NACA-WR-L-373 · Wind-Tunnel Investigation of Perforated Split Flaps for Use as Dive Brakes on a Tapered NACA 23012 Airfoil

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ADVISORY COMMITTE E F OR AERON A UTICS

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ORIGINALL Y ISSUED November 1941 as Advance Restricted Report WIND-TUNNEL INVESTIGATION OF PERFORA TE D SPLIT FLAPS FOR USE AS DIVE BRAKES ON A TAPERED NA CA 23012 AI RFOIL By Paul E. Purser and. Thoma s R. Turner Langley Memorial Aeronautical Lab or atory Langley Field, Va.

NAC~

WASH I NG TON NACA WARTIME REPORTS are reprints of papers o riginally issued to provide rapid distribution of advance research results to an authorized group requiring them for the war effort. They were pre - viously held under a security status but are n ow unclassified. Some of these reports were not tech- ni cally edited. All have been repr oduced without change in order to expedite general distributio n.

L - 373 FO ~ VSE _~ DI~E BR ~KE S ON A ~APERED iAGA 23012 AIRFOIL By Paul Eo P urse~ and Thomas R. Ttrner Aer o ,lyna1ui c chc .r acteristics of a ta pered. :r:: AC .i 230 12 ai rfoil with ~ ing l e an d dou b le pe r forated s p lit flaps have been detormined in t h e ~ACA 7- by l O -foot wind tun - n e1e Dyuamlc pr essu re surv eys we~0 mado behind the air - foil at the a~~roximate location of the tail in order t o deterci n e tle CXt6~t ant location ai tho \aka fo r s e vera l o f the llar a r :;: '2 .LgE'i1 ents I n D.dcl i tion , co mpu tations hav e o been mad e of ~n application o~ pe rforated doubl e s~lit fla ps for use as fighter bra es ~ T~3 r c su lts in di c~tod that sin g le or d Q able perfora t- ed s ::.;::.it f la.J?s UlD.y 'e used t o obi'l.in satisfactory d5. ;,r e cont v'L rrith , )u'C, und1:..e buffeti l!" effec ts a :1d that sin g le or 10 111 e perf orate' spiit fla p s ma~ also be sed as =i ~ ~J.'li c r 0raklO;s ~ Th e ::?e rforatGd spl i t fl~,s had approximate l y the s am e cffe~ts on the aer od ynamic and uake cha racte risti cs o i ' t'lC t-:'}JQ rc d c..i r f oil as on a. c o mpnrablc roctangula.r airfoil o The H CA hRS underta ren an extensive investigation for t h e purpose of doveloping dov ices suit ab l e for li m it- ing tl e divi ng speeds of airp l an es. As a p art of t hi s i nvestiga ~ ion Q stu ~- has been n a d e of test results ob - tained du ring t h e develop m en t of devi ce s ~ esigned primar i- ly for ot~ e r purp o sGs~ such as h i gh lift or l ateral con - trol, but ~h ich may also b e uscd fo~ d i ve control. ~ho slot -li p ai leron co mb ined wi th a full-span slotted f~ap is o ne of those d ual- purp o se d avices, and data fo_ its u se hav e be en p resented in ref e renco 10 A study was also made of a l~r g e amount of un co rrelated da t a on vario u s a i rfoi l- fl a p co nb inat i ons f ro m tests previously made f or the Bur e au of Aeronautics This study indicated t hat pe r - o fornte floublo spljt flaps would give the desired ~har ~ c t oristics ' for use as div~-control devicos . FolloTIing t his stu cc yo [.11 invo stigat ion as made of sove::.'al I1rran<;e - ments o~ Ain~lo and double split flap s on n recta~ ~ ular NACA 23012 airf oil (reference 2 ) to detorcine in 2~rc io - tail the c .crodyna::Jic an d '\'Iako cho.ractoristics of th so devicoe in orde r that dosigncrs might Doro closely eva luate their e~:ects on t~e periormance oi co ~lete nirplal es, The prcGont t~Bts TIGra uad e to dotercino tho cor Jd ynami c an~ ~ ak c c har~ctori s tica of soee of tho singlo and d ouble s plit-fl~p n ~ nngcDon ts on a tapered NACA 23012 airfoi l .

