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HEADQUARTERS AIR MATERIEL COMMAND

WRIGHT FIELD. DAYTON, OHIO

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tfSGoftRNMENT IS ABSOLVED

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203U* Flaaoott, R. H. Aoradynonioo (2)

Wings and Airfoil* (6) Airfoils - Drag (08800)| 11 Z.J6B7 AKHD-«153

(081i21.7) Airplanes - Drag Reduction (08lj21.7)|

Profile drag measurenents on hurricana U Z.36S7 fitted with "Low Drag" section winga *

Royal Aircraft Establishment, Fambo rough, Hants

Ot.Brit. Eng. JUjpi" Restr. Ssp'iib 15 tables, graphs* drags

Teete ears oonductsd to deteraln* the improvement obtained by reducing the surf ao* warineea on the experimental "low drag" wings fitted to the Hurricana XI Z. 3687, to thousandth of an inch variation fron the neon curse doflootlon on a too inch gauge length* Results show thai the drag coefficient has boon reduced to O.OOltU over a range of lift coefficients fron 0.1 to 0.5. This corresponds to transition at 50-60* chord. flow was maintained op to Reynolda Numbers of nearly twenty millions.

• •? 1 -

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• I • • . • . - .'».-•. "

SUITABLE FOR CONTROLLED DISTRIBUTION. RESTRICTED

REPORT No: AERO. 2153.

BRITISH RKTMC-It.-, UNITED biMlti ftuiw-iu--

ROYAL AIRCRAFT ESTABLISHMENT Farnborough> Hants.

PROFILE DRAG MEASUREMENTS ON HURRICANE II Z. 3687 FITTED WITH

"LOW DRAG" SECTION WINGS

R. H. PLASCOTT, B.Sc.(Eng.)

331003

fW l?K* *v *3

1

5^ HTENTKM IS CALLED TO THE PENALTIES ATTACHING

fo TO ANY INFRINGEMENT OF THE OFFICIAL SECRETS ACT ^

THB DOCUMENT IS THE PROPERTY OF H.M. GOVERNMENT

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ANY PERSON OTHER THAN THE AUTHORISED HOLDER.UPON OBTAINING POSSESSION OF TMS DOCUMENT, BY FINUING OH OTHERWISE,SHOULD FORWARD IT, TOGETHER WITH HIS NAME AND ADDRESS.IN A CLOSED ENVELOPE 10 " THE SECRETARY. MINISTRY OF SUPPLY,

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S/» w INCIPSUW.(/...TO RrPORT No.:/\y^ff*~ c/( . -"NH^RY AriACHE. LONBOPJ" **

RESTRICTED

Class No: 533.691.13.001.5.

Report No. Aero. 2153.

September, 1946.

ROYAL AIRCRAFT ESlABITgmnm'P, TUBNBOROUGH

Profile Drag measurements on Hurrioane II Z.3687 fitted with Special rfinga of "Low Drag" Section built by

Armstrong .Vhitworth Aircraft Ltd.

by

R.H. Flasoott, B.Sc. (Eng.)

SUiQtARY

This report describes flight tests to determine the improvement ob- tained by reducing the surface waviness on the experimental "low drag" wings fitted to this aircraft to _+ one thousandth of an inch variation from the mean deflection curve on a two inch gauge length.

Provided no flies or other insects were picked up during the flight, the drag coefficient has been reduced to 0.001(4 over a range of lift co- efficient from 0.1 to 0.5. This corresponds to transition at 50-60Jt chord. .Yith the reduced surface waviness it was possible to maintain laminar flow up to Reynolds Numbers of nearly twenty millions. The slight rise in drag coefficient at Reynolds Numbers above fifteen millions pro- bably arisesbecause the surface did not meet the above requirements at all points on the surface.

LI iT OF CONTENTS

Introduction Description of the Aircraft Description of the Tests Measurement of Surface Waviness Results 5.1 Surface ffaviness 5.2 Profile Drag

6 Maintenance of the Surface 7 "Conclusions References Circulation

LIST OF T>JT^

Hurricane 2.3687. Ordinates of Test Section

Table

I u

r- M i

Report No, Aero. 2153.

