at '%EI^Nov. 19^1

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NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

WARTIME REPORT ORIGINALLY ISSUED November 1941 as

Advance Eestricted Eeport

WIND-TUNNEL INVESTIGATION OF PERFORATED SPLIT FLAPS

FOR USE AS DIVE BRAKES ON A TAPERED NACA 23012 AIRFOIL

By Paul E. Purser and Thomas R. Turner

Langley Memorial Aeronautical Laboratory Langley Field, Va.

NACA WASHINGTON.

NACA WARTIME REPORTS are reprints of papers originally 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 now unclassified. Some of these reports were not tech- nically edited. All have been reproduced without change in order to expadite-general distxihut W\stel SSSfe

373 LANGLEY MEMORIAL AERONAUTICAL LABORATORY

Langley Field, Va.

J 3 1176 01403 4690

WIKD-TUEFEL UmBSTIGATIOIT 07 PIBFOBATBD SPLIT PLAPS

FOB trSK'AS JDIVH BAASES" ON A TAPEBBD HACA'33013 ATSPÖIL

By Paul B. Purser and Thomas B. Turner

SUkliABT

Aerodynamic characteristics of a tapered HACA 33012 airfoil with single and double perforated split flaps have been determined in the UACA 7- by 10-foot wind tun- nelo Dynamic pressure surveys were mado behind the air- foil at the approximate location of the tail in order to determine the extent and location cf tho wake for several of the flap arrangcnents« In addition, computations have been mado of nu application of perforated double split flaps for use as fighter brakes*

Tbo rosults indicatod that single or double perforat- ed spile flaps may be used to obtain satisfactory dive control without undue buffeting effects and that single or doiible perforated split flaps may also be used as fighter brakes«

The perforated split flaps had approximately tho samo offects on tho aorodynamic and wako oharactoristios of tho tnporod airfoil as on a comparable rectangular airfoil.

IJT TBO DUCT IOU

The HACA has undertaken an extensive investigation for the purpose of developing devices suitable for limit- ing tho diving speeds of airplanes. As a part of this investigation a study has been made of test results ob- tained during the development of devices designed primari- ly for other purposes, such as high lift or latoral con- trol, but which may also bo usod for divo control. Tho slot-lip aileron combined with a full-span slotted flap is one of. those dual-purpose dovlce.8, and data for its use have boon presented in roforonco 1. A study was alBo made of a large amount of uncorrelated data on various airfoll-flap combinations from tests previously made for the Bureau of Aeronautics« This study indicated that per-

forated double split flaps would give the desired charac- teristics for use as dive-control devices« Vollowing this study, an investigation was made of several arrango- monts of single and double split flaps on a roctangular NAOA 23012 airfoil (roforonco 2) to determine In moro do- tail tho aerodynamic and wako characteristics of thoso dovicos in ordor that designers might moro closely evaluate their effects on the performance of complete airplanes. Tho prooont tosts woro made to dotormino tho aerodynamic and wako characteristics of some of tho single and doublo split-flap arrangononts on a tapered HACA 23012 airfoil.

AFPABATÜS AHD TESTS

Model

The airfoil model used (fig. l) was of laminated mahog- any 'built to the 2IACA 23012 profile. The model was tapered 3 to 1 in plan form with a span of 60 inches and an aspect ratio of 6.0, The trailing edge of the model was straight and tho maximum upper-surface ordlnates of tho various sec- tions woro in one piano. The perforated split flaps were made of sheet steel and had a chord of 2 inches (20 per- cent of the airfoil mean geometric chord). The perfora- tions In tho flaps woro symmetrically spacod circular holoe (sec flap dotall, fig. l) and removed 33.1 porcont of tho original flap area« In order to facilitate partial- span-flap tests each flap was made in ten equal segments, each segment having a span of 20 percent of the airfoil semispan. The segments on each semispan wero numborod from 1 to 5 procroasivoly from tho piano of symmetry out- board to the airfoil tip. Split-flap doflections woro moaourod with rospoct to tho airfoil surfaco at tho hingo point and the gap between the airfoil surface and the flap was sealed with modeling clay.

