NASA NACA-WR-L-447-1943 Wind-tunnel investigation of control-surface characteristics XI - various large overhang and internal-type aerodynamic balances for a straight-contour flap .pdf

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1、d,1. ” IIARR .Tnn. 1 c)w .-. . . -.ORIGINALLYISSUEDJanuary 1943 asAdvence Restricted ReportWIND-TUNNEL IXVXSTXWI!3X OF CWTROL-SURFACE CHARAC!CERIWTCS= - VARIOUS IARGE OVERHANGAND lNTEFUWL-TYPEAERCIOYNAMICBAIANCES FOR A STRAIE3T-CWN3URFIA2 CEV.TKE NAM 0015 AIRFOILBy Richard 1. Seerd end H. Page Hogga

2、rd, Jr.Iangley Memorial Aeronautical LaboratoryLangley Field.,Va.FOR REFERENCE, - NcTTTOT-HIUs_RooH -_ _._-, NACA,-” . .- ,.H J)”,.- 1W the wide plates, seven-eighthsthe distance. The distance from the trailing edge of theseplates to the flap hinge aqi.s was 0.072c, 0.036c, and 0.018cfor the narrow,

3、 the mediym, and the wide cover plates, re-spectibelybBecause of the shape of the sharp-nose balance, the .distance from the trailing edge of the cover plate normal tothe sharp-nose balance varies with flap deflection (fig. 2).This distance is referred to in this paper as the Ilvent width,ll “lhen t

4、he flap is not deflected, the vent width is 0.0052c withthe wide cover plates in place, 0.0130c with the medium coverplatesb and 0.0260c with the narrow cover plates. The ventwidth varies inversly with the width of the cover plates.Ifithflap neutral, the ratio of the gap at the flap nose tothe width

5、 of the vent for the various arrangements tested isgiven in table II.l?or tests with the gap at the flap nose sealed, a rubber-sheet seal vaa attached to the nose and the ends of the sharp-nose balance and to the tail 11.ock and the end ,platas of theairfoil. Care was taken to keep the rubber sheet

6、slack enoughto prevent interference with the readings of flap hinge momentat all flap deflections.The model, when mounted in tha tunnel, completely spannedtho test section, With this type of installation! two-dimensional flow is approximated and +he section. characteris-tics of the airfoil and flap

7、may be determined. The model. wasattached to the balance frame by torque tu%es that extendedthrough the sides of the tunnel. Tha angle of attack was setProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-4. .,.from outside the tunnel 3Y rotating the torq

8、ue tubes vrithan electric drive, Flap deflections were set inside thotunnel hy temlets and were held %y afriction clamp onthe torque rod that was used in measuring the hing moments.TI?STSThe NACA 0015 airfoil model with a 0.30c straight-contour flap was tested with a 0.50cf blunt-nose balance on the

9、 flap. Several modifications of the blunt-nose balance(figJ 1) were tested to determine the effect of sharper nose.8hape8 on the flap hinge-moment characteristics.Only the flap hinge moment was read when the flap wastested with the blunt- and the modified-nose balances. Thevalues of lift, drag; pito

10、hing morcent, and flap hinge momentwere read when the sharp-nose balance was tested both withand without cover plates.The tests were made at a dynamic pressure of 15 poundsper square foot, which corresponds to an air velocity ofabout 76 miles per hour at standard sea-level conditions.The offectiva R

11、eynolds number of the tests was approximately2,760,000.(Effective Reynolds number = test Reynolds num-ber x turbulence factor. The turbulence factor for the 4-by 6-foot vertical tunnel is 1.93.)The blunt-nose flap was set at deflections from 0 to30in5increments. The modified-and sharnose shapes “yer

12、e set ai deflections of oo, 2ot 50, 100, 150, and 200.lith the narrow c“over plates in place, the deflections werethe same but, with the m“edium and the wide cover plates, itwas not possible to reach 20 before the rear portion of theflap-nose balance touched the trailing edge of the coverplate. The

13、maximum deflections were thus limited to 15 for “the tests with the medium and the wide cover plates.The blunt-, modified-, and sharp-nose flaps were testedwith a 0,005c ,gap throughout the deflection range. ilor eachflap deflection, force tests we:e made throughout the angle-of-attack range at 20 i

14、ncrements from negative stall to pos-itive stall. When either stall position was approached, theincrement was reduced to 1 angle of attack. - ,.-.-.-. -, L, 2:, s - :.,-: - :,. . . . - -.-.q_ -. . . . . . . . .*, . - *:. .-. .;.;,. . +,- ;:?.,;,: . .-.,;-. . .:.:,:,s,. ., ,Provided by IHSNot for Res

