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ORIGINALLY ISSUED July 19k4 as AdvanceConfidential ReportL4G12 EFFECTOF COMPRESS~lUTY CN PRESSURE DISTRIBUTION OVER AN AIRFOILWITH A SLOTTEDFRISE AILER~ By Arvo A. Luoma LengleyMemorialAeronautical Laboratory LengleyField,Va.
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NACA WARTIME REP,ORTS are reprints of papers originally issued to provide rapid d.ktribution of advance research results to an authorized group requiring them for the war effort. They were pre- Some of these reports were not tech- viously held under a security status but are now unckssified.
nically edited. All have been reproduced without change in order to expedite general distribution.
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NACA ACR NO. d+G12 “ NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS .-. - ... . . .. . . . !.. . ... - - ADVANCE CONFIDENTIAL REPORT HT!ECT OF COl?FRESSIBILITY ON PRESSURE DISTRIBUTION OVER AN AIRFOIL WITH A SLOTTED FRISE AILERON By Arvo A. Luoma SUMMARY Complete pressure-distribution measurements were made over an airfoil w:th a slotted Frlse aileron for Mach nmbars from 0.2~ to approximately 0.76 for various airfoil angles of attack and ailercn deflections.
Sec- tion characteristics were determined from these pressure data.
TIIO tests showed a los3 In aileron rolllng Dower for aileron deflections from -12° to -l$G. At high diving spaeds, a decrgase in tk.grate of rol-1 can be expected because of a loss in aileron effectiveness at “ci?ese speeds.
Aa/A6a High stick forces fcr non- diffe~ential aileron do~lecticns at high speads were indicated; and, owing to a ter.dent: of the upgoing atleron to overbalance, serious control difficulties As a reSUlt of at high diving speeds may be expected.
the present data, the Alr Force specifications for the calculation of’aileron loads have besn revioed to take into account the actual loads at high speeds as shown bv these data.
INTRODUCTION Flight tests to improve the aileron characte??lstlcs of the P-47B airplane had already bean started by the NACA when serious structural difflcvlties of the ailerons ware encountered by the RepublZc Aviation .Corporation In the flight tests of a F-47B airplane. The present tests NACA ACR NO.-I@2 in the RACA &foot high-speed tunnel-were then inaugurated to determine, specifically, the loads on the ailerons of the P-&7B airplane -d, generally, the effects of com- pressibility on the aileron characteristics. An aileron model based on the winq of’tke XP-~73 airplane was tested and the aerodynamic characteristics of the ai.r~oil and the allsron were determi.r,ed l’rom complete pressure dis- tributions over the main portion of the atrfoil and the atleron, The tests-were made for Mach nuubera from 0.25 to a:~proximutely. O.76 and included various w~ng an~les of attack mid aileron deflacttons.
SYW30LS The term ‘airfoil” 1s hereti ussd to mean the combination of aileron *d the lnaln portion of the air- “ The term “aileron aln~letf refers to the chanac- foil .
teristic8 of the aileron in t].ePresefic~ of tkle main portion of the airfoil. Aorociianic coefficients and other symbols are defined as follcws: a angl”e of attack v velocity iriundisturbed strefm local static prescure ct a potnt on atrfoil section ‘ p static pressure in undisturbed stream Po mass density h “undisturbed 3tream P a speed of sound in undisturbed stream .
dynamic pressure in undisturbed stream ;P’3 “ q () P-PO pressure coefficient P q () \ M&ch number M (v/~) aileron deflection; positive for clown deflection f3a ..
Ca total chord of aileron (sac fig. 1) chord of main portion of airfoil (without aileron) CM Cw chord of’airfoil (with aileron) ,.
.
..
.— NACA ACR No. I)+G12 x distance along chord from leading edge of airfoil or alle~n, -. ... . . ... . . ,.
hinge-axis location along chord from leading edge ‘ha of aileron hinge-mds location along chord from leadlng edge .
