FILE copy NO. 2-W

N 62 65854

CAS MRJan. 1944

NATIONAL ADVISORY COMMITTEE FOR A ERONAUTICS

"Tl'llrl'I)II~ 111~p()llrl' ORIGINAllY ISSUED

January 1944 as Memorandum Report

HIGH-SPEED AERODYNAMIC CHARACTERISTICS

OF A FOUR-ENGINE TRANSPORT AIRPLANE AS DETERMINED

FROM TESTS OF A O.075-SCALE MODEL

By Robert H. Barnes

Ames Aeronautical Laboratory Moffett Field, California

NACA WASHINGTON

FILE COpy To be returrOO to

the files of the National Advisory Committee

for Aar~utics Washington, D. C.

NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution of advance research results to an authorized group requiring them for the war effort. They were pre­viously held under a security status but are now unclassified. Some of these reports were not tech­nically edited. All have been reproduced without change in order to expedite general distribution.

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https://ntrs.nasa.gov/search.jsp?R=19930092673 2019-02-03T23:55:44+00:00Z

NATIONAL .h.DVISORY COMMI'rTEE FOR AERONAUTICS

MEMOR.~NDUM REPORT

for the

Air Materiel Command , U. S. Army Air Forces

HIGH-SPEED AERODYNM,UC CHARACTERISTICS OF A F01JR-ENGINE

TRANSPORT AIRPLANE AS DETE!1MINED FROM TESTS

OF A O. 075 - SCALE MODEL " . ~Y .Robert Ho Barnes

'SUMMARY'

'The 'tests ' reported h e rein were made in order to determine the differences in high- speed aerodyn~mic characteris~~cs between models of'a four - e ngine transport Qirplane and a similar bomber airp l a ne . The main conclusion to be drawn from the resuits is that the critica l Mach nmnber of the transport model is about 0 . 05 l es s thr..n that of the bomber model ..

INTRODUCTION

Tests of a 0 . 075 - sc a le model of a four-engine transport airplane were carried out at the reques t of the Army Air Forc e s . The purpose was to de t e rmine the aerodynamic characteristics of the model at high speeds~ Inasmuch as it was very simil~r to the model of a four-engine bomber airplane , e xtensive tests of which have been r eported in refer6nc e 1 , the tests were designed to detect differences betwee n tho character istics of the two models only. Consequently they were' brie f .

APPARATUS AND METHOD

The tests were cnrric d out in the Ames 16-foot high­speed wind tunne l . ~hc model was mounted on a three-strut support system as shown in figurG 1.

2

The tr anspor t mode l (f i g . 2) wa s the s a me a s the mode l of . I a bomber airpla ne exc ep t ' ,for the fu s e l age shn pe a nd size a nd the empenn nge loc ,~ tion . Figure 3 s h ows a compari s on of the fus e l age s. The s a me wing , empennage , a nd n a c e lles we re used for b oth mode ls. Owing t o t he diffe~ence betwee n the fus e l a ges , the pos i tion of the e mp E:; nnage with r esp e ct to the wing diffe r e d f or t he t wo mode ls a s s h own. A de t a ile d description of the wing of t he mode l appears i n refe r e nc e 1. The principal dimensions a nd area s of t he mode l we re a s foll ows:

Mode l sc a l e • • • • • • • • • • • • • • • • 0 . 075 full s c a le

Wing aIle a • • • • • • • • • • • • • • • • • 9.65 square feet

Wi ng span • • • · · · · • • • • • • • • • • • • • 10.592 f ee t

Mean aer odynamic chord • • • • • • • • • • • • • • 0 . 965 foot

Aspe ct ra tio •• • • • • • • • • • • • • • • • • • • • 11.62

Tail a r ea (inc l uding e l e va tors) • • • • • • 1.873 square feet

Tail l e n g th • • • • • • • • • • • • • • • • • • •• 4 . 42 feet

The t e sts r e porte d h e r e i n were made with all the control surfa c es ftx e d in tho ir ne u t r a l po s i t ion s e Ina smuch a s the s ame wing a n d s upport s y stem we r e u s e d for both mode ls, the same 'tunne l-wall corre ctions a nd v a lue s of the flow inclina tion we re use d . No cor r e ct ions f or t a r e s we re a pplied a nd the change in pitch ing - mome nt-coe ffici e nt corre ction due to t h e c h a n ge of t a i l posi t ion wa s negl e cted . '

