^khL'l}^ i^ NATIONAL ADVISORy COMMITTEE FOR AERONAUTICS WARTIME REPORT ORIGINALLy ISSUED August 1914-2 as Memorandum Report AERODYNAMIC TESTS OF AN M-3I BOMB IN THE 8-FOOT HIGH -SPEED TUNNEL By Donald D. Baale and Norman F. Smith Langley Memorial Aeronautical Laboratory Langley Field, Va. NACA WASHINGTON 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 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 1(1 f^yry JEIJORANDOT;! REPORT for Army Air Forces, Materisl Command aerodyi:amic tests of an m-ji bomb ik the 8-poot hic-h-spesd tunnel By Donald D. Baals and Nor-inan F. Smith INTRODUCTION In corinecbion with a study of the bomb flight path, the riateriel Coranand of t?ie Amy Air Forces requested the NACA to conduct aerodynar.ic testn of a JOO-pcund M-Jl demolition bomb. Force tests at angles of attack from -15° to 50° were made up to a Mach number of 0.72^, v/liich corresponds to a speed of 8lO feet per second at sea level. These tests vrere made in the NACA 8-foct high-speed wind tunnel at Langley r,!emorial Aeronautical Laboratory. SYIffiOLS V free-stream velocity, feet per second p f ree-streain densiby, slurbs per cubic foot q free-stream dynamic pressure, pounds per square foot f I pV^ j a velocity of sound in air, feet per second M llach niomber, V/a D drag, pounds L lift, pounds LI pitching moment measured about tiie point of support, inch-pounds P maxiiviujn area of cross section of bomb, O.707 square foot I ovei'-t-.ll length of bomb, 50»575 inches a angle of attack of bonb, degrees C^, drag coefficient, -— - L) ^ qF C^ lift coefficient, ~ L qP ¥ C pitching-noment coefficient, n Hi' 6 APPARATUS A::D methods The case of a JCO-pound M-Jl deriolition bomb with altiLiinLun fins \.vas svpplled by the Materiel Division for the tests. The- bomb was supoort-;d on the tunnel center lino by a single vertical streL.raliiie strut of IJAGa section OOO9-6I). (fig. 1). A streamline fairing shielded the vertical striit to v/lthin 11 inches of the bomb case. A side brace housed v/ithin a stD'oar.iline fairing braced the vertical strut. Because additional lateral support was found necessary during the tests, tv;o hoir^izontal guy wires were attached at the point of sv-nport of the bomb. The vertical support strut, side brace, and stays v/ere attached to the balance ring and vifore included in the force raeasure?nonts . The angle of attack was variable throvigh fixed increments by means of an intjrnal indexing mechanism. The bomb v;a3 rotated aboi-'.t its point of sw-.