NASA NACA-TN-4044-1957 Ground effects on the longitudinal characteristics of two models with wings having low aspect ratio and pointed tips《带有低展弦比和尖头电极机翼的两个飞机模型纵向特性的地面效应》.pdf

1、ii1.-1a71a15a14NACA:l used a conventional tail.The tests were made in the Ames 12-foot pressure wind tunnel atReynolds numbers of from 2.5 to 10 million mid at a Mach number ofapproximately 0.25.-A flat plate spanning the wind.tunnelwas chosento represent the ground. The disadvantage of a boundary-l

2、ayerbuild-up.along the plate, pointed out in reference 1 for example, was minimizedinsofar as was possible in the plate design._-Limitedpressure measure-.ments were made to evaluate this discrepsmcy in the ground representation.The experimentallydetermined ground effects were compared withthose pred

3、icted by the theory of Tani, et al., (refs. 2 and 3). This -.theory had the advantages of simplicitywith a certain amount of flexi- . .bility for adapting it to wings of low aspect ratio. The method is dpartially summarized and somewhat simplified in reference 4. The -remainder of the applicable ele

4、ments of the theory is summarized in anappendix to this report. .- *ANOTATIONaspect ratio, sb wing spanCD drag coefficient,Ch eleven hinge-moment coefficienthinge momente +qMeCht tab hinge-moment coefficient,hine.ment2qMtProvided by IHSNot for ResaleNo reproduction or networking permitted without li

5、cense from IHS-,-,-NAC!ATN 4044 3CLC%ailcmCmtailc!EhitZtL5MMeMtqRsStvYlift coefficient,Wincrement of lift coefficient, CL2 due to the tailpitching-moment coefficient about the moment centerin fig. 2), yitching momentC(specified .increment of pitching-moment coefficient (at a constant angleof attack)

6、 due to the tailwing chord measured parallel to the plsme of symmetry2Jb/2wing mean aerodynamic chordE. C%ydistsnce from the surface of the ground plate to the 0.255(specified in fig. 2)i.ncldenceof the horizontal tail with respect to the wing chordplsne, degtail length, longitudinal distance from t

7、he moment center to thehorizontal-tail hinge lineliftlift-drag ratio, dragfree-stream Mach numberfirst moment of area of the exposed eleven behind the hinge linefirst moment of area of the exposed tab behind the hinge linefree-stream dynsmic pressureReynolds number, basedwing areaarea of the horizon

8、tal-Lt Sttail volume, distance perpendicularon the wing mean aerodynamic chordtailto the plme of symmetryProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4 NACA TN 4044a8angle of attack, degelvon deflectionwith respect to the wing-chord plane, measure

9、din planes perpendicular to the eleven hinge line, degflap deflectionwith respect to the wing-chord plane, degtab deflectiontith respect to the eleven-chord plane, measuredin planes perpendicular to the tab hinge line, deghorizontal-tailpitching-moment effectiveness,measured at aconstant angle of at

10、tackeffective downwash angle at the tail, degincrease in effective downwash angle at the tail due to proximityof the ground, deg.APPARATUS AND MODELSThe ground representation is diagramed in figure 1. The ground pltespanned the test section and was attached to the tunnel walls and to sup-porting str

11、uts on its lower side. The plate was made of l/8-inch aluminumsheet fastened to an aluminum-angleframe with countersunk screws. The *leading- and trailing-edge fai.ringgwere approximatelyelliptical. Theleading-edgefairing was cambered to reduce the possibility of separation.-Wover the ground plate b

12、y keeping the stagnationpoint on the upper surface._The model waa supported by a sting which could be controlled in angleof attack amd in elevation. A slot slightly larger than the sting wasbuilt into the trailing edge of the plate so that the model could be movedas close to the ground plate as desi

13、red at aH positive angles of attack.The forward 16 inches of the slot were sealed with a flush plate for por-tions of the test.Provision was made for determining the boundary-layer thichess onthe groundTlate, and the static pressures both on the plate and at severalheights above the plate. The two l

