REPORT No. 718.-

DISTRIBUTIONOVER AN NACA 23021AIRFOILWITH A SLOTTED AND ASPIJTFLU?

slmfMARY

By THOMASA. HABBXSfind JOHN G. Lowxtr

A vre~edieti”bution investigation ha% been con-ducte~ in the IVACA 4-~ 6~oot ;M”cal un”ndtunnel todetemine the air loads on an iVACA 4?30$1 airfoil incombind”on with a 5Y6.66-percen&ohord810tted&p and aW-percent-chard @it @p. Preeeuree tie rneammd onboih the upper and the lower eurfaoes of the main airfdiland the &pa for 8e?era.1trngle8 of attack and a4 8ecmdjfap 8e#ing8.

The data, presented aapressure diagmme and m graph%oj the 8ection coejlicient8for the @p alone and for theairfoil+lap combination, am applicable torib and&p de-sign for a combindion of a thick ai@i.1 and a slotted ora @it jfap. l%e re8u[t8 of prm”oue ieste of an NACABOlfi ai&il with a slottedflap are mmpared with thepreeent results. ~i8 CO?IIpatiO?t8houxd: l%e &pnormal-force coejk+nt8 were approm”mateiythe same athigh angle8 of atiack. lh jlap gn”tching-momentcoefi-m“entswe approximately the same for the range teeted.2’7ie chord-force coejtcient8 for tti jlap on the NACA%9091 a@bil were genemll~ 8tight~~higher than for theflap on the NACA 9S019 aitfd. Z%arwhfor the split

&p Were about the 8mne CMfor prm”ou8 ieet8 of 8plitJap8 on thinner ai~i.

INTRODUCTION

The National Advisory Committee for Aeronauticsis undertaking an extezmive invWigation of variousairfoiI-flap combinations to furnish information applic-able to the aerodynamic and thestruotural design of high-hft dsvioee intmded to rnorease the safety and the p-formanoe of Sir@nes. One of the promising arrangement.s is an airfoil in combination with a slotted flap.Data are available for aerodynamic and structural d-sign of 12-paroen&tMok airfoils in combination with aslotted flap, but little data are av&lable for the designof oombinatione of thiok airfoils and flaps. The preemtinvestigation was oonduoted tQ add load data to theaerodynamic data already available (referenoe I) and toexhmd the data for loads on slotted flaps (references 2and 8).

Some form of split flap is cmnmordy used at present.Aerodynsmio information ie available for the S@ flapin oornbination mith airfoils of sevd thiolmesses (ref-erenoe 4); but most of the load data for w@&p com-binations are for thin airfoils, suoh as the Clark Y and

the NACA 2212 (refenmoes 5, 6, and 7). The presentinvestigation will furnish load data for the split flap incombination with a thiok airfoil.

The present pressure-distribution tests vmre pmde ofm NACA 23021 airfoil in combination with the 25.66-peroenkhord slotted flap 2-b (referenoe 1) and the20-peroent-chord split flap (reference 4). Teds weremade at various angles of attaok and flap settings.

APPARATUSAND TESTSMODEM

The airfoil model used in three tests had a +Lfootspan md a 3-foot ohord; it conformed to the NACA23021 airfoil profle and was constructed of laroinatedmahogmy with a hollow seotion to accommodate the . . .oopper pressure tuba. The baeio model, whioh eon-sieted of the airfoil in combination with a fuil-epanslotted flap (fig. 1), was furnished with a mahoganytiller bloc-kwhioh fitted the slot entry in the lower swface so that a smooth airfoil was formed. The slottedflap was attmhed to the airfoil by tww hinges looatedon the tips of the airfoil. The full+pan split tip wasconstructed of quartsr-inoh plywood and was attachedto the airfoil by several braces equally spaced alongthe span.

The full-pan slotted flap (& 1 (a) ) was developedby the NACA and is designated 2-b in reference 1.It has a ohord of 9.238 inohes (26.66 peroent of theover-all airfoil chord). A full+pan metal lip Iooatedon the upper+wrface trailing edge of the &foil sotsas a partial seal when the flap is undsfleoted and direotsthe flow of air over the dtieoted flap. The path ofthe flap nose (@g.1) is the optimum one reported inrefersnoe 1, where the nose of the ilap was defined asthe point of tengenoy of 8 linenormal to the airfoilohord and tangent to the leading edge of the flap inits neutral positiom The flap wes arranged for look-ing at downward, or positive, flap direoticme.