-oort, the center of gravity for the loaded condition. - 3 - TESTS Lift, drag, and pitching moments were measured at angles of attack from -15° to 30° up to a r.ach number of 0.7''^5' These testis ware run with the tail vanes set at an angle of I|.5° to the horizontal (fig. 2) in order to minimize the effect of the wake of the support strut on the tail. One run was made at the 5 angle of attack with the tail rotated Ii-5°« Additional tests v/ere made at 5°, 15°, and 50° angles of attack v-ith the tail removed. Tare forces on thr3 strut were measured with the bomb guyed in position (fig. 5). Forces on the two side stays were determined by measuring the forces at zero angle of attack with and without stays. RESULTS AND DISCUSSION Figures I4., 5* "^^d b show the drag, lift, and pitching- moment coefficients of the complete bomb at angles of at back o o from -15 to j>0 througli the speed range of the tests. It will be noted that the maximum speed of the tunnel was considerably reduced at the high angles of attack due co the large increase in drag at this attitude. All of the data presented have been corrected for tares. The magnitude of the tare forces for a = is also shown in figures l;, j, and 6 to give an indication of the probable accuracy of the bomb force data. The tare forces did not change appreciably with angle of attack. - 1^ - / Figure 7 is o. cross plot of figure o showing the variation of pitching-r;oment coefficient v;ith angle of attack for various Mach numbers. Figures S, 9^ ^^^<^^ 10 show the drag, lift, and pitching-inoinent coefficiencs of the bomb v;ithout tail and the increments from the addition of the tai]. . Figure 11 is a photof'raph of the bomb tail after structural failure. Drag . - The drag coefficient of the complete bomb for a range of positive and negative angles of attack is shown in figure 1;.. The tare drag for the model support is shown to be approximately one-half of the minimum bomb drag. Where corresponding positi^^e and negative angles were run, the drag coefficients were approximately equal except for the 1'; angles. At the high Mach nur.,ber3 the drag for the negative angle, v/here the tall is well within the wake of the support strut, is less than the drag for the corresponding positive angle. In free air vdiere no su]"iport strut interfer- ence is present, the drag for the negative angle would likely be the same as that for the positive angle. At low angles of attack the critical speed of the bomb v;as reached at a L.ach nu2iiber of approximately O.725 (fig. 5), a value which is higher than is usually obtained on stream- line bodies of equivalent fineness ratio. In view of the very high drag coefficient of the bomb at the sub-critical Mach numbers, it appears that the flow over the bomb has - 5 - separated. Th?.s separation has reduced the local velocities and thsrefore Increused the critical speed. Lift. - The lift coefficient rsKained essentially co;istant at lev; IJach nujnoers (fig, 5) ^'^t increased slightly at the higher speeds. This increase in the value of the lift coefficient corresponds to the shift in the -oitching-moin-nt-coeff icient curve in nagnitude and direction (fig. 