NASA NACA-WR-L-339-1942 Wind-tunnel investigation of control-surface characteristics IX - some analytical considerations and experimental test results for an internally balanced fl.pdf

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1、1-“a71,. ;. . . . . -. -=,- ,-?-1”,-;:.,P “.+/”c“h=tlWASHINGTONNACA WARTIME REPORTS arereprintsofpapersoriginallyissuedtoproviderapiddtstributlonofadvanceresearchresultstoanauthorizedgrouprequiringthemforthewareffort.Theywerepre-viouslyheldunderasecuritystatusbutarenowunclassified.Someofthesereporta

2、werenottech-nicallyedited.Allhavebeenreproducedwithoutchangeinordertoexpeditsgeneraldistribution.1Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS31176013542726 - _m.3,.-ANATIONAL ADVISORY COMMITTEE FOR AEROITAUTICS. ADVANCE RESTRICTED R31ORTI?IND-TUITNEL

3、 INVESTIGATION 01CONTROL-SURFACE CHLILACTERISTICSxx - SOiZZ ANALYTICAL CONSIDERATIONS AND EXPERIMENTALTEST! R3SULTS FOR AN INTERITALLY BALA3TCED ILAPBy Richard I. SearssumuLRYAn analysis has leen made to determine the probableaerodynamic section characteristics of a plain flap with .various arrangem

4、ents of an internal balance. Tests in two-dimensional flow have %een made in the HACA 4- 3% 6-footvertical tunnel of an NACA 0009 airfoil with an internallybalanced flap in order to check the validity of the analyt-ical calculation. The results of these tests, presented. in this paper, indicate that

5、 the calculations are in agree-ment with exriment. The analysis has been extended on “the I)asisof the lifting-line theory to include an approx-imate method for the design of an internal lalance for a .control surface of finite span.The present investigation indicates that an internalbalance is am a

6、erodynamically desirable means of control-ling the magnitude and the direction of the rate of changeof flap hinge moment with angle of attack and with flapdeflection. Because the internal balance is entirely con-cealed within the airfoil contour, the lift, the drag,and the pitching-moment characteri

7、stics of the controlsurface are in no vay affected by the presence of the %al-ancing surface. Analytical considerations indicate that afull-span balancing tab actuated by an internal balanceshould prove to be a feasible method of reducing controlforces.IJJTRODUCTION.The desiralillty of redcing the h

8、inge moments of air-plane control surfaces has long been apparent. The reduc-Provided by IHSNot for Resale-,-,-_ _ 2. -. . . . . . . . . . - . ,- _ . . - - _,_ .2Lion of control-surface hinge moments ghou.j.d _greferably be accomplished in such a canner as to improve andnot to impair the frying qual

9、ities of the airplane. In aneffort to solve this problem, the NACA is conducting anextensive investigation of the aerodynamic characteristicsof control surfaces. The main objectives of this investi-gation are to arrive at a rational method for the designof airplafie control surfaces, to determine th

10、e typ offlap arrangements best suited. for use as control surfaces,and to supply oxporiman$al data for design purposes.Seeral years ,go the NLCA made measurements in two-dimensional flow of the pressure distribution on an NACA0009 e.iifoilwith plain llays Qf various chqrds. The re-sults of thso tsg

11、rg reported in roforeac9s 1, 2, and3. !Fho pressure-distribution records of thaso tests havebaen analyzed to determine tha possible characteristics ofa flap vith an internal balance. The internal balanco is .a mechanism by vhich te prssuro difference betmen twoponts on tb. i?:oil is usd to act upon

12、a flat plcte orstutlr device entirely enclosed within tke a3.rfoil prD-filo and thus to de torl:in do?lecting the contol surface.By the proper loc;tion of vents on the airfoil au.rfac, itkas foun to betheoretically possible to vary independent-ly the flap hinge-momerit parameters to any des:ued rwgn

