Aerodynamic tests of an M-31 bomb in the 8-foot high-speed tunnel

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Material Information

Title:
Aerodynamic tests of an M-31 bomb in the 8-foot high-speed tunnel
Alternate Title:
NACA wartime reports
Physical Description:
7, 10 p. : ill. ; 28 cm.
Language:
English
Creator:
Baals, Donald D
Smith, Norman F
Langley Aeronautical Laboratory
United States -- National Advisory Committee for Aeronautics
Publisher:
Langley Memorial Aeronautical Laboratory
Place of Publication:
Langley Field, VA
Publication Date:

Subjects

Subjects / Keywords:
Projectiles, Aerial   ( lcsh )
Aerodynamics -- Research   ( lcsh )
Genre:
federal government publication   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )

Notes

Summary:
Introduction: In connection with a study of the bomb flight path, the Materiel Command of the Army Air Forces requested the NACA to conduct aerodynamic tests of a 300-pound M-31 demolition bomb. Force tests at angels of attach from -15° to 30° were made up to a Mach number of 0.725, which corresponds to a speed of 810 feet per second at sea level. These tests were made in the NACA 8-foot high-speed wind tunnel at Langley Memorial Aeronautical Laboratory.
Statement of Responsibility:
Donald D. Baals and Norman F. Smith.
General Note:
"Report no. L-132."
General Note:
"Originally issued August 1942 as Memorandum Report."
General Note:
"Report date August 25, 1942."
General Note:
"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."

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 003612647
oclc - 71192474
System ID:
AA00009450:00001


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SI.CA


L-/lj3


NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS





WARTIME RE PORT
ORIGINALLY ISSUED
August 1942 as
Memorandum Report

AERODYNAMIC TESTS OF AN M-31 BOMB


IN TEE 8-FOOT HICG-SPEED TUNMEL


By Donald D. Baals and Norman F. Smith

Langley Memorial Aeronautical Laboratory
Langley Field, Va.


WASHINGTON


SNACA 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 pre-
viously held under a security status but are now unclassified. Some of these reports were not tech-
nically edited. All have been reproduced without change In order to expedite general distribution.


L 132


DOCUMENTS DEPARTMENT






































































































































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IMET'ORAUDUM REPORT

for

Army Air Forces, fMateriel Comm:ancd

AEROD'.-T.AM.IC TESTS OF AN :'1-7l BO~'IF

IN TIE 8-FOOT HICH--SPEED TUNNEL

By Donald D. B.als and Norman F. Srnith

T T,1 0 LCT IO

In connection with a study of the -orQ' flli;,t path,

the T'ateriel Corimand of the A"-n.: Air Forces rc'.uested

the ACA to conduct acroirlla.r.ic tests of a 500-r'cund M-51

demolition bomb.

Force tests at ianles of attack frcrl -150 to 50

were made up to a E.ach number of 0.725, which corresponds

to a spEed of 810 f-et Cp.r eoccnd at sea level. These

tests were made in th.' ItCA : 8-foot highl-speed wind tunnel

at Larinlejy 1cr:o1rial Acrcnautical Lab.ratory.

SYTIEOLS

V free-strean -'elocity, feet per second

p frce-strea-i densi'.y, slu'-s ''er cubic foot

q free-stream cdrnamic presreuo, pi-unds per square

foot pV2

a velocity of sound in air, feet pePr secon.i

L,. IIach number, V/a

D drag, pounds

L lift,pounds

' 1 pitching moment measured about tie point of cupzport,

inch-pounds








- 2 -


F m-aximi'; n area of cross section of bomb, 0.707 square foot

I ove-'-all length of borrL, '0.3575 inches

a aiile of attack! o-f horb, decrees

C- ,r-a coe fi cie t, F-
L
C lift coefficient, D
L aF
C pltching-noment co:ff'cient,



Thl- case of a C'O--ound i!-31 der.!olition bomb with

alu i.:n1u ri fins '..as s.'Fpp -l d by thie rlt,.riel Division for

the tests. The bomb wvas sunor,'-t-.i oni the tunnel center

line by a single vertical stre ,..iniue trut of IACA section

0009-61 (fig. 1). a strzamline fairing shielded the

vertical strut to within 11 Inches of the bomb case. A

sird brace housed ;iithi l a st'ean'll-;. fairin't brac.'! the

vot.,cal strut. Because ad1;ic rnal lt':rLtl support was

fo'.;.nd. nc.cessarl' during thi' tests, u'.o horizontal guy wires

'%.- attached nt the1 point; c st;., rpo ft of the br;" TIhe

vcrti.cal support strut, side bracc, and stays were attached

to the balance: ring and w-re included in th3 force

msasu-ren -nts.

