Document
REPORT No. 689
PRELIMINARY WIND-TUNNEL INVESTIGATION OF AN N. A. C. A. 23012 AIRFOIL WITH
VARIOUS ARRANGEMENTS OF VENETIAN-BLIND FLAPS
By CARL J. WENZINGERand TEO~AS A. HARRIS SUMMARY are also included for comparison with the data for venetian-blind flaps.
An investigation has been made in the N. A. C. A. 7- by MODELS 10-joot wind tunnel oj a large-chord N. A. C. A. 2301.2 PLAIN AIRFOIL airjoil with several arrangements of venetian-blind$aps to determine the aerodynamic section characteristics as a~- The basic wing, or plain airfoil, used in these tests was fected by the over-all $ap chord, the chords oj the. slats built to the N. A. C. A. 23012 profile and had a chord of used to jorm the$ap, the slat spacing, the number of sluts, 3 feet and a span of 7 feet; it was previously used for the and the position oj the @p with respect to the wing.
slotted-flap investigation of reference 1. New trailing- Complete section data are given in the form of graphs for edge pieces were made for the model with necessary cut- all the combinations tested.
outs for the new flaps.
The optimum arrangement oj the venetiam-blind jiap VENETIAN-BLIND FLAPS was a combination in which the jfap was located near the These arrangements oj the venetian- wing trailing edge.
The venetian-blind flaps were made of small slats blind$ap were superior to any jfaps previomly tested jor arranged to pivot on arms that were, in turn, pivoted to producing l~t and giving low drag coefitients at high I@ the wing. The deflection of the complete system of coefficients. The wing m“th this jlap, however, had very flaps is referred to as 63.. The deflection of the indi- large pitching-moment coej%ients. When operated as vidual slats on the arms is designated 87. When the split jfaps, the venetian-blind $aps were injerwr to the individual slats are deflected differentially with respect simple split $ap in producing lift.
to each other, the subscript carried by 6r refers to the number of the slat on the supporting arm starting from INTRODUCTION the one nearest the axis of the arm. The various arrangements of venetian-blind flaps are sliown in fig- The National Advisory Committee for Aeronautics is ures 1 to 4 with the flap both retracted and in the undertaking an extensive investigation of various wing- optimum deflected position as determined from the flap combinations to furnish information applicable to tests.
the design of high-lift devices for improving safety in flight. One of the most promising arrangements devel- ~c =““~ oped to date in this research is reported in reference 1.
The arrangement is a slotted flap capable of giving high I
I
.—. —.—. — .—. — .—. —
.-, . . . . . . . . . . . .-.---A --=-
-.-.:. .,.
maximum lift coefficients, low drag coefficients at mod- .40C .45C
1’
erate and high lift coefficients, and high drag coeffi-
R==l o
-w ~ S/of dek?il cients at high lift coefficients. This combination was
still further improved by the addition of an auxiliary ~’”~pj ....... y“ 0>4--50”
b, 4,.60” slotted flap, the investigation of which is reported in C,=.04: =[44” reference 2. The results of these tests indicated that ‘Y + = hinge axes still further improvement might be obtained by the use x \ of a nmltiply slotted flap. Special ty-pes of multiply FIGURE I.—Section of N. A. C. A. 23012airfoil with a venetian-blind flap hfnged slotted flap-for example, the venetian-blind flap-have at 0.55c;ten 0.04cslats.
been suggested by E. l?. Zap and also in,reference 3.
The arrangement of the 10-slat venetian-blind flap is The present report gives the results of an investiga- shown in figure 1. Each of the slats had a chord 4 per- tion of an airfoil with several arrangements of venetian- cent of the basic wing chord; the sum of the chords of blind flaps. The spacing, the chord, the position, and the slats was therefore 40 percent of the wing chord.
the number of the slats composing the venetian-blind Each slat was of solid brass with a round nose and a Some data for simple split flaps flap were considered.
a. —.-. . -k—..
