RESEARCH MEMORANDUM NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WASHINGTON. TRE LOW-SPEED AERODYNAMIC CHARC1CTEmTICS. - " OF LARGE-SCALE SWEPT h G S

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1 -. " " RM No. AEC13 a RESEARCH MEMORANDUM AN INVESTIGATION OF T6E EFFECT OF TIP SHAPE OM. TRE LOW-SPEED AERODYNAMIC CHARC1CTEmTICS. - " -."." OF LARGE-SCALE SWEPT h G S By Walter C. Walling Ames Aeronautical Laboratory Moffett Field, Calif. NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WASHINGTON.. November 13, 1947 I

2 By Walter C. Walling liz an effort to renedgr 8- of the mbsireble pitching+nment chmacteristics of swept wing8 with relativelg hi& mgect ratios and to improve the maximum lift coefficient obtainable, 821 investi- &ation ha8 been nade of the effect of tip 8ha.pe on the aerodynamic characteristics of large-ecale 45' ewepfforwa.rd mil 45' swept-back wings. Also taresd this end, the mpt-bsck wing was tested Hth bodies of revolution, vlth and without ducts, mounted on the tips. me results ehov that none of the variations of tip shape investigated nor addftlon of bodiea of revolutim at the tips produced major chmgee in the characteristics of the swept vinga. Tips cut off oblique to the air stream efiibited slightly better pitchbg+nwnent cb&ra~terietice at high angles of attack for the Bwept-f ory83"d and swept4back wfnee Tuft atu&ies indicated that.-the unstable pitching-mament chazacteristics of swept-back wiwa at high -0s of attack are cauaed by a rapid development of leadingedge stall, beginning at the tip and progressing inboard.

3 2 NACA RM No. Am13 In addition to the foregoing, studies were made of the effect of bodies of revolution mounted at the tip of the swept-back wing. Since tihe. boundary la.yer of ewept-back wings flows outward, accumulating at the tips and precipitating early tip stall, it w a ~ hoped that the 1ouLpressure field surrounding the unductad bodfee would create a suction poverful enough to draw off the accumulated boundm~~ layer. In the case of the ducted bodies, it was hoped that the tip vortax would flov off the wailing end of the body thereby lowering the pressure in the duct enough to effect scam bomdazylayer removal., pitchimamnt coeff lcient &out 0.15 M.A,C. rate of change of lift coefffclent with angle of atmk, per degree marlmum Lift coefficibnt dynajplc PIWSSUre, pouad8 per 89- aspect ratlo based on effective ap($) foot effective span, measured normal to plane of synmretry, feet (refer to fige. 1 aad 2) actual epan, meaeurea normed to plane of epneky, feet wing mea, square feet mean aerodynamic chord of wfng meamd peulallel to plane

4 NACA RM No. Am13 3?he 45' mp&forva3d and the 45' eweptiback large-ecale wings were tested with four differently ahapd pairs of tips. The airfoil sections of the wings, normal to the quarte-hord line, &re WCA 0015 near the root and IWCA at the tip, as designated in figure8 1 an& 2. The specified sweep of each wing ie the sweep of its qusrte2c chord line. The tip8 are designated as parallel, oblique, nomal, and rounded, The nnmenclature of them first three shapes refers to the approximate -e of the edges relative to the air stream.) h each case the -8 with parallel t1p8 &re wings investiwbd and reported in reference 1. Geapaeiiric chesacterieticer of the wings wlth the wious tips &own in figures 1 an& 2. The 45' ewept-back wing ya8 ale0 tested with body4-revolutfan tips, wlth esd without ducts basic bodies have anrllca airfoil section and a lkeoot chord which is approximately twice the tip chord of the wing. mey were mounted with their center lines pamllel to and 3 inches above the chord plane of the we ducted bodies have 2 feet of the rea portion rammed to obtain sufficient duchrft &rea. Ihe duct inlet at the upper surpace junction of the ving and body is approximately 4 feet long, averwing 2$ fnche~ in height, and faire into a CincMiameter outlet, Figure 3 shows characteristics of the sweptback wing with body-of-revolution tips. The tests were- conducted in the Ames kcb by 809oot wind tunnel, The wings were attached to a boam and mounted in the tunnel 8.8 shown in figure 4. For most of the tests the win@o+ocen incidence WBB 5'. Emver, with the Bvept"forwe;rd Kizig at 5' incidence, angles. of attack beyond that for e lift could not be realized because of limitations imposed by the support eyatem. In order to determine the trend of poet-~tall characteristics, one test of the sweptforward wing with pardleg tips was made with the Ving-tcGboCan incidence increa~ed to 15, Tests were made varying the angle of attack from zero lift through stall for the Sxept-fmwaxd and mpt-back wings with each of the several tip ehapes installed. Each test was made twice, first for the purpose of obtaining force data and second vith the wing completely covered with tufts to obtain observations of the stdl progression.