. ‘%
of airfoil distance nomal to chord Y hinge-axis location normal to chord yh - Subscripts: cr when local speed of sound has been reached on some point on airfoil section upper surface of airfoil. section u L lower surface: of airfoil section ahead of maximum ordinates of aileron ah r to the rear of maximum ordinates or aileron max maxinwm .+ . .
mln minimum section r.ormal-force coefficient of aileron alone Cna from pressure-distribution. data ‘a= +Jca (PL - ‘u) ‘x section normal-force coefficient of main Dortion cnrn aileron) from presiure- of airfoil (without distribution data P~ - Pu) dx ( section norma3-force coefficient of airfoil (with cn~ aileron) from nrossure-distribution data; component of total normal-force coefficient due . . ..
---- ——-. . .
.—— —— .-— — .-.
.— .. . . ... —. .-— -1 . .
NACA ACR No. L4G12 to aileron clvmdmforce ne~lected; maximum absolute error thus introduced only about 0.01 cn=— + cat+ COS 6a q!cn Cw
w )
d ‘a
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s.ectlor, chord-force coefficient of aileron alone cCa frm preflsure-dist~”itutioz; data
= (&)’[~co- @J - FL)(x - ‘he) -
Cl?a .
. .
,.
l— NACA ACR NO. I@2 o “ sectlan center-of-pressure coefficient of aileron cPa malone (ratio of’distance of C.pfi- of-a$ler.on .-..
m -- from L.E. of aileron to total chord of aileron) APPARATUS AND TESTS The tests were made in the NACA 8-foot high-speed which is a single-return, circular-section, tunnel, closed-throat wi:-,d tunnel with tileairspeed continuausl controllable h an approximate Mach number range of 0.1f to 0.75.
The model used in these tests was a 2&lnch-chord 10.5-percent-thick airfoil with a slotted Frise aileron, was of uniform section, und spanned the tunnel. The main portion of tineairfoil :]assed through the walls of the tu.nel in a manner typical of model installation in the NACA ~-foot h~gh-speed tunnel and, to permit deflec- tion of the aileron, a gap of 1/16 inch was included between the ends of the hilero~l and the tunnel walls.
The dimensions o: the model section were obtained by reduci:~ scaled dinensicms of the vfln3 of the P-.47B-5 air.~lan~ at the midsection of tke aileron. (See fig. 1 .md tablas I and II.) SuI’ficiant static-?ressure orifices were located on t% main portflon of the ~;mdel and on the ailaron to deta.mine Lhe conplete pressure distribution over the airfoil.
Static-pressure measurements were made for Llach numbers from. 0.25 to approximately 0.76 for various air- At the foil angles o~ attack ard aileron deflections.
higher speeds, the range o? mgle of attack was limited by structural load coasi.deratlons. The ~ests were made with aileron daflectlons from -19° to 16 .
Simultaneous observations of the static pressures acting over the air- foil were obtained by photo&raphing a multiple-tube liquid (tetrabromethane) manometer.
RESULTS The aerodymndc force ad moment data presented herein were determined from mechanicQ inte~rati.on of diagrams of pressure coefficient P plotted against L —.- —.
NACA ACR No. 14212 chord for pressures over the upper and lower surfaces of airfoil and of the aileron. At the main portion of’ the the highest speeds, some of the peak negative pressures exceeded the range of the manometer bo~-d and consequently were not obtained; in these cases, however, the falred pressure-distribution plots with the peaks estimated are believed to ylald data sufflclertly accurate for mgl- In order to illustrate graphically the ne3rlng purposes.
nature of the pressure distribution over the airfoil, a few of the preseure diagrams are inciuded in figure 2.
a has been corrected for me wing wqgle of attack model twist arx3most of the aerodynamic coefficients are plotted against this corrected cngle of attack with aileron deflection 8a as a parsmter. Cross plots of the aaradynmcic coefficient against aileron deflec- tiOIl C!a have been r.mde iron the basic dRta for several values of Mach number. In this report the aerodynamic which nre derived from pressure-distribution coefficients, data, can be taken as saction characteristics.
Airfoil section l’?OI’rlal-l’Oi’CO coefficient C* is plotted againat angle of attnck a at various aileron deflections in fig’ne 3. Gther slrfoi.1 chcracterlstics ~cn~~a and ~cnw/d5a, (slope of’normal-farce curve far normal-force coefficient of’0, and .
angle of’ attack eileron eff’ecti’~eness Au/A5a), based on the data of figure 5, are gtven in ~igureg 4 to 6.