Wind Tunnel and Equipment

The tests were made in the NACA 7- by 10-foot closed- throat wind tunnel doscribed in references 3 and 4.. Tho wako survoys woro made with a rako of oight 3/8-inch diam- etor pltot tubos spacod 3 inchos apart. Tho rako was ad- justable so that dynamic prosBuro could bo recordod at 1- inch intorvala along a vortical lino 27 inchos long which was locatod 30 inchos (3.0c) behind tho quarter-chord

3

point of tho airfoil moan aerodynamic chord, and 5 inchoa (0.5c) to tho right of tho jplano of Bymmotry, Thia posi- tion was "believed to "be ropreadntative of the location of the hinge line and midpoint of the aemlspan of the hori- zontal tall surfacea of airplanea on which divo-control deviooa would bo uaod. Tho ratio of tho dynamic proeaurea in tho wako to tho dynamic proeauroa at tho saao pointe with tho modol removed (support atrut in place) was dotor- minod from readinga on an inclined-twee alcohol manometer« ffigure 3 is a three-quarter rear view of the model mountod In tho wind tunnol,-

Tosts

Te B t ogn dl t j^on s. - The dynamic pressure maintained for all teots nas 15,37 pounds per square foot, which corre- sponds to a velocity of about 80 milea per hour under standard soa-level conditions and to an average test Reynolds number of 609,000 based on the moan geometric chord of the modol (10 in,),

T£gt ^"P-roc?edr. ra. - The tests consisted of the determl- nati-o'i of the lift, drag, and pitchlng-moment coefficients and o2 -fho wake characteriatlcc for various arrangements of tho flaps. iJoublo cplit flaps wero locatod 20 percent of tho nioau geometric chord from tho airfoil trailing odgo and single split flaps (lower surface) wero located on the line of the 30-pcrcont-chord stations of tho air- foil sections, The forces and moments were detorninod at intervals of 2° throughout the anglo-of-attack rango from bolow zoro lift to abovo mazimum lift. Tho wako survoya woro mado at intervals of 4° throughout tho sano anglo-of- attack range

"So teste wore cade with the flap perforationa covered aince the data in reference 2 showed that while covering the perforations increaaed the drag coefficient, it also caused a very unstoady condition of the model.

B3SULTS AHD .DISCUSSION

In the presentation of results the following symbols are used:

CT lift'coefficient, L/q0S•

4

OJJ drag coofflcient, D/qQS

OJJJ pitching-moment coefficient ahout the quarter- °/4• chord point of the airfoil moan aorodynamic

chord, m/q0cS

q/q0 dynamic pressure ratio

whore

L lift

D drag

m pitching moment

q dynamic prosaiiro at point in wako, ^ p Ta

q0 averago dynamic prosBU.ro for air stream,

i p V a airfoil moan goomotric chord

o airfoil mean aerodynamic chord, chord through centroid of area of airfoil semispan

c-2 flap chord

5 airfoil area

D airfoil span

Of flap span

and a angle of attack

8f upper-surface split-flap deflection

5.» lotrer-surface split-flap deflection

The subscript L0 refers to the characteristics at zero lift.

Since the support strut interference and tares were relatively small, these corrections were applied only to

the plain airfoil data. She standard Jot-boundary correo* tions which wore appliod to all the forco-test data aro:

,o _ ä S AaJ = 6 a oL 67.3

S * a 1 "0 A°D, = 6 S °L

where 0 1B the Jet cross-sectional area, A value of 8 a 0.1125 for the olosed-throat wind tunnel was used in oorreotlng the results. It should bo noted that duo to tho various span-load distributions of the airfoil with tho various split-flap arrangements, these corrections are not strictly applicable to all the data. Vo correc- tion for tunnel offoot has boon appliod to the wake loca- tion. This oorroction is small because of the relatively small modol used.

