N66 (ACCESSION NATIONAL ADVl SORY COMMITTEE FOR AERONAUTICS. WASHINGTON April 15, 1958 TRANSONIC FLUTTER INVESTIGATION OF MODELS OF THE

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1 1 GPO PRICE $ - CFSTI PRICE(S) $ I I - ff 653 July 65 TRANSONIC FUTTER INVESTIGATION OF MODES OF THE SWEPTBACK WING OF A FIGHTEX AIRSANE By Smuel Smith 111 nd Robert W Boswinkle, Jr ngley Aeronuticl bortory ngley Field, V c - i 4 -I N66 (ACCESSION NU,:IIBER) (NASA CE OR TMX OR AD NUMBER) (THRUI <CATEGORY1 I NATIONA ADVl SORY COMMITTEE FOR AERONAUTICS WASHINGTON April 15, 1958

2 NATIONA ADVISORY COMMITTEE FOR AERONAUTICS RESEARCH MEMORANDUM TRANSONIC F'UTTER INVESTIGATION OF MODES OF THE SWEPTBACK WING OF A FIGHTER AIRPANE By Smuel Smith I11 nd Robert W Boswinkle, Jr SUMMARY A trnsonic flutter investigtion hs been mde of models of the wing of current fighter irplne The models were dynmiclly nd elsticlly scled in ccordnce with criteri which include flutter sfety mrgin The wings hd n spect rtio of 342 nd were swept bck 41 lo long the leding edge nd 193' long the outer prt of the triling edge A lrge triling-edge fillet extended out to 50 percent of the semispn The investigtion ws mde in the ngley trnsonic blowdown tunnel nd covered Mch number rnge from 075 to 132 The flutter boundry ws locted t simulted ltitudes below se level, the models being flutter free t ltitudes bove se level However, region in which the models exhibited lrge responses to the turbulence of the tunnel strem extended to ltitudes bove se level t supersonic Mch numbers The significnce with regrd to the irplne of fie lrge responses of the models is not known The flutter boundry shifted to higher ltitudes but remined below se level with the ddition of 15-percent-chord leding-edge extensions over the outer 35 percent of the semispn - INTRODUCTION The flutter chrcteristics of the wing of current fighter irplne hve been under study The wing is swept bck 411' long the leding edge nd 193' long the outer prt of the triling edge A lrge triling-edge fillet extends out to 50 percent of the semispn Clcultions indicted tht flutter would result t trnsonic speeds t se level if the stiffness were reduced only slightly Experimentl dt on similr wings (refs 1 to 4) indicted tht possibly sufficient

3 ' 2 stiffness mrgin existed; however, it ws felt tht the wing in question ws sufficiently different from those Of the references to wrrnt seprte experimentl study The investigtion ws mde in the ngley trnsonic blowdown tunnel with models which were dynmiclly nd elsticlly scled in ccordnce with criteri which include flutter sfety mrgin The wing spr ws cntilever-mounted inbord of the wing root nd the tests were mde t Mch numbers from 075 to 132 nd t simulted ltitudes extending to below se level The effect of instlling 15-percentchord leding-edge extension over the outer 35 percent of the semispn ws lso investigted * I SYMBOS b C 2 typicl wing semichord, ft locl stremwise chord, ft length scle fctor, Typicl model length Corresponding irplne length 8 m mss scle fctor,?&-pic1 model mss Corresponding irplne mss m' M 9 S t T mss of exposed pnel, slugs Mch number dynmic pressure, lb/sq ft vlue of y t wing tip time scle fctor, Time required for tunnel irstrem to move 1 model chord length Time required for irplne to move 1 irplne chord length 0 sttic temperture, R v velocity, ft/sec c