The spIit flap (fig. 1 (b)) has a ohord of 7.2o inohee(2o peroent of the over-all airfoil ohord). The leading ‘“edge was sealed with plaetioine for all tests to preventany leakage. The flap waa arranged for looking atdownward, or positive, @p datleotions. The flapangle8 ware measured from the lower surfaoe of theairfoil as shown in @re 1 (b).

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The model wss mounted in the olosed ted motion of ‘be NACA 4- by 6-foot vortioal wind tunnel (referamms .and. 10). Booause the modeI oomplet~ spanned theTho modsl waa fitted with a shgle Ohordwb.mw of

pressure osiiha at the midspan looated as shown intable I and figure 1. A single row was used beoausethe resuh of the teets of.refereuoe 8 &owed oqp to besufficient. Tubes leadjng from these otiow worebrought out through one ~d of Lhe wing (tig. 2) snd

unnel exoept for small olesranoea at eaoh end (J&. 2),he iiides of the tunnel aoted as ad plates and approxi-:,-IakJY Wudimtmaional flow ma obtained. Torauoub&”att-aohed to the bslanoe fm.me held the mo&J. .igidl~ and also smved ss a conduit for tbe prewro

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tubes. The angle of attack was set from outside thetunneI by rotating the torque tubes with a calibratedelectrio drive.

TmTsThe tests were run at an average dynamio prwaura

of 11.05 pounds per square foot, corresponding to anaimpeed of approximately 66 miks per hour and to anaverage Wt Reynolds number, based on the chord ofthe airfoil with flap fully retracted, of about 1,840,000.The effeotive Reynolds number R, was about3,660,000 and is equal to the ted Reynolds numbermultiplied by the turbuhme factor, which is 1.93 forthe 4-by 6-foot vertical tunnel.

The model was tested with the slotted flap deflectedfrom 0° to 60° in increments of 10° and the split flapdeflected from 0° to 76° in 15° hmmmnta. The testswere made through an angkwf-attaok range from zeroto approximately maximum lift in 4° increments.

With the model at a given angle of attack and flapsetting, time was alIowed for conditions in the tunneland for the manometer to become stable before Lhepresmwea were recorded.

PRESENTATIONOF DATAP-UEE DIA(31UME

All the diagrams of pressure over the upper and thelower surfaces of the combination me given as the ratioof the atatio prtwsure p at a point, or an orifice, on theairfoil to the free+tresm dynamio pressure g for theindividual flap and angleof-attack settings. Presamwover the airfoiI in combination with the slotted flapare shown in figures 3 to 13, and premuree over thesplitdlap combination are shown in figures 14 to 19.A comparison of the loads on the plain airfoiI and theloads on the airfoil-flap combinations for the same liftand a~e of attack is shown for three flap eettinge in&urea 20 and 21.

In@uree3t08, the pmsmres over the main airfoiIare plotted normal to the airfoil chord and the pressuresover the slotted flap are plottbd normal to the flapreference line. The flap reference line is a line throughthe nose point of the flap and parallel to the main airfoilchord line with flap neutral. In figures 14 to 19, thepreeeur~ over the airfoil and the split flap me plottednormal to the airfoil chord but the flap preesuros areplotted from an imagina~ flap chord line. This ima-ginary &p chord line is the deilscted-flap chord linemoved normaI to the airfoil chord line until the lead-ing edge intersects the airfoil chord line. The ima-gina~ flap chord line is not ehowm because it wouldonly complicate the figures.

coEmKmwrs

The pressure diagram were mechanically integratedto obtain data from whioh standard section codicientewere computed. Where the term “flap alone’J is used,it refers to the forces on the flap in the presence of the

main portion of the airfoil. The section coei%cienteme defined as follows:

Cll”=ZJJQC normal-force codkient of airfoil withflap

C.I=nffgcf normal-force coefficient of flap aloneC%=mW/q& piu-mommt ccndlicient of airfoil .