_.— . . ..-4.JL+ . .. . .. ..,-.. -—e. -~_ —------ - ~~ -.. -, ‘.
-. .-:. —...,. L —
198 REPORT NO. 68-NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
The venetian-blind flaps shown in figure 4 are the sharp trailing edge, as shown in the detail of @gu.re 1, and was made to pivot on the supporting arm about the same as those shown in figure 3 except for the position midchord point of its lower surface. The supporting of the arm axis, which is on the lower surface of the main arms were, in turn, pivoted 5 percent of the wing chord ahead of the first slat to provide a slot between the slats and the wing when the complete system was deflected.
Several arrangements of a venetian-blind flap with an over-all chord 40 percent of the wing chord are shown in figure 2. In all arrangements, the flap was composed of slats with chords 10 percent of the wing chord. These slats were built of wood to the Clark Y profile. They were pivoted on the supporting arms about the quarter- chord point of their lower surface. The arrangements of the five, the four, and the three slats shown in figure 2 were made to determine the optimum spacing of the slats. The filler blocks shown on the arrangement with (b) three slats retracted were removed for tests with the - 6,==60” .
,,./’ Y\ flap deflected. f’+ = In order to determine the effect of over+-dl chord of the venetian-blind flap, the models were tested with \ flqp chords 40, 30, and 20 percent of the wing chord, as .— .— .— .— .
shown in figure 3. The same Clark Y slats were used .. ..- ---- .
-----.:: for this model as are show-n in figure 2. As may be
~d
.=_C,<-~ 6,=6,==600 seen from figure 3, the 40-percent-chord flap was com- (c) + = hinge oxes C$= .Ioc.-..
posed of four slats, the 30-percent-chord flap -was com- k posed of three slats, and the 20-percen&chord flap was w (a) The 0.55clocation; four slat.% composed of two slats.
(b) The 0.65location; three slats.
(c) The 0.75location; two slats.
FIGWBE 3.—Sections of N. A. C. A. 23012airfoil with srveml mmmgeruents of venetian-blffd flaps hinged at ditlerent axis locations; O.1OC slats.
I tioil one-half of 1 percent of the wing chord ahead of ~he trailing edge of the wing. This position of the mm (a) E& was estimated, from results of previous tests of dotted and I?owler flaps, to be the most promising axis c ‘sd”~ —.— .—. — -—- -.--..= .
---~==<.-~-::..: --- ~ f—.40c “ (a) , \.
(b) (c) .—— .— - 6,.40.
“’:.M+c-
--7 4
.20C
1-
6,; 60’ (c) 7$ + = hi-rgeoxes c, == Joe...” + = hinge oxes d ‘!
(a) Five data spaced 0.75r/. (a) Four slats.
(b) Four slats spaced l.rlk,.
(b) Three aiats.
(c) Three sIats spaced 1.5fkf.
(c) Two slats.
FIGURE2.—Sections of N. A. C. A. 23o12airfofi with saved arrangements of FIGURE4.—Secff ons of N. A. C. A. 23012airfoif with several mrongements of venetian-bifnd flaps hinged at di5erent 0.55GO.1OC slats. venetian-blind flaps hinged at 0.96%;O.1OC slats.
N. A. C. A. 23012 AIRFOTL WITH VENETIAN-BLIND FLAPS 199
Iocation forthevenetian-blind flap. Thisarr.angement %2. C.)o section pitching moment.
dynamic pressure (M p~).
provided a gap of about 1 percent of the wing chord !l between the first slat and the trailing edge of the wing c chord of basic airfoil -with flap fully retracted.
when the arms were deflected to the optimum position. md a. angle of attack for irdinite aspect ratio.
Is, deflection of individual slats.
TESTS % deflection of complete system of flaps.