4 0 Y NACA RM S A ~ ~ - V e : : :* : :- 3 reduced velocity bsed on representtive nturl frequency, s Y x,y distnce from wing root mesured perpendiculr to wing root, ft stremwise nd spnwise coordintes, respectively, defined in figure 4 11 stiffness reduction fctor used to provide mrgin of sfety in ppliction of model flutter-test results to the irplne P P mss rtio, m'/pv sttic ir density, slugs/cu ft Subscripts : representtive nturl frequency, rdins/sec A M irplne model MODES Geometry The models were 3125-percent-size versions of the wings of current fighter irplne The wing models hd n spect rtio of 342 nd were swept bck 411' long the leding edge nd 193' long the outer prt of the triling edge A lrge fillet t the triling edge extended out to 50 percent of the semispn A sketch of the model is given in figure 1 nd some of the more importnt geometric properties re listed in tble I The fct tht the pln-form spect rtio is twice the exposed-pnel spect rtio (tble I) is coincidentl Becuse of dmge to the models t flutter, six models were required in the investigtion Three models (designted wings 1 to 3) were without leding-edge chord-extensions nd were intended to be identicl The other three models (designted wings 4 to 6) hd ledingedge chord-extensions nd were intended to be identicl In ddition, the only intended differences between the two sets of models were differences cused by the ddition of the leding-edge chord-extensions Smll differences between models 1 to 3 nd lso between models 4 to 6

5 :-' 0 e 0 0 e s 0 e* * : 0 * e NACARMSAl? 0 0 e e I did exist, s evidenced by the mesured nturl vibrtion frequencies nd node lines (presented in the section entitled "Physicl Properties") The chord-extensions were over the outer 35 percent of the semispn nd incresed the locl wing chords by 15 percent A model with leding-edge chord-extensions is shown mounted in the fuselge mounting block in figure 2 (As shown in figure 2, the wings were pinted t intervls long the leding edge to id in observing the motion of the models during the flutter runs ) The wings without leding-edge chord- extensions hd smll mount of positive cmber nd the leding-edge chord-extensions of models 4 to 6 ccentuted the cmber b * Scling The nondimensionl mss nd stiffness distributions were required to be the sne for the model s for the irplne The mss nd stiffness levels for the model were obtined by specifying the scle fctors for the fundmentl quntities involved: length, mss, nd time The size of the model ws limited by tunnel-wll-interference effects, nd on the bsis of pst experience the length scle fctor ws chosen to be The mss scle fctor ws obtined from requirement tht the mss rtio p should be the sme for the model s for the irplne, which results in In order to locte the simulted se level ner the middle of the tunnel density rnge vilble t Mch number of 1, the density rtio ws chosen to be p p = 197 This loction of simulted se level llows M/ A ltitudes below se level to be obtined nd flutter mrgins to be indicted for cses where flutter 3oes not occur bove se level The time scle - fctor ws obtined from requirement tht the reduced velocity V should be the sme for the model s for the irplne, which results in

6 * & NACA RM fs8a t=t) Since the Mch the time scle number is the sme for the model s for the irplne, fctor my be written The sttic temperture for the irplne is function of ltitude TA only, nd for se level it ws tken to be 519' R However, in the tunnel during run, the temperture continully drops s ir is expended from the reservoir nd the tempertures obtined t the vrious flutter points during n investigtion re different A study of previous flutter dt indicted tht 408' R ws ner the verge vlue of the sttic temperture tht would be expected during the present runs, nd this vlue ws used to obtin the temperture rtio used in the scling: TM/TA = 0786 A list of the pertinent wing nd flow quntities nd the design scle fctors used is given in tble 11 It my be noted tht the fctor q is used in the scle fctors fer some sf the quntities iisted The fctor q hs the vlue 076 nd occurs becuse the stiffnesses of the models were mde 76 percent of those which would result from ppliction of the scle fctors s specified (eqs (l), (2), nd (3)) The purpose of reducing the model stiffnesses ws to provide mrgin of sfety in the ppliction of the model fluttertest results to the irplne Thus the design reduced velocity for the model is equl, not to tht of the irplne, but to tht of n irplne hving stiffnesses 76 percent of those of the ctul irplne The dynmic pressure nd Mch number re quntities which re controllble during run, wheres the temperture is not If the dynmic pressure nd Mch number re considered to be fixed nd sttic temperture different from the design vlue is obtined, both the density nd velocity will be different from the vlues considered in the scling The density nd velocity chnges result, respectively, in vlues of mss rtio nd reduced velocity different from the design vlues However, combintion of reduced velocity nd mss rtio which cn be expressed in terms of the dynmic pressure