Double Split Haps

Tho aorodynamic and wake characteristics of a 60-lnch span 3-to-l taporod 3ACA 23012 airfoil with doublo split flaps located 0.20c from tho airfoil trailing odgo aro presented in figures 3, 4, and 5. The aerodynamic charac- teristics are presented as curves plotted against lift coofflcient; and tho wako charactoristies are shown as curvos of dynamic proesuro ratio, <l/q0, plotted against distance abovo and bolow tho oxtondod chord lino of tho root soction. of tho airfoil. Tho mothod of presenting the wake characteristics is illustrated in figure 4. The double split flaps had practically the same effects on the aerodynamic and wake oharaotorlstios of the tapered air- foil as they had on those of the rectangular airfoil of reference 2. The wake surveys were made of selectod rep- resentative arrangements based on the results of reference 2 and the data presented are sufficient to show the wako characteristics of all arrangements.

Sinco the aerodynamic characteristics at and near sero lift were considered of particular interest to the de- signer, the results from figures 3a and 5a were plotted against flap span In figure 6. Keither flap span nor air- foil plan form had a marked effect on the pitching-moment coefficients or angles of attack at sero lift. The drag coefficients obtained with center-section double split

flaps; were practically the same for both, the tapered air- foil and the rectangular airfoil of reference 2, but the tip-section flaps gave higher drag coefficients on the tapered airfoil than on the rectangular airfoil. On both airfoils the conter-section flaps allowed higher available maximum lift coefficients than the tip-section, flaps ex- cept for one unexplained instance (60-percent-span flaps, figo 6). The difforcnco botwoon tho maximum lift coeffi- cients obtainable with tho contor- and tip-soction flaps was less for the tapered airfoil than for the rectangular airfoil of reforenco 2„

Singlo Split Flaps

Tho aerodynamic and wake characteristics of a 3-to-l tapered L'ACA 23G12 airfoil with lower-surface perforated split flaps located on a line through the 30-percent-chord stations of the airfoil sections are shown in figures 7 to The use of these flaps produced the same large decrease in angle of attack for s.oro lift on the tapered airfoil as on tho rectangular airfoil of rofcronco 2. Sinco tho aerody- namic characteristics at and soar ssoro lift woro conaid- orod of particular intorost to tho designer, tho results of fi.;;iros 8 and 9 woro roplottcd against flap Bpan in figure 10.

Jn view of the agreement shown between the tapored airfoil tests and the rectangular airfoil tests of rofor- ence 20 the two sets of data together should afford suffi- cient information for the prediction of the performance of perforated split flaps when used as divo brakes.

Diving Spood

The relationship between drag coefficient, wing load- ing, and indicated velocity for an airplane in a vertical dive is shown in figure 11. Tor other diving angles, tho velocity given on tho chart should bo multiplied by tho square root of tho sino of tho diving anglo, roforrod to the horizontal. From this chart, the data in figures 3(a) through 10, and the data in figures 3(a) through 21(a) of reference 2, it may be shown that the use of full-span perforated double split flaps would probably limit to 200 mileo per hour the Indicated diving speed of an airplane with a tring loading of 35 pounds per square foot and lim- it to 250 miles per hour the diving speed of an airplane

with a wing loading of 55 pounds por square foot. Corre- sponding value's "obtained with the .'use Of perforated sin- gle split flaps are: 200 miles per hour for a wing load- ing of 30 pounds per square foot, and 250 miles per hour for a wing loading of 45 pounds per square foot.

Fighter Brakes

In addition to the need for devices which will reduce the diving speeds of airplanes, it appears that a need has arisen for some device which will temporarily reduce the speed of attacking fighter aircraft in order that the pilot will have more time for firing. Some of the roquiro- monts which a flghtor brake should moot are: littlo or no chango in tho attitudo of tho airplano with fixod controls, sufficlont lncroaso In lift coofficiont during oporatlon of tho brakos to maintain lovol flight as tho spood Is ro- ducod, and onough lncroaso in drag coofficiont to docolor- ato tho airplano within a reasonable timo aftor tho brakos aro appliod.