LIST OP imiSTRATICKS

d.\. of Hurricane

Profile of test section showing ooaib

Teat section surface waviness as measured by curvature gauge with 2" base

Top surface waviness as sieasured by curvature gauge with 3" base

Bottom surface waviness as measured by curvature gauge with 3" base

Section profile drag obtained from flight tests

Results from all flights - including those during which flies or other insects were pinked up

Fig.

1

2

3

4

5

6

- 2

It

*

T Report Mo. Aero. 2153*

1 Introduotion

A new type of construction thought to be suitable for the maintenance of laninar flour on a wing of "low drag" section has been designed by Arm- strong rfhitworth Ltd. In order to determine the characteristics of such a wing in flight, special wings of this construction have been fitted out- board of the wing Joint at the undercarriage to a Hurricane II 2.3687.

During the previous flight tests on this aircraft (Ref. 1), it was found that the waviness of the surface was large enough to prevent full laminar flow being established, especially at the higher Reynolds Nuanbers. The aircraft was therefore returned to Armstrong «hit»vorth Ltd. for re- duction of the surface ffavine-ss, by use of an appropriate filler and care- ful rubbing down.

The present testa were undertaken to determine the improvement ob- tained by reducing the surface waviness to + one thousandth of an inch variation from the mean deflection curve on~a two inch gauge length.

2 Description of the Aircraft

The aircraft is fitted with a Merlin XX engine (Fig.1). The wings are ::adt to a design by Armstrong 7.'hitworth Ltd. There is no spar, the stresses being taken in a thick skin (16 S.W.G.) stiffened by sponwise stringers of 3 inches spacing. The top and bottom surfaces are connected by ribs 15 inches apart. The leading and trailing edges are constructed in a normal manner and are connected to the "low drag" construction, which ex- tends from 5* to 62?. of the chord on both surfaces.

The wing profile was designed by the K.P.L. to give a peak suction at 50£ chord. The root thickness is 17.9£ and tip thickness 14.8& The junction of the "low drag" wing with the "conventional section" wing root was covered by a fairing panel to bUnd the different profiles into each other.

The ti.at section was 9 feet from the fuselage centre line on the port wing (Fig.1). The detail of the test section, together with its profile, is shown in Fig. 2.

A leading-edge pitot-statle head -arm fitted to the port wing tip.

3 Description of the Tests

j'he profile drag of the 3eotion wag measured by a pi tot-static comb mounted 8.17 inches (9.94* chord) behind the trailing edge (Fig.2). The loss in total head in tho wake was measured by connecting the tubes to airspeed indicators in the automatic observer. Mi altimeter, aircraft .4.3.1. .'.nd accelerometer for normal "g" were included in the observer.

The profile drag of the section w is calculated by analysing tho wake traverse by the method jf Ref. 2.

All the tests won. made in level flight at 10,000 feet. In order to obtain the high speeds, the aircraft had to be dived from some height above 10,000 feet and then levelled out before taking readings. This of course meant that the aircraft was decelerating whilst the readings were being t vkun; but the deceleration warn only about 1 ft./sec./sec., and the correction to drag o efficient due to this wan negligible.

4 ih. asurement of Surfaoo ;avinis3

She; surface wavincRa . s m> .aiu-ud by means of a dofleotiun gauge ./hich consisted of an -JHes di:.l jiiunte-d -n an adjustable base. Traverses

Report No* Aero. 2t53.

of the wing were made with a three inch gauge length on the test seotion and on auctions five inches and ten inches inboard and outboard of the test seotion. -A the spaoing of the spanwise stringers was three inches, these measurements tend to exaggerate the wavineas for comparison with thu flight tests on King Cobra FZ.440 (Ref.3), a traverse of the test seotion was mode with a two inch gauge length.

5 Results

5.1 Surface Waviness

The results of the measurements with the deflection gauge are shown in Figs. 3, 4 and 5. The improvement in the surface waviness is apparent on all the sections, the variation from the mean deflection curve being mostly less than one thousandth of an inch on the two inch gauge length. The bottom surfaoe is the worse in this respect.

