naca arr 3g06 some yawing tests of a 1 to 30-scale model of the hull of the xpb2m-1 flying boat

7/27/2019 NACA ARR 3G06 Some Yawing Tests of a 1 to 30-Scale Model of the Hull of the XPB2M-1 Flying Boat

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ARR NO. 3G06f.. n u #, W 4-, , - ~ %R$%%%3

NATIONAL ADVISORY COMMITTEE FOR A,%===--

.

wfurIm ItlnwlrORIGINALLY ISSUED

J uly 1943 a sAdva nce Rest r ict ed Report 3G06

SOME YAWING TESTS OF A l/30-SCALE MODEL OF THE HULLOF THE XP B2M-1 FLYING BOAT

B y F. W. S . Locke, J r .S tevens I nst it ut e of Technology/

. . . .. . . . --- ..,.,

:.NAC


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i i nl l l l l l l m31176 Olm 47s4NATIONAL ADVIS@tY 00MMITTEE pm AERONAUTICS

ADVANCE ll~STRIOTED RrnPORT

SOk@l YAWI~GTIESTSOFA-l/30-SCALE MODEL-OF-TEE-~LLOr THE XPB2M-1 FLYING BOAT

By F. W. S. Loake, Jr.

SUMMARY. .

The results obtained from yawing teete of a 1/30-ecale model of the complete hull of the XPB21bl (SteveneModel No. 404) are shown to be in substantial agreementwith preliminary full-scale fllght tests on the flyingboat. The model teets aover the entire range of speed6up to get-away, on the basis of the designed gross weightof the flying boat (140,000 lb).

Reports of preliminary flight teete of the xPB2M-1flying boat indicated that there was a definite tendencytoward directional Instability in tke.vicinity of thehump . The model teste show that the hull is unstable at.speeds up to and juet past the hump. It was found thatwithin the range CT s 2.0-2.5 the curves of yawingmoment are discontinuous at small yaw angles, and thishas been associated with the difficulty found In thepreliminary flight tests.*

IITRODUCTIOI?

It has not been neceeaary, in t he pa st , t o give mchattention to the directional etabillty characterlstica offlylng-boat hulls. Gott, in reference 1, suggested thatdirectional instability was to be met with, only occasion-ally. Ilecently, the reverse has apparently become true.At least three moderq flying boats have exhibited varyingdegrees of directional Inetabillty on the water.

.

-.

*Since the tests herein reported were completed~ smallalterations to the hull, based upon model t est flndin~ s,are reported to have substantially improved the direc-tional stability oharacte~imtice.


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Although the preliminary flight tests of the XP32M-1had show~ directional instability primarily in the regionof the ilump, Gott)s experience had shown instability athigh speed. It was thought worth. wb-ile, t-herefore, tomake an investigation which would cover the ei~tire ran~eof speeds from zero to get-~~ay. !I!llisnvestigation hadtwo objectives:

1. To find curves of y-awing moments agai.ilstyaw, andto attempt a correlation of their shapes withthe reported fuli-size behavior2. To provide a background for future workThis investigation, conuucted at the Stevens instituteof Technology, was sponsored by, and conducted With fiaan-cial assistance from, the Natioiie.1 -4dvi:ory Committee for

Aeronautics,iJZSCRIFvTI037!)IMODEL

The Model was built for ZfieGlenn L. i!arti~ Company,to their Drawing Xo. R24007d, aild was used uy then forseveral tr.vesti.gatioc-s. It was used for the present irl-vesiigation, in preference to other i~odels, because itwas a full model of the hull, cow,nlete with top and tailcone. The body plans are given ii figure 1.

2he ceilter of gravity was located in the specifiedlongitudinal and vertical positions, and on the center-line pla.iie. !lhe xodel was allowed to pivot freel~ a%outboth the transverse and vertical axes, except in certaintests at high speeds, during which the trim angle waslocked.

Particulars of ihe model anti of the fuli-size flyinglost are listed on page 7.

.4PPARLN3S ANI) FROCEIXJRE

The model was mounted on bearings in a yoke, Thebearings aJ.loredpiicfi.irisfreedom. and ihe ycke could beadjusted to produce fixed heel angles. The yoke was at-tached to a staff which allowed freedom ~n yaw and heave.