7 6-2 vm - PM &I is independent of the temperture, nd this combintion is exctly simlted in the runs by the expedient of interpreting the simulted ltitude in terms of dynmic pressure Thus, the scle fctor in tble I1 for dynmic pressure is used to convert the dynmic pressure for the irplne t ny ltitude nd Mch number to the dynmic pressure for the model t the sme ltitude nd Mch number The dynmic pressure for the irplne is ssumed to be tht clculted by use of the ICAO stndrd tmosphere (ref 5) It my be noted tht, for given ltitude, q/m2 is constnt The effect of not hving the mss rtio nd reduced velocity of the models exctly equl to those of the irplne is believed to be negligible in the present investigtion Experience with wide vriety of flutter models hs indicted tht, t lest within the opertionl limits of the tunnel, flutter t given Mch number tends to occur t constnt vlue of dynmic pressure regrdless of the individul vlues of density nd velocity - Construction The construction of the models is indicted in figure 1 The min spr ws mde of luminum lloy, nd luminum-lloy ribs hving U-shped cross sections were welded to the min spr The leding nd triling edges were of pine Bls ws used to fill the wing to contour ed weights were plced in the wing t vrious loctions nd the wings were wrpped with silk cloth nd pinted Ech wing pnel ws i-nstmented with strin gges on the min spr ner the root The min spr ws clmped inbord of the root, s shown in figure 1, nd thus llowed some root flexibility The mounting block shown in figure 2 ws mde of luminum lloy Physicl Properties The first severl nturl cntilever frequencies nd node lines of ech of the six wings re given in figure 3 In obtining the dt n electromgnetic shker ws used to excite ech pnel seprtely The shker stem cted on the extended wing sprs t the loctions indicted by x in figure 3 nd the sprs were clmped s indicted in figure 1 The positions of the node lines were indicted by slt crystls sprinkled on the wings

8 7 b The right pnel of model 2, which survived the flutter tests undmged, ws used to obtin the flexibility influence coefficients Influence coefficients were obtined t 22 sttions (fig 4) on the wing by the method described in reference 6 The influence-coefficient mtrix is given in tble 111 This mtrix hs been mde symmetricl in tble IV by tking the verge of ech pir of coefficients symmetric to the digonl The devition of the coefficients in tble I11 from the verge vlues in tble IV gives some indiction of the ccurcy of the mesurements Only 26 percent of the coefficients devite more thn 2 percent, nd the grete st devition is 36 percent The right pnel of model 2 ws cut into strips nd the center of grvity, mss, nd moment of inerti bout the center of grvity of ech strip were mesured The dt re given in figure 5 Ech strip ws then cut s shown in figure 4 so tht ech section corresponded to one of the influence coefficient sttions The mss nd center of grvity of ech section were mesured nd the vlues re listed in figure 4 The msses given in figures 4 nd 5 for the sections nd strips include n llownce for the mteril lost in the sw cuts APPARATUS AND TESTS The investigtion ws mde in the ngley trnsonic blowdown tunnel, which hs slotted test section The test section is octgonl in cross section nd mesures 26 inches between flts During the opertion of the tunnel, preselected Mch number is set by mens of vrible orifice downstrem of the test section, nd this Mch rxber is held pproximtely constnt (fter the orifice is choked) while the stgntion pressure, nd thus the density, is incresed The sttic density rnge is pproximtely 0001to 0012 slug per cubic foot, nd Mch numbers from subsonic vlues to mximum of bout 14 my be obtined Becuse of the expnsion of the ir in the reservoir during run, the stgntion temperture continully decreses, nd therefore the test-section velocity is not uniquely defined by the Mch number Additionl detils of the tunnel re contined in reference 1 Excellent greement between flutter dt obtined in the tunnel nd in free ir hs been observed (ref 7) n the investigtion, ech model ws cntilever-mounted in the mounting block shown in figure 2 The mounting block ws fitted into sting in such wy s to form fuselge 3 inches in dimeter which extended upstrem into the subsonic flow region of the tunnel This rrngement prevented the formtion of shock wves from the fuselge nose which might reflect from the tunnel wlls onto the model A sketch of the model mounted on the sting nd instlled in the tunnel is shown in figure 6 The sting nd model weighed pproximtely