with flap about quarter-chord pointof airfoil with flap neutral

G,= mr[qc$s pitching-moment coe%icient of alottedflap alone about quarter+hord pointof flap

c.r=hf[qc~ hinge-moment codkient of split flapalone about leading edge @nge axis)of flap

ce,=xf/gcf chord-force ocefMmt of slotted flapalone

(c. g+= (Om~5-alXIO0 ~tmf-Pr=we hca-

()(c. p.)~ 0.-: X1OO

(c. p.),=– : )(100r

tionof &foil with flapin percentage of airfoilchord from Ieadingedge of airfoil

cent+x-of-pressure lcca-tion of slotted flapalone in percentage offlap chord from lead-ing edge of flap

oenter-of-pressure Iota-tion of split flap alonein pmcentage of flapchord from leadingedge of flap

where the forces and moments per unit span are:na normal force on airfoil with flapnf normal force on flap alone normal to chord of flapm= pitching moment of airfoil with flapm~ pitahing moment of slotted flap aloneh, hing moment of spIit flapZr chord force on slotted flapq dynamic pressure of free airstreamc chord of airfoil with flap neutralCr chord of flap (measured from nose to tail)

and4 angle of attack for *t-s aspect ratio& @of flap deflectionThe coeflhienta for the combination were derived

from the normaI forces alone, the chord forces on theflaps being neglected. Ih the case of the slotted flap,however, neglecting the normal-force component of thechord force of the flap in the calculations for the com-bination reduced the values by an average amount of0.04. Because the skin friction of the flap wilI enterinto any correction for this discrepancy, no attemptwas made to include a correction for flap chord forcein the &al results. Incsmuch as the model complete~yspanned the jet, the integrated reeulta, which are incoef%cientform, may be used as section characteristics.

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244 REPORT NO. 7 l&NATIONAL ADVISORY C@MlTJ31El R(IR AERONAUITCS

IHguma 22 to 27 chow the motion chara.oteriatica of flap, h figure 28 (b), the ioroes on the split flap whenthe combination and of the flap alono for the slotted neutral were fetid by aeauming that the only leakage

flap; &urea 28 b 33 ahow @e eeoticm ohara@@.im betwean flap and airfoil was at the trailing +ge; theof the combination and. of the flap alone for the split loads were computed on that baeia..-

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PRCCISION

NoZi.Pflow alinement tests were made in the tunnelwith the test arrangement ua8d in the present investi-gation,__The ab@h angle of attack may thereforebe in error, but the relative angles of attack of the modd.are acc.urfite ti within +0.1’. The flaps were set atspecfied angles to within + 0.6°. The results fromcheck tests, in which both the angle of attack and theflap setting were independently changed, show that theofice pressures agree within +2 percegt, with thoexception of upper-surface pressures near the leadingdgm yhich, at _high angles of attack, chctcked wifhh! _ .

about +6 percent. The individual free-stream dy-namic p~ures are accurate to within + 1 percent. At~el-w.dl correction (reference 11) has been appliedonly to. the normal-force coefficients of the airfoil-flapcombination. This correction tads to. reduce themagnitude of the preaau&; the other results, whichare uncorrected, should therefore be conservative.

DISCUSSION

13EOTION PR-UEE DL13TEIBUTION

The pressure curves (figs. 3 to 21) show .&e didribu- . . .,.tion of load over the upper and the lower eurfacee ofthe airfoil-flap combinations for several flap defections.These curves may be appbd to the design of ribs andflaps and are also useful for ahowing the change indistribution of pressure over the airfoil as the flap isdeflected. In ganeral, theee curves are similar in ahapoand magnitude to the on.ea .obtaimi from presauro-diatribution, inv4gations of the thinner airfoil-flapcombirititioris (refarances 3 and 6).

The shapes of the pre8aure ourvea for the slotted flap(@s. 3 to 8) ~egenerally similar to those of the curvesfor the I!TACA23012 airfoil tith a slotted flap (reference3); this similarity shows that the flape have the sameticteristice aa to extent of peak pressures , occurrenceof douhls peak pressures on the upper surface, andmagnitude of peak negative preaeuma. In the preeentinvestigation, the double peak disappeared at flapdefleotioxwof 30°.

Figuree 3”to S ahow an inoreaae in velocity at theslot entry. b some oases, this velmity exceeds thefree+tream velocity; however, the area of increasedvelooi@ is small because the deflected flap retards theflow to the rem of the slot.

PR.PlSSUR21DIS~UTION OVHJRAN NACA 23021 AIRFOIL 253

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PRJISSITIUilDIS~UTION OV21RAN NAOA 28021~OIL 265

The chord-pressure diagrams (figs. 9 to 12) wereinc~udd to show that rebtively high forces existedwhioh would tend to retraot the flap from the maximum-lift setting, as was found for the NACA 23012 airfoilwith slotted flap. (See reference 3.) The negativecomponents overbalance the positive ones for almostall flap settings, which creates a form forward. Theskin-friction force, if taken into account, will reduceall negative values and increase all positive valuesbecause it acts nemly parallel to the chord and to therear.