15、aleNo reproduction or networking permitted without license from IHS-,-,-RBSUL!JSSymbolsThe coefficients and symbols used in this paper aredefined as follows:cl airfoil section lift coefficient (1/qc)Cdo airfoil section profile-drag coefficient (do/qc)cm airfoil section pitching-moment coefficient (m

16、/qc2)Chf flap section hinge-moment coefficient (hf/qcf2)where1domhfcCfand*o6fairfoil section liftairfoil section profile dragairfoil section pitohing moment about quarter-chordpoint of airfoilflap section hinge momentchord of basic airfoil with flap neutralflap chorddynamic pressureangle of attack f

17、or airfoil of infinite aspect ratioflap deflection with respect to airfoilProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-6. .()actcl =a(free) a% Chf. ()”% f!I!hesubscripts outside the parentheses indicate the . -factors held constant during the meas

18、urement of the param- - ,eters.,PrecisionThe accuracy of the data is indicated bY the deiqtion ,from zero of lift and moment coefficients at an angle of “attack of OO. The maximum error in effective angle ofattack at zero lift appears to be about *0,2. Flap deflec-tions were set within *0.2. Tunnel

19、corrections, experi-mentally determined in tha 4- by 6-foot vertical tunnel, wereapplied only to lift. The hinge moments are pro%ably slight-ly higher than would be obtained in free air and, consequently,the values presented are considered conservative, Relativevalues of drag should be reasonably in

20、dependent of tunnel.effactl although the a%solute value is subject to an un-known correction,Presentation of DataTlap section hinge-moment coefficients as a functionof angle of attack for a 0.30c straight-contour fl”ap on theNACA 0015 airfoil having 0.50cf blunt- and modified-noBe bal-ances are pres

21、ented in figures 3 to 6. Section aerodynamic -characteristics of the same airfoil and the same flap with a0.50cf shar-nose overhang without cover plates are given infigure 7 and with cover plates of various sizes in figures 8 -.- . , .,- . + .x - : ,.,. - -“.-. - , *,.: .:.7:- : - . . . . . . . . .

22、. . . . ”. - XT- : :- - -. “x,. .,., . .-,-. : . . . . ., :.” ,- . . ., . -,. - . . . . . ,:.: . ./ . . - -.-. - ,. $ . . . . . -. ,-,-.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-9“effect on the magnitude of the balancing moment. Forpositive fla

23、p daflaction, the blunt-nose shape gave pro-nounced overbalance at negativa angles of attack but gave relatively little balance at positivs angles of attack. .As the flap-nosa shape was tapered$ the flap became less: overbalanced at negative angles of attack hut, at positiveangles of attack, the hin

24、ge-moment characteristics re”mainednearly the same? !Chenose shapes for the 0.50cf overhang,which gave reasonably acceptable hinge-moment curves (figs.6 and 7), gave hinge-moment characteristics substantiallythe same as those for the 0.35cf blunt-nose overhang (refer-ence 5)V Hence these results ten

25、d to indicate that hinge-moment characteristics of a large flap-nose overhang oftapered profile canbe nearly reproduced by a smaller noseoverhang of blunt profile. A rudder with a long sharp-noseoverhang should have slightly less tandency tolfard rudderlock in a forced sideslip and should require sl

26、ightly lespedal force to hold zero sideslip under unsymmetrical powerconditions than a rudder with a shorter blunt-nose overhang,. .In an effort to decrease the drag of the sharp-noseoverhangl cover plates of various widths were fitted overthe nose of the balance.This arrangement caused the aero-dyn

27、amic balance to resemble an “internal balance both in formand in hinge-moment- characteristics (figs. 8 to 19)* Theextent to which this resemblance occurred varied directlywith the width of the cover plates. The widest plates gavecharacteristics most nearly like those of an internal bal-ance; wherea

28、s the narrowest cover plates gave characteristicsmore nearly like those of the uncovared sharp-nose balance. .Vlith a sealed gap at the nose of the balance, the pres:sure on that” part of the balance nose under the cover platesis expected to be the same as that existing on the airfoilsurfaca at the

29、rearward edge of the cover plate The dis-tribution of rasultant pressure over the surface of an air-foil in two-dimensional flow is discussed in reference 6.From the experimental data prosonted in this reference, itcan be seen that tho rata of change of rasultant pressure.withangle of .ttack increas

30、es toward the nose of the-airfoil andthat the rate of ch:.nge of resultant pressure with flap de- .flection increasas toward the flap hinge axis. As was expectdwith a sealed gap at tho nose of t,he b,alance the balanco withthe widest cover plates, which was effectively vented nearestthe hinge axis,

31、thus gave the smallest value of chff andthe largest value of Chfa (table 111), The” balance with .Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-10. .-the narrowest cov”er plates! which was effectively ventednearest the airfoil nose, gave the larges

