Wi’’lrlmll lum)mORIGINALLY ISSUED

Septeniber1944asAdvanceRestrictedReport~12’j

A FLI~ IEVESTIGATIOEOF THE EFFECTOF SUKl?ACEROU_SS

ON WING PROFILEDRAGWITH TRANSITIONFIXED

By JohnA. Zalovcik and ClotaireWood

LangleyMemorialAeronauticalLaboratoryLangleyField,Va.

NACAWASHINGTON

NACA WARTIME REPORTS are reprints of papers origimlly issued to provide rapid distribution ofadvance research results to an authorized group requiring them for the war effort. They were pre-viously held under a security status but are now unclassified. Some of these reports were not tech-nically edited. All have been reproduced without change in order to expedite general distribution.

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31176013639076

NACA ARR No. ~125 “

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

ADVMTCE RESTRICTED REPORT

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A FLTGHT INVESTIGATION OF THE EFFECT OF SURFACE ROUGHNESS

ON WIN(3 PROFILE DRAG WITH TRANSITION FIXED

~ John A. Zalovcik and Clotaire Wood

suMMAI’iY “

A f’llghtinvestigation was made on a wing section of& F’-)_L7Dairplane to deternlr.e the effect of rau@ness onwing profile drag with transition fixed far forward.Surveys of the wake were made for two surface conditionswith transition fixed ‘bya thread at ~ percent chord backof the leading edEe on the upper and lower n.mf’aces. OneOf the S’JI’V6YS WLIS it23G9 with thd surfaces smsoth: the othersurvey was made with the surfaces r~ugb*ened by an appli-cation of ca.mo~~fla~ep~lnt beMnd the tlmewi. The surfacerm@ncss nrodllced by the camouflage ~aint was made upof’particles of cbout 0.0012 Inch in height and numberingroughly ,40,000nbr square Inch.

The results of the invtistigation Indictited that theraughness lncreascd the tarbulent skin frictian by anamaunt corr~?sp3nd.in3to an incredse In sectiionprcfile-drag coefficient of 0.c)o13,or 16 percent, ct a lift

coefficient of 0.16 and a HeynsIds numb~r of 17 x 106.Below the Mach number at which shock occurred, variationsin Mach number of as much as 0.16 appeared to have noa~preciable effect on the sectian prof:le-drag co~fficientsof either the sm’>oth.or rou~hened surfaces with transitionfixed.

INTRODUCTION

The results of tests reported in references 1 and 2indioated that roughening the external surfaces of anai.rnlanemay cause large increases In drag. In order to

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2 NACA ARR NO. L4125

provide further Inisormation, a brief Investigation wasmade of’the effects of surface rouglmess as one n~se ofa series of flight test~ to detemnine the profile-dragcharacteristics of the wing of a P-1:.7Dairplane. Thetc”jtscsnsisted af surveys of’the wake of a wing section,with trar.sitton fixed on t-neu~ner md lower surfaces bya thread at 5 percent oi’the c~mrd, for two cor.ditionsof’the surf’aces. One of the sur-.’eyswas made with thesurfaces smooth; the ohher sur-;eyvas made with thesurfaces roughened by an application ot’camouflage paintbehind the t:hread. In addition t~ the effects of roughness,some information on tke ei’fectso: comarcssibility or~profile drag was obtained.

Measurements were made in lev~l flight and in divesat altitudes of 12,000 and 2)4,000fcet,and over a rangeof indicated airsnced of’from 150 to 300 miles Fer hour.The lift coefflciants obtained in the tests ringedfrom 0.12 ta 0.68, the Rcynalds numbers ringed

fro~ 8 x 1C6 to 20 x 106, and the L!hch numbers ra~edfr~m 0.25 to 0.75.

APPARATUS AM TEST’S

The Investigation wns conducted on a ri@t tiin~section of a P-~7D &lr~lene (figs. i and 2). This v:ingsection, a Rsnubllc S-3 section, kd a chord of8S.05 incl.es,a thickness of il.-oercentof tilechard,and was located at 63 nercent of the sem:span fram theplane of sy.nmetryor ab~ut 2 feet outboard a~ the flup.At tbls spanwise station the test ~oction was outboardof the pronellcr slipstream, the gun gorts in the leadl~e~e, and the &hell ejector S1OLS in the lowur surf’tice.The ordinates of the section are given in table I. TheRqmblio S-3 seetion tested has pressure-ciistribut!loncharacteristics similar to tho~e of the NACA 23011 airfoil.