No tests were made to determine the efleot of a E@tdeviation from the optimum nose path for the alottedflap but, es pointed out in reference 1, a alight deviationshould only slightly change the charactmistics. If thechange in characteristics is small, there should be littlechange in the pressure distribution.

A comparison of the pressure distribution over aFowler, a pkin, and an exterqrd-airfoil fklp with a slottedflap is given in reference 3. k no great difhrencesesist between the mrves in reference 3 and those of thepresent investigation, no comparison with other typesof flap is made.

The shapes of the presauie curves for the split flap(figs. 14 to 19) are verysimilarto *eshapesof themrveeShown in references 6, 6, and 7. This agreement wasexpected because reference 4 shows that, with & 0.20csplit flap, the maximum lift is prmtically independentof the airfoil thickness.

Comparison of thi pressure &grams for the plainairfoil with hose for the airfoil-tip combinations at thesame lift (figs. 20 (a) and 21 (a) ) shorn hat decrea@ngthe angle of attack and increasing the flap angle had thefollowing effects: The pressure at the nose of the airfoildecreased as the flap @e was iuoreased. Thenegative pressures at the trailing edge were increasedfor both flap combinations. The positive prwsures onthe rear part of the splitAlap combination irmreused,but there was little variation in the same region for theslotted-flap combination. The flap loads on bothcombinations inoreased with flap angle.

Comparison of the pressure diagams for the pkiinuhfoil with those for the @foil-flap combinations atthe same angle of attack (@s. 20 (b) and 21 (b) ) showsthat increasing the flap angIe had the folIowing effects:The pressure over the entire oombiition increased,oausiug the airfoil to mrry a much greater load. Thepressure gradient remained @out the same throughoutthe rang~ of flap angles shown. The loads on the flapincreased with flap deflection.

The shapes of the prwmre curves for the slotted flapare similar to the shapes of the pressure curves for theairfoil alone. The wake of the flap as well as of the cOm-bmtion should hmsfore be narrow, which accounts forthe low drag of the slotted-flap combination as shownin the reeulta reported in reference ‘1.

Figures 20 and 21 show that the main dleot of eitherflap on the airfoil is its abtity to ohange the flowaround the airfoil in suoh a manner as to decrease theadverse pressure gradient and to oause the airfoil tomrry a mmih greater load without stalling.

-.

AERODYNAMICSEtX’xONOHABA(XEEISTI~

A compsxieon of the seotion characteristiea of theflap alone and of the combination (figs. 22 to 33) showsthat the loads on the flap build up more slowly thin

..

do the loads. on the combination. The loads OR @eslotted flap (figs. 22 to 27) build up more rapidly withflap deflection than do the Ioade on the split flap (@e.28 to 33) md reach a higher maximum value. The

rmmx MAhwrbm afaecuonXrJmJ-fwm and Smchfwmcmmlt MeEtcbnbIX09W3calottedEwOnNAOA9WlmndMO19MrMb.

greatw part of the inorement of section normal-force - _coefficient ori the combination is the result of thernoreesed load taken by the airfoil. For the elotted-Eap oombkation, approximately 75 percent of the loadincrement is taken by the airfoil.

The chord-force omfficienta of the slotted flap (&e. 22to 27) me praotimlly all negative in sign; that k, theforce acting parallel to the flap referenoe line is direotadforward. The magnitude of these foroes is greaterihan for the NACA 23012 airfoil-flap combination(reference 3). Jn the mhmlation of the rwltent forcem the slotted flap, the ohord foroee should be taken intoMOouut but it should be remembered that these foroea10 not include akin friotion.

266 REPORT NO. 71&NA!HONAL ADVISORY ~ FOE ~ONAUTICZl -

Tlw hinge-moment ooefficieuls for the split flap onthe NACA 23021 Sil’fOfl”SrO Slightly greater tian thOSS

found for the split flap on the thinner airfoils (rdwenoea5, 6, and 7). In addition, for both thin and thick air-foils, tlm hinge-moment ooeflioienta for the split flapsme muoh greater than the pithing-moment .mticientafor tho a~otted flap, which are about the flap quartar-ohord point.