6). Pitching; moment . - An analysis of the pitching-moment coefficient for a given angle of attack (fig. 6) shows a decrease at the high Mach numbers through the angle range from -15° to 20"'. This decrease is not considered a compressibility effect but instead is believed to be an interference effect of the strut wal:e on the bomb tail. For the runs with the tail removed, the pitching -noment coefficient regained essentially constant thi'ough the Mach nxinber range of the tests. The moment decrease is most pronounced at the nega- tive angles of attack where the bomb tail is in the wake of the sup'^ort strut and fairing. The magnitude of the pitching-noment-coeff icient increments due to the addi- tion of the tail (fig. 10) indicates that a change in load on the tail equivalent to a 1^ change in angle of flow would be sufficient to account for the naximiim moment - o - cosfficiant decrease at the high Mach numbers. The inter- ference effects of the support Ptrut and fairing, and the end flow out of tl^e strut fairing gap could account for a moiuent chan-:e of this magnitude. The ta.re forces as measured did not include the int.erference effects on the flow over the body. For the angles of attack from 20 to ^C* , the pitching- moment coefficients remained essentially constant vjith Iilach number except for the JC^ angle wiisre the tail definitely deflected under the aerodynamic load encountered, o Tail failure . - During the JO n.tn structural failure of the tail occurred at a Mach number of 0.^75 ('-1 ~ 595 Ih/sq ft). Prom extrapolation of the tail lift and drag increment carves (figs. 8 and 9)> the resultant normal load on the tail was computed to be about Y\2Q pounds at the point of failure. A maximrj'i tail load of 510 pounds was attained at a Mach number of 0.u7S (q - 501;. Ib/sq ft) at an angle of attack of 25*^ • The subsequent failure of the tail at a lov/er load indicates that the tall was weakened during the 25° test. Bending of the tail at this angle is indicated by the slight increase in moment co-o-f f Icient near the m.axiraum load. The nature of the tail failure can be observed from figure 10. Tv;o fins failed at the point of attachment to - 7 - the tail ring, one in shear throi^gh the supporting web, and the other in shear at the riveted Joint. The re- maining two '.vebs buckled but did not fail coniple toly. Langlej Meiiiorial Aeronautical Labors i;ory, National Advisory Committee Tor Aeronautics, Langley Pieid, Va., August 25, 19)4.2. Digitized by tine Internet Archive in 2011 witli funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation http://www.archive.org/details/aerodynamictests31lang FLOATf/^0 BALANCE F/A/G TUNA/ EL WALL STREAMLINE FAIRING MAIN SUPPORT P/N AT CO. OF SO MB TCA/NEL ^- NKTIONAL ADVISORY COMWmEt FOR AERONAUTICS Fiqure /.