It iS to be noted that the effectiveness patio Ac/L5a is directly proportional to the vclue cf pb/2V at unit aileron deflection fov a rigid WIU in pure roll, where p Is the rste of roll in radiar pm second and b/2 is the semispan In feet.
Rofevence 1 shaws that, for usual rates of ~.ileron application on cu~rent fighter-type alrplsnes, the rete of roll OC +Je airplane wh!le the ailerons are bolng deflected nearly ettalns the till value of’ the steady ratq of roll corresponding to any given alloron deflection. Fl#.me ‘? slwws the section steady rate of roll per degree deflection of single aileron Rr/A5a against Mach number at two altitudes.
The section steady rate of’roll is calculated on the basis that the section rolling r.oment r3sulti~ fron deflection of the aileron is simply balanced by the section damping moment due to roll rind,based on this assumption, the following equation 1s used: I .- . .— -—-— — .,- .
NACA ACR NO. 4.Gl2 ‘?
Where -.
‘section steady rate of rol~l, degrees per second Pf bf/2 distance from plane of symmetry of airplane to midspan of aileron (taken as 15 ft) A6a deflection of single aileron, degrees aileron effectiveness Aa/A6a The curve of section steady rate of roll 1s included (fig. 7 ) to show the nature of the compress i.blllty effects on the rate of roll. For the actual airplane, the rate of roll would be anpreci~bly less than the seotion values shovm becaune aamplng moments are clevel- oped by the entire win~ w.d wins twist is p~esent.
Aileron section hinge-nor.ent-coefftciant data are Included In f’igures ~ to 10.
Figure 11 has data for aileron section center-of-pressure coefficient.
11lus - trativ~ stick-force data based on nondifferential aileron deflections and hir.~e-moment coefficients at airfoil section lift coefficients carrespondin~ to those of the ili.Cllt aue riven In fi~ure 12.
P-L7B airplane In level These data were calculated f’or an aileron llnkage of 1.7° aileron deflection per irich ol’stick mover,ent, an area for tti single aileron 01’13 square feet, an aileron n.ean chord of lC.75 inches, and a hin~e-axis locatlon 25.7 percent buck from the leading ecige of the aileron.
No acco~t has been taken of variation of the section aileron balance along the aileron span or of the effect of three-dimensional flow on actual stick forces.
Data on peak negative pressure coefficient and section cri,tlcal Mach number for the aileron are given in figures 13 ad 14, respectively. Figures 15 and 16 contain ~ileron section normal-force-coefficient data, and figure 17 shows the average aileron section loadlng against Mach number at two altitudes for steady rate of roll.
Figures 18 to 20 have data on peak negative pres- sure coefficient and section orltlcal Mach number for the mati portion of the airfoil. Airfoil section pitohing-moment-coefficient data appear in figures 21 and 22.
Figwa 25 has aileron section chord-force- Onq .- . . . .
‘--+ Pm.kq ——— . - I ..
NACA ACR NO. L@2 DISCUSSION Control Characteristics a decrsase In aileron For a given Mach number, deflection generally results in only a small decrease ?l ~~da in the slope of the normal-force curve (fig. 3) and the effect of this decrease is--tomake the ailerons smnewhat more effective Qt the higher airfoil normal-force coefficients. The rapid rise in slope at supercritlcal speeds (fig. 4) has been shown by plain airfoils that have the maxhnun thickness well forward (reference 2 ). At Mach numbers beyond the range of’the present tests, the typical fall in Elope shown by plain airfoils (reference 2) und attributable to flow ch&ngas associated wtth tlie formction of severe comrprcssion shocks can be Gxpocted. Also ticluded h figure ); is ~Cn#b5* fCl r tho slope of tho normal-force curvo and the sir.ilarity between moderate aileron de~lection, the compressibility effects and those shown by the dcz~da is evident.
slope Frise ailerons are characteristic~ly tiefficient at large up deflections.
The data of these tests indicate ~ actual decrease in rolling-moment coeffic- as shov.m by an increase in airfoil normul-force ient, coefficient (fig. 3) when tho &ilercn deflection is -12~ to -190.