l.Iodel rh a airf ei l model used (fig. 1) was of laminated mah og - any bu i~ t t o ~he N CA 23012 profile Th e model was ta~ere d c 3 to 1 in p l ~~ fc~m wit~ a s pa n of 60 inc hG3 and an as p ect rati o c,l G~O., ~ne trailing e '_ {"B () : t:ne mo d .al TIas stre.i f- 'h t an e. tl, .Q .l'"1c.xL~' 1 u p~cr- s 'l1'fa ce Cl'd. L l 18 .te s of tll0 various sec - t:l.O ~lS ,7 01'0 iil or.o ~l2. nc ~ The per::' o_.?ted split f la ::;Js were mad9 cf sheet s te el and had a chord of 2 inches (20 pe r- ce nt o f the air~ oil m aal geou0tric cho~i). The perf or a - tio ns i n tho flap s ~oro symmetrically s p acod circular hol08 ( aoo fl~ p d ot~ i l, fig. 1) an d re m ov od 33.1 p ercent of tho originnl flnp ar OQ I n or der to fac il itat e pa rti a l - e sp an - flap tests oach fl a p was mad e in ten equal segments, eac h se g~e nt havi _g a span 0_ 20 percent of t~e airfoil se mispan~ Th e secffients on Bach semiRpan were numbered from 1 t 5 ~ r ~~r cs s ivel y fro~ the p lano of sy cm ct y out- bo ard to t h e a~ rfoil tipo S ? lit-~l~p doflections wor D mo&ouro d uith respect to tho airfoi~ surface at the hingo point anJ the gap b et we e n t h e a irfoil sur fa ce and th e flap was sealed with mO~91ing clay, ~ind Tun el ~nd Equipment The t es ts wer e cad e in the NACA 7- ~y IO-foot closed - throat ~ind tunne l io scr ibed in references 3 an d 4. The wake surve y s wore m~ dc uith a rake of eight 3/ 8 -inch diam - eter pitot tubes s~acod 2 inc hos apart . ~he r&ko was ad- just ab le so that dynamic p re osuro could bo recorded at l - inch i ntorvals ~long a vortical line 27 inches long uh ich uas l o c ated 30 inc~os (3 . 0c) behind tho qua rter - chord point 0 the a irfoil me a n aer o Qyna~ic chord and 5 inc h8s (Oe 5e) tJ tho right of tho p la n o o~ sY~illotryo This p osi- tic u ~as be li eved to be repres entativ e o~ the l o c ation of t he hinge line and m idpoi l t of the scm is pan 0 2 tho hor i- zontal ta::' l su::-facos of airplanes on which dive -e o~trol a e vicns wou ld be usad. The r3t i o of the dynam~c prossure s in t~e W~~O to tho dyna ic pr e ssuros at the sa~o points "it:l -::ho nodel romovod (support strut in p : _a ce) was ,,,,-ete r - minod fr0~ rea~ings on an inclined-tute alcoh~l manODete r.

Figu~e 2 ~s a three-q~ar t or r ea r vi ew of the ~odel mou nted in t~e uind tu~nolc ~os ts J,§~i_C~!}_ , tt _ J).9I)~. - T h8 dynaJ:'1ic Pi"CSSUre rr..aintaincd for a ll tests ~us lo.~7 pounis per sqa3r3 foot . which corre - spond.s t o n "Velocity ' of a-bout 80 miles per h ou r under stal1do . rd 8::-0.-1e'-e]. c ond.i tior..u u.nc'l_ to ar. average test Eeyno lds numbar of 609 , 000 bas~d on tho mean ge o me t ric c hord of tho illoJol (10 inQ) o '.f"j. ::' ;..§~ ~_9 ~c1~!,~o - The ~ cst e c 2n 3 i s t ed o:Z' t:1e de '>3rrli - no.ti~ '1 cf he l " it , c'i.r2g, and :pilchi:ll;-mo-:Jor.t coeffieie:1 ts and ol t:e W~kR c~ar"cteristics fo r vnr1ouo arrnn Ge~ont s of t~~ f l ~pso Double sp li t flapc wore located 20 percen t of t~o boau ~C~ atric chord from the cirfo~l tr~ilin~ e dg e a~d single sp lit flaps (lo~er surface) ~erc located o n t~e JiJe of t~e 30-pcrccnt - c~ord stations of tho atr - foil Rectionc T.ho forces aua. mO-ients i~e r e dcto:'oir..cd at o intor va: s of 2 thrc~ghout tho a~~lo-of-attack r ango iron 'oelo' ,7 zero lift to ao)\ -o Jla:~ir;:;u lift. J:'ho i'7ako Durvc~'s 1,'701'0 nnd c at interva l s of 4° throlghout tho 8a~e a~glo - of n. '~tack :'a!1g , :3 o ~o tests ~ore ~ado with th e flap perforati o ~s cove ad since the dat a in refe r ence 2 s10TIed that w~ile covering the perforations incre as ed the drag coe ~f i cient , it als o caused a very unsteady con iiti o _ of the mo del .