- /ns^aZ/af/on defai/s of M-3/ bomb. i i' e o £1 to I o 0) ■ nJ Li c 0) I C\j 0) (-1 3 bo E O Xi to I u o CL I (U CO 0) E-" to (D 3 bo m t'r «t fi m i*lt sgw tsttipi 1 m ^sipj w spi St? piii E P m 1 .'. i^ ti4; H ftf" _ii*- —u. --■ -■(- • 1 i y :f Imi ■ " !':) / ' i; ■fji 1 /: ■ ■ -- ■ !:^- riLt : :: h : 1;!' \,i fcX [„ -'-• nf Z - — ^1 : : 2 ^. ,— r— •I •-I'l ■ ?l : :;.: : : : r~ ■~ — f '^ ■~ ' I ^^-:— — r~ ]'i "■■ : " [':- """ ^^ "^1: \\ ■■ ■ r -. — ~i zH 1?- I - — -'- — -■- — 1 — j- 'I ■ 1:7; t. . ^ \- : : ■: \ ^ ' 1 : ■ -- -- ?.?'^ ::■ ... ' : m ■ m _// 1 — -\ ■ -^t ■ a j '-iN^iJ ^-- ,*y '*< 1 1- \ - \ — --■-; _4 - -;- .^-i- 4 -. ■ ' JUfT TTTi TiTriTiT' ■ ^11 k :' .. , >;:• -:« ^-^'' i '■ M\t ii-1 K_i i • i . I I f i i 1 ,■■' •-i ^ ■fit ^ iij 1-^ to4 f^^ ^ i*rr ^1 r:"^:^ %%' \ Iw "r-?^;t -'ii A^ - - %z\ r^ ti': if^' : '^■■^ ■ ! -' -4 ^■r\ r. .;.' '•>; h-i 'M '■'■ ■; '■-" ' '■;! ^•■Ww\ V,W':\':\ ' 'la + ^*-r :h ^ -^ ■ . : - i; 1 Ltii 1. ■i ••■:■ ..- 1 _... .L»t| 'i + -^ '■* \ 7-:; ": \ :■. '- :• ] - - 1 - 4,' i9< fj i ;_! 1 tiii ;- , 1 *■!■ , ' - -~^ -'- -/< / n'^ ii: 1:,' \ i ; i-t g -,■■ ;. '■ ' :-:\ !-:'M|2g ileU ' "1 111] h [■■■■ t:, ^'- ■ 1 ; ti: 14'; , h 1!:' '■'X\ '•-'- "^SB J llii >-4 *>■• h: "■- : r_B . Hii ■ -" ■ liil Jit : : : |^_j( : h f,\ #.! -r "^i ". ";; tIj "[-_ b- -^ •.ri|i ira^ "_-t '■' i ■'r »*i«^td^ 1!.. :■ . . I — ;: ":'} •i ': t^ ;. 5 ■ -\ 1 — -i r-^ f-i f^-^tr :'-.-";, \--n.^ ■ '■w 'I'l r.V -'/ v'' 7 * ; •!:;:; j- 'Ml. ^^% /< /t :''' vl^ I, J. '■'■X '::•- h;i 1:1. ;:■; :i-'. '" "3lffiis i: . . ,.,.1. \ !r.' 1 .' :-:■'■ C>A ?* r^ . j; ■■^^ iiilli !■ -' r ' n - ^ \ ■ ■:■< l^\l "Z !■■ : f-.i: -4 fi Jil ^^■^- ■ ■ ■ " 1 .t,,-i4.r4n:-.TFfd J:', - (6>( "■ J* •* '• ; t :- : '■: ;t?i,.dH U Ihr gii jg w ■ 11^ 1- '-''^ \ .: 5 \' "\- t r !■: ■f r-;:;£i§ij. 3i:i: '^'rf i^ i^S '-' .! J f'l; i'-' ' N ,R * l-'f ' ; ' ' i ' :*-- ji3?|^}i ^n. !='[ iirl '■''H ^ •ii' I ^ L nil i ' ,) Vv ml r-f N d^^" -4 ^'^ •••■ f p ,+ ;'-■ CN /: 1 -i; 1-. rM| ■ . > ' ■ I- ■■ "i.rH^!^- ,1 ' ; J;i :i.:;f ■' , , ,# _ ■f ■ ! 1 ■--. . ■ " /eS V .■ ■,r '£ - ^•.-~ _: "'' -'v''^ *: -t ■■.-"; ■^:-fil V'- jtn ^ 1 1- . ,i /(:i l< ■t ^ i|4: ■' ;;■; ' ' "1 ' i 1 jS I '■ ■ ; ' r\ j'.> ' : \ \ .. ' .] :'■; ••j "■': .itit i'- " ■^ ■,.iil -:r ^, iy L T- i •r': ■ t-f' " I* " ■ ,rdt^^ 1;1 .\ \ fiV t: ^ ' J^ ,- - 1' 1 ^ ^ i;ji ikL ^ ki H«i 'M N liiti Ui^-^^ 1)1: 1-^^ -7« > \ lis J( ^,,, .'- aij r N \ '■ I -.:, ■p ■ -^ '■' .:. ;;^S ■ ^ :' x: >•- \, \ ,-^}f -• _ 1- ;. "'1 — — ^ \ N \ S^ r- 1 — l-^-H -*-i gd^E ' s-i'^ ' " -'i ■^ f\ ^ ter: sti ri r~ _; J^^' ,, -3 y" jC / iir f ; '.:.[ [K, r; i Es ^ ;>— , 'i;! V" '■■'i ■ ■ : 'r' -l-iM' 't 1" i-i- ' . , ^ r-~ .;- /I ' .- :'4| ■' - 4 ■ "!;:i ;■ i: ■'■ ^,; -- 7? f/S" f^ — \ r-~_1 : rr ;"4:f ^' ' I r~ ' ■ ' r ^■■ri ti 1 s ■'-■:: 3 "' <— -^^ L~ ^- li 1 : .i '■ \ _ , "- --< •— ' — — - -.,-.■■ \^ hM or Nft lU «' \ ,' \ c -r \'-- - ■! .