Tht anglr of attack was variable through fixed incruments

by : ;ans of an internal indexi' n:chlnism. The bomb was

rott ed ribout 2ts poL.nt of sr- o: t, the center of gravity

for tLh o loa.d-d condition.








-3-


TESTS

Lift, drag, and -:itchin,3 irimrients were measured at

anglej of attack from -li0 to 50 up to a T.'.ach nuiter

o"' 0.7"25. :Thee test v.ere run with the tail v-nes set

at an angle of 450 to the horizontal (fig. 2) in order

to minimize the effect of the wake of the support t strut

on the tail. One run was moide at L'"-J C' anle of attack

with the tail rotateld ,o,. additional tests were :r:ade at

5, 150, and 30 anrles cf attack with the tail removed.

Tare forces on the strut were' measured with the

bomb ~uy~ed in position (fi7. 3). Forces on the two

side stays vwre rctermined b; rne'ias~rinr the forces at

zero anrle of attack "itt. and' without stays.

RESULTS AI:D DISCUSSION

Figures 4, 5, and u show the d(raa, lift, and pitchling-

moment coefficienltr of 'the co:pletu bomb at angLles of attack
O O
from -15 to 50 throiu;z the speed range of t's tests. It

will be noted that the maxir.:im speed of the tunnel was

considerably reduced at the hiLih anriles of attack due co

the larfe increase in drag at this attitude. All of the

data presented have been corrc cted for tares. The

magnitude of the tare forces for a = 0 is also shown in

figures 4, 5, and 6 to giv? an indication of the probable

accuracy of the bomb force data. The tare forces did not

change appreciably with angle of attack.












r'itur. 7, is a, cross r. lot of figure o showing th. variation

of pit'chi ._I-r..orment coefficiert ".:ith anLle of attack for various

-ach n-.'b3rz. Figures c, and 10 show the drag, lift, and

pit I,:'! -::.oir.en.t coef'" iciencz of the bcn.rb without tail and

the '.icrenints frc.m the radllition of the taii. Figure 11

is a -hlotaoranh cf t.le tornb tail after sLructural failure.

Dr-a.. The dra coe'i icie-nt of tihe complete bomb for

a rande of' ;osit.i'v. an. n. .1:-. ti-'.r an- ,,l- of' attack is shown

in figure I,. The tare d'ra fo-- th.e rcdel Lur.port is showna

to be approxi.mrately one-hnalf of the minipaurn bomb drat.

Ybhrc"^ ccr-espond:'nr porsiti e an-i. re t-i.ive Vnflr-L- v _e-r run,

the dr-. co ,fficients w-ere -ro-imatelry ecial e:.-cept for

the 1 ann.-s. At th hih ich nur bter the dLra.- for the

negative anrle, 'here the tail .s v- .l v. iti 'n tihe a Ie of

the support s.:i.t, is less th-.r. the ira.7 for the corresponding

positive an rl. In free r' hIero no su-r'port strut interfer-

encie i orent, the dra s "or hc; nc-ative- angle would likely

be the sa:-,p as thnt for 'he positive a-irl'.

/.t low an:..le- of r:tt.ci t .-. critical speed of the bomb

v:as rjacched at I i.ach nLua er of a 1.p-i o::in.at'.ly 0.725 (fig. 5),

a value which is higher th.n is usually obtained on stream-

line bodies of equivalent fineness ratio, In view of the

very hi.h drag coefficient of the bor.u at the sub-critical

Mach nuinbars, it appears that the floyv over the bomb has
%.,


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seoarated. This separation has reduced uhe local velocities

and therefore increased the critical speed.