R~SULTS AND ~ISC~SSIO~ In the ~resentat io n of results the f ollo i'7 in g symools are use eL C ~ift coe ff icient, L C - p~tching-mo~Bllt coefficient about the qua rt o r - J . C/4 ch o rd poin+ o f the airfoil mean ~crod~namic eho d; m/qocC!

1 li~ t ill pitchin~ mo~cn t .1 P V 8 d;'{na~ic prosrn . ro at po.'nt i nako, q average dynamic pressuro for ai r stream,

i P V 0 '2

ai~foil caa~ g oo~o tr ic chord airf0il mean aerodynam~c chord , chord throu~h c centroid o f area of ~irfo il seoispan flap c~ord airfoil area b airfo i1 spa.n flap span and a anGle of attack Of upper - slrface spli~ - fl ap deflection U O ~ lo~er-surface split-flap de~le c tion -1 ~he suoRcript Lo refers t o the characteristics at zero l ift" S ince t ~ e support strut interference and tares were r elatively scall thes e corrections were applied only to the pl~in airfoil data . The standard jet-boundary corre c- tio s which vvore alJplio cl t o .... 11 t:1El f o rce-test dato. arc : where C is the jet cro ss - sectional area. A ~alue of

6 = OGl135 f or tIe closed - throat wind tunnel 1a s used in

correctin g tho results It should be noted t~at due to tho various spRn - load distri~utions of the airf oil ryith th e vario:s spl it- flap arrange l ents, these corrections are n ot strictly a l)p licable t') all tht) data. £) 0 cerrec- tion for tunnel ef ~~c t has b~ ~n applied to the wake 10ca - tion This correction i~ sma ll because of the relatively e small model uscd Q Double Split Flaps The cr0dyna m ic and wake ctaracteristics of a 60 -i nch span 3-to-l tapered ~ACA 23012 air_oil ~ith double split flaps locnted 0.20c fro~ the ai~foil trailing ed~o ara pre ~0ntei in ~igures 3, 4, and 50 The ae oiyna~ic charac - teristics are presen~ed ~s CQrves plotted against lift coefficient; and tic wa~o characteristics are shown as curves of dynawic prcssu_e ratio, q/qo' plott ed a sa inst distance D.-cove nnd belo';1 the e: :t e n cd chord. line 0_ tll0 roo 'G seccion of t' e c.irfo:' la The moth o d of presenti:r.e tile wa~e ch ar~. ctcr:'stics is illustratei in fi.;ure 4 . Th o double split f~aps Dad ?ractical l y t'le sawe ef~ects on tho aerodynamic and wa~e characte=istics of tIe tapered air- foil as they _aQ on those uf the rectangular a irfoil of reference 20 The wake surveys were made of selected rep - resentati e &_rangenents based on the restlts of ref e rence 2 and t~e dat a presented are sufficient to s~ow the ~ake charact ~risti cs of al l arrangoMents.