14、ocations of the rake used in theboundary-layer survey are shown in figure 1. The figure also shows thelocation of the row of orificesused to measure the static pressures onthe plate. The static pressures above the plate were measured along atube containing several sets of orifices. This tube was mou

15、nted on the model support in place of the model. bThe geometry of the models is given in figure 2 and in tables I andII. The tailless model had a wing which was built around a steel spar.The forward part of the wing was made of a tin-bismuth alloy bonded to theProvided by IHSNot for ResaleNo reprodu

16、ction or networking permitted without license from IHS-,-,-NACA m 4044spar, and the rear part consistedby hinges and internal brackets.side of the model were restrained5of solid steel elevens and tabs attachedThe eleven and tab on the right-handfrom rotating about their hinge linesby strain-gagememb

17、ers of the cantilever bending type for the purpose ofmeasuring hinge moments. The ting section was the NACA 0005-63 modifiedslightly to provide straight-he elements from the eleven hinge line tothe trailing edge. .-The tailed model had solid steel wing and tail surfaces. The wingwas provided with si

18、ngle-slotted flaps attached with l/4-inch-thickexternal brackets screwed to the lower surfaces. The ailerons, whichwere not deflected during the tests, were similarly supported. For thetests with flaps up, the ailerons and flaps were replaced by a solidinsert with no slots or external supports. The

19、fuselage could be shortenedby the removal of a cylindrical portion, which was 6.5 inches in length.(See table II.)Both models are pictured installed over the ground plate in figure . The forces and moments on each model were measured on a 4-inch-diameter, four-component, strain-gage balance enclosed

20、 within the modelfuselage. Provision was made for measuring the pressure inside the baseof the model between the sting and the model. TESTS.The tests were conducted in three parts: (1) boundary-layer surveyson the ground plate and static-pressure surveys on and above the groundplate (with no models

21、installed), (2) force tests of the models in thepresence of the ground plate, and (3) force tests of the models withoutthe ground plate. The tests included measurement of the modelst lift,drag, pitching moment, and hinge moments (the latter on the control sur-faces of the tailless model only) with v

22、arious control-surfaceand flapdeflections. Most of the tests were made at a dyasmic pressure of 80pounds per square foot with the wind tunnel at atmospheric pressure. Thesetest conditions correspond to a Mach number of 0.25 and Reynolds numbers of3 million for the tailless model, and 2.5 million for

23、 the tailed model.Since the accurate measurement of drag characteristicswas difficult atthis low Reynolds number, some data were obtained at higher Reynoldsnumbers (8 million and 10 million for the tailless model and tailed model,respectively).For most of the tests the angle of attack was varied fro

24、m -4 to themechanical limit of the model-support system (approximately 14 with theground plate installed, 24 without the ground plate). With the groundplate installed, angles of attack up to 28 were reached by mounting themodel on a bent sting and making the force tests at large mgles separatelyProv

25、ided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-6 NACA TN 4044from those at small angles. At the smallest ground heights, the angle zof attack was limited to that beyond which the model would collide withthe plate (23 for the taiess model, 12 for the tai

26、led model). the average chord is givenby the expression .and the mean wefghted value ofwithc/H is expressed as .,-c the wing chord at spsm station qH the height from the ground to thestation quarter-chord.point at the span q a ratio of distance from the plane of symmetry to semispan, y/(b/2) .The us

27、e of these relatiom was generally of more importance to the resultthan the inclusion of such refinements as the effects of wing thickness.Tanits method for estimating the groundeffects on the,tail (ref.3)are summarizednext, togetherwith a modification to the method for usewith flapsdown. It was desi

28、red to estimatethe ground effec”tson the-pitching moment contributedby the tail, at a given tigle of attack. wLet (ACm)tfil=ACm= +A%= = increase in due to ground effects onthe tall where -Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-IWCA TN kokh 1

29、3acmcm=-m “T for thiscondition, k is taken as l.The second increment in pitching-moment coefficient ACm2 resultsfrom a change in tail lift which occurs for the same reasons that the winglift changes near the ground. In the case of the tail, only the majorground effect is considered, this being the i

30、nduced angle of attackcaused by the trailing vortices of the hage tail. This induced angle ofattack is then transformed into an increase in tail lift coefficient,expressed asProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1412SinAt NACA !rll4044this