. . . . ... _______ _ . ..- . _______________ ..____ ... _.. _ . . . .. .... . . . . . ____


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The ~gular motion of the staff was restrained D Y a calibrated spring, thus allowing determination of the yawingmoment . A dash.pot ras provided for damping in ya~, whichsome preliminary experience had shown to he desiral)le.A sketch of the a~paratus is shown in fi~ure 2 and aphotograph in figure 3.

The calibrated spring merltioned previously constitutedt~e yawing moment dynamometer. The spring was relativelyweak, and provision was made for changing its stiffness.The na.gr.i.tudend direction of the yawi-ng monent, at therllilnillgaw angle, was determined by notin~ the differencebetween the angles of yau when stationary and in motion..411 noaents and angles are referred to the wind axis (i.e.,to the horizontal plane),

Up to about 12.5 feet per second (haif get-aray),the model was tested free to trim according to the sched-ule of loads previously used for a series o: resistancetests on the same model, reported in reference 2. Athigher speeds the model was tested at fixed trims, forwhich the loads were calculated from the aerodynamic char-acteristics of the flying boat. At eacii speed, sufficienttests were made to defiae the shape of the curve of yawingmoment against yaw angle, especially in the region ofsritailyaw angles. When free to trim, the trim and hea-,rewere recorded. JQl ih~ tests ~e~e run at zero heel ~n~le.

R.SWLT S

The following nondimensional coefficients are Used:Load coefficient, CA = 15jTb3Speed coefficient Cv = T~/J~FTrimming moment coefficient CM = x/wlFYawing moment coefficie:it Cp = M@734wZeave coefficient c~= IL/b

where

.-.. . -. ..-.- ..- ... . --. -.. .,.. -.- . -- .-.


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load on water, poundsspecific weight of water, pounds per cubic foot(62.3 for Stevens)beaa at main step, feetspeed, feet pe~ secondacceleration of gravity, 32.2 feet per secondstrimming monent, pound footyaving moment, pound footheave at center of gravity (height above position at

rest and. zero trim an6~e), feetMoment data ar e referred to the center of gra~;ity.?iate.rtrimming moments which tend to raise the bow are

co:?siderei positive. Water yawing mo~ei~ts whith tend toroia.te the bow toward the right (starboard) are co~sideredpositive. Yaw angles to right of the course are co~sidere~positive.Trim (~) is the engle between the base line of tkehull and the korizoi~tal.Yaw (~) is the angle between the center line of the .hu~~ and the course, measured in a plane parallel to thestill-water surface.

!lhe large char% in figure 18 is considered an impor-tan-i presentation- of the results; it provides a comprehen-sive ;iew of all of the iiirectional stability character-istics uruler the give~ se% of particulars. Each enclosedrectangle (or special shape W~iere necessary) shows th-ecurve of yawing moment against ya~~ angle for ~ke speed andtrim angle indicated hy its Cerlter. study S-hews that, ingeneral, there are four types of curves. ~aki~-g the slopeof t-he moment curve at zero yaw angle.as a maasure of thestability of the flying ooat iu yaw, the four tyues maybe defined as follows:

\..-. . .. _______ ...- . . .. .. .. ... . .._. ..____ ___ . - ._ ..-.


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TvDe dc% /a*PoOltive stability Begat iveMeutral Very emall positive or zeroNegative 6tability PositivenEooklngll instability Curve discont inuous a t sma ll a ngles ~It will be seen that the hull *S directionally unstableup to about half the get-away speed, except fur a verysmall region. This small region of positive stability isencloeed by a contour line. The. cases of hooking insta-bility occur within a small region, which is also enclosedby a contour line. It will be noted that tha region ofinstability starts at zero speed and extends elmost up tothe hump. At speede above the hump, the hull is stable at high trim angles, where the afterbody is normally wetted;and neutrally stable at low trim angles, where the after-body is normally clear. It would be expected that, oncethie hull hae paseed the hump, no-trouble from directionalInstability would be encountered. .