This reduction in rolling changed from efficiency can be explained b~ a cor.sideration of the For a given static pressures acting over the airfoil.
angle of attack, the ail.~ronCormal-force coefficient -120 to -lg~ (fig. 15).
dacrsases as da changes from T’nenorm~l-f’orce coefficient on the zain portion o? the airfoil, howev~r, fncreases for the -19° deflection which are more positive for since the slot pressures, cause an increase in the pressures the -19° deflection, on the lower surface of the main portion of the airfoil forward of the slot to Ubout tke 25-percent-chord The upper-surface yessures over the main location.
portion of the airfoil, in addition, are scnewhat nore -190 deflec~ion and tnts condition negativb for tke further increases tLe normti ~crce of the airfoil main portion. For vhe ~irfoil tested, the net effect of -120 to -190 is ch-ging the aileron deflection from to cause an Increase in airfoil normal torte sirice the increase in normal force over the main porticm O: the airfoil is greater than tho d:]creaso in normal force —.
NACA ACR NO. UQ2 “ over the aileron.
This increase in airfoil normal- ‘force coefficient’results “in’’ a”deera-asb--f~r blllngng- moment coefficient which, Iri terms of airplane control characteristics, means a reversal in control effectiveness.
The effectiveness of the aileron as a means of changing the angle of at back for an airfoil normal- force coefficient of O 1s illustrated by figure 5; and.
it is to be noted that the greater the negative slope of the curves, the more effect.lve the ailerons axe for producing a him rate of’roll. The oi’feet of compressi- bility on the slope is more clearly brought out in fig- ure 6, in wlLicll the nileron eff’cctivenGss or propor- tionality factor Aa/L6a is taken a? th~ average value for aileron daflection~ fror,l -6° to bo. For a constant airfoil norFal-forcf3 coeffici.mt of O, Aa/A6a decreases from 0.435 (tho r.inus si~n is o~.itted) to 0.52, or 2b per- cent, QS the ?Aacl. number is increased fro~z 0.25 to 0.76.
Most of the decroese results at Mach numbars above 0.70, which is approximately the critical itiach n!unber of the main portion of the tiirfoll.
The data sho~Ysome increase in Aa/A6a with inc~ae~se ~rl~.~rfoil r.())?Jfl~-fO~ce coeffi- at a Mach Y.m”ber of G.70, cient; Aa/iEa increases ‘ore.ecoefficient ir.creases 5 percent as the normt.1-.
from O to 0.2. The sipnifictice of Aa/A6a is broup~t shows the variation ViLtJkt Mach out in figure ‘7,which num,ber or thG Soctioii ctea~~r rato of roll per degree aileron def’lectlon.
For Xnch nlu,lbeitn up to 0.4, the rate of roll por degree aileron deflection pl/AEa IS nearly a linear functicm of Mach number sir~ce tho aileron effectiveness AG/A6~ is essent~.ally constant. At Mach numbers above 0.4, however, the r&te of roll increases less rapidly with Xdachnumber owing to the decrease in aileron effectivenes~ until, at the critical Mach number of 0.70, there is actually a decrease in rate of roll.
As was broupjht out previously, the rate of roll of the actual a?.rplane for rigid-viing conditions would be proportionatal~ smaller than the section rate of roll since damping moments in roll are developed by the entire wing.
Wing twist would modify further the rate of roll shown .
The inefficiency of Frise ailerons at large up deflec- tions is borne out by these tests, which show a loss in -120 to -190.
rolling power as the deflection changes from The shift in the ~gle of attack for zero normal ~orce with Mach number decreases the aileron effectiveness at Iii@ speeds; and this decrease may be sufficient, Aa/A6a as in these tests, to cause am actual decrease in the . .
.— , NACA ACR No. 4G12 section steady rete of roll per degree aileron deflection.
The aileron effectiveness Increases somewhat with ati- foil nwnal.-force coeff’ld.ent.