An application of flghtor brakos to an airplano with a wing loading of 30 pounds por squaro foot has boon com- putod by an approximate, stop-by-otcp mothod. Tho arrango- mont usod was tho full-span porforatod doitblo split flaps located at 0.80c on tho roctangular NACA 23012 airfoil (fig. 3(a), roforonce 2). It was assumod that both tho uppor-surfaco and tho lowor-surfaoo flapB woro doflocted to 30° within 1 second, and thon tho uppor-surfaco flap remained stationary whilo the lower-surfaco flap was de- flected to 60° in such a manner as to afford sufficient increase in lift coefficient to maintain level flight at the reducod speeds without a change in angle of attack. Although maintaining a constant power output of the ongino would slightly decrease tho offoctivo drag incromont and lncroaso tho time roquirod to slow down, this offoct was nogloctod in ordor to simplify tho problem.

The results of the computations are given in figure 12, which shows curves of speed; lift, drag, and pitchlng- moment coefficients; angle of- attack; flap deflection; and acceleration plotted against time. As is shown in figure 11, the use of full-span perforated double split flaps should reduce tho airplane spood from 300 miles por hour to 176 miles per hour in about 8 seconds, with a nogligiblo chango in anglo of attack and a change in wing pitching-momont oooffioiont of only -0.03. It should bo

8

noted that at the end of the 8 seconds the airplane still has a deceleration of about 0,6g and in order to continue in level flight the lift coefficient must be incroased by an incroaso in anglo of attack or by a docroase in tho uppor-surfaco flap dofloction (which would also docroaso tho drag coofficiont and decoloration).

The effect of the flaps on the pitching-moment coeffi- cient due to the tail should be determined on a comploto modol of any proposed installation. Also a moro comploto dotormination should bo mado of tho variation of lift and drag coefficients with flap deflection, since the lift and drag data used in computing the characteristics' shown in figure 12 were takon from curves drawn between 5f = 30° and 6; = 60° with no intormediato points«

In \ising double split flapB as fighter brakes, the in- itial acceleration of l.lg could be reduced by decreasing the initial 30° flap deflection or by reducing the rato of deflection and using a differential between the two flaps, so that the greater, deflection of the lover-surface flap would supply the lift coefficients needod to maintain a constant anglo of attach.

It also appoars possiblo to use lower-surface perfo- rated split flaps located near tho wing leading edgo as fighter brakes if a somewhat lower docoloration and some chango in tho attitude of tho airplane is conslderod ac- coptablo«

Operating Torcos

A largo amount of data has boon published on tho hingo-mctont charactoristloB of various split-flap combi- nations, some of which are prosontod in roforoncos 5 to 8; and tho hingo-momont characteristics of a slot-clip ailoron for uso as a Aivo brako whon combined with a full-span slottod flap ore prosontod in rcforonco 1. Comparatively little is known, however, about the effects of flap per- forations or of various methods of operation on the forces required to deflect split flaps. Some work has boon done in England on various methods of oporation of split.flaps (roforonco 9) and briof mention is mado of the loads to be expected on dive brakes in a report of some Q-erman re- search (referonce 10). The dive brakeB of reforence 10 woro slats placod normal to the airfoil surface with a gap between the airfoil and the slats« Pressure distribution!

9

tests on these slats indicated that the load on the slats was about 75 per bent of the-drag" increase~and that the distribution of this load on the slat was approximately rectangulara

Additional research is recommended on the effects of perforations and method of flap operation on the hinge- moment characteristics of perforated split flaps.

COITCLUSIorS.

The results indicated that single or double perforated split flaps may he used to obtain satisfactory dire con- trol without undue buffeting effects and that single or double perforated split flaps may also be used as fighter brakes,

The perforated oplit flaps have approximately the same effects on the aerodynamic and wako characteristics of the tapered airfoil as on a comparablo rectangular airfoil«

Langley liomorial Aoronauticnl Laboratory, National .Advisory Commlttoo for Aoronautlcs,

Langloy tflold, Va.

10

REFERENCES

1* Rogailo, F« M.t Aerodynamio Characteristics of a Slöt-Lip Aileron and Slotted Flap for Dive Brakes. NACA ACR, April I9I+I.

2. Purser, Paul E., and Turner, Thomas R.t Wind-Tunnel Investigation of Perforated Split Flaps for Uso as Dive Brakes on a Rec- tangular N4CA 25OI2 Airfoil. NACA ACRf July 19l*l.