Lift. The lift coefficient remained essentially

constant at low r.:ach nuimers (fig. 5) but increased

slightly at the higher spsedz. This increase in the

value of the lift coefficient correston-.:, to the shift

in the pitchi-ir-moment-coefficient curve in magnitude and

direction (fir. 6).

Pitch in moment. An analzyis of the pitching-momrent

coefficient for a given angle of attack (fig. 6) sho':.s a

decrease at the high Mach numbers through the angle range

from -150 to 200. This decrease is not considered a

comrressibilitv effect but inste:l is believed to be an

interfer'enc- effect of the strut wal:e on the- bomb tail.

For the runs with the tall rei.oved, the ritchinTr-'norent

coefficienrt 'ensin-ed essentially constant through the

Mach nruner range of the tests.

The moment decrease is most pronounced at the nega-

tive angles of attack where the boc.ib tail is in the walke

of the support strut and fairing. The magnitude of the

pitching-mornent-coefficient incremei:nts due to the addi-

tion of the tail (fig. 10) indicates that a change in load
1lo
on the tail equivalent to a 1- change in angle of flow

would be sufficient to account for thl r.aximum moment












coeffici.it d-croasd at thL hiL Mlach numbers. The inter-

ferrene- efi'cl' ts ofr the s.i.rnort trout ,nd fairing, and

th.e .~1..: flnv out of li.e st;'it 'airi::r .-ap could account for

i ::e .t c.h r -'e cf L:s ;i ': r i t'.;do 'The L a.. 2crc s as

nmeasiu'-rd lId not i-ci':.d:e the int. rfcrrce-- ,fects on the

flow over 'he bod;y.
O O
Per r-.e an-l s of attack : frrn 20 t: tihe pitching-

m.omenti- cc -ffici'--rts 1 .-.:. .,-, .nti ll' c. nst'i.t with Eiaich

nuwnmbr exc." t for the 7C0 arnle w'i.)r the tail del'initely

defle t -Led ui.,er the ,,ero''edtynr iic3c l.oa L-i,Ccountered.

'i-il failure. Du.rin:i th 500 r.rn structur.ali failure

of the t1j ocC:urrCl l ..it r:ach. nfl.b-'" .. 0. '75 ('. = .5% 1l' /sq ft).

Frc:n c.:tranolatir.n of the tail liaft 1' J."o,.. incrcient curves

(figs. j s n, ?), the ruLsultant. norrai l oal on t!i' tail was

cor.nut(i to be about ,.?C pounds s at th: point of failure.

r.&x-r:, ur, tai.l loa-l of 510 -'ounds- \ ,: t uttainrI.:l at a

hch n.mb-r of 0.u07 (ft CI l.b/sq ft) at an angle of attack

of 25. The su;b:sc -i.nt failure of th,:: ti.l at a low r load

indicate that th- tal] Iws :. >irL-rne -'urinz the 250 test.

BEndin, of the tail at this an-l: Is Icdica' ed byr the slight

i.ncrja3,e in r.c;n-nt offii cie'nt n'-.nr th. n.r>;imu:; load.

'h--. n.'.ti.rce of th.; tail l:.filure ca1n b1 obsrv-. d from

figur'. 10. T:'o fins fail-:d at th, cirnt of attachment to








-7-

the tail ring, one in shear through the supporting web,

and the other in shear at the riveted joint. The re-

r.i.-ining two webs buckled but did not fail co:.nr`.tely.



Langloy J'.v.-ial Aeronautical Laborat;ory,
I'atiron-l Advisory Committee for Aeronautics,
Langley Field, Va., ;.uLu;st 25, 1942.








































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in 2011 will luinding from
Universiiy of Florida, Geolge A. Smathers Libraries with support Irom LYRASIS and the Sloan Foundalion


lllp: www.arcllive.org details aerodynamiclesis311ang













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NATIONAL ADVISORY
COMMITTEE FOR AERONAUTICS


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Figure 11.- M-31 bomb tail showing structural failure.


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UNIVERSITl OF FLORIDA

3 26 81326


UNIVERSITY OF FLORIDA
DOCU-MENTS DEPARTMENTr
120 MARSTON SCIENCE LIBRARY
PO. BOX 117011
GAINESVILLE, FL 32611-7011 USA


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