1、NASA TECHNICAL NOTEO(:O!NASA TN D-8260A DESIGN APPROACH AND SELECTEDWIND-TUNNEL RESULTS AT HIGHSUBSONICMOUNTEDSPEEDS FORWINGLETSWING-TIPRichard T. lVhitcombLangley Research CenterHampton, Va. 23665_JJTIO/Ve_- A_, %“2“76 .,L91 E,NATIONAL AERONAUTICSAND SPACE ADMINISTRATION WASHINGTON, D. C. JULY 1976
2、Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1. Report No. 2. Government Accession No. 3. Recipients Catalog No.NASA TN D-82604. 5. Report DateJuly 197612.Title and SubtitleA DESIGN APPROACH AND SELECTED WIND-TUNNELRESULTS AT HIGH SUBSONIC SPEEDS
3、FOR WING-TIPMOUNTED WINGLETSAuthor(s)Richard T. WhitcombPerforming Organization Name and AddressNASA Langley Research CenterHampton, Va. 23665Sponsoring Agency Name and AddressNational Aeronautics and Space AdministrationWashington, D.C. 205466. Performing .Organization Code8. Performing Orgamzation
4、 Report No.L-1090810. Work Unit No.505-11-16-0811. Contract or Grant No.13. Type of Report and Period CoveredTechnical Note14. Sponsoring Agency Code15. Supplementary Notes16. AbstractWinglets, which are small, nearly vertical, winglike surfaces, substantially reduce dragcoefficients at lifting cond
5、itions. The primary winglet surfaces are rearward above the wingtips; secondary surfaces are forward below the wing tips. This report presents a discussionof the considerations involved in the design of the winglets; measured effects of these sur-faces on the aerodynamic forces, moments, and loads f
6、or a representative first-generation,narrow-body jet transport wing; and a comparison of these effects with those for a wing-tipextension which results in approximately the same increase in bending moment at the wing-fuselage juncture as did the addition of the winglets.17. Key Words (Suggested by A
7、uthor(s)Nonplanar lifting systemsAerodynamic drag reductionInduced drag18. Distribution StatementUnclassified - UnlimitedSubject Category 0219. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price*Unclassified Unclassified 30 $ 3.75* For sale by the Nati
8、onal Technical Information Service, Springfield, Virginia 22161Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-A DESIGN APPROACH AND SELECTED WIND-TUNNE
9、L RESULTS ATHIGH SUBSONIC SPEEDS FOR WING-TIP MOUNTED WINGLETSRichard T. WhitcombLangley Research CenterSUMMARYWinglets, which are small, nearly vertical, winglike surfaces mounted at the tips ofa wing, are intended to provide, for liftingconditions and subsonic Mach numbers, reduc-tions in drag coe
10、fficientgreater than those achieved by a simple wing-tip extension withthe same structural weight penalty. The primary surfaces are located rearward abovethe tips. Smaller secondary surfaces may be placed forward below the tips. This paperincludes a discussion of the considerations involved in the d
11、esign of such surfaces; themeasured effects of these surfaces on the aerodynamic forces, moments, and loads nearthe design conditions for a representative first-generation, narrow-body jet transportwing; and a comparison of these effects with those for a wing-tip extension which resultsin approximat
12、ely the same increase in bending moment at the wing-fuselage juncture asdid the addition of the winglets. The experiments were conducted in the Langley 8-foottransonic pressure tunnel.For the configuration investigated the winglets reduce the induced drag by about 20percent with a resulting increase
13、 in wing lift-drag ratio of roughly 9 percent for the designMach number of 0.78 and near the design liftcoefficient. This improvement in lift-dragratio is more than twice as great as that achieved with the comparable wing-tip extension.Also, the negative increments inpitching-moment coefficients ass
14、ociated with the additionof the w_ingletsare less than those produced by the wing-tip extension. The experimentalresults also indicate that the increase in overall performance improvement provided bythe winglets in comparison with thatfor a wing-tip extension is significantly dependent onthe angles
15、of incidence of the upper winglet.INTRODUCTIONIt has been recognized for many years that a nonplanar lifting system should haveless induced drag than a planar wing. As early as 1897 a patent was obtained byLanchester for vertical surfaces at the wing tips. Since that time a number of theoreticalanal
