F1LE r oPY NO. ? V

N 6Z 657~9

L6D24

NA llONAl ADVISORY COMMITTEE FOR AERONAUTICS

ORIGINAll Y ISSUED

~ 1946 as Memorandum Report L6D24

STATIC--'.rHIIJST 11MBTIGATI

PV-2 HELICOPl'ER ROl'Om HAVING NACA/ OO12.6

AND 23012.6 AIRFOIL SECTIORS

By Stanley Lipson

Langley Memorial Aeronautical Laboratory Lal:l8ley Field, Va.

NACA WASHINGTON

FILE COP To be returned to

the fi les of the National d' ry Committee

ro autlcs ·_ ...... ,,,....ft, O. c.

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 pre­viously held under a security status but are now unclassified. Some of these reports were not tech­nically edited. All have been reproduced without change in order to expedite general distribution.

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https://ntrs.nasa.gov/search.jsp?R=19930093093 2019-02-10T09:22:30+00:00Z

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NACA LAN''!LEY J:E~I;ORIAL AEB01-JAUTICAL LABORATORY

MEMORANDUM REPORT

for the

Bureau of Aeronautics, lGVY Jlepartment

MR No. L6D2L~

STATIC - THRUST l NVES TIGA'nON OF FULL-SCALE

PV-2 HELICOPT:SH RO'I'ORS HAVING NACA 0012.6

AND 23012 . 6 AIRFOIL SECTlbNS

By Stanle~ Lipson

SUM~.1ARY

An investigation to com~are the performance of two 25-foot-diameter rotors const r uct ed by the P- V Engin.eering Forum has been conducted at the Langley full-scale tunnel. The rotors, which were designed t o operate on the PV-2 helicopter, had i den tical dimensions and were similar in construction but differed in blade airfoil section - one having an NAC A 0012 . 6 airfoil sectton and t he other, an NACA 23012.6 airfoil section~ The tests were conducted at three di fferent rotational speeds including the design rotor speed of 371 rpm .

The results of the tests are presented as the vari­ation of torque coefficient vi th thrust coeff icient. A comparison of the results obtaine d with the 0012 .6 rotor from the present tests . and from a previous investigation shows excellent agreement . Only s~all differenc es were apparent between the~?erformance.characteristics of these symmetric al - and c ambered- s ec t ion blades a1 til.ough at the higher thrust coefficiel''lts. ·the performance of the cambered blades became increasinely better, The comparison of their performance is probably i mpai red by the poorer surface condition of the cambered rot"or. The performance of both rotors could be substantially inproved, as indlcated by pre v i ous full - seale- tunnel tests, by the elimination of certain surface irregularities. The test

2 MR No . L6D24

re s u l ts al so showed tha t t:l.e effec t . of a dis cus whic h was 84 inches i n d i aille t e ~ (28 percent o f t he r o t or d i ameter) wa s negl i g i ble in t he r ange o f nor ma l ho ve r ing f light c ondi t .i ons .

INTRODUCTION

At t he r equ es t of t he Bu~ea~ of Ae r onauti c s , Navy Depar t ment , t es t s ere made at tr..e Lang l ey' f ull - s c a l e tunne l t o compar e t he perfo r manc e of two 25 - foo t - d i amet~

roto r s c ons tru ct ed by t he P- V Engineering Fo r um . The r o t ors , which we r e designed to operate on the PV- 2 hel i ­cop t er , were simi l a r in cons t r uction but d i ffe r ed i n their b l ade airfo il s ection , one having an NAC A 001 2 . 6 se c tion and t he other us i ng . an NACA 230 12 . 6 sect ion . Pr e v ious stat ic - t h r us t and fo r ward- flight pe r fo r mance t es t s were made at r educed rot ~r speeds on t he rotor ha v ing t he symme t r i cal sec t ion and a!'e r epor t ed i n r e f erence 1 . '1'he present report p r esents stat ic - thrus t dat a obtained for t he two r otor s a t three r o t a ti6nal .. speeds , including t he design rotor speed of 371 rpm . The effec t on the r otor char ac t eris t ics of 8Qtli~g a d i scus with a diame t e r of 84 inches ., wh i ch i s' 28 percent of t he rotor d i ame t er , was also investigated .