Aileron Hhge-Moment Coefficient The hinge-moinent coefficient for modorate positive aileron def’lect~ons Is essentially !nseasitive to small the v!.cinity of m angle changes in angle of attac?~in wherein the hinga-illoxan~coefficient of attack of 0°, for negative aileron daflectlons decreases with Increasing ~le of attack (fiL. 0). In otheu rorila, the rate of ch~e of hi ,e-?nornont coefficfl.cnt with mgle of attack ACha Aa is prHctlcall~ zsro fOi’noderate positive for negative cleflectionc. A deflections and is negat:vo Ac@c ddrin~ roll introduces a negative vel’ue of hinge-mment componmt that tends to Increasa the total aileron deflection and, tor an ~-.nderbalanced htn~e-nornent componsnt due to aileron deflacti~.1, will decrease the We reduction i.~ sttc!: force due to roll stick force, of the atrplane 1S a deslrsbSe i’eature Wit, for a closely the p~ssibllities of overbalance must balanced aileron, be considered. In ?igure 9, iiChm/&a is tahen as the average of tho slopes for eqllalu; and down aileron def’lecttons SM apjlies for aii’f’oi.l normal-f’oi-ce coeffi- cients from 0 to 0.2. It is fieen tlmt ~cha/Aa becomes more nsgative with (1) increasing aileron deflection and (2) Increasing Mech number for the larger moderate de~lections (*60). The t16crease In Pverqye slope is matnly due to tk.9decrease with Mach number of the slope of the upgoi.w, aileron.
The typical rnpid increase in the hhge-noment coefficient of Frise ailerons at the larger up deflec- tions due to flow separation off Lhe lower surface i.s shown in figme 10. The pr9ssure distributions over the aileron indicate that, for the -190 aileron deflec- tion, the flow ovar the lower surface has completely saparated right from th~ sharp nose of The aileron, with a consequent shift in center of pness~me back to about 59 percent of the aileron chord (fig. 11). The pres- s~e data for the -120 aileron defle~tio~~ also s~w separation off the lower surface of’the aileron but, in this case, the separation is 19ss drastic than with the -19° deflection. Compresslbillty effects aggravate .— .—- NACA ACR HO. 14G12 11 the separated flow of the -12° deflectlo~... Even for the -.. .
:60- ~lel,on ~OflOciion, incipient” a6p&atlon 1S indicated with decreasing angle of attack at the highest Mach numbers. This separation off the lower surface of the aileron at the larger negative deflections with the con- sequent rearward shift in center of pressure causes the l-& inCrOesO in”hi~O-mOment Coefficient Cha at these deflections.
For atleron deflections of -4° and -6o, the center of’pressure moves forward as the Mach number increases (fig. 11) owing to the building up of the negative pres- sures about the nose and the forward portion of the ailerons. For some of the airfoil normal-force coeffi- cients, an overbalance of’ the indlw!dual aileron exists, particularly at the highest Mach numbers (fig. 1O(C)).
For positive aileron del’lectiorm, there is a general rearward movement of’ the center of pressure (fig. 11) and consequently a morg negative hinge-nom.ent coeffi- cient with botk. increasing ailerm deflection and Mach number. For aileron deflections of 12° snd 160, the pressure plots indicate some separation off the rear- ward portion of the upper surfcce of the aileron; this separation is much less severe, however, than the separation off’ the lower surface at large negative deflections.
At high Mach numbers, the ailerono ae limited to small deflections, particular at low altitudes, because of large stick forces (fig. i2 .
Y At a Mach number of 0.525 (400 mph for sea-level conditions) and an aileron deflection of t.40, the calculated stid.c force is 55 pounds. As has been pointed out previously, the calculations were made by assuming the same hinge-moment coefficient for all sections of the aileron, and no correction was made for three-dimensional effects on stick forces. !I!ne calculated section steady rate of roll for these conditions Is 66° per second; the rate of roll would be less for the actual airplane, since the entire wing In roll contributes to dcmping am! the wing Is not rigid. Tests of the Spitfire have shown that wing twist at )+00miles per hour decreased the steady rate of roll 65 perccmt (reference 1).
Alrpl ane speeds In dives approach a ldach number of 0.88 (61o mph at 25,000 ft), and figure 12 shows that aileron difficulties can be expected at such high speeds.
, NACA ACR NO. *G12 . .
At a Qtitude of 25,000 feet md a Mach number of 0.76 (525 mph)~or exmple, the data show a regi an of aileron deflection that ta unstable since the stick force decreama w~th increasing aileron deflection.
i3es1des being unsuitable for well-c”ontral.led maneuvers, this region of unstable aileron characteristics can well lead ttodsg;:;gural difficulties 01’tne ailerons from v~bratim . At speeds beyond those of the teet data, ccntrol difficulties may be even worse.