13、i-tuda and to provide the cntrol surface vith any .desirodinitial hinge moment at O ngle of attack and flap deflec-tion.Tho present yaper presents a theoretical analysis ofthe c3acteristics of an iaternal haiace and a methodOf 5aicu3aing the physical charact,ezistlcs of s-ach a %al-anclng device to

14、give any desira.i Eec*ion hinge-moner.tcharacteristics to a cntrol surface. In order to checkthe analytical calculations, tests of an internally bal-.ancei fla hae 3Gn made in two-cilmeusienal flov ,and therssul%s vi t.ese ests are fLIiscus30L. Yne application ofinternal talance to tabs is brisfly t

15、reaed.The symbols used in this Taper are:CL airfoil lift coefficient (L/qS) “.Provided by IHSNot for Resale-,-,-3-,.Cm3?hMmsSfcfairfoil section lift coefficient (2/qc = dL/qcdb)flap hinge-moment coefficient (H/q;fSf)flap section hinge-moment coefficient(/h qcfa = dHqcfadb )airfoil section pitching-m

16、oment coefficient(/ dMm w2 = qcadb )(Pu - Ptresultant pressuro coefficient q )airfoil liftairfoil section lift (dL)flap hinge momentflap section hinge moment (dH)airfoil pitching momentairfoil section pitching moment (dM)airfoil areaflap areachord of airfoil sectionchord of flap measured at airfoil

17、section from hingeaxis to trailing edge of airfoilroot-mean square chord of flapchord of balancing platedynamic pressure of free air stream ,static pressure at point on upper surface of airfoilstatic pressure at corresponding point on lover sur-face of airfoilProvided by IHSNot for ResaleNo reproduc

18、tion or networking permitted without license from IHS. .- -. .4angle of attackalu6IIxanglo of attack for infinite aspect ratiodeflection of flap with respect to airfoilspan of surfacechordvise location of vent neasured from airfoilnose.R“knose radius of flap.constant defining size of balancing plate

19、span-load-distribution factorspan-load-distvibut ion factorA aspect ratioCha =G?-)ao=(2).0=c%,ch8 =(3, =(),=%3cl =. a3.*Cz63=Provided by IHSNot for Resale-,-,-. . 5. , . .(C%l) (*)” “:,:.: .“” ., .f (c%,)= “(*L: :-a .,()P“”.:=”. .;:.a2 - a+a .,.“-., .,.” ,3.”,., -,., . .3.ao “ “ “+ . . ., ., “., . (

20、) ,. .“”. , ,.,.:”r. P () . . . .Tq$hA 0.3Qci a 0.50c; .e.ndan0.80c plain flap with sealed gap at the flap nose. Be- .Cause .of segaratinphaqomena, the”variation of p :,jtfi,aa;hs,the siofie .YaA. .only vitbip the li.mits a; a“lo”r . . .,. . r a+. . ,.! .,.,. ,. .(2), ,.” ?.,. Ch .! =.c -t-kP6. :.,.

21、! . . . . . . . 6 6“J3.“:. J.,lfiththe hinge-moment parameters ch a“fidchof theQ 6flap to be bdl.anc.dand the dbklred parameters ch 1 andaCh .;fox,the balanced flap known, the required values Of8 :” -.$ ,: ,= .+d “ F “. “can.”%dcomputo”da .62 The verit locaion that, .,.), . :- . . .gives these rates

22、,of chane o; pressure can. then he picked .from the curves of figUr8 2; The physical dimensions ofthe balancing-plate and the mechanical advantage” of thelinkage system$hat .connects the plate to the flap are de-termined by th. faft,dr k which can be evaluated from “.equation (2): “ , “. . .: - . .