Surveys of the wake were made for two surfaceconditions of’the test section wltk transition fixed bya Ehread at 5 ~ercent chord back of tho leading edge onthe umer and lowe~ eurfaces. One cf the aorveys wasmade with the surfaces omooth: th~ ~thor survey waa madewith the surt’’acesroughened bf-hind the fixed transitionpooition by an annlicaticn of ca~.ouf’lagepaint. Thesmooth surfaces were obtained by fairlng the various

— .—,. —. ,—— —-urn- . . . Ilmmm mm mm mm

NACA ARR NO. LLu25 3

surface irregular lt~es with glazing putty, aaplylng, several coats of white lacquer-based paint, and sanding

In a chordwlse dlrectian with No. 320 Carborundum paper.Transition was fixed at 5 percent of t?aechord by meansof a thread 0.036 inch (or 0.(.)42-,?ercento.fthe chord)in diameter, taped snanwise to the surface. This threadsize, according to the results of reference 3, Is greaterthan the minimum size necessary to fix transition at5 Dercent of the chord for all test conditions of thisInvestigation.

Profile-drag measurer,ents wem made with a wake-s-.u?veyrake (fig. k) located 15 uercent of the chordbehind the tralli-ng edge of bhe test secti~n. ;Vak2totaland static pressures, free-stream imFact pressure, Endthe positian of the right aileron were measured withNACA recordi~ instruments. T%e section proi’ile-dragcoefficients were determined by the Integrating methodof reference 4; that is, the total-prsssure loss wasintegrated across CM wake and then multiplied by factorsdepending on f’ree-stream impact pressure, maximum total-pressur~ loss, static pressur~ in tlzewake, and flightMach nuuber. Wool tufts were used on the upper surfacenear the trailing-edge area about 2 feet on either sideof the center line of the test s~ctlon to determlno .

4 NACA ARR NO. 4125

whether any cross flow existed in the boundary layerthat wo~ld invalidate the wake surveys.

The tests were xade in level flight and in dives atalt~tudes CP 12,000 and ~,OGO fest and over a range ofindicated alrsneed from 150 to 560 miles per hour. Thelift coefficients obtained in the tests ringed fr~m C.12

to 0.68, the Reynolds numbers ranged fron 9 x 106

ta 20 x 106, and the Mach numoers rcnged frm 0.25 to ~.73.

RZSIJLT3 AND DISCUSSION

During the tests the waal tuft% on the win~ surfacewere obser~ed to trail streignt back and thereby indicatedthat the wake surveys we?% not influenced by cross flow.Tne right aileron was round t~ be defleckcd from aoproxi-rnately 0.75° Im 1.5°downward. This mall variatlcm inailel”cndeflection was believed to h&ve no a~nreciableeffect on the prof’~le-drag coefficients measured.

for the tvio sdrface conditions are plotted against airplanelift coefficient CL in figme 5. Tkc correspondingvalues ~f Vach mmbcr i+ , F.eJnsl~s mmber R, an~inilicatsd airs:)eed ~;is are ~lottod a?mv~ the prai’ile-

dra~ curves. ~ndicated airs~e~d Vis is defined JS thsreading of an fil.rspeedIndicator of standard calibrationc~r~ected for positicn error of the tiirs?eedheed.

Frm figure 5 It mav be seen that roughening thesurfaces Increased the section profile-drag coeffic.lentby 0.0013, or 16 ~ercent, at a lift coefficient of 0.16,and a Reymolds number of 17 x 10b. At a lift coefI’icient.of 9.65 and a Reynolds niiber ~f 8 x 105, the increasein section rmofile-drag coefficient was 0.0008, or8 percent. Inasmuch es transition was fixed at 5 percentof the ch~rd, these lncrca~es h section nrofile-dragcoefficient are believed to be causad by increases inthe turbulent skin-friction coefflci~nt.

Although a ccmnarison of the fli~ht results of thepresent tests with the results of ref~rcnce 1 wasconsidered desirable, no direct comparison was possible

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NACA ARR NO. tiL125 5

because the correction of the results of reference 1 formovement of transition could not be determined.—

The total-presst~.reloss across the weke for therou@ened and smooth surface conditions is presented infigures 6 and 7, respectively, for several Mach numbersas a plot of AH/q. against y/c, where AH is theloss in total nressure at position y in the wake, qc

is the free-stream imnact nressure, and c is the chordof the wing section. The total-pressure lossat y/c < 0.023, beyond the limits of ths wake-surveyrake, was estlmeted from wake surveys made in other testswith the rake extended.