Fr~se ~~leron rlff’icflt~es For moderate negat~ve Prise aileron deflections, there is a typical ab~upt il.crease of tie aileron peak negative pressure coef~lci9nt in the supercritical repion &nd then a COl~!J~Se ~+ still hiGher Hach nur.ibers as illustrated b~ f’ique 15, which is for an aileron l deflection of’-)+a Z1mn at bkese b.igher Mach num~ers, ‘nowever, a ~cnaeral incre&se of the air loads occars on the f’onvar~ ~orttcxi or tke uilerm with a restilting Increaaed tonc!ency tol~ard ovorbal~.ce.
Although theru may be no net ovorbalsnce of tka co~.blned ailerons, the tendency of tl.eupgcinfl ailgrcn to overbalance produces an unstable stick-i’crcc vnriaticn that C- well lead to furthar control difficulties. The high peak negative pressures and Vie steep cdvarse prcssaw gradient about the nose of a FrIse ailercn at up deflections are in themselves undeslrcble, but equally si~lficant is the fact that the air flow, end hence tke pressure d~stribu- about the aileron nose may be very sensitive to tion, nose shape. small riose-~hape dif~erences resulting from manufacturing irropularities or michamdling in aileron ~ssor.bly or in subsequent operations ccn give rise to appreciable chwges in aileron behavicr, particularly hinge-romer~t characteristics. Variations in aileron riggiqj my s-I.so have an appreciable e~fect on the aerodynamic characteristics of the aileron.
Figure l~; cloc.rly illustrates the bosic charac- teristic of a Frise ailorcn for daflecticns with the nose nrotrud!nE into the air stremn, namely, low aileron criticcl I.!ach numbers uue to hlch negative pressuzzes about the Qileron nose.
A knowledCe of’ the critical speeds of ailerons o? this type is important in determining speeds at which aileron difficulties can be exnected.
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__— . . .
— . . . .
NACA ACR NO. 14G12 13 any type of alle~on balance For hi@-speed airc~af%, ., ‘th~tideper.ds ~or lt~ ope~atlon end balance on the air loads acting about an aileron nose which protrudes into the air stream Is undesirable beer.use of i Es aerodynamic drawbacks.
Aileron Seotlon Loads The present tests briri out the fact that, in the structural design of slotted Frise ailerons, equal con- sideration must be ci.ven the magriltude O? the dcwnloads (See figs. 15 and 16.)
and the uploads on the aileron.
Compressibllit~ has a gr~ater effect on aileron loading tkan fcr positive deflections.
for negative deflections For en airfoil nor-flal-f%rce coeffi.c?.ont oi’ O, the value et m aileron of aileron normel-force coefficient Cn clvanges fron -0.~u toa;0.42 with deflcctton of -6° increase in Mach number I’rcm3.25 to 0.7b; whereas, f’cr an Eileron deflection at’ 6GS the clhm.ge is from 0.25 For an ta 0.29 ‘or the same inmo~~sa.!.n Hach nunber.
Eirfail normal-force coa.ti’icient af 0.2 nnd the sazm Mach numbers, the v~i~~ 01 aileron ncrmal-forco coef- ficient vGri3s frsm -0.2~; to -0.34 f’cr a deflection of’-Lo ?)Ut, for a d~Flec3?.on of’60, it remieins essentially fir Corps speci- csn~tent at O.jO. ‘JTL9 Inc.dequrcy o.0 the ficnti~rm of mfermce 3 for tl.estructural dssign of ailerons js brought out An fiqure 17, which S]1OWS the actual avers~e aileron section loadir?g at twa nltltudes fop airfoil section lift coefficients corresponding to those Of the P-4.7B airplane iilleval fli@lt. By using the Air Corps specifications to caiculate aileron nverage design loads (thoso specifications include a factor of safety of 1.5), values of 112 pounds per square foot for uplo&ds ati 56 pounds per squme foot for downloads are It is quite evident that the actual loads in obtained, high-spaad fll&ht can well exceed bhe calculated values, particularly for downloads.