The report on prelimina ry flight tests of the actualxPB2&l flying boat bears out these Indications of themodel teets, at least In part. It states that, at epeeds below the hump, constant attention must be given to keepthe flying boat headed very close to the couree, and un-balanced power must be applied rapidly to check any devia-tion from the oourse. If corrective moment is not appliedrapidly to check the firet sign of yawing, the boat maybecome unmanageable. Cross-wind taxying may be very nearlyImpossible, even with maximum unbalanced power.11 As noremarke are made concerning directional stability past thehump, it is assumed that no trouble was experienced.Some of the model test results are ehown in detail

In figures 4 to 17. The maximum available momente due tofull rudder deflection, with balanced power, are.markedon these charte. It will be seen that at low speeds theruddere are not nearly powerful enough to overcome thehydrodynamic yawing moments for anything more than a verysmall yaw. On the other hand, at high speeds, the avail-able rudder moments are more than sufficient to control.any deviation from the course. It apqeare, thereforethat any further work on directional stabillty may well .be concentrated on the low- end hump-epeed regions, a nd


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6that, in these rerions, no help should be expected fromthe aerodynamic controls. A satisfactory hull shouldpresumably have neutral stability at all spee~s.

Visual.observations made during the tests indicatedthat the hooking instability in the vicinity cf the humpwas caused mainly by water which passed over the after-body sides In the vicinity of the stern roet and wettedths tail cone. Although sometimes noticeable under etherconditions , this was especially noticeable where hookinginstability occurred. In one or two of the tgsts withlarge yaw anples, at speeds in the v:cinit~ of the hump,water washed rlfht over ths tail far enou~h forward toleave the rea r pun turret out.cf water, and would mroba-bly have damaged the tail surfac~s on the actual flyingboat .

(30tt (reference 1) used lightgr loadings than thetests herein remorted, and he used only relatively lnrperyaw an~les. He found comparatively lr+rge unstable yawingmoments fit high smeeds under these conditions. The mres-ent tests indica t e tha t ~ robsbly the same thing would hmvebeen found ha d they been ca rr ied to htgher yaw a nples.lZiFh yaw angles were not considered to be particularly im-mortant at high sDeeds for ths flying boat under investi-gation because of the larg~ available rudder moments.Gott found that, in gsneral, increasing the trim angleimproved the directional stability characteristics at hlphSmeedg , which agrees with th? findin~s in the mresent tests.

COECLUSICES1. The type of instability which gives most troubleIn the full-size flying boat shows up as discontinuousmoment curves in the model experiments - referred to asWhooking. n2. dater clingin~ to the aft?rbody aides nnd tailcone seems to be the cause of the discontinuous moment

curves ~ and this Is the region in which furth~r work is .likely to pay (in fact, already has maid) divid~nds.3. In the region from just beyond the humm to get-

away, the hull Is either directionally stablq or the nvail-abls ~erodynamic moments are sufficient for control.S t evens Inst itut of Tschnolopy,

Hoboken, N. J ., December q , 1942.


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REFERENCE S

--=-l...Gott, J. P.: Xot; on the Directional Stability ofSeaplanes on the Water. R.& M. No. 1776, BritishA. R. C., 1937.

2. Davidson, Kenneth S. M., and Locke, F. W. S., Jr.:Some &stematic Model Experiments on the PorpoisingCharacteristics of El~ing-Boat Hulls. HACA A.E.R.,June 1943. .

RTICULARS AED SH3CIEICA!TIONSWawy DesignationMartin Model Xo.Mertti Drawing Ho.Stevene I.iodol0.SmJ.e

Nl SizenB2M-1170R2400713

1

Beamatmahs tep,inches . . . . . . . . . . . . .162Angle betw een forebo~ v keel a ad%a so line,degrees. . . . . . . . . . . . . . . . . . . . .2.0Angle betwea afterbody keel and base line,d.egree8.. . . . . . . . . . . . . . . . . . . .5.0Height of ma in step a t keel, iuches . . . . . . . . g.1Ce:~terof gravity forward of main st~ (26. 5Spercemt M.A.C.), inches. . . . . . . . . . . . .70.0Center of grevity above base line, inohes . . . . lM.7Gross weight, A, pounds . . . . . . . , . . . 1~,000Wingspen, b, feet . . . . . . . . . . . . . . .200Wing area, S, sqzarefeet . . . . . . . . . . . 35g3Mean aerodynamic chord (M.A.C.), Inches . . . . . . 249

