . Harris, Thomas A.: The 7 by 1 0 Foot Wind Tunne l of the Na tiona l Ad vi sory Comm i ttee fo r Ae r o nautics . Rep . No . 4 1 2 , NACA, 1931 .

3 . Wenz i n~ e r , Ca r l J ., and Harr i s, Thomas A.: Wind - Tunne l Invest i ~ation of an N . A . C. A . 230 1 2 Airfoil wi th Var ­ious Arra n~em ents of Slott e d Fl ~ps . Re p . No . 664 , NACA, 1939 .

4 . Fr ee man , Hu~h B . : Model of the U. NA C1\. . 1 932 .

Force Measurem e nts on a 1/40 -Sc a le S . Air s h i p IIAkro n . 1I Rep . No . 432 ,

NACA Technical Note No. 785

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NACA Technical Note No. 785 F1gs.3,4

Figure 3.- Side view of streamline circular fuselage B with faired type 2 fin in place. mounted in the 7-by IO-foot wind tunnel.

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IACA Technical late Io 785

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HACA TecbDioal Jote 10 . 785

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J ACA Technical Note no . 785

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Fig.8

1igure 8 . - Effect on fueelage charact~ri8tioB of various fin arrangements forwa rd and r earward .

BACA technical lot. 10. 785

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risure i.- Coaparison of ae~od~o ohar acteri.tio. of fuselage A alone with combinat ion. of looat ion of fina of 0 .3" i DCb width on f u.elage A.