As a result of the present data, specifications for the calculation of aileron loads as glvon in reference 3 have been revised so that due account i3 taken of the actual aileron loads attained in t-hen~m.al operation of the airplane at high speeds.
Other Alrfoll Characterlstlcs An exmple of the usual type of plot of pedk negative pressure ooefficlent of the main portion of the airfoil ——— — I . .
14 NACA ACR NO. & (312
against Mach number is included in figure 18 for an aileron deflection of OO. For the airfoil tested, the maximum crlticai Mach number of the main nortion of the airfoil for moderate Rileron de~lect~.ons is approximately constant at 0.70, and this maximun Mach number is of course for tne values of ar.gle of attack at which both ui)per and lower surfaces become criticul simltanecusly (fig. 19).
For airfoil normal-force coefficients fnor. O LO 0.2, the u~per surface of the main portion of’the cirfoil is criti- CQ for negative aj.leron deflections and eitiior the lower surf&ce or the uoper slurf’ace ?.scr~.tical for positive aileron dol’lect~.ons (fig. W), The difference in critic~l speeds - hmce, differer.ce in drags - of an airfoil wtth upgoinC a~d downGoinq tiilerons of col~rse afi’ects the yawing tendencies of &n airplane.
Chazzacteristic of ~ilermls w}lichhuve a r]ose protrudln~ into the L!r strean on u~def’lcctions, it is to be noted that tile critical spesd of the aileron may be reached at ~pesds lower tnau LA:?critical speed of the miain portion of +k.eairfo~.l; f’oc exe~pl.e, with an 0 End ~t an aj.rfgllnormal-force ailercn deflectio.~ of -6 coef’ficiont OS O, tke aileron tested (lower surface) becomes critical. at a Mach nlumber or 0.545 whoraas the main pov~lon of’ the airf’oil (upFer tiurface) become3 crftlcal Qt a I!achnumber of 0.~6. For high-speed airplenas, the adverse Gercdy.MIRic effects due to the development of rompi-essior shock oa ailercns of this typo cannot be cverlcoksd.
Th9 rate of cil~n~e of, pitching-moment coeffic~ent with angle Of attack dci~tia gene~til.ly is positiva for all aile~~or, dol’lecticns e;:ce~t at the hiGi~est l,iach n~l-~ers at wh~dl ~il~ d~~e becomes r.e~at~ve for ne~ative aileron deflections (fig. 21).
This ch~lCe in slope in the s“uparcritical region is d~e to ~he rearward shift of the center of pressure cf the uploads on tho rain porticn or the nfl.rf’oil with increase in angle of athack.
Compressibility has a greater effect cn the airf611 pitching-moment coofficlent at ~cde~ata ,msitlvo aileron deflections tilan at moderate necative defloctior.s (fig. 22). Fo1’ the P~si.ti7:~ d~fl~c~ions, tk~~~itc~rlE- monmnt cotifficient consist~nbly decrcasos with Mach number and, for the negative doflsctlons, the pitching- momer.t coefficient Rmerally lncr3astis w:tb. Mach.number except at the highest spe~ds, at which th3 Fitching- moment coefficient decreases.
,. ., NACA ACR NO. I@J12 For ailerms that have. the hinge sxl$ located well -.
below the chord llne, the hinge-moment component due to the chord force may be appreciable. ~ the present tests, this component amounted to about 8 percent for the largest aileron deflections. Figure 25 Is inoluded to show the magnitude and variation of the aileron chord- force coefficient with aileron deflection. These data are based on pressure forces and of oourse do not include skin-friction forces.
CONCLCDIYG REMARKS Complete pressure-distribution measurements were made over an airfoil with a slotted Frise aileron for ~,!ach ntuabers from G.25 to approximately 0.76 for various a’lrfoil ongles of attack and aileron deflections. Sec- tion characteristics detemined from these pressure- distribution measurements indicated the following conclusions: 1. A loss in aileron rolling power was found for “190 , aileron deflections frm -1.20to 2. A 26- ercent decrease in aileron effec- tiveness Au A6a occurred between Mach numbers of 0.25 and 0.76 and, even without wing twist, this decrease would cause an actual decrease in the rate of roll at him divin~speeds.
3. High stick forces for nondi.f’ferentlalaileron deflections at high speeds were indicated.
4. Control difficulties at high diving speeds can be expected because of a tendency of the upgoing aileron to overbalance.