31、relation, the induced up the other geometric terms are described infigure 21. The tail lift coefficient is-app-mximatedas.-where Cmtail is the increment of pitching-moment coefficient due to thetail and is taken from the experimental data with no ground plate. The change in lift coefficient of the m

32、odel resulting from the effectsof the ground at the tail is expressed asThe above relations for estimating downwash at the tail were inade-quate for the case of flaps down. Here, the angle of downwash was assumed -to be the sun of two components (as in ref. 8), the first stemming fromthe flaps-up li

33、ft distributed over the original wing vortex span, and thesecond stemming from the lift due to flap deflection distributed over *he . -flap vortex span. With the assumptionthat the flap lift had an ellipticaldistribution, it was possible to calculate a value J(E, )f for thatwing area ahead of and in

34、cluding the flaps. Then,here Acky is the increase in lift coefficient resulting from flap .deflection. It was noted that by suitable factoring,AC.00 1.06 5.00 .8010.00 1.69 10.00 1.4415.00 2.16 15.00 1.9420.00 2.52 20.00 2.3223.00 2.78 25.00 2.6030.00 2.95 30.00 2.7935.00 3.04 35.00 2.9040.00 3.06 4

35、0.00 2.9745.00 2.99 45.00 2.9950.00 2.84 %1.25 a3.0055.OQ 2.61 97.75 a3.0060.44 2.25 61.75 2.9965.75 2.9069.75 2.6772.00 2.44Removable section.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MCA TN4044Locations of rake19.-120 bGround plate(top view)“

36、4:6.” /:J”:”r#v .- +-4.5 Station of static-pressure orificesI I Approx.-65+Allsrusdimensions in inches unless otherwise notedFigure 1.- Diagram of the ground-plate installation.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-20 NACA TN 4044Other geom

37、etric data in tables I and All dimensions in inches unless otherwise notedEleven hinge line=Tab hinge line _Moment center=06 45.0 - 56.3-8.50- -=.250C+460.44 F(a) Tailless model.Figure 2.- Geometry of the models.Provided by IHSNot for ResaleNo reproduction or networking permitted without license fro

38、m IHS-,-,-.T.aOther geometricAll dimensions indata in tables I and Uinches unless otherwiseryYQq J .00 ,12 .6 .20 .24 .28 .32 .36 .40CDFigure 4.- The effect of ground height on the longitudinalcharacteristicsof the taillessmodel;R = 8 million, 5 = 0, t5e- OO.Provided by IHSNot for ResaleNo reproduct

39、ion or networking permitted without license from IHS-,-,-1.2Lo.B.6CL .4.20-.2-.44 0 4 8 12 16 20 24 for8m=o” .08 m o -.04 -m -.1200=cmfort$#Y for-lOO(a) 8=0Figure .- The effect of ground height on the lift and pitching-mcment characteristics of thetailless model; R = 3 million., . I!,Provided by IHS

40、Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-1.2Lo.8.64,.20-.2-.4-4 0 4 8 12 16 20 24 for JR = 3 million, 8t = OO.rom* . zII I ,. IProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-, , , aLo.8.6CL.4.20 4 8 12, 16 2

41、0 24ao“ .04 .08 .12 .16 .20 .24 .28 .32CDFigure 7.- The eect OY? gnmnd height on t IiPt. and drag characterLTticB of the tailless modelin a balanced condition ( = O); R . 3 million, bt . OO.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1.2I .0.8.6C

42、L .4.20-.2-.4.12 .08 .04 0 -.04 :08 -.12 -.16 .04 0 -.04 for tle a75 -10c ce ht00(a) bt = W for =-5 for 0Figure 8.- The effect of ground height on the hinge-mcment characteristics of the eleven and tabon the tailless model; R = 3 million., * , . . 1IProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-.-, , , 1I1.2Lo.8.6CL .4.20-.2-.4.08 .04 0 -.04 -.08 -.12 -.16 -.20 0 %04 -.06 for 8eS-10”Che Chtofor Qf5” for O“(b) 5t = 5Figure 8.- Concluded.tProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-