Si nc e the aerod~namic characteristics at and near zer o lift were consiiered of pa rticular interest to the de - signer, t~e results fr om figures 3a and 5a were plotted against flap span i~ figure 6~ ~either flap spa~ nor air- foil plan fo rm had a ~arkea e ffect on the pitch ing- ~omen t coefficients or angles ot attack at zero lift . The drag coefficients obtained with center-S Qcti o~ Qoub~c split - .------.--- ~- flaps were practically the SFl.Ille for b o th the tape_ed a ir - foil and the ecta~gu].ar airfoil of reference 2~ but t~e tip section flaps gave high e r dra~ coefficients on the tapered airfoil than on the rectangular air oil . On both airfoils the center-section flaps all o wed hibher available ma.ll.imu . lift coefficients than the tip - section _ fla-os ex - cept for one unexplained instance (60 - pcrcent-span-flaps , figo 6)v The Qifference bet~ oon the maximu~ lift coeffi - cients obt a i~able with the con tor- and tip-scction flaps was 1&8s for t~e tapdre~ airfoil than for the rectangular airfo:l of reforenco 20 Singlo Split Fla9s Th8 aerQdy~am:c and ~ake cha act eristics of a 3-to-l tap ered :~ACA 23012 airfoil wi th lowor--surface perforated split flaps locate d on a line th~o~gh the 30-percent-c : ord statioDo of the airfoil sections a_e shown in figures 7 to 9 .

The u.:'e of these flaps produceci t~e sa_ e large decrease in angle of attack for ~oro lift on the taporcd airfoil as on the r~ ~~ angula r airfoil of ref eTu,ce 2. Sinco the aerody - n am ic ' : ·~J. aracf,eris·cir.s at and noc , .~' zo:r' O lift were consid- ore d of p~rti cul a~ i~ torost tG tho designer , the results of ::iC ~' :"":'os t: , :>.no 9 wor0 roplottoc. a.gainst flap span in figu: c c 10 ..

In view 0_ t he agreement shown bet7een the tapered air f 0 i 1 t cst san d. t ~ G r () G t a. n g"C~ 1 E t r a iI - f 0 i I t G S t s 0 f ref G r- ence 2) the t ~a sets of d2 ta ~ogether should afford. su:fi - cient information ~cr t~e prediction of the performance of pe rfo ' ated split flaps when used as dive brakes o Di v ing Sl )eod T~e relatio~ship bct~ee drag coefficient , win g load - ng, and i nd ic at ed ve l ocity IO~ an airplane in a vertical i dive is s h own in fiGure 11" For otlor diving angles, t:1.C vel o city g iven on tho chart should bo multiplied by tho squaro root of tho sino of the ciiving an g le, reforrod to the horizontal. Fro~ this cha:-t, the data i n figu es 3(a) through 10c and the data i n r i g ures 3(a) through 21(0.) of reference G, i t may be shoun that the use of full-span pe~forated double s p lit flaps ~ould probably limit t o 200 miles per hou r the indicated diving speed of an air p l ane uith a 7ilg loa~in · of 35 pounds per square foot and li m- it to 250 miles per h o ur the diving speed of an airplane 7ith a ~ing loadin G of 55 pOlnds ~er squaro foot . Co r r o- spondi~ . valu e s obtained w it h the use of perforated sin- ele split flaps are : 200 ~iles per hour for a winb load- i n~ of 30 po~nds ~er square foot, and 250 miles per hour ~ for a ning loa d inG of 45 p o unds per squcre foot o r'\ ~ Figllter 3rakes In addition to the need for devices which will re duc e the diving speeds of airplanes. it appears that a need has arisen for some d e vic e which TIi ll tem~orari ly reduce the sp~ed of atta c ~ ing figh ter aircraft in order that the pilot will havo more tiwG for firing. Som e of the require - mont s which a figh t er ~rBko should ~eot arc : littl o or n o chango in tho attitudo of the air:lane 7ith f i xed controls , s ufficient "ncrcas c in lift coefficient dur in g op eration of the "0 akos to mnintain level flig"_t as t::'e speed is re - duced, and enough increas e in drag coefficient to dncele r- ate the ~irplan e TIithin a re asonable ti~e after the brakes arc ap~lied(\ n ~pplicction of fighter brakes to an airp l ane 7ith a wing !oading of 3 0 pounds per squc~c foot has beot com - pu.tod" by a: '1 a?IH' o :dmate , stop-bY-3tcp mo·c" od Tuo arrang e- o mo::).t used was the fIll syan porforated dO F. ble split flaps

located at 0.80c on the rect.a:1 g ular rAe! .. 23012 airfoil

( fig 3(a" reforence 2)0 It TIas assu~ad that both t h e a u pp er-surface and t~e lo we r-s urface flaps r cre deflectcd to 30 TIit~in 1 scco=d. and t: on the uDDer-surfaco f l a D 'I ..L. _ .J: re mained stationary uh il o the ~oTIer-surfaco flap was : e- flected to 60 in such a manner as to afford sufficient increas e in lift coefficient to maintain level fli gh t at the red i.. 1C o d speeds without a chc:.nge in angle of attack.