5 4 NACA RM No. Am13 dynamic preeaure of 25 pounds per square foot, These correspond to Reynold8 nlzmbere baaed on the mean "IC chord of approximately 7.2 x 1W for the body-af-revolutlon tip teste, 9.3 x 1W for the other swepobeck wing teats, and 10.7 x 10s for the mpfforwapd. wing tests. The f mce data for the svegt-f orward wing are shown in f 1gu-m 5, and the records of the tdt obsematiune in figure 6. Similar data for the swept-back wing are shown in figures 8 Rnd 9, respectively. Force data for the swept-back wings with the bcdy of revolution tips 8;re shown in figure 10.!t%ere are a m differencee in the results presented for separate teste of apparently identical configurations, It ie reasoned that these differences a m the result of elight changes in configuration caused by reassemblies of the model between the various tester, Considering the objective8 of this investigation, these differencee do not appear to be of great signlficetnce. DISCUSSION It Is evident from the force test rebulte that no major chqe in maximum lift coefficient or pitching-mament characteristice were realized through the installation of any of the varioue-shaped tipa or the bodies of revolution. The maxlmum Improvement in C k waa To a large extent the VarieLtions in CI, occurring in the linear portion of the cme can be attrtbuted to differencee in. aepect ratio of the variaue configurations, rather than tip-shape change 0 The oblique tlpe effected so~me change^ in pitching moment at high anglee of attack for both the swept-f orward and the mpt-back wings, although the imgrovemente realized did not approach those that had been hoped for. For the evept-forward wing, pitching moment fe given in figure 7 lor a oente"grav1ty location of 0.15 M.A.C a reaflonable location with regard to bslance. Here it Is seen that the wetable pitching moment which sxleted near atall has been almost eliminated by the InakU.ation of the oblique tips. Thie change 18 accompanied by acme increase fn stability at lower anglee Of attack. the case Of the mept-back wing, the Oblique tips reduced the sfx&illty slightly in the low aagled-attack range in etdditlon to decreasing the unstable pitch- mament above a = 20 (fig. 8). d

6 NACA RM No. Am13 5 The tuft observations shared that tip shape had saw control over the stall progession of the swepiiforvard wing, though this was not reflected, except by the abov-ntfoned pitchimment chaqps, in the force measurements. 5 normal tips and, to a lesser degree, the oblique tips evidenced tip atall not shown by the other tip &apes and, &B a result, might reduce laterd~ootrol * effectivenees at high lift coefficiente. On the swept-back King the mioue tipe had little effect 011 the stall pro@ession indicated by the tufts (fig. 9). In each case the sfall wag characterized by a strong leadtnmdge separation progressing inboard from the tipe which, it might be erpected, could be little affected by tip shape. In thie and other swep% back wins studies, force teste ehox this sudden leadfng-dge flow separation is accompauied by a strong positive pitching+nnent increment, It would eeem, then, that if thie separ&tion can be delayed by 6-0 meam, me of the moat undesirable chazacterietice of sweptaack wings will be overcame. L Tuft obaervatiane nmde with either the ducted or the unducted body"-revolution tfps indicated that while the bodies tended to draw off the boundary layer at lov a&le of attack, the bounderrlayer drain control yebe so weak it became inadequate, asd the no& stall pattern appeared at very low lift coeff iciente. The tufts indicated a flat existed through the ducted body prior to stall, but it was apparently BO slight as to have PO measurable effect in &lam the stall. At the first appemance of tip stall, the str- tip'vortex moved inboard, end there xae no longer any flow through the duct. Ames Aeronautical 'laboratory, National Advieory Camittee for Aeronautics, Moffett Field, Calif..

7 NACA RM No. Am13 ROUNDED TIPS PARALLEL MOMENT CENTER LOCATED AT MAC/4. OBLIQUE Tipa NORMAL TIPS llbtkybl bwl5uw CoYyIlTEe mn IuIoNAIrrl- FIGURE I. - GEOMETRI CHARACTERISTICS OF 45-OEGREE SWEPT-FORWARD WlNG WITH VARIOUS TIPS..

8 NACA RM NO. A7H13. 7 ROUNDED Tips i- OBLLQUE T r PS NORMAL Ti PS t FIGURE.2_- GEOMETRIC CHARACTERISTtCS OF 45-DEGREE SWEPT-BACK WING WITH VARIO~~S TIPS-

9 8 NACA RM No. Am13 BODY OF REVOLUTION AIRFOIL BECTION: NACA DUCTED FIGURE 3.- BACK WING WITH BODY-OF-REVOLUTION TI P6. GEOMETRIC CHARACTERISTI'CS~~OF 45-DEGREE SWEPT-

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14 NACA RM No. Am13 13 FIGURE 5.- AERODYNAMIC SWEPT -FORWARD CHARACTERtSTlCS OF 45 DEGREE WING Wt I H VARIOUS TIPS.

15 14 NACA RM No. Am13.

16 NACA RNI No. Am a NATtONAL ISVlSORY COMMITTEE FOR AERONAUUTICS.o "08 "12 PITCHING-MOMENT COEFFICIENT, m.15 FIGURE 7"COMPARISON OF PITCHING- MOMENT COEFFICIENT ABOUT.I5 MAG. FOR SWEPT-FORWARD WING WITH PARALLEL AND OBLIQUE TIPS.

17 16 NACA RM No. Am13 I? J 4 FtGURE 8.- AEROOYNAMIC CHARACTL;R\STICS OF 45-DEGREE SWEPT-BACK WING WITH VARTOVS TIPS.

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19 18 NACA RM No. Am13 FIGURE 10.- AERODYNAMIC CHARACTERISTICS OF 45-DECREE SWEPT-BACK WING WITH BODY OF REVOLUTION TIPS.

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