q

p

V

S

SYMBOLS

The symbols use d in this r e port a r e :

dynamic pre s s ure (~pV2), pounds p e r squa r e foot

mass de nsity, slug s pe r cubic f oot

v e locity , f ee t pe r s e cond

wing a r e a , square f ee t

--- - - - ."---~~~-~-~---~--~

M. A . C.

a

C Dgross

mean ue r odynamic chor d , feet

angle of attack of wing-chord plane

angl e -of - attack c orre c tion due to tunnel-wall effects end f l ow inc lination

lif t c oefficient (l~~t)

drag coefficient (meaSUred qS

drag + 6CD )

drag-coefficient c orrection due to tunnel-vmll effects and flow inclinetion

3

[Ei tching momunt lJ pitching- moment c oefficient

qS (M.A.C.)

M

pitching- momcnt - coefficient correction due to tunnel - 1Nnll effec ts

~ II h b (fr ee - stream v e loci t y) 1\ [tc num er . -

veloclty of sound

RESULTS fiND DISCUSSION

The results of the t e sts are shown in figures 4 to 6 and ere presented as comparisons between the characteristics of the transport and bonilier models. Figure 4 shows the variation of the angle of e tt 0,ck, drag coefficie nt, and pitching-moment coefficient with lift coefficient for the tail-off conditions; and figure 5 shows the corresponding varic.tions for the tail on. Figure 6 shows the v~rintion of the pitching-momont coeffici0nt, dreg coefficient, and lift coefficient with Mach number a The f5..rst two are given for constant vo,luGS of the lift coefficient, while the lift coefficie nt is given for constant values of the angle of attack.

For Mach numbers bolow those approaching the critical, there are no important changes in the li:t coefficiep-ts at constant angle of attc.ck

J while at supercritical speeds the

transport model has a lift coe fficient a bout 00075 less than that of the botilier. At subcritical speeds the transport

- - -----

~.

model has about o. ooh greater 0.ra3 coefflcient t.han the ~")omber , and at supercritical speeds this difference is increased about fivefold .

F'rom inspec"Glon of ~i[;t1I'e 6 (a) it is seen that tte pi tching- moment coeffic:~Gnts lJegi?l to decrease rapidly at a lower Mach nUlillJElr for the tr811C'.port model , t.he magnitude of the Vach nUluDer difference i)eing o..:::-rro]~ima t.e ly 0 . 05. Figures 6 (b) to 6(d) show that marked changes in the lift and drag coefficients also occur at lO'Ner ?iach numbers with the transport model . These facts indicate that the critical ~peed of the transport airplane is les s than that of the bor,lber . This difference is believed to be due to the difference in shape and fineness ratio of the fuselages . The change of 0 . 05 in the cri tical Bach l11..1.mbe:c' is e(!l.:ivalent to 35 miles per hour at 20 , VOO feet altitude .

Inasmuch c..s the tranf'port and bomber airplanes are similar , it may be exp.ec ted ·::;h.O'. t the trans port airplane 1'lill l~ave similar characteristics tc those predicted in referenc e 1, for the bomber , except ins ('f'ar as the ir cri tical Mach nUl.lbers are involved .

knes Aeronautical Laboratory , :rational Advisory COl'll"!1ittoe for Aeronautics ,

I:offett Field , Calii" .

RLI'L11EHCE

· 1 . Barnes , Robert E.: Eigh- Speed Aerodynamic Characteristics of the ZB- 29 AL"'l~lane tlS Determined frOlh Tests of a 0 . 075 - Sc ale Hodel . I{\G.h. C"R, Jan . 19L!4.

.~~-.~~--~---------~-~ - -- - - ~~--

Figure 1.- The four-engine transport airplane model mounted 111 t he Is-root wind tunnel.

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