PRECISION The models were mounted in the closed test section of the N. A. C. A. 7- by 10-foot wind tunnel so as to The accuracy of the vm.ious measurements in the tests span the jet completely except for small clearances at is believed to be within the following limits: each end. (See references 1 and 4.) The main airfoil -------- % ------------ 4=0.1° &O.0006 ‘Wcl=l.o) was rigidly attached to the balance frame by torque P
.lmm ---------- Cdo *0.002
&o.03 (CI=2.5)-------- tubes, which extended through the upper and the lower
Ln (~ . c.)i)-------- +0.003 8,c_______________ %2°
boundaries of the tunnel. The angle of attack of the $mmfn--------.-.
model was set from outside the tunnel by rotating ,the +0.0003 af-------------- +0.5° torque tubes with a calibrated drive. Approximately Slat position _____ +0.00Ic two-dimensional flow is obtained with this type of The accuracy of the individual slat deflection tif refers installation and the section characteristics of the model to the settings of the slats relative to each other; the under test may be determined.
accuracy of the setting to the reference line (the lower A dynamic pressure of 16.37 pounds per square foot mrface of the wing) is & 2°. Likewise, the accuracy of was maintained for most of the tests, which corresponds the slat position is the spacing on the supporting arms.
to a velocity of 80 miles per hour under standard atmos- The data have been corrected for the error due to pheric conditions and to an average test Reynolds support interference as determined from special tests Number of about 2,190,000. Because of the turbulence with dummy supports in place.
in the wind tunnel, the effective Reynolds Number R, PLAIN AIRFOIL was approximately 3,500,000. For all tests, R, is based on the chord of Ihe airfoil with the flap retracted and The aerodynamic section characteristics of the plain on a turbulence factor of 1.6 for the tunnel.
N. A. C. A. 23012 airfoil as determined in the two- Each arrangement of the venetian-blind flaps was dimensional-flow installation are given in figure 5.
tested with the flap fully retracted to determine the These data were taken from reference 1 and require no effect of the breaks in the lower surface of the airfoil further discussion here.
on the drag. Tare tests were also made to determine the effect of the supporting arms.
All arrangements of venetian-blind flaps were tested with the arms deflected 30°, 60°, and 90°. For each arm deflection, the slats were deflected various amounts to determine the optimum arrangement from considera- tions of maximum lift. Tare tests were made to deter- mine the effect of the supporting arms when deflected 60°, An angle-of-attack range from –4° to the angle of attack for maximum lift was covered in 2° increments for each test. Lift, drag, and pitching moment were measured at each angle of attack.
RESULTS AND DISCUSSION COEFFICIENTS All test results are given in standard section nondi- mensional coefficient form corrected as explained in reference 1.
c, section lift coefficient (1/gc).
c~ section profile-drag coefficient (dJgc).
c~(= ~.)Osection pitching-moment coeffitiient about aero- d~amic center of plain wing (m{=. ..JO/gC2).
where 1 section lift.
& section profile drag.
FIGUBE5.—Aarodynamic section chardctmisties of N. A. C. A. 23012plain airfoil.
407300°-41-14
200 REPORT NO. 68*NATIONAL ADVISORY COiMMI’lWEE FOR AERONAUTICS
VENETIAN-BLIND FLAP figure 7 on the basis of the increase of section maximum lift coeilicient Acz.U Effect on cti of retracted fiaps.-The increments of due to deflecting the flap. This profile-drag coefficient caused by the breaks in the wing *cI.~ is the difference between the maximum lift coefficients of the wing with the flap deflected and the lower surface with the various arrangements of venetian- the flap neutral, both at the same air speed.
blind flaps retracted are shown in figure 6. The drag The effect on Acz.~ of varying the spacing and the size of the slats composing the venetian-blind flap is .0040 shown in figure 7 (a).
The 10-, the 5-, and the 4-slat flap arrangements all give about the same *cIm.. at a ~a” given arm setting. The optimum setting in all cases ~..0032 was with the slat+upporting arms down 60° and with $ @ the slate deflected so that the flaps were similar to a $$.0024 0.45c split flap with a gap. The flap arrangement with Ual $8 the three slats was inferior to the other arrangements <b as a lift-increasing device. It appeared, therefore, o Q.0016 i.< ~-p that the optimum spacing of the slats (distance between E* slat hinge axes) -was a spacing of one slat-chord length w.0008 Lo and that there was no advantage of using a large num- o~ z~ ber of small-chord slats instead of a few slats of large o chord.