9 8 290 pounds nd the system hd fundmentl bending frequency of bout 15 cycles per second Wire strin gges were mounted on the wing sprs ner the root nd were oriented so s to indicte model deflections bout two different xes The strin-gge signls, the tunnel stgntion nd sttic pressures, nd the stgntion temperture were recorded on recording oscillogrph The strin-gge signls were used to indicte the strt of flutter nd the flutter frequency High-speed motion pictures were mde during some of the runs r The wings without leding-edge chord-extensions were tested t zero ngle of ttck The wings with leding-edge chord-extensions were tested t -2O ngle of ttck in n ttempt to reduce the sttic lods RESUTS AND DISCUSSION Presenttion of Dt The results of the investigtion re given in tble V() for the wings without leding-edge chord-extensions nd in tble V(b) for the wings with leding-edge chord-extensions The dynmic pressure t the vrious test points is plotted s function of Mch number in figure 7 for the wings without leding-edge chord-extensions nd in figure 8 for the wings with leding-edge'chord-extensions ines of constnt simulted ltitude re lso indicted in figures 7 nd 8 Ech circle symbol in figures 7 nd 8 indictes the point of the strt of definite flutter nd ech squre symbol indictes the point of the mxim dynmic pressure ttined during run without obtining flutter A dshed line below symbol defines low-dmping condition In the low-dmping condition, the strin-gge records nd the motion pictures indicted periods of nerly sinusoidl, lowly dmped oscilltions The point for the beginning of low dmping in ech run ws indefinite nd ws somewht rbitrrily chosen On the other hnd, the point for the beginning of flutter in ech run in which flutter ws obtined ws definite nd ws chrcterized by rpidly diverging oscilltions The low-dmping region is indicted for the wings without leding-edge chord-extensions in figure 7 by dotted shding The response frequencies of the wings re indicted ner most of the dt points in figures 7 nd 8 The response frequency for noflutter or low-dmping points ws tken s the predominnt oscilltion frequency of the models; t flutter, of course, the flutter frequency is listed

10 3R t * 9 The flutter node for both configurtions investigted involved bending nd torsion of the wing with some rottion in pitch t the wing root The rottion in pitch of the wing root ws possible becuse, s previously noted, the min spr ws clmped inbord of the root A typicl oscillogrph record showing the strin-gge trces during low dmping nd flutter is given in figure 9 Interprettion of Results As stted in the section entitled "Scling," the stiffnesses of models were 76 percent of the scled irplne stiff'nesses The simulted ltitudes indicted in figures 7 nd 8 re thus to be interpreted s ltitudes which, if clered by the model, could be reched with 32-percent (1/076 = 132) mrgin of sfety in stiffness by the irplne This sttement ssumes, of course, tht in ll other respects the model exctly simultes the irplne An lternte interprettion of the results rises from the fct tht for most configurtions the dynmic pressure required for flutter vries, to first pproximtion, directly with the stiffness level Thus, flutter point obtined with the model indictes tht the irplne will flutter t the sme Mch number t simulted ltitude corresponding to dynmic pressure 32 percent higher thn tht for the model Wings Without eding-edge Chord-Extensions The trnsonic: flutter boundry for the models of the wing without leding-edge chord-extensions is locted t ltitudes below se level (fig 7) The dynmic pressure for flutter is indicted to be minim t Mch number of bout 087 The low-dmping region extends t supersonic Mch numbers to ltitudes bove se level With regrd to the irplne, the significnce of the low dmping obtined with the models is not known Photogrphs of the wings without leding-edge chord-extensions fter flutter re given in figures lo() to 1O(c) Wings With eding-edge Chord-Extensions Becuse of vrious dt-recording difficulties, the flutter points t the three lowest Mch numbers for the wings with leding-edge extensions (fig 8) re known only to n estimted ccurcy of tloo lb/sq ft for dynmic pressure nd ko03 for Mch number However, the shpe of the trnsonic flutter boundry is shown to be similr to tht for the wings without leding-edge chord-extensions (fig 7) Although the