3. Harris, Thomas A. 1 The 7 by ID Foot Wind Tunnel of the National Advisory Committee for Aeronautics. NACA Rep. No. 1+12, 1931»

4» Wenzinger, Carl J.a and Harris, Thomas A.: Wind-Tunnel Investigation of an NACA 25012 Airfoil with Various Arrange- ments of Slotted Flaps. NACA Rep. No. 66^, 1939»

5. Weiok, Fred E., and Wenzinger, Carl J.1 Wind-Tunnel Research Comparing Lateral Control Devioes, Particularly at High Angles of Attack. XII - Uoper-Surfaoe Ailerons on Wings with Split Flaps. NACA ROD. NO. U99, 193U.

6, Wenzinger, Carl J. c Wink-Tunnel Measurements of Air Loads on Split Flaps. NACA TN No. 1J98, I95U.

7« Wenzinger, Carl J.» Pressure Distribution over a Clark T-H Airfoil Section with a Split Flap. NACA TN No. 627. 1937.

8. Wenzinger, Carl J., and Rogailo, Francis If. 1 Re'sume" of Air- Load Dati on Slats and Flaps. NACA TN No. 690, 1939.

9* Irving, H. B., and MoMillan, G. A.1 Some Experiments on the Balonoing of Wing Brake Flaos. R. A M. No. I86I4., British A.R.C., I939.

10. Jaoobs, Hans, and Wanner, Adolft DFS Dive-Control Brakes fcr Gliders and üirolanesi and Wanner, Adolf1 Analytical Study of the Drag of the DFS Dive-Control Brake. NACA TK No. 926, 19140.

.NACA Fig. 1

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F/GUHE /.- The. 3* / tapered M/tcA 230/2 airfoi/ with O.ZOc perforated split flaps. Perforations remove 33.1 percent of the original flop area. Airfoil span}60 inches; mean oeornetr/c chorcf, 10'/h.jmean aerodynamic choral. 10.8 33 inches.

& - 373

Figure 2.- Three-quarter rear view of the 3:1 tapered NACA 23012 airfoil with 0.20c, 80-percent-span tip section perforated double split flaps mounted in the NACA 7-by 10-foot wind tunnel.

8 1.0 1.2 -.4 -.2 O .2 .4 .6 Lift coefficient, CL

(a) Aerodynamic characteristics. Figure 3 (a).- Iffect of 0.20c partial-span center-section perforated double split flaps located

0.20c from the airfoil trailing edge of a 60-inch span 3:1 tapered NACA 23012 airfoil. 6fu,60°; 6^,60°.

(b) Wake characteristics. Figure 3 (b).- Effect of 0.20c

partial-span center-section perforated double split flaps located 0.20c from the airfoil trailing edge of a 60-inch span 3:1 tapered NACA 23012 airfoil. 6fu,60O; 6fL,60o.

-3.0c

as o >

Chord line, section 0.50c / from plane of symmeiry

.•Root chord line

-1.50c

Figure 4.- Wake characteristics of a 60-inch span 3:1 tapered NACA 23012 airfoil. O .4 .8 1.2

q/qo a

cr

Fig. 5a

.4 .6 Li ff coefficient, CL

(a) Aerodynamic characteristic«. Figure 5 (a).- Effect of 0.20c partial-span tip-aection perforated double split flaps located

0.80c fro» the airfoil trailing edge of a 60-inch span 3:1 tapered NACA 23012 airfoil. Sfjj.öO5; 6^,60°.

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full-span lower- surface perforated single split flap located on a line through the 30-percent-chord stations of the airfoil ejections' of a 60- inch span 3:1 tapergd NACA 23012 airfoil. 6fT,60°.

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span tip-section perforated double split flaps located 0.20c from the airfoil trailing edge of a 60-inch span 3:i tapered NACA 23012 airfoil. Ofö,600; 6fL,60O.

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Figure 6.- gffect of flap «pan on eoae of the aerodynamic cnaracteriatice of a 60-inch epa* 3:1 tapered HAOA 23018 airfoil »1th O.aoc perforated double eplit flapa

locate« 0.30c fro« tbe airfoil trailing edge. 6fU(60°; 6fL,60°.