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C'l' thr ust c oeff i cient , T p (.DR) 7TR

CQ t or que coeffic i ent, Q/p( OR ) 2 7TR2 R

R r o t or r adius , fee t

T rotor thrust , pounos

Q r o tor t o r ~ue , foo t - pounds

o ang~l ar ve l ocity o f ro t or , r adi ans pe r second

p mass dens i ty o f air , sl~g s per cubic foo t

o so l idity , b C/7TR

iAR No . 16D24

b number of r ot or blades

c blade chord at 3R 4 ' f ee t

APp ARATUS AND TESTS

3

The rotor s tested i n t'his i nv.estiga tion were des·igned to operate at 371 r pm on a hel i cop t e r hav i ng a gross weight of 1000 pounds . 'The tes' t r otors had'a diameter of 25 feet , a solidity of 0 . 0605 , and were three - bladed. They are refe rr ed to by t he ir airfoil sections which were HACA. (,1C 12 . 6 an '~ 23012 . G, ::'.6spcc tl.v61J . Ot :lP, r c\-3 t uils ~; f me dimensions and t he cons tr'uc t "lon (f i gs . 1 and 2) were iden ­tical except as no t ed i n t he fol l owing description . Each blade consis t s of a t ubular. s t ee l spar tp which wooden r i bs are attached and covered wi t h fabric. which is rein-. forced over appr o~ i mat e ly the fo r ward third of the blade chord by a layer of , 3/64- inch :~lywOQd blued to trJ.e ribs·, Similar reinforc i ng i ~ used at the extreme tip of the blades with t h e symme tr ical s ection ar;tj for the wid.th of the entire chor d ove r the out er' 20:percent of the 23012 . 6 blades . The surf ace of · t he 0012 . 6 r otor blades has some flat spots a t the tip and ~ome depar tuP6s from a smooth· airfoil.cont orir near t he leadinE edg~'and just aft of the thin ply-wOOO r einforcing . . These lat.t.e r de,viations fro-r:1 an accurate .contour are A~pedially n6t~ceab16 on the 230l2 . 6 ro"t or bl'ades i f. which there is .. 8P?r.o.xi:r:at.e ly· a 1/64- inch jog in the si.rioil· contour on th'e uppe r- and . lower surf aces of a 11 three bl ad.e~ at approximate ly 0. 04c , and just rear warc of' the spr uce lea.ding- edge fairing strip . :

Details of'the (Hscus" used : in the ' tests are, shown in figures 1 and 3 . ' It consiste 'd of a ' fab r ic - covered frame ~ work of thin - wall metal tubes and had a diameter of 84 inches, ' rh l ch' 'is ' 20 , percent ' of the ro t or Giia'l1eter . ,

, "

The general arr~ngement of t~e r o t or ,mqunted in ,the f ull- scale tunnel i s shown in figur e 4. , The rotor was " dr iven by an elec tr ic mo t or and t he ppwer input to the rotor was measur ed by a s t ra i n- ga~~ torquemeter and by a pneumatic to rquemet~ r . The r otor thrus t, the rolling moment, and t he p i tching moments ware ffieasured by a~ auxiliary str a i ri - gage balance . Force r ecords were also ' obtained f tom th~ ' conventional wind- t unnel balances . A

4 !VIR No . L6D24

more comple te description of the tes'ting' arrangement and instrumentation is given in r e ference 1 .

Following t he t e sts of r efe renc e 1, the pylon was stiffen e d sufficiently to enable t he ,p r e sent series of tests to be made at t he rotor de s ign spe e d of 371 r pm without ser ious vibrations . The static- thrust tests were made with the rotor shaft ve rtic~l over a r ange of i ndi ­cate d blade p itch angle s from 30 t o 11 . 50 for rot or speeds of 200 , 290 , and 3 71, r pm . The r o tor was kept triw~ed in roll and p itch . '