The effect on AcJ~a. of varying the over-all chord of 0 .2 4 -.6 .8 1.0 /.2 /.4 Secfion lift coefficient Cz the venetian-blind flap by varying the number of slats ‘- is shown in figure 7 (b). The arrangements with threo FIGUREO.—Effectof retracted venetitm-blind flaps on profile drag of airfoif.
and four slats were slightly superior to the arrangement with two slats. None showed any improvement, how- increments were obtained by taking the difference be- ever, over a simple split flap of corresponding ovcr+dl tween faired drag curves of the respective combinations chord length, as shown by some curves for the simple (after deduction of the drag due to the slat-supporting split flaps, which are plotted for comparison. (See also arms) and the plain wing. The drag increments are reference 5.)
therefore only the increases due to breaks in the wing When the two-, the three-, or the four-slat flap surface.
arrangements were moved to the trailing edge of the The flaps composed of two and three slats hinged, wing and deflected (similar to a l?owler flap), the Ac r~~= respectively, at 0.75c and 0.65c showed practically no was greatly increased (fig. 7(c)). The optimum set- effect on the increment of profile-drag coefficient for lift tings for each of the combinations were obtained with coefficients less than 0.3 within the experimentffl accu- the 60° deflection of the supporting arms. In order racy of the tests. The increments of profile-drag co- still further to improve these arrangements, differential efficient reached about 0.001 for these combinations, slat settings were tried with the combinations deflected however, at a lift coefficient of 1.0.
60°. In all cases, the effect was to increase Acl~az (fig.
The flaps composed of three and four slats hinged at 8); the best arrangement was the one with four slats, 0.55c gave an increment of profile-drag coefficient of which gave a Aclma. of 2.1. In order to show the efl’ect about 0.0008 at a lift coefficient of 0.2, which increased of over-all flap chord on Ac t~==,the optimum Aczmazfor to about 0.0014 at lift coefficients greater than 0.7.
each of the three arrangements is plotted against flap The flap composed of 10 slats hinged at 0.55c gave chord in figure 9 along with the results of the tests of a an approximately constant increment of profile-drag coefficient of about 0.0014. If snfiicient care is used Fowler wing from reference 1. When based on the area in the design and the construction of the slats and the of, the wing with flap retracted, the Ac t~az increased learly linearly with flap chord over the complete range supports, none of these arrangements should be in- jested. When based on the sum of the areas of the wing ferior to the arrangement with two slats hinged at the md the flap, the Aczn==will be little increased by using 0.75c location.
:hord lengths of the venetian-blind flaps greater than The arrangement with five slats hinged at the 0.55c ).3oc. The loading per unit area was about the same axis gave increments of profile-drag coefficient of from ‘or the three- or the four-slat venetian-blind flap as for 0.003 to 0.004, which are prohibitive. This arrange- ment (fig. 2 (a)) appears to be aerodynamically inferior ihe corresponding split flaps. (See figs. 7 and 9.) The ~enetian-blind flap was superior to the Fowler flap when retracted.
Effect on cl~= of deflecting flaps.-In order to references 1 and 6) of the same over-all chord. It is nwbable that better arrangements of the venetian- determine the optimum arrangement of venetian-bliid )liid flaps can be obtained by a better location of flaps from considerations of maximum lift coefficient, ~uccessive slate- the various arrangements have been compared in N. A. C. A. 23012 AIRFOIL WITH VENEM.A??-BLIND FLAPS .
.?0 o Five O. 10c .sIofs [.6 O Ten ~” Four II II 1.2 % , !