Althou gh rnaintuin i ng a onst~n t po~e r output of the enGin e w oul d slightly decreas e the e~fective drag increme nt and incro ase tho t~De required to slow dOTIn , this e f fect uas neglected in orQcr ~ o si~plify tho p roblem.

The results of the computations are given in Ilgure 1 2, which shows curves of speed; lift, d~ag , and pitching - moment coefficients; anole of attack; flap deflection; and acceleration plotted against time . As is shown in figure 11, the use of full -s pan perforated dou Ie split flaps should reauco the airplano speod from 300 miles per hour to 176 miles per hour i n a bout 8 seconds, with a negligible ch ang e in angle of attack and a change i n w ing pitching - Doment coefficient of only - 0 . 03 . It should be

J

ncted that at the end o f the 8 seconds the airplane stiJl has a dece 1 0rat ion of about O.6g and in ardor to continue i n level fli~Lt the lift coefficient must be increasod by an in~roaso in anslc o f attack or by a decroase in the upner - surfaco flan ~oflcction (w ~ich w oul d also docreaso t h~ d r ng cooffici~nt and deco lerat i on).

Th e effect of the ~ laps on t~e pitching - moment coeffi - cient due to th~ tail s hou l d b e determined on a complete modol of any propcsed in~tall&tion. Also a nore comploto determinatien should bo ~ado of the variation of lift and drag coe ff ic ient s with flap ~eflection, since the lift and drag data use d in computing the characteristics shown in

figure 12 w8re takon from curves ~ rawn between 8 = 30

f with no intermediate points o and I n using double sp~it flaps ns fi~hter brakes, th8 in- iti al accelcrD.tion of 1.1g could be reduced by decreasing the initia l 30 flap daflecti on or by reducing the rate of deflcct~ on and using a diffo~ential bet7een the tw o flaps , so that the sreat8r defle ction of the lower-surface flap would s upply the lift c efficient~ needed to maintain a con stant angle of ~tta c ~ o It also O- p po"l.rs p ~ s s iblo to URc lo ;rer-s lrface For: o- ratod split flaps locatod nenr thc wing loading edge 68 fighter brakes if a somewhat lower decoloration a- d so~o chango i~ t~ e attitud e of the. ir?lano is considered a.c - coptabl('le , Oper" ting FcrcoG A lar g o ~moun~ of data has boon published o~ tho hinge-~OLent c h aractoris t ics of various split-flap combi - nations , somo of Wilich arf.) presonted L1 referonces 5 to 8; an the hinge - momont character ' stics of a slot_Ii, aileron f or ~se as a dOve brake Jh c n combi~od ';7ith a full-s p an slotted flnp arc presentod i~ rcforo~cc 1. Coruparatively li ttl e is knorn , houevcr, about the ef:ects o f flap pe r - forationG or of vaiious methods o~ operation on the forces required t o deflect split flaps. Some 70rk has been dono i n England on various ~ethois of operation o f split,flaps (reforonce 9) and brief menti on is mad e of th e loads to be

8z pected o~ dive brakes in a re port 0: some Gorman re -

s earch (reference 10) . The dive brakes o f reforence 10 wera slats placed 110rm'1.l t o the airfoi l surfnce "ith a gap b et~een the airfoil and the slatso Pressure distributiorr tAs t a on these slats in d icated th a t the load on t he slat s was about 75 percent of the d~ag increase and that th9 d is trib u ti on of this load on t he slat was approximately r e c ta. n g'J.la I' 0 A ddit ion al research is recom m en ded on the e ffects of perforations and method of flap o pe ration on the hinge - mo men t c haracte ristics of perforated split flaps .