11 10 flutter boundry shifted to l,$itudes with the ddition of the leding-edge chord-extensions, no flutter ws obtined t ltitudes ebove se level ow dmping preceded the flutter points t the lowest Mch numbers, but the loction of these points could not be scertined nd they re omitted in figure 8 nd tble V(b) A photogrph of one of the wings with leding-edge chord-extensions fter flutter is given in figure 10(d) CONCUSIONS The trnsonic flutter chrcteristics of models of the sweptbck wing of current fighter irplne hve been studied in the ngley trnsonic blowdown tunnel The models were dynmiclly nd elsticlly scled in ccordnce with criteri which include flutter sfety mrgin The scling ws such tht if t given Mch number certin ltitude is clered by the model, tht Mch number nd ltitude could be reched with 32 percent mrgin of sfety in stiffness by the irplne The following results were obtined: 1 Although the flutter boundry for the wings without ledingedge chord-extensions ws locted t ltitudes below se level, region of lowly dmped oscilltions tht extended to ltitudes bove se level ws obtined t supersonic Mch numbers 2 With the ddition of 15-percent-chord leding-edge extensions over the outer 35 percent of the semispn, the flutter boundry shifted to higher ltitudes but remined below se level ngley Aeronuticl bortory, Ntionl Advisory Committee for Aeronutics, ngley Field, V, December 20, 1957

12 r m mom em ee e em+ e eee em m e m e e m m me e e m e ee eem ee mme e m em e e eem m REFERENCES 11 1 Unngst, John R, nd Jones, George W, Jr: Some Effects of Sweep nd Aspect Rtio on the Trnsonic Flutter Chrcteristics of Series of Thin Cntilever Wings Hving Tper Rtio of 06 NACA RM 33Il3, 19% 2 Jones, George W, Jr, nd Unngst, John R: Investigtion To Determine Effects of Center-of-Grvity oction on Trnsonic Flutter Chrcteristics of 43' Sweptbck Wing NACA RM 33K30, 19% 3 Ruhlin, Chrles : Experimentl Trnsonic Flutter Chrcteristics of n Untpered, 45' Sweptbck, Aspect-Rtio-4 Wing NACA RM 5522, 19% 4 nd, Normn S, nd Abbott, Frnk T, Jr: Trnsonic Flutter Investigtion of Fighter-Airplne Wing Model nd Comprison With Systemtic Pln-Form Series NACA RM 55B16, Anon: Stndrd Atmosphere - Tbles nd Dt for Altitudes to 63,800 Feet NACA Rep 1235, 1955 (Supersedes NACA TN 3182) 6 Jones, George W, Jr, nd Young, ou S, Jr: Trnsonic Flutter Investigtion of Two 64' Delt Wings With Simulted Stremwise Rib nd Orthogonl Spr Construction NACA RM ~56127, Bursnll, Willim J: Initil Flutter Tests in the ngley Trnsonic Blowdown Tunnel nd Comprison With Free-Flight Flutter Zeszlts KACA IiM 52K4, 1953

13 e NACA RM 58A15 TABE I- GEOMETRY OF MODES WITHOUT EADING-EDGE CHORD-EXTENSIONS Stremwise irfoil section tip Stremwise irfoil section root eding-edge sweepbck deg Triling-edge sweepbck deg Spn ft Pln-form re bsed on extension of pnels to model center line sq ft Pln-form spect rtio bsed on extension of pnels to model center line Fuselge dimeter ft Ekposed-pnel spn ft Exposed-pnel re sq ft Exposed-pnel spect rtio Modified NACA 65~006 Modified NACA

14 TABE 11- DESIGN SCAE FACTORS OF PERTINENT WING AND FOW QUANTITIES Quntity = 197; - TM = 0786; = 076 TA I 1 Design scle fctor Fundmentl quntities : ength Mss Time t = E) Derived quntities : Strem velocity Strem dynmic pressure Moment of inerti Flexibility influence coefficients Nturl vibrtion frequencies Bending nd torsionl stiffnesses I 1122 x 10-6