23、. 2.aa kPa ch t -.Ch.,.J .- ! a:.=“kP8a= .h“1 (3) , -:c. . .2 . .,6. 6, :“, . . :.- ). . In”order to locate the.prope.vent, it is convenient.-toplotithe ral$ia Pti2P8a. as:a ftintioriof”chcrrdwise po- sition. The vent location fhatgives he ratio. a2/F82“. ,;”cof”tcient ch at an angle ofoattack and R

24、 flap deflection of O . In”this manner thoiritie”tinal”bblan-ce “call.”tie:-desined“to supply the flap with.,”.-+.: Tli6“appl.f%atfon o;the zinalys.is already derived -is il-lustrated ly the following exampl.worked out fqr ome par- a71. .; f-icularporit on:the”.curvesof fi5re3; Tlre,higge-moment par

25、ameters c. and Ch for the 0.30c plain flapa 6Provided by IHSNot for Resale-,-,-.9on the ITACA 0009 airfoil can be found by taking the momentabout the 0970c station of the areas under the curves ofP= fl(x/c) and Pa ,= f2(x/c) in figure 2. For theazm 2t.7 unbalanced flap, Ch = -0.0075 and ch = -0.0130

26、.I.n a 8h The vent locations and the length of the balancing platerequired to nako ch = O and ch 1 = O may be calcu-a .6lated froa equation (3)Pm o- (-0.0075)=62 0 - (-0.0130)Figure 2 shovs that Pa./P62 has= 0.577the calculated value ofC0577 at s/c = 0.66. Tho vents should be located, there-fOre. at

27、 this station. The required length of the bal-ance-plate can be found fron tfie(4),k=” - (-0.0075)0.04?Fron equation (5), fcr bb = %ffactor k. Fron equation= 0.160and 8f/8 = 1cl=Cf 2(0.160) (1) (1) = 0.56.The section hi.ne-monent characteristics for O.SOCand 0,50c flas on the NLCA 0009 airfoil were

28、coaputed,for 7arioqs arrangements of internal balance (fig. l(b),to make t(+ = cha/2? 0, and -cha/ 2, The length of-athe %alancing plate required to give the specified valuesof Cha and the resulting values of Ich6 are plottedas functions of vent location in figure 3. The nochanicaladvantage of the s

29、ysten is unity.An inspection of figures 2 and 3 togother indicatesthat small valaes of Ch 1 nay be obtained hy locating8the vents near the flap hinge axis because in this regionthe rate of change of rewltant pressure with flap deflec-tion is large. The size of balancing plate required fora given Val

30、ue of ch 1 will decrease, therefore, as the6vent location approaches the hinge axis. Conversely, snailProvided by IHSNot for Resale-,-,- . . ,= . .A “s.= + . . .-10values of ch 1 without much reduction in ch 1 may bea 8obtained by locating the vents near the airfoil nose 3e-causo the size of %alanci

31、ng plate required for a givenvaluo of ch t decreases as the vent location approachesathe airfoil nose. Comparable auounts of %alance are ob-tained for the 0.30c and the 0.50c flap hy balancing platesof practically the sane size relative to the size of theflap and by practicall the sane location of t

32、he vent withrespect to the hings axis. For either flap, therefore, aalancing plate approximately 0.50cf long with vents locat-ed approximately 0.15cf ahead of the hinge axis is requiredto reduce both ch 1 and ch 1 to zero.a aApparatu-s, Model, and Tests.Tests of a model wing with an internally balan

33、ced flaphave teen nade in the IULCA 4- %y 6-foot vertical tunnel inorder to check the validity of the theoretical analysis.This tunnel, de.scri%ed in reference 4, has been nodified.for tests in two-di.nensional flow. A three-conponent lal-ance syste. has been installed in the tunnel in order thatfor

34、ce-test aasurenents of lift, drag, and pitching no-nent can be nade. Vhe hinge nonent of the flap was neas-ured by an electrical strain gage built into the model.The 2-foot-chor the relative values, hovevers aregenerally independent of tunnel effect.Computed Characteristics of 171ap TestedThe balanc

35、ing plate was rigidly fastened to the flapin such a way that the flap nose formed the rear wall ofthe balancing chamber (fig. 4). The predicted character-istics of figure 3, therefore, do not strictly apply forthis particular type of installation. Because the pres-sure in both sides of the balancing