Horizontal tail area, square feet . . . . . . . . . 50gVertical tail area, square feet . . . . . . . . . . j50Distance, center of gravity to 5 percent M.A.C.7orizont~ tail (tail leqyth , feet . . . . . . 63.6Thrust line, stove base line at main step,inches. . ... . . . . . . . . . . . . . . . . 230. 3Thrustline, Inolined upward to base line,degrees 5. 5

trim angles referred to base line.

Model

4(I U1/ 30

. 5. !)0. 272.33Q.qj5.196.674.0$12g. 300. 5650.3~92.127. 6g595

..


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ic Oharacterlebioa~*tT = 5 ( rel ati vetohm~e)( f l aps @O). .l.5g5L at~= 50 . . . . . . . . . . . . . . . . . 6. 95+d~ /d7. . . . . . . . . . . . . . . . . . . . . O.l@jI-dL/d7, pounds per degree . . . . . . . . . . . . 0.b5tl+d~~d T(av. ) . . . . . . . . . . . . . . .=.-0.0150dMCflJd7,pound-foot per degree (av.) . . . . . . 1.365 @d~CG/d~(av.) . . . . . . . . . . . . . . . . . -0.C096~CJw(av.) . . . . . . q . . . . . . . . . . CJ.546Va~ ch (max.z-adderforce). . . . . . . . . . . s 0.0148Get-awxy speed, feet per second. . . . . . . . . . 130Get-Pw~ ~ . . . . . . . . . . . . . . . . ..l. G90Get-away T, degrees . . . . . . . . . . . . . ..~.3

Ratios ~1-sigaModal

1/aA 5. 477 .

1 q ggg7.72 X 10-3#0. 1045-30. 509x 10 +-0. 01505. 05x 10-5e

-0.0006 ~2.02 x 10-5Va

Omolu

A j.ox IoaAa g.o x 10A= 27.c x lo;A4 i n. ox lC


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Fig. 1

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Figure 1.- Body plan of model XPB2M-1.


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PLANE OF SYMMETRYw MODEL- -

9\ !xMEWI

iAw #--

;. AxIs-k CALIbRA~ED YAW MOMENT SPRING\YAw DAMPINGPOINTER

FIG. 2~CHENRT\C 5KUCH

OFhN\NG (+PRRRTw

CARRIAGE--------------------------------------- .---------------------- ------ -

------------------ -------------------------- -.------- ---------------- --------

hVJ &ALE MAIN TOWING GATETOWING FoQCC

c 5


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Figure 3.- Appa ra tus setup for ya wing t est s.


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I I ISP.NO. H,5STEVENS MODEL No. 404-1 I

FREE-TO-TRIM - GV=I.04I \ IcA0.89CM.- c).oo*= O.OO

.

UNSTABLE

6+QJ g !o -

u-d

-*z

1 > APt?Rox. MAx.Ru ? Mmm4Tv= ~P k!- - -9 s-b .\ / u. PORT T< .\, , / STAR0

.0 j # ; ,, q -T q Tt b 4 z 77 4 -o-d!

_;_ _Jt YAW,ANGLE, DEG /3 P_z ) +0,2~* / / ?J0 +(JJ

-0.1. JA lb~/ v~ -0-ch - 0z

Fg . 4 -o.1-

1 I I ~SP.NO. H26_ _ c)*STEVENS MODEL No. 404-1

FREE-TO-TRIM G/= 1.87I [ Icd0.83CM= 0.00Q= O.OO

UNSTABLE

+ 0.1-- i lo-APPROXIMATEMAXIMUMAVAILABLEMOMENT tiFROMRUDDER s\ \

_ * _ _ _ _ > * -b- &d 1 # 5-0=i ~ -i /IL ~ ~, PORT o STARNO

-ol!~~.e I6 4 7L+2 4 0-z YAWANGLEtOEG,g /o %y

= \ +0,2g ~ ~ .::~

c 1 *o a J .-0.1. Ch g_

: 0 FF;g. % ,:0,1-;


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1 I I zgSR NO. HZ7STEVENS MODEL NQ404- *

FREE-TO-TRIM CV=2.Q21 1CA O.82(jM, -oo15@=o.o

.