5.2 Prafile prag

The profile drag coefficients, calculated by the method of Ref.2 are plotted against aircraft lift coefficient in Fig.6, for all cases in which it appeared that no flies or other insects were picked up during the flight. It will be seen that the drag coefficient has been reduced over the v/hole "low drag" range, the greatest improvement being at the higher Reynolds Number end. The lowest lift coefficient recorded was 0.097 and the drag coefficient at this point was 0.0049. For caparison,

-the drag curve obtained in the previous flight tests is plotted on Fig.6 and it will be seen that the drag coefficient for a lift coefficient of 0.097 was then 0.0066, the present tests thus showing a reduction in drag of 26$. The "low drag" range now'extends from 0.1 to 0.5 lift coefficient.

In Fig.7, are shown the results of all the flights made, including those during which flies and other insects were picked up. The increase in drag due to flies was quite large and it is clear that unless some means can be found to prevent the -insects sticking to the surfaoe, the full advantage of smooth low drag sections will not be achieved in prac- tice.

•$ Maintenance of the surface

Most of the surface held very well; however at two points ->n the port wing, ohordwise cracks developed and extended from the leading edge to about 60£ of the chord on the bottom surface, though on the top sur- faoe it only extended to about 4% back. One of the cracks w .a only two inches outboard of the test seotion and required filling and rubbing doro after each flight.

J'o trouble was experienced with the drying out of the filler, though it was noticed that a substance, which presumably had been used in pro- cessing the wing, tended to oose out of the skin joints and around the rivet heads.

7 Conclusions

The tests confirm the conclusions reached in previous flight tests on wing3 of "low drag" section. A. great improvement has been achieved at the high. Reynolds Numbers by reducing the surface waviness to + one thousandth of en inch variation from the mean deflection curve on""a two inch gauge length. It in u.-.s^ntial for the maintenance of laminar flow at Keynolda Numbers of twenty millions that the surface waviness should not be larger th-au thin. '£he same conclusion was reached during flight tests on King Cobra F.,.440 (iil".3) when drag coefficients of the order of 0.0028 were measured J"ter the surface waviness had been reduced to

- k *

r Report No. Aero. 2155.

this standard. The alight rise in drag coefficient at the high Reynold* Numbers is probably due to the fact that the surface wavineas did not meet the above requirements at all points on the surface; particularly on the bottom surface which will be the more critical at high speeds due to de- creasing incidence.

The drag coefficient has been reduced over the whole "low drag11

range whioh now extends from 0.1 to 0.5 lift coefficient as compared with the 0.17 to 0.45 of the previous tests. The full reduction in drag was of course obtained only in those flights during whioh no flies or other inseots were picked up by the wing.

R-f. No. Author

1 Smith, Higton & Bramwell

Thompson

Smith & Higton

4 Winttrbottam & Squire

Title etc.

Flight tests on Hurricane II Z.y68? fitted with special wings of "low drag" design. R.A.E. Report No. iiero. 2090. October, 1945.

A simple method of computing CQ from wake traverses at high speeds. R.A.E. Report No. Aero. 2005. 1944.

Flight tests on King Cobra FZ.440 to investigate the practical requirements for the achievement of low profile drag on a low drag aerofoil. R.A.E. Report No. «ero.2078. 1945.

Note on further wing profile drag calculations. H....K. Report No. B.^.. 16*34. 1940.

^.ttaohed; • 193773 - 19383S. Table I.

Circulation: - C.S.(u) D.G.S.R. (...) D.S.R.(A) <>..D.„..R.D.(Res.) ~.D.3.R.(Records) D.A.R.D. P.D.T.D. R.T.F./T.I.B. D.D. ..R.D.(Serv.) •U.R.C. .Armstrong rfhitworth per R.T.0.

(action copy)

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% chord

5

7i

10

15

20

30

40

50

60

70

80

90

95

100

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3.04

4.42

5.42

6.19

7.55

8.63

10.07

10.67

10.34

«.83

6.60

4.27

2.03

1.07

(o.?i) . 0

Report No. .iero. 2153.

% chord lower surface

2.29

3.09

3.68

4.19

4.89

5.43

6.20

6.46

6.21

5.16

3.76

2.26

1.04

0.61

(C.21) 0

ifljakiajES Z. 3697.

Oraiiyitoa of Teat fj>.ptivin.

N?.-.jaans-. REPORT AERO 2153

FIG. I.

SCALE OF FEET.

G.A. OF HURRICANE Z.3687.

193768. REPORT AERO 2153.

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REPORT AERO 2153.

FIG. 3.