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span 3:1 tapered 1ACA 23012 airfoil.

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rig. s

.4 .6 Lift coefficient, CL

Figur« 8.- Effect of 0.30c partial-span lower-surface center-section perforated single split flaps located on a line through the 30-percent-chord stations of the airfoil sections on the

aerodynamic characteristics of a 60-inch span 311 tapered IACA 23013 airfoil. Sf.,60°.

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located on a line through the 30-percent-chord stations of the airfoil section«. 8fL,60°.

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Figure 12.- Computed time-history characteristics during deceleration of an airplane equipped with fighter brakes consisting of 0.20c full-span perforated double split flaps located 0.80c from the wing leading edge.

TITLE: Wind-Tunnel Investigation of Perforated Split Flaps for Use as Dive Brakes on a Tapered NACA 23012 Airfoil

AUTHOR(SJ: Purser, Paul E.; Turner, Thomas R. ORIGINATING AGENCY: Langley Memorial Aeronautical Laboratory, Langley Field, Va. PUBLISHED BY: National Advisory Committee for Aeronautics, Washington» D. C.

f.TTC- B246

(None)

MKUBOKO AOZXX xzxr co. (Same)

HID

WOT Ml eocoAtx

Unclass. oomnar U.S. Eng.

oil TtiAiaai

photos, graphs, drwgs ABSTRACT:

Tests consisted of the determination of lift, drag, and pitching-moment coefficients and wake characteristics for various arrangements of the flaps. Results indicated that single or double perforated split flaps may be used.to obtain satisfactory dive control without undue buffeting effects and that they also may be used as fighter brakes. The perforated split flaps had approximately the same effects on the aero- dynamic and wake characteristics of the tapered airfoil as on a comparable rec- tangular airfoil.

DISTRIBUTION: Request copies of this report only from Publishing '.gency DIVISION: Aerodynamics (2) SECTION: Control Surfaces (3)

ATI SHEET NO.: R-2-3-36

SUBJECT HEADINGS: Flaps, Spilt (37470); Flaps - Aerody- namics (37450.3); Flaps, Dive - Aerodynamic effects (37455.2)

Dhiston, badUgoaeo Department Alf Matoriol Command

AIR TECHNICAL INDEX KfrlfjM-Pattoraon Air Fores Beta Dayton, Ohio

Purser, Paul E. Turner, Thomas P..

AUTHOR(S)

RESTRICTED DIVISION: Aerodynamics (2) SECTION: Control surfaces (3) <5 «—ki/ CROSS REFERENCES: Flaps, Dive - Aerodynamic effects

(37455.2); Flaps, Split (37479); NACA 23012

1LJ ATI- 15187 OR1G. AGENCY NUMB

AMER. TITLE: Wind-tunnel investigation of perforated split flaps for use as dive brakes on " 23012 airfoil * a tapered NACA

FORG'N. TITLE:

ORIGINATING AGENCY: TRANSLATION:

National Advisory Committe for Aeronautics, Washington, D. C.

COUNTRY U.S.

LANGUAGE

Sng. FORG'NCLASS) U. S.CLASS.

Restr. DATE

Nov'41 PAGES 22

IUUS. 12

FEATURES photos, graphs

ABSTRACT Dynamic pressure surveys were made behind a tapered airfoil to determine the wake'

characteristics of several flap arrangements, and the application of this type flap to fighter brakes. Results indicated that single or double perforated split flaps may be used as dive brakes without undue buffeting and that they may also serve* as fighter brakes. These flaps had approxLmatley the same effects on the wake characteristics of the tapered airfoil as on a comparable rectangular airfoil.

NOTE: Requests for copies of this report must be addressed to: N.A.C.A., Washington, D. C.

T-2, HQ., AIR MATERIEL COMMAND AIR TECHNICAL INDEX RESTRICTED

WRIGHT FIELD, OHIO. USAAF Z WT-O-Sl MAI 47 UM

EO ICECI del 5 NOV I353