POSITIVE STABILITY

q

al i lo-- ~ ,-T $ -

-? 13

ZB> APPROX. MM -m T g 5-k \0=

u I i* 3A RBOd, , 0-

q_5 ; L %s \ ! +0.2

g~ - A * ,- Ch X@~ ~1+OCJ

-al k8vFig. -o#l- :


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4$ I a:SR No. H28 R No, HZ8STEVENS MODEI. No. 404-1 STEVENS MODEL No.404-lFKE -TO-TRIM CV =217 FREE-TO-TRIM CV= 2.17

I I ICAS().8 I * ~@3iq. 0.00 q.-Cl.l5

x O.OO =O. 0*

I%slTIVE STABILITY HOOKN13lNsTA6iLlTy\

hml g 10 *.1 - y 7. J lo-,t , Ay-b ~F- + - L11

~Au - L a 2*: -F- -

APRROXIMATEM A%IMJMAVAILABLE -MT: L _: FROMRIIICER, \

! 5 -0= ~ *APBROXMAxUODERMCUENT 0=u- pu. - h ~ *J pfiRT STAREIO J -;!g k PORT

08 ~f 8 e +4 3- -o#~ O-G 8 ; -i I -it 4YAWANGLE, DEIi 1-1 z YAWANGiLE, OE~g Glq a!+0.2 ~\ +o&g C9 1 1 q 9~ %- + -z q s q + s ) %0= +o,J- \ 0 +0.j -q - Gh< q q ~ ~ ~ J

0.1 k \c~ ,-o.1- t-~0 0 , ~7 0 -

Z i 0 - 2\Flg,8 % 0 mFig9 s ,m- 0. 1- - 0, 1-mI n

q


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\I I ISE NO. HZ9

STEVENS MODEL NQ 404-1FREE-TO-TRIM CV = 2.33\ I I

Q.0.0

W -

_ n>u= APPROX, MAX.RUOOERMOK~

+HSTE!ENJMJDELL!4-l+H+ &HHEFREE-TO-TRIM cv = 2.74I I ICA0.74CM* 0, 00~=Q. oI I I

NEUTRAL STABILITY \

HIol- g lo--1


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:.. -.--. -T*!

I I ISE No, H~ 18STEVENSMODELNa 404-1FIXED TRIM Cv = 3.711 IcA,oc6~

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Fig. 12 I-ILO.J

1 I I I zSRNO.H* 1 8 gSTEVENS MODEL NQ 404-1 - *FIXED TRIM Cv = 3.71[ I ICA, 0.55

fJM, Q. 0,03 =10

POSITIVE STABILITY

tat # 103

-? APPROX.MAX. RUWER ~WNTz

ZZoL

a

-o.1-0

Fig, 13


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S! NO.Ht30STEVENS MODEL NQ404-I

FIXED TRIM Cv = 5.57

NEUTRAL STAhILITY

,

-0.1 ii- . 8 0-~2Fig, 14 -0,1


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P

=1Cf)0.55CHART No. I (CONTINUED)

I EWRIMENTATuwr& TM 1

\CA?3%

? k,.38 0.59 %* O;O y CA0.23I< 0.63 o.mm,m rL0.27 -EL/~3 0.52 ms 0.67 0.35NEUTRAL STABILITY T. 0.51I I

:d ~ ~,. c,xrrm,)m c . ~ 50 55 6\ 24 I@

15 16 17 18 19MODEL ?PEED - $!c, 22 3

,

\.\\%.w ,cd *,~ 0.12 \\ \

n 0.19n Q25

. 031n ~ 0.3705 Ms

24 25 26


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Illlllllllllllmmll[llll31176014034764 I

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naca arr 3g06 some yawing tests of a 1 to 30-scale model of the hull of the xpb2m-1 flying boat

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