As a result of the rmesent data, the Air Force 5.
specifications for the calculation of aileron loads have been revised to take into account the actual loads at high speeds as shown by these data.
Langley Memorial Aeronautical Laboratory National Advisory Committee for Aeronautics Langley Field, Va.
.
16 NACA ACR No. L)+(312 REFERENCES 1. Mo??wIs, D. E., and Yorgan, M. B.: Aileron Tests on SpltfiYe K.99i#. 5057, S. & C. 1219, Rep. No. B.A. 16u7, R.A.E., April 19!@.
2. Stack, John, and von Doonhoff, Albert E.: Tests of 16 Related Airfoils at High Speeds. NACA Rep. I~c. !I.92, 1954.
5. Anon.: Stress!Analysis Criteria. Air Corps C-1803-.A (foz%flerly X-1505-A), Speclf’icat+.cn No.
170v. 15, 1958, an~en’li~ D, ~. 8.
d+m2 17 NACA ACR NO.
TABLE - I .- ..
..- .- .
ORDINATES FOR mm PORTION OF AImOIL (\’iITHouT AILERON) model of section of P-k7B-3 wing taken PMn. -chord e.
through midsection of slotted Frlse kile=n; stations and ordinates in in. from airfoil L.E.
and chord line, respectivel~ Ordinate ~d nate Lower Station Statlo~ Unper surface surface 1= - o 9.53 .03 .15 10.10 10.6 11.3 3 i :; lz.-q -.32 -.~u
1~ .24
1.(-)C -.J}3 15.)}5 1.12 lb,25 -.47 1.2.2 -.51 1.6.65 I 200a 1.30 16.73 .E42 ‘.1;.9 ‘5 -“1 16.93 2.38 .20 -=!j~ -943 I 2.67 -.42 17.0s .;; -.20 I 2.97 -.66 17.25 .01+ 5.27 l.ji -.69 17.38 .20 :75 .56 -.71 . q 17.>2 .31
1“54
.16 1.59 -m 17.07 .
i ; l ( 1.?)2 i .
17.E12 1:85 z 5.3 J! $ 1 897 :4 -.89 i 1 .12 .50 z 6.53 1.63 18.27 .64 7.13 1.62 .63 18.42 l 5 .72 1.60 18.56 .61 ?
“5 z .32 18.73 .56 1’57 8.91 18.7b ? .58 1“54 95 L.E. radius: 0.].8 Slope of radius through end of chord:. 0.100 3hroud trailing-edge radius: 0.01 NATIONAL ADVISORY CONMITTEZZ FOR AIX30NAUT1CS ..— — — . .
.—.— ——. —— “ . .
TAJ31XII , ( OI?DIHATES FCR AIIJ3R(!Y ALOIE I-h. -chord model of section of P-~7B-3 Winp ta”kenthro mldsection of;
pL
slottad Frise aileron; Grdlnates in in. from chcrd lin T Iiece Tall tece I Ordinate Station Ordinate!
- (ti. from (in. from (in. from Lower Upper airfoil aileron aileron surface surface II-E- ) L-E. ) L.E. )
E
i7.& o 19.75 2.21 0.4s -0:2 -O*43 -Cup 17.55 .01 -.40 ly.?o ‘6 2.> ?
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-.$; -.02 21.3~ i .27 .b3 ~; :14 -. 1 .56 .07 21.tJ .23 -.+ -.1:1 21. 9il -. 1i .lb l 20 4.44 .88 22.28 .17 -.12 18.42 , ‘5 ‘ -.O h.74 : gl -.zd 1.02 22.57 5.03 l 13 -.10 18.56 5.33
-. 22.87 .10 -.08
18. ~ 1.17 :; ;
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23 .~7 5.63 -.06 18. 0 .07 J 1.72 -.04 . 23.k7 .05 19.01 =:34 t lo 7 45 I 5.93 -,33 -19.16 1.62 .48 2 .76 6.22 .02 -.02 IJ 6 .~ 0 0 .00 19.71 -*3Z 1977 .49 ;.% .50 -.jl 1 19. 6 -,~(,) 19. () .0 t -.29 1.0 2:16 i l 9
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