16、yses have indicated the significant improvements possible with nonplanar systemsincluding vertical surfaces at the tip. (See refs. 1 to 3, for example.) On the basis ofProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-these encouraging theoretical stud
17、ies, a number of experimental investigations of variousend plates at the wing tips have been made. Usually these surfaces have reduced the dragat very high lift coefficients but have resulted, at best, in only slight reductions in dragnear cruise lift coefficients. Near cruise conditions the viscous
18、 drag increments associ-ated with the end plates were nearly as great as the reductions in induced drag.An analysis of the effect of vertical surfaces at the tip on overall airplane perform-ance must include consideration of the effect of such surfaces on the structural weight.Loads on the vertical
19、surfaces and the increased loads on the outboard region of the wingassociated with adding these surfaces increase the bending moments imposed on the wingstructure. The greater bending moments, of course, require a heavier wing structure.Aircraft designers have found that for the same structural weig
20、ht penalty associated withadding end plates, a significantly greater improvement in drag could be achieved bymerely extending the wing tip. As a result, no aircraft designs have incorporated suchsurfaces for the sole purpose of reducing drag. However, vertical surfaces have beenplaced near the tips
21、of some sweptback and delta wings to provide directional stability.The objective of the work described herein was to develop nearly vertical, tip mountedsurfaces which would provide, near cruise conditions, substantially greater reductions indrag coefficient than those resulting from tip extensions
22、with the same addedbendingmoments imposed on the wing structure.The factor that most previous experimental investigators have overlooked is that tobe fully effective the vertical surface at the tip must efficiently produce significant sideforces. These side forces are required to reduce the lift-ind
23、uced inflow above the wingtip or the outflow below the tip. Obviously, a low-aspect-ratio flat end plate as generallytested previously is not an efficient lifting surface. To achieve the stated objective of thepresent work, the nearly vertical surfaces placed at the tip for the purpose of reducingdr
24、ag due to lift have been designed to produce significant side forces, even at supercriticalconditions, according to the well-established principles for designing efficient wings; hencethe name winglets. Flow surveys behind the tip of a wing with and without winglets, pre-sented in reference 4, indic
25、ate that the basic physical effect of the winglets, which leadsto drag reduction, is a vertical diffusion of the tip vortex flow at least just downstream ofthe tip. The large inward components of the vortex flow near the center of the vortex aresubstantially reduced while the small inward components
26、 in the region above the tip of thewinglet are increased slightly. Thus these surfaces could be called vortex diffusers.The initial development investigations of wing-tip mounted winglets were conductedat subsonic speeds on a representative second-generation, wide-body jet transport wing inthe Langl
27、ey 8-foot transonic pressure tunnel during 1974. The results of that investigationare discussed in general terms in reference 5. Complete results for the final configura-tion of that investigation are presented in reference 4. Recently, improved winglets havebeen investigated on a representative fir
28、st-generation, narrow-body jet transport wing forProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a wider range of flightconditions than that of reference 4. This report describes theapproach used in the design of the winglets, presents selected resul
29、ts from the morerecent wind-tunnel investigation,and compares the results with the design objective.SYMBOLSThe longitudinal aerodynamic characteristics presented in this report are referredto the stability axis system. Force and moment data have been reduced to coefficientform on the basis of the ex
30、posed area of the basic wing, except for the normal-force coef-ficients for the winglets. The reference for pitching moments is the quarter-chord of themean aerodynamic chord of the wing. All dimensional values are given in both the Inter-national System of Units (SI) and U.S. Customary Units (ref.