15 14 I Id f rl N of nw r-m m o d N nf nw r-m mo rl N drlrlrldrlrlrlrlrlnnn

16 0 0 e NACA RM 58A15 : : :' : :- 0 - N 9'9 N??????\9 N t?"?f\9?\9?<? fu) Nu) rlrl r\-+frlu)o\rlonnnp-orr\no\od NN Xnrl rl NN Nf rl rl N N Nf drl t-t- rl N N 0 rl m r- W OD rl H t- rl W rl N rl B c9 rlrl rlrl d rl gognoo %< 6-q? p-,"p--ic\o t--*\o\mrc\ Nn+rc\- 4 \9 %%YR rl *" m V I $32, I, e "N FN 4 9

17 e NACA RM 58A15 TABE V - COMPIATION OF TEST RESUTS Pnel behvior* Response frequency, 9, v, P, T, - cps ring Run Point lb/sq eft Right ft ft/sec slugs/cu ft or to Q Q Q F Q X X X X X X X X F Q Q F - () Wings without leding-edge chord-extensions Q Q Q Q Q Q 9 F X X N Q N N N , ,228 e099 2, , , ~022 3,622 ~211 2,821 ~218 4, , ,747 ~056 2,860 ~030 3, , , , , , , , , , , , ~, 0892,0708 t, 2430 t, 2154!, , 1749, 1153, 1282!,0%7!, * m oog W om * * * * (b) Wings with leding-edge chord-extensions eft Right *Pnel-behvior code: F - flutter; - low dmping; Q - mximum q, no flutter; X - pneldmsged; N - no flutter?complete records were not obtined on these runs The vlues given re estimtes bsed on vilble informtion

18 I R NACA RM ~38~15 : E : : c 676 Fuselge--/ Extended sper-q I ~ Spr clmped long this line, I I Figure 1- Drwing of model ed weights re not indicted iner dimensions re in inches

19 I cu

20 2 B t 1 rn d i Y) 2 I " J 4w E * X N X h P U X I f

21 20 i Y C I, x 3 c b c 0 * m 5 u e 3 VI, 3 c 3 cm o n o w I S m - Vc 3 m m 36 *-tl E Y e m -E 8 A -P -(v A c4-l 0 I

22 21 ij cc B o

23 rd t 9 k 0 I

24 23 0 Definite strt of flutter 0 Uiximuri dynmic pressure, no flutter bw-dmping condition olr-dmping region Numbers beside dt points indicte response frequencies in cps 4,000 > 3,200 d ) f (D k 2, E! B 1, o W h number Figure 7- Trnsonic flutter chrcteristics of wings without ledingedge chord-extensions

25 24 0 Definite strt of flutter YI Definite strt of flutter; loction of flutter point estimted _-- ow-dmping condition Numbers beside dt points indlote response frequencies in OPS t: P 3,200 > E 2,400 0 i!$ 1, e Boh nwnber Figure 8- Comprison of trnsonic flutter chrcteristics of wings with nd without leding-edge chord-extensions (For runs 14, 15, nd 17 the ccurcy of the dt is less thn tht for the other runs, nd lthough low-dmping conditions preceded flutter, they re not indicted here )

m Z NACA RM ~ 5 8 ~ 1 5: f : :* om m m m * o m 0 m m 0 0 om 0

26 m Z NACA RM ~ 5 8 ~ 1 5: f : :* om m m m * o m 0 m m 0 0 om c Figure 9- A typicl oscillogrph record (run 4, wing 1) 25

27 26 m NACA - lngley Field, V

GITHRU ICODEI (CATEQORYI

GITHRU ICODEI (CATEQORYI 5 GITHRU z ICODEI (CATEQORYI 1M NATIONAL ADVISORY COMMI'ITEE FOR AERONAUTICS RESEARCH MEMORANDUM for the Bureu of Aeronutics, Deprtment of the Nvy ZEXO-LIFT DRAG OF THE CHANCE VOUGHT REGULUS I1 MISSILE