32、t value of chffand the smallest value of ChfaThe, effect of increasing the gap or leak at the nose ofthe balance was to decrease the effectiveness of the balanoe (fig. 21). l?or the balance with wide cover plates, both.Chf and chf6f ware considerably increased; hut, for theanarrowest oover plates, t

33、he effect of nose gap was muchsmaller, this arrangement being more nearly like an over-hang without cover plates. Figure 20 illustrates the effectsof a leak through the nose gap on both the lift and the bingomoments of the flap with cover plates of various sizes.The hinge-momont characteristics of t

34、he various sealedinternal balances were computed from the pressure-distribution ,data presented in reference 6. These data were arbitrarilycorrected for change in airfoil thickness by the ratio of thehinge-moment slopes for a plain flap on the NACA 0015 and onthe.NACA 0009 airfoils. The calculated h

35、inge-moment charac- .teristics vere in fair agreement vitb the test results forthe cover plates of various widths when -the pressure actingon the balance was assumed to be that at the rearward-edgeof the cover late.The tast results tend to indicate that the addition ofcover plates over a long sharp-

36、nose overhang to form an in-ternal halanc.e adversely affects the hinge-moment chaacter-istics of the control surface unless the air leak through thenose gap is sealed. This fact was particularly evidant forwide cover plates. The shortest cover plates with the smallest. .nose gap gavo hinge-moment c

37、haracteristics nearly the same asthose of the sharp overhang without cover plates, Subsequenttests indicate that the exact position of the cover plates,thpi is.,whether they. lie exactly. on the airfoil contour orare bent slightly in or out, has a critical effect on thehinge-moment characteristics.P

38、itching Moment .The slopes of the curves of pitching moment as a func- .-tion of lift at constant angle of at”tack and at constant flapdeflection are given in table 111. The aerodynamic center ofthe lift due to angle of attack was at approximately the 0.23c!station for the airfoil having a sharp-nos

39、e flap both with andwithout cover plates. The aerodynamic center of the lift dueProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-11to flap deflection -was at about the 0.41c station for the,.t-17airfoil with cover plates and a sealed gap at the flap n

40、ose.Itith an unsealed gap or without cover plates, the aerodynamiccenter shifted slightly farther rearward. The position ofthe aerodynamic center of the lift caused by changing theeffective camber of an airfoil is a function of aspect ratio(refereflce 7) and moves toward the trailing edge as the as-

41、peot ratio is decreased.Beoause of the unknown tunnel correction, the valuesof drag coefficients cannot be considered absolute; therelative .values should, however, be independent of tunneleffect. No drag measurements were made on the blunt- ormodified-nose balances but their minimum profile-drag co

42、-efficient values will probably be between the value (refer-ence 2) of 0.0135 for the 0?50cf blunt-nose balance and thevalue -of 0.0162 for the sharp-nose balance without coverplates,The addition of the cover plates reduced the minimumprofile-drag coefficient as was expected (fig. 22). Theprofile-dr

43、ag coefficient dscreased as the cover plates weremade widerO presumably because the break in the airfoil con-tour between the cover-plate edge and flap hinge axis be-came smaller, The airfoil with the straight-contour plainflap had a minimum profile-drag coefficient of 0.0131 withgap sealed or uns.s

44、aled (reference 8), Trom these resultsit is apparent that tho addition of cover plates over along sharp-nose overhang does decrease the minimum drag ofthe uncovered balance, The shot cover plates reduce thedrag of the sharp-nose balance to a value which is nearlythe same as that of a hunt-nose balan

45、ce of the same size,Ilide cover plates give a still greater reduction in drag.CONCLUSIONSThe results of tests of an NACA 0015 airfoil with astraight-contour flap having a dhord 30 percent of the air-foil chord and several flap-nose overhangs 50 percent of theflap chord indicate the following general

46、 conclusions:1. The addition of cover plates over the nose of aflap having a long overhang of sharp profile materiallyProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-12. . .reduced t,e drag. as compared with that of the uncoveredoverhang; the reducti

47、on in drag was greatest for the widestcover plates. Lk2. lYhen the gap at the nose of a long sharp overhangwas not sealed, the addition of wide cover plates increased ,the slope of the lift curve. With the gap sealed, howeverpthe slope should be nearly the same with or without coverplates.30 All arr

48、angements of cover plates tested materiallydecreased the slope of the lift curve with controls free ascompared with that for the sharp-nose flap without coverplates. The addition of cover plates should, therefore,decrease the control-free stability of an airplane withcontrol surfaces having a long sharp-nose overhang”,.,s, .,”.- . .for Aeronautics.-T-T- -.-; - -=TT -” - . . . . _ ._, :-,cono.or f/gn of on NA CA 0015 oirfoilProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-