155 A7T~ 5-o DISTANCE ROUND SURFACE FROM LEADING EDGE (FT).

15 GAUGE

DEFLECTION x 1000 (INS)

30 6-0 DISTANCE ROUND SURFACE' FROM LEADING EDGE I FT.).

TEST SECTION SURFACE WAVINESS AS MEASURED BY CURVATURE GAUGE WITH 2" BASE.

HURRICANE Z.3687.

19360 S.

10 G.AU&E

DEFLECTION tlOOO (INI)

REPORT AERO 2153

FIG. 4. .

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TOP SURFACE WAVINESS AS MEASURED BY CURVATURE GAUGE WITH 3" BASE .

HURRICANE Z.3687.

N9...J13M!*-.. REPORT AERO 2153.

FIG. 5.

20 6AU6E

DEFLECTION IIOOO(INS).

60

0 10 20 30 40 5-0 6-0

BOTTOM SURFACE WAVINESS AS MEASURED BY CURVATURE GAUGE WITH 3" BASE.

HURRICANE Z.3687.

'...lASMJU REPORT AERO 2153.

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AUTHOR(S)

DOOTOOCTG® DIVISION: Aerodynamics (2) SECTION: wings and Airfoils (6) CHOSS REFEBENCES, Airfoils - Drag (08200); 11 z.3687 (0Si£1.7) Airplanes - Drag Seduction (08^21.7);

ATO- 20^ ORJG. AGENCY NUMBEn

ASSO-2153

REVISION

AMER. TITLE: profile drag measurements on hurricane 11 Z.36S7 fitted with "Low Drag" section wings

FORG'N. TITLEs

ORIGINATING AGENCY: Royal Aircraft Establishment, Farnborough, Hants TRANSLATION:

COUNTRY

Gt.Brit. LANGUAGE FORG'KCLAJ

Eng. I Reatr. BATE I PAGES

• Sep'k6, 15 FEATURES

graphs, drugs ABS7QACT

Tests were conducted to determine the improvement obtained by reducing the surface waviness on the experimental "low drag" wings fitted to the Hurricans II z. 3687, to one thousandth of an inch variation from the mean curve deflection on a two inch gauge length. Results show that the drag coefficient has been reduced to O.OOUi over a range of lift coefficients from 0.1 to 0.5. This corresponds to transition at 50-60? chord. Laminar flow was maintained up to Reynolds Numbers of nearly twenty millions.

T-J, HO.. AIR MATERIEL COMMAND AIR "LTECHNJCAI. ONDEX BOflraOTLTia

WRIGHT FIELD. OHIO, USAAF

ESItJFCJISXS (BfwlCT)

Plascott, R. H.

AUTHOR(S)

r ^ [DIVISION: Aerodynamics (2) --, SECTION: Wings and Airfoils (6) '< J

ICROSS REFERENCES: Airfoils - Drag (OS200); 11 Z.36S7 (OSI42I.7) Airplanes - Drag Reduction (021(21.7);

^ITD" go^iiu 1|CC!G. AGENCY NUMBED

AEED-2153 BEVISMJM

AMER. TITLE: profile drag measurements on hurricane 11 Z.J687 fitted with "Ion Drag" sect: wings

FOBG'N. TITLE:

ORIGINATING AGENCY: Royal Aircraft Establishment, Famborough, Hants TRANSLATION:

COUNTRY Gt.Brit. I Restr. I Re

LANGUAGE [FORCN.CUS; Eng. I Restr.

S.CLASS.

Restr. DATE

Sep'li6 PAGES lUVSJi

15 I II tables, FEATURES

graphs, dross

Tests were conducted to determine ths Improvement obtained by reducing the surface uaviness on the experimental "low drag" wings fitted to the Hurricans II Z. 3687, to ons thousandth of an inch variation from the mean curve deflection on a too inch gangs length. Results show that the drag coefficient has been reduced to O.OQW* over a range of lift coefficients from 0.1 to 0.5* This corresponds to transition at 50-602 chord, '^n" flow was maintained up to Reynolds Numbers of nearly twenty millions.

-- - _-_" R wn\/ 1953 :o >w i. *_

T-2, HQ„ AIR MATERIEL COMMAND Anffi ECHNICAl UNDEX WRIGHT HELD. OHO, USAAF oa-o-fl OAQ ta rt£=3