■■yt'.t'i BSHttllttn \l\ /) _-"--■ ^ i:t c •\ ^ t . ) f . c ■ '' ■- *|r * ^ ■, r " 'I13 ( / «' al *» " J 'Ix r •^ ? :a it ' ■< 3 '' '111 C7 1( Ti Li lUA /a y/ 7/7 (^ /, tn 7^ /, '"''t '* « *■ i tv ^z 5 M£i £j6- ■ - -■'■'• ^ I »"- LtL ^ C- ka \r- \L •u 'i Oi jai id LilrflZfe £kG&^l ^li- tyEJli^ WfS TttSifeimHiii'' i m&ttT^ ' t H • • • fi .sj S !St rftWW w^ -tii £ m ''^l ■iS IS 1 ^ Hi: rS ^ fig If i^il sP 141- -JH a Ub 1 B itJ ^ -^~ ^: ifi jjB ui^ •wl s P tJ.' ^1 ^ i fit- ■- rl rPJ 3 t:j:ffi3] ^l^f^ ■.J '3 IS rm ^^. i-' tF -J -- - t.- " s rrft 'tfi vjit V.r. ■;rf ^ -i-nrl S;." ''H t^ i^ u ^ -^ 3-- :' .'f 3 :-T-. *j ' Tt 4 " H /^ : -^ ^ ^} ^;_"' ^'-" ^ i x, :^ ^ ^^ :*" " "~ sv ¥1 /-'^ Kl— R^ tr** «: 1^ J^+ tf/fi [ffll ja'/ji^ ^ ("' -1 ' 4 -'-_ ,-■■; --'■ V '"^ - ^1 . - :: - - " : - ;\ ^: '--^ -|-- ■ ■ ; f V. r .^; --J-! \ ' -'r. _;__::; fr ilTl •1 > \ : r- -L 72 : : _^ X T; - ■• - •• :-:r - ,j '^ •rr\ ^ »-" -" "---" .- C-- J r : 1 H M^ r - ■ ;:." ""." '-'.TV ■fT iv: / 1 "^ :-l ?■• ^ ■ -2 .... - 1 -■ . .:! fi^- - --^ - -: -J w ^; -- - F^ - ;-4 —.-- ' tFI ^ , \ ^'^ f;-.'"t .^^ -, — ; - ^ .. .:& rrti - — "-' -r^i -. « - - ._-- -;f- -- .^1.-. -- M t; .-^: l^j --| ~i\- Tr^f A '1 v> - — „-. :;'- T J 1 N \ :.'"' r,;. " Li . " ::- -" "" .'""'^ ;r ;:"" 7,1 L J # f / 1 ;: ; '--■ =r ii .- ~l t ; 1 r "; V !*"! I 41 .- f— ^'" V^ f»" 7" .< J 1! i ^ ^ 7 i ^ • F ". ■- A > ^ ]lf a: ;- f/^ore 6. - Variaiion of tail and bomb case dmg wiih Moch number. E- - ; . » A !^71J C/L-/. "7/ h'^ s > f M l-z ir__ - .. - :a 5 ?* fci y-] T-. i-M k ""-- -:.; ■■:.- ■ ■ / ■N. ;/ ^ -tT' Tt^l ''r'- 'M ^ £r- i'^- y'f- i - s 1- - ; / i s / lilyl \' .■;u il ^ ~:' a-,. % ■ - J K ■ ri . ^ / -.4 '. r.'r "43 '"■"t". ■s '^ ■i i» J ll ;i i- ■ ^^ ■5 1 ■y 4 f ?» i' ^ f| ^E a-- -i.- 1 "rr!/ -:: s ' ; ^'? itr '-'fi .3 |: .;H *J A 1 •S "ffl r, r^ *i -- ^ " : :- i .^ T, 1, . •^ tM 5£ 1 », - i^ ; - i 15 ■- ' I ■ i-!^ ir "if ife E '^" /i 's ■'-; V * T--: '•■r r .1 :--l- '--' f '-: !^ r k ^ -1 , j5 - 1 ;. ;_! '^j- fi H h Cl ~ »s K ■ 1 *■ , J ... rr^ ■ '■ 'I-' 1^ f , ilr 1 zM : L : Q ^ / :■. f ri s ■' n t :^ '"':• ■;.] '='-H J* 1 itt :J3 £* ■ - ; ^ t^ - - N i/\' t \'\ ff 1* j' ^ ■^ ^ :' ■ \ / ■S >* f'' 0[ "i 't 'T^9[jri ^ P A^ -< r s. / V -p '^ c 3-; E* f 1^ ^ ' •■1 5 1 ^ II J t ;^ - - -} : 5J; - r."^ r . ^ : ; . t-'!' , -i^ i--: r % - ' --, = r ■ ^: ■"{ - 1 1 r-" " - '":- -G > , \ -■. ^ ':" T- -: *< :+: ■ ^ " t" - I'-t -■•M hU T ;- - !^ yV " , ■ :■ -"r^ p-^i^ f^;? • \ % J," tt *# ti 4S fe ;'■•' -•--r _ " '1 s 1 5 1*1 1 4 ^2 A "■■• ■ ^^3 K' -# W;i 1 ?lt-#fffl ml. a^ it iia ita. la & id bs d tL ia k. fci d tA Ll -,-■51 u Id •* IfeJ y bii J K^ 'iulm L IHi m.i'iTi itii ftt-K ^ t^ACA LMAL 2804-9 Figure 11.- M-31 bomb tail showing structural failure, UNIVERSITY OF FLORIDA 3 1262 08103 266 5 UNIVERSITY OF FLORIDA DOCUMEWS DEPARTMENT GAINESVILLE.FL 32611-7011 USA \ \