.8 ) , Y / / f / ~ / / / / ,4 d / / / A I I I (a) — I I
.l
Ti I
,
3°
i 2.0
Q *.
c al ..
w GE& splitflap ~ Four O.IOC slots a+ O. 55c “A n ‘t “ $ 1.6 v Three II u u .65,1 v .40” 11 ‘!
.75= x Two II “’ II e) o t “~ /.2 g E .5 , I//.
1- .8 / }/ ,4/1/ I Z?V ,X < I co - O.fOc slafs +1 Four q Three O.IOC sl@
$ D TWO O. IOC Sk?fS
2.0 + \h , ~ + Y + / 1.6 / -+. %J / A (a) Sr.veral arrangements hinged at 0.55r.
(b) Several arrangements hinged at different axis locations.
(c) Several arrangements hinged at 0.995c.
FIGUBE7.—Increments of maximum lift coefficient for various arrangements of vanetiau-blind flaps.
202 REPORT NO. 6S&NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
(a) Twoslats. (II) Three slata.
(c) Fourslats.
FIGuaES.-Iasrementa 0fmeximumlift we5cienta forseversl arz’8ngements ofvenetian-blind flaps at 0.W5cwith differantIaI slatsettings; O.lOcslnk.
Aerodynamic characteristics of arrangements hinged slats (figs. 10 to 12) are all about the same. The most at 0.55c.—The complete aerodynamic section charac- striking thing abou$ these results was the large decrease teristics of the various arrangements of venetian-blind in profile-drag coefficient with lift coefficient for the flaps hinged at 0.55c are given in figures 10 to 13. Each large flap deflections.
The arrangement with three of these figures is divided into three parts, the character- slats (fig. 13) was inferior to the others from considera- istics for one arm setting being given in each part. The tions of high lift.
A slat spacing of one chord length characteristics of the arrangements with 10, 5, and 4 therefore appears to be most desirable because it is L least complicated and closer spacing is not beneficial.
There being practically no choice aerodynamically bet~een the 10- and the 4-slat flaps, the 4-slat flap is somewhat superior because it is simpler structurally.
~} V..eticL)ind !/ap GE2.4 -i Aerodynamic characteristics of combinations at dif- Fowler flop [ref~ence JI a :} *.
ferent axis locations.— The aerodynamic section char- c u act@stics for the three- and the two-slat flaps hinged, :$ 2.0 respectively, at 0.65c and 0.75c are given in figures 14 t u and 15. The characteristics of the two-, the three-, and the four-slat flaps are directly comparable, respec- ~ 1.6 tively, with the 0.20c~, the 0.30c~, and the 0.40c~ .> Based on area g of wing, flap — split flaps of reference 5. The drag was higher for all E . .
refracfed & deflections for the venetian-bliid flap than for the ) / 1 & 1.2 simple split flap. The pitching-moment coefficients c > - ‘ ) -$ were about the same as for the split flap of the samo / o chord. The venetia.n-blind flaps hinged as simple split P >K’ ~ .8 . . : flaps were therefore inferior to the simple split flap / / Q ‘Based on sum of / areos of wing — except for very high drags. The four- and the three- $ and flap ~ slat flaps (figs. 12 and 14) gave both higher drags and / ‘ .4 ( larger pitching-moment coefficients than the two-slat k ~ 4 / flap (fig. 15).
Aerodynamic characteristics of combinations hinged o 10 20 30 40 at 0.995c axis.-The complete aerodynamic section flop chord, percent c characteristics for the four-, the three-, and the two- )?IQUBE 9.—%riation of increment of maximum lift seeffisient with shord of slat flaps are given, respectively, in figures 16 to 18.
venetisn-blind tfap; O.1OC slsts at 0.995caxis.
z
N co o # N (a)6/,=30”.
(b)8/,ao”. (o)6).-00”.
~IGuRE 10,—Aorodynomio 6oct10n ohomotorlstiw of N, A. O. A. 23012nirfoll with n vonotlm-blind flop Mngod ot 0J5c OXIS; ton 0.04cSMS, (8)3/.=30”. (c) &c=9w.