COliCLUS IO~~ S The results indicated that single or doub le perforat ed sp l :. t flapt; ma.y be used to o bt:~in sati:3factor y dive con- tr ol wi th out undue buffeting effects and that single or double psrf0rated ~p lit f la ps may also be used as fighter br akes:;> The perforated op lit flaps have approximately the sam e effect'3 (Jl the aE.l'ocl.ync..mi c and wake charac te:List ics of th e t apered airfoil as on a cemparab l o rectangular ailfoila L angley Uom orial Aeronau tic al L aboratory , National Advi90~y Oommittee for Lc ~onautics , Lan5ley .'lo ld, Va ..

REFER.ENCES 1. Rogal l o , F. M .: Aerodynami c Characteristics of a Slot - Lip Ailer on and Slotted Fla p fo r Div e Brakes . NACA ACR , Ap ri 1 1 9L. l , 2. Purser, P au E ., and Turner, Thoma s R. : Wind - Tunnel Investigation of Per forated Split Fla ? s fo r Usc as Dive Brake s on a Rec - t angular NACA 23012 Airfoil . ACA ACR , July 1 94 1.

3. Ha rr is , Thomas A .: The 7 by 10 Foot Wind Tunnel of the Nationa l

Ad vi s"ry Cornn, i ttee fo r Ae r onautics . NACA R.ep . No . 412, 193 1.

4. Wenz i nge r, C arl J. , and Hal" ris , Thomas A. : ~i'ind - TUlmel

Invest.ig ,· tion of an NACA 230 12 Airfoil with Various A rr nge - monts of Slotted Fl~ps . NACA Rep . No . 664, 1 939 .

5. Weick , }' r ed E. , and Wenz ing e r, Ca rl <T .: Wind - Tu:nnel Research ComparinG L!l.teral Co nt r ol De vi ces, Particularly at High Anlj l es o~ Attack . XI I - U Dper - Surface idle ro ns on Wings with Sulit Fh s . NA CA Rel?' No . 499, 193L. .

6. liYonzinge r , Ct:.~rl J . ~ : i nk -T unn.e l l\~easurement s o f A ir Lo~ds on Split Flaps . NL.CA TN N o. 498, 193L~ .

7. Wenzinger. Carl J. : Pr ess ure Distribution ove a Cl a rk Y- H Air "foil Section with a Suli t Fla p . lECA TN No . 627 , 1937 .

8 . Wenzinge r, Carl J . , and Rogallo , Francis M .: Resume of A 'r- L oad Dat on Slats and Flaps . NACA TN No . 690 , 1939 .

Irving~ H. B ., and Mc~"i l lan, G. A. : Some E :<pe rim en t s on the Ba1a.ncin of li ' ing B ra ke Fla~s . R . & M. No . 1864, B ritis h A.R . C ., 1939 .

10 . J acobs, Hans , and Wanne r , Ado lf: DFS Dive -C ont rol Br~kes fc Glide l"S and Airplane s; and Wanner , Adolf : Analytical Study of th e Drp~g of the DFS Dive - Control B rak e . NACA TY. No . 926 , 19 40 .

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figure 3 (a' .- Effect of 0.20e ~artial-span center-sec ti on perforated double split flaps lo cated 0.20c from the airfoil trailing edge of a SO-inch span 3:1 tapered NACA 23012 o ~irfoil. OfU,60 ; Of L,600.

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(a) Aerodynamic characteristici .

rigure 7 (a).- Effect of a 0.20c full-Ipan lower-aurface perforated aingle aplit flap located OD a line through thl 30-percent-chord atationa of the airfoil aectiona of a SO-inch span 3:1 tapered _ACA 23012 airfoil.

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Lift coefficient, C L Figure 9.- Effect of 0 . 20c partial-span low e r-surface tip-section perforated Bi ngle split flaps located on a line ~hrough the 30-percent-chord stat i ons of the airfoil s e ctions on the aerodynamic characteristics of a 60-inch span 3:1 tapered NAOA 23012 airfoil . OfL , 600.

Fig . l C NACA E ..

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0 4 /00 .1 ; o o o 6 8 2 4 o Time, t,se c Figure 12 . - Co m puted time-history characteristics during deceleration of an airplane equipped with f ighter brakes consisting of O.20c full-span perforated double split flaps located O.SOc from the wing leading edge.