The wake ‘~rof.tiesshow that compressibility shockoccl~rred on the upper surface, as lndicat~d by the rapidIncrease in width of the wake, at a Lath nuxocr between0.68 and 0.69 at a lift coefficient of 0.15 f?r theroughened surfaces and at a Mach nuwb~r sor,ewhatlessthan 0.71 at a iift coefficient of 0.13 for the smoothsurl’aces. It Is estimated, h~wever, that at a liftcoefficient of 0.15 shock wouid occur at about the sameMach number (between 0.6~ and 0.69) for the smoothsur:aces as far the r~ughened surfaces. Tkis estimateis based on the varlatisn with Mach n~mhor at variousllft coefficients o? the total-nressure lCSS due to shockat msitlon y,lc= 0.023 in the wa-~esof the snooth andra’u,~henedsurfaces. The formhtion of’shock is reflectedin a ranld increasa in sectian uroi’lle-drag coef’fislentfar the smooth ~nd roughened surfaces in figure 5. AtMach numbers below that at which shock occurs, variationsin Me.chnumber of as much as 0.16 a~pear to have noannreciable e~fect sn ths sectlcn orof’ile-drag coefficientsof either the smooth or roughened surfaces.

C@MLUIHNG RENARKS

The results of the investigation toeffect of roughness on wing nrof’ila dragfixed far forward indicated that surface

determine thewith transitionrau@ness made

up of particles of about 0.0012 inch in height andnumbering roughly 40,000 ner square inch increasedthe turbulent skin friction by an amount corresponding toan increase in section aroflle-drag coefficient of 0.0013,or 16 uercent, at a lift coefficient of 0.16 and a

6 NACA ARR NO. L4.125

Reynolds number of 17 X 106. Below the Mach number atwhich shock occurred, variations in Mach number of asmuch as 0.I.6 appeared to have no apDi%ciable effect onthe section profile-drag coefficients of either the smoothor roughened surfaces with transition fixed.

Langley Memorial Aeronsutlcal LaboratoryNational Advisory Committee for ~oronautics

Langley Field, Va.

1. Hood, lianley J.: The Effec~s of Scm.eCorm,on SurfaceIrreLulai-!.tiesan “Jingi)rti~.NACA TN NO. 695, 1939.

2. %lalt, R., and Hi~tcn, U. J.: Meacuremcnts nf theDrag of Rcn]gh ?ainted Surf&ces on a Khstang.Eep. l:a.Aera. 15~9, I\.A.Z., AU~. 19&3.

3. ?)kvison, F.: Nets cm the Use of Threads for SnsuringForw&rG Transition ~n a i!lng. B.A. Dept. Note -WifidTunnels N3. L2~, R.A.E., Jan. 15)@.

~. Rllvergtein, A. , and Katzoff, S. : A siifl~lifl~d Methodfor ~~terqlning Wing Pr2filc DraG in ~light. Jnur.Aer~. Sclo, val. 7, nc. ?, ?iay 1540, pp. 295-3U1.

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NACA ARR NO. U125 7

TABLE I.- ..- -. .

ORDINATRS OF EEPUELIC S-3 WING SECTION TESTED ON P-47D AIRPLANE

rAll values given In fractions of chord; ordinatesieasured relative tc an arbitrary chord and withinboard trailing edge of aileron in line with trailingedge of flap]

—— —-

Stati3n

0.0125● 025.C5.C75.10●15.PG

.901.00

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NATIONAL ADVISCllYCOWMITTE!l IUllAER’3NAUTICS

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Figure l.- P-47D airplane used for tests.m

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NACA ARR No. L4125 Fig. 2

Figure 2.- Test section of wing of P-47Dairplane with smooth surface.

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NACA ARR No. L412!j Fig. 3

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Figure 3.- Microscope with prism at”tached to base used inmeasuring surface roughness.

NACA ARR No. L412!j

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Figure 4.- Wake-survey rake installedon P-47D airplane.

Fig. 4

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NACA ARR No. L4125 Fig. 5

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Profi/e-drug coefficients for smooth and rouqhene~:~rofrudces with transit 1on fixed Ot 5 perc@n +

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