(b)r3/e+&.
FIQURE11.—Aemdynamic %ction ehmacterfstics of N. A. C. A. 23o12 airfoil with a -mnetian-bllnd !bIp hinged at 0.55caxiv five O.IOC siak.
.
.
(0)afc=90”.
(b)3r.=60”.
(a)J/.=3o”.
FIGURE13.—Aemdmmmicsection characteristics of N. A. C. A. 23012 airfoil with a vonotiarr-blind flap hinged at 0.6& axis; tbrse O.1OC sMs.
N. A. C. A. 23012 AIRFOIL WITH VENETIAN-BLIND FLAPS 207
-4 -i ti N o Sectiontiff coefficient, ct (a) 3fOE300.
(b)6/.=60°.
(c) $/.-s4”.
FmmJRE 15.—AerodynamIcsection cbnmcterktim of N. A. C. A. 23012 akfoll with a venetkm-blind flap hinged at 0.7.%nx@ two O.IOC slats, N. A. C. A. 23012 AIRFOIL WITH VENETIAN-BLINB FLAPS . .
1~~ I I I I I ;G 0 1 1 i -.81 .
,32 ,28 .24 .20 .16 ‘.12 .08 .04 ,0 C2 ., ~ /6 N“ w $ 8 I WI I I I I I I I I&l I I I I I b % w z I / I & to / / o / ~ . v v f * (a)
(b) P -8
I II
I
+
-.4 0 .4 .8 L2 I& 20 2.4 .?8:4 O .4 .8 [2 L6 ,?0 2.4 2.8 3.2 3.6-.4 0 .4 .8 L2 1.6 2?0 2.4 28 3.2 Secfion Iiffcoefficient,ci (a) tf.+o”. (b) L+JC40”. (C) df.=@3°.
FIGURE 17.—Aaradynandc section cbaracterLstics of N. A. C. A. 23o12 airfoil with a venetfan-blind flap bingad at 0.995caxi$ three O.1OC slats.
Ei
M o
!7
ki
Ii
UI Sectionlift coefficient, ct (8)8/,=80”, (b) IVO=OO”.
(o) 6/.-00”.
FIGURE 18,-Aerodynnmio sootion ohnmctorlstlcs of N.A.O. A. 23012nirfoll with a vonetlan.blind flop blngod at 0.006coxfs; two O.IOC slots.
REPORT NO. 68*NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS the optimum uniform setting of the slats. Apparently, These arrangements -were the only ones that showed any particular promise from a consideration of high the flow over the slats is controlled much better with maximum lift. The effects on profile-drag coefficient the differential angle settings of the slats. It is probable at various lift coefficients are listed for these arrange- that better differential arrangements may be obtained by a different spacing of the individual slats.
ments in the following table.
The pitching-moment coefficients of these mrange- COMPARISON OF VENETIAN-BLIND FLAPS LOCATED ments (figs. 16 to 18) were about the same as for 11’owler AT 0.995c flaps of the same over-all chord (references 1 and 6).
cd~ The pitching-moment coefficients were very large, reach- {umber 6, (de?J —.
ing a value of about 1.0 for the arrangement with four of slats .
C,=l. 5 cl=2.o CI=2.5 ct=3.o slats.
— — —— — — CONCLUDING REMARKS 30 o. 03s 0: ~~ 4 0: rg ..~:tii..
.032 4 % .03s .062 .0s9 .240 The results of these tests indicated that the venetian- 3 30 .026 .037 .056 -..:i@-- 3 .02% .036 .055 blind flap, when operated near the wing trailing edge, 3 % .036 .055 .0S6 .290 2 30 .027 .039 .069 --------- was superior to any previous flap tested as a lift- .0E3 2 .026 .03s --------- a .095 2 .032 .052 --------- increasing device and was also superior on the basis T — , —, — — of low drag coefficients at high lift coefficients. The O.2667C. Fowler flap (re&mce l)-----.027 .040 .062 ........- wing with this flap, however, had very large pitching- . — — moment coefficients The venetian-blind flaps, when 0.XG6C slotted tlap .075 --------- (reference I)------ .020 .042 operated as split flaps, produced less lift than simple split flaps of the same over-all chord.