36、 chamber acts uniform-ly on all walls of the chamber and because one wall ofthe chamber was the flap itself, the balancing moment mustbe calculated to include the moment of the force on thefla,p nose. The forvard edge Qf the lal.ancing plate wassealed to the forward wall of the chamber by a rubbersh

37、eet . For a proporly designed seal , therefore, half theProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS12force on this seal may %e considered as %ei.ng transmittedto the flap as a balancing moment . For the type of install-ation tested, with the dimensio

38、ns shown in figure 4, thebalancing moment isPR + cb/2)bbq = kpcfabfqTherefove, because b = 3+k= C3(R + ch/2) 2.945(0.680 + 2.945/2) = 0.122., = Cf (7.200)aWith the forward location of the vent, at X/C = 0.56, fromfigure 2Paa = 0.062P52 = 0.060The hinge-moment parameters of the plain unbalanced flapa

39、re, from reference 5,Ch = -0.0070aCh =8. -0.0120. . .These values are slightly less than those neaaured in tho pressure-distribution investigation (reference.1) but, be-cause the ckord of the model of reference 5 was smaller(2 ft instead of 3 ft) possible tunnel effects are smallerthan for reference

40、 1 and therefore these values are con-sidered more accurate.From equation (2), the computed characteristics ofthe internally balaaced flap teted arec = (-0.0070) + (0.122) (0.062)a= 0.0006Ch :,= (-0.0120) + (0.122) (0.060)a= -0.0047Sinilarly, with the vent loca%ed slightly forward of thehinge axis,

41、at X/C = 0.69,Paa = 0.041P6 = 0.120a.Provided by IHSNot for Resale-,-,-c,tnInA.13For this vent location, therefore,Ch= (-o.oo70j+ (0.122) (0.041)a= -0.0020Ch = (-0.0120) -f- (0.122) (0.120)6= 0.0026Ex-perimental ResultsThe experimentally determined aerodynamic sectioncharacteristics of an internally

42、 balanced flap on the NACA0009 airfoil are presented as functions of airfotl sec-tion lift coefficient in figure 5 for two vent locations.The values of kertain aerodynamic parameters measured fronthe data presented by the curves of figure 5 are listed intalle II. The effect on the aerodynamic sectio

43、n charac-teristics of sealing the outer 25 percent of the forwardvent holes at each end of the span is shown for flap de-flections of 0 and 10 by the dashed curves in figure “5(a).The lift, the drag, and the pitching-moment charac-teristics of the internally balanced flap were the sameas those for t

44、he plain, unbalanced flap of the sane chordon the sane airfoil (reference 5). This result is to beexpected because the air flow over the airfoil is not dis-turled in any way by the presence of the balancing device.The computed hinge-noment characteristics are in re-markably good agreenent ?vith the

45、experimentally deter-mined characteristics. A comparison of the measured andthe computed hinge-monent parameters is nade in table II.Vith the forward vent location, at X/C = 0.56, the slopech 1 was nearly the sane for all flap deflections tested;awhereas vith the conventional inset-hinge type of aer

46、ody-namic blance. ch generally increases negatively as theaflap is deflected. The hinge-nonent characteristics werenot affected appreciably by sealing the outer 25 percentofothe vents at each end of the span. Because, at 0 and10 flap deflection, the curves ch = f(c because the lifting-line theory as

47、sumes the induced downvmsh to be constantalong ths chord, the chordwise distribution of resultantpressure at a section of a wing in three-dimensional flow cannot be accurately computed by the application of theo-retical aspect-ratio corrections based on the lifting-line theory to the chordvise distr

48、ibution of resultantpressurs $(cr a ring in two-dimensional flow. Until the “lifting-surface theory provides an adequate method for thecomputation of chordwise distribution of resultant pressureat any section f a ving of finite aspect ratio or untilempirical correction factors are experimentally determinedfor the existing lifting-line theory, the pressure distri-bution and hence the hinge-moment characteristics of con-trol surfaces of finite span ca