31、6). All measurements andcalculations were made in U.S. Customary Units.Coefficients and symbols used herein are defined as follows:b Y exposed semispan of wing with basic tip, 124.26 cm (48.92 in.)Ab incremental increase in exposed wing semispan, 0.38h, 7.62 cm (3.00 in.c local chord, cm (in.)mean a
32、erodynamic chord of exposed basic wing, 39.98 cm (15.74 in.)Cav average chord of exposed basic wing, S, 37.41 cm (14.73 in.)Cn section normal-force coefficient obtained from integrated pressureme asure merit sct tip chord of basic wingCbCDCLbending-moment coefficient of wing at wing-fuselage junctur
33、e,Bending momentq Sbdrag coefficient, Dragq SLiftlift coefficient,qoo SProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-AC LCmincremental liftcoefficientat constant drag coefficient,(CL)with winglets or -(CL)basic wingtip extensionpitching-moment coef
34、ficient about moment reference center, Pitching momentqooS5CN normal-force coefficient obtained by integrating span load distribution, basedon winglet areaCp pressure coefficient,PZ - PooqcoCp,soni c pressure coefficient corresponding to local speed of soundh span of upper winglet from chord plane o
35、f wing tip (see fig. 3), 20.32 cm(8.00 in.)incidence of winglet measured from free-stream direction, positive with lead-ing edge inward for upper winglet, with leading edge outward for lower wing-let (see fig. 3), degMooPlfree-stream Mach numberlocal static pressure, N/m 2 (psf)Poo free-stream stati
36、c pressure, N/m 2 (psf)qoo free-stream dynamic pressure, N/m 2 (psf)S area of exposed basic wing, 0.4649 m 2 (5.0034 ft 2)X chordwise distance from leading edge, positive aft, cm (in.)Y spanwise distance from wing-fuselage juncture, positive outboard, cm (in.)vertical coordinate of airfoil, positive
37、 upward, cm (in.)4Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-z distance along winglet span from chord plane of wing, cm (in.)OL angle of attack, degDESIGN CONSIDERATIONSMethodologyThe theoretical calculations of references 3 and 7 provide an ind
38、ication of the spanload distributions required on the wing and vertical surfaces at the tipto obtain the opti-mum induced drag in subcritical flow. However, they do not describe how the configura-tion should be shaped to obtain these load distributions or how itshould be designed toachieve the maxim
39、um improvement in overall performance. The tip mounted winglets ofthe present investigation were developed with the available theoretical calculations, phys-icalflow considerations, and extensive exploratory experiments. Consideration has beengiven to the effect of adding the winglets on the structu
40、ral weight and the high-liftoff-design performance as well as to the drag reduction at design conditions. Because of thelimitations of the methods used, the winglets of this investigation are undoubtedly notoptimum.Since the development of the design approach described herein, several new theoret-ic
41、al liftingsurface methods for analyzing and optimizing nonplanar liftingsystems forsubcritical flows have been developed. Among them are references 8 and 9. These meth-ods should greatly aid in future aerodynamic designs of more nearly optimum winglets.Calculations based on the method of reference 9
42、 have already been used to verify a num-ber of the assumptions made in the design procedure presented herein. They have alsoindicated several areas where the design might be improved. Some of the applications ofthis theory are described subsequently in this report.Upper WingletArrangement.- The prim
43、ary component of the winglet configuration (figs. 1, 2, and3) is a nearly vertical surface mounted rearward above the wing tip. The upper wingletis placed rearward so that the increased velocities over the inner surface of the wingletare not superimposed on the high velocities over the forward regio
44、n of the wing upper sur-face. Thus adverse flow interference effects at supercritical design conditions arereduced. The results of exploratory investigations suggest that to minimize adverseinterference effects at supercritical conditions, the leading edge of the root of the wingletshould probably n
45、ot be significantly ahead of the upper-surface crest of the wing-tip sec-tion. Conversely, if the leading edge of the upper winglet is moved aft of this crest,attachment of this surface to the wing becomes a greater problem since the structural boxProvided by IHSNot for ResaleNo reproduction or netw
46、orking permitted without license from IHS-,-,-for the winglet moves aft of the usual rear spar location for the wing. Also, analyses andexploratory experiments indicate that the shorter winglet root chord caused by moving theleading edge aft of the wing section crest results in a perceptible loss of
47、 winglet effective-ness. Therefore the leading edge of the winglet has beenplaced near the crest for cruiseconditions. Results of exploratory experiments also indicate that the greatest wingleteffectiveness is achieved with the trailing edge of the winglet near the trailing edge of thewing.Loads.- T
48、he theories of references 3, 7, and 9 indicate that to achieve the reductionsin induced drag theoretically predicted for wing-tip mounted vertical surfaces requiresnot only substantial inward normal loads on these surfaces but also significant increasesin the upward loads on the outboard region of t
49、he wing. Exploratory experiments madeboth during the investigation of reference 4 and during the present investigation indicatethat the greatest measured reductions in drag due to adding the upper winglet are achievedwith normal loads on the winglet, and associated addedloads on the outboard region of thewing, substantially less than those indicated as o
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