The results from reference 1 for the I?owler flap and The tests also indicated that the best spacing of the the best slotted flap are included in the table for com- slats in the venetian-blind flap was one slat-chord parison.
length and that there ‘was no advantage in using 10 At a lift coefficient of 1.5 for the optimum settings, small slats in preference to 4 large slats in a flap of a all arrangements of venetian-blind flaps gave results given over-all chord length. Additional test? are de- equal to or better than the best slotted flap or the Fowler sirable of the 30- and the 40-percent chord venetian- flap of reference 1. With the supporting arms deflected blind flaps operated near the wing trailing edge and 60°, all three arrangements of venetian-blind flaps were using d.itt’erent numbers of slats and slats of different of about equal merit.
airfoil sections. In these tests, particular attention At a lift coefficient of 2.0, the venetian-blind flap with should be devoted to the differential angle settings of two slats had profle-drag coeilkients about 10 percent the slats and to the slat spacing.
less than those of the best slotted flap of reference 1.
The three- and the four-slat flap arrangements were pro- gressively better than the two-slat arrangement. The LANGLEY MEMORIAL AERONAUTICAL LABORATORY, venetia.n-blind flap with four slats had proiile-drag co- NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS, efficients 25 percent less than that of the beet slotted LANGLEY FIELD, VA., January 10, 1939.
flap of reference 1. All the venetian-blimd flap arrange- REFERENCES m ents with the best settings were superior to the I?o-wler flap at a lift coefficient of 2.0. All the arrangements I. Wenzinger, Carl J., and Harris, Thomas A.: Wind-Tunnel Investigation of an N. A.C.A. 23012 Airfoil with Various give the lowest drag with the supporting arms deflected Arrangements of Slotted Flaps. T. R. No. 66% N. A. C.A., 60° at this lift coefficient.
1939.
At a.lift coefficient of 2.5, the venetian-blind flaps had 2. Wenzinger, Carl J., and Gauvain, William E.: Wind-Tunnel lower drag coefficients than the best slotted flap of ref- Investigation of an N. A. C. A., 23012 Airfoil with a Slotted erence 1. The profile-drag coefficient was from 16 per- FlaD and Three Types of Auxiliary Flap. T. R. No. 670, cent less for the two-slat arrangement to 35 percent less N. ~. C. A., 1939--- j. Grey, C- G.: On Venetian Blind Landing. The Aeroplnnc, for the four-slat arrangement than that for the best vol. LII, No. 1353, April 28, 1937, pp. 499-504.
slotted flap of reference 1. The two-slat arrangement L Harris, Thomas A.: The 7 by 10 Foot Wind Tunnel of the in its best setting, however, w= s~ghtb ~erior to the National Advisory Committee for Aeronautics. T. R. No.
Fowler flap of reference 1. The optim~ supporthg- 412, N. A. C. A., 1931.
j. ~enzinger, Carl J., and Harris, Thomas A.: Wind-Tunnel arm deflection was 60° for this lift coefficient also.
Investigation of N. A. C. A. 23012, 23021, and 23030 Air- At a lift coefficient of 3.0, the four-slat arrangement foils with Various Sizes of Split Flap. T. R. No. 668, had a profile-drag coefficient only 10 percent higher than N. A. C. A., 1939.
that of the best slotted flap at a lift coefficient of 2.5.
j. Platt, Robert C.: Aerodynamic Characteristics of a Wing With the optimum differential setting of the slats with Fowler Flaps Including Flap Loads, Dowmvash, rmd (figs. 16 to 18), the variation of angle of attack with lift Calculated Effect on Take-Off. T. R. No. 534, N. A. C. A., 1935.
was approximately linear. This result was not true for