The comparison of the dotted flap on the NACA23021 airfoil and a eimilar dotted flap on the NACA23012 airfoil given in figures 84 end 36 should be useful

Flwlauaa.-conl@B0nofmctklndumMarmOmmOhtl lMo9tUWslourd fiWollNACA ~snd~drblls

for. th interpolation of flap oharaoteristics for similarslotted fkips on other NACA airfoils of the 280 ties.Figure 34 show+ the relation between section normal-force and pitddng-moment tieflioisnts. of the flaps forthe two combinations ut a low wgle of attack, aO=OO,and at a high angle of attack, ~= 12°. “ The normal-force ooticienta me approximately tho mine for thetwo flaps untiI tbe flap deflection exceeds 26°. At lowangk of attack, the slotted flap on the NACA Z3012airfoil oairiea more load for flap deflootions greaterthan 26° but, at high anglea of attmk, tlw loads remainabout the same throughout the useful range for theflaps on either airfol The ourvee of pitching-momentcoeflhient show little difference throughout the rangeteateil. A campmiaon of the section ohord-foroe 00’e.flioienta (fig. 86} shows the fihp”on We thi.nndr airfoil

b have lees ohord foroe in almost all comlitioua t.astexi.At the high angle of attack, tho ohord-force coefficionl.of the slotted flap on the NACA 23021 riirfoiI is pro-portional to the flap deflection.

COLLUSIONS “

A camparieon of the results foi the alottcd flap onan NACA 23021 airfoil with” the results of pressure-. .-distribution’teata.of an NACA 23o12 airfoil in oomhina-tiog with a alottad flap showed: The flap normal-foroe cOMcienta were approximately the same at a~ %@s of atti ovar thQ useful range of ,flap d+fkoticme. The flap pitahing:moment ooeflicients wore .about he samo for the range tested. The ohord-foroecmlhi@t was higher for moat conditions tested forthe fla~ on, the NACA 23021 airfoil. The results forthe split flap ware qbout the same as previous reaulbfor sp~t flaps on ,thinnur airfoils.

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NAiIONA~ Anvmony COMMITrJSBFOR AE.RON#UTIW,

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lZKFBItENCES ; ,_ . ..., ..”

Wepdnger, Csri J., mad H- Thomas A.: Wii&TLU]ni4@eat&a@on “d an N. A. C. L 28021Akfoil wfth Varlouq=E@I of SIottad Flaw. ~p. No. 677; NACA,

. . . .K~~”&rg: Premmm Diatrhutioh on a Wing Seo&m wik ““

SIotted F18p in Free. ~t TM&.. T. M. -No. 886, ‘-~C& 1087.

Wednger, Carl J., and De4no, JamoEB,: Pm&e Diw .@butfon over an N. A. C. A. 28012 “Airfoil.with a Slottad

. ~d a Plain Flap. Rep. No. 688, NACA, 1988.Wm@nger, @rl J., and Harria, Thoma8 A.: Wind-’flmnd

Invdgatlon_,of N, A. C. A: 2@2, @l, and 28o9OA@oila with Variouo $Ia~ of Split F18p. Rep. No. 068, -, ,,NACA, 1989;

Wallace, RudoW Inwstigaticm of FuL&xde SpIit Trailh)g-Edge. Wtng Fiaps with Various Church al!d Hinge kIdom. Rep. No. 589, NACA, 1.985.

Wanzing~, Carl J.: Pressure DMbution over a Clark Y-H “”AfrfoU Seotion with a Split F1ap. T. N. No. &, NACA,lfi~.

Wenzinger, CM J., and Harria, ThomaE A.: Premuru DIs-trfhutlon over a Iteotaogular Airfoil wfth a Partial-SpanS@t F18p. kp. No. 871, NACA, 1886.

Wenzbger, Carl J.: Prwure IMrfbution over an N. A. d. A.23UI?4AidoiI-ivith an N.”A. C. A. 28012 )ikternal-Atrfoi]~p. kp. No. 614, NAC& 1988.

Wensinger, Carl J., and Hairis,. Thomaa A.: The VcrtioalWind Tunnel of the Natknud Adv!sory Commit& forAeronautics. Rep. No. 867, NACA 1981.

_ William (1., and &a, Milton B., Jr.: Pmaum- ‘“ ‘–Distribution Investigation of an N. A. C. L 0002 Mrfoflwith a 50-Percent-Chord Plain Flap and Thtwe “T@@.T. N. No: 784 NACA, 1989,

Wermfnger, Cad J., and HarrfE, Thomaa A.:”Wfnd-Tunuel ‘-”-.ti@d@@% of a!! N. L C. A. 23012MM with VariOUBArrangement of Slotted Flspa Rep. No. 664, .NACA,1989. .