RESULTS AND DISCUSSION

The static- thrust r esults obtained for the 00 12 . 6 r otor a r e pres ente d in figure 5(a) in , terms of t he variation of the thrust c oefficien t with the torque , coeffic ient . Similar results for the 23012 . 6 rotor alone and in combination with the 84- inc h discus a r e given in fi gur es 5(b) an d 5(c) . Vfuil e t heore tica l consider ation~ might indicate some scale effect, ' t hese r esul t s , like previous rotor t es ts made i n the ful l - scale tunnel (see r eferen c es 1 and 2) , show no consistent effeqt on curves of thrus t c oefficient against. torque c oeffici ent du e to change s in rot a tional speed . On l y one curve , the r ef6 r e " was f aired through t he data in each of t hese figures . ' The f aired static - thrust curve for the 00 12 . 6 rotor g iven in refe r ence 1 has b ee n included in fi gure 5(a ) for ~he p urpose of c'omparison with the more r e c ent results . The two sets of da ta are in excellent agr eemen t .

The resul t s of the static - t hrus t t e sts are summarized in figure 6 . The performance of the 23012 . 6 r o tor become s increasing l y bett e r t han that of the b0 12. 6 r o tor for thrust coefficients greater than about 0 . 0030 . The fli ght c onditions fo r the PV- 2 h e lic op t e r corresponds t o operation at a r o t or ti p speed of 485 feet p r second and a rotor t hrust coefficient of 0 . 00364 . At t h ts des i gn thrust coefficient the difference in ho~sepowe r r equired to hover with each r o tor is l e ss than 2 pe rc ent . It ap pears probable that a somewhct t large r d iffe r ence :might have b~en shown we r e it no t f or the s lightly be tt e r surface condition of t he sJ~metrical- sec ti on rotor~ Also , since the cambered section shows increasing g ains at thrus t coeffici ents beyond t he design value up to the highest value covere d by the data, the max i mum gains

MR No . L6D2h 5

~btainable would presumably be realize d at still higher thrust coefficients . rrheory indicates that the maximum effect of the blade camber would be reali,zed just prior to the stall; however , powe r limitations on the electric drive mptor pre vented obtaining data nearer the blade stall. ' ,

The imperfect surface conditions of the two rotors tested undoubtedly impairs their static- t hrust performance. The data of reference 2 ind ic ate that elimination of surface defor mat ion and irre gul ariti es ma y result i n an average povve r savirlg in horsepower of as, much as 10 percent. The close rib spacing and'doped finish of the two rot ors tested should prevent excessive drag l osses due to surface deformation . The el i mination of the rotor blade surface irregularities , however , should appreciably increase the performance of t hese rotors.

Figure 6 also shows t hat the 8h- inch-diameter discus has no effec t on the stat ic-th rus t performance throughout the ' norma l ope r atj.ng range of the rotor although it produc e s a s light detrimental e ff ec t at the lower thrus~ coefficients .

CONCLUDING REMARKS

Static - thrust tests of t wo PV~2 helicopter ro t ors in the Langley ful l - s cale tunne l show t he following results:

1. At the design thrust c oe ffici ent of 0 . 00364, the 23012.6 rot o r requi~es a~proximat e l y 2 percent less power to hoye r : than the symmetri cal b l ades. This differ ­ence would probab l y beincreai~d if the surface of the • cambered blades was as relativ~ly smooth as that of the s,yrmnetrical b lades. At thrus t coefficients above the des'ign value ,the, pe rfo.r manc'e of' t he 23'012 . 6 rotor ,becomes increasingly , be tt ~ r than' that of the 0012. 6 rotor.

2 . As ind icat ed by pr evious full - scale-tunnel tests, improved pe rformanc e of bo t h rot ors can pr obably be obtained by el iminat ing their surface dis c ontinuities.

6 MR No . L6D24

3 . The use of an 84- inch- diame ter discus had no appreciable effect on the static - thrust performance throughout tte no~mal,operating range or the rotor.

Langley Memoria l Aeronautical Laboratory National Advisory Committee for Aeronautics

Langley Field , Va.

REFERENCES

1 . Migotsky , Eugen$ : Full - Scale - ~~nne l Performance Tests of the PV- 2 Helicopter Rotor . NACA MR N~ . L5C29a , 1945 .

2 . Dingeldein , Richard C., 'and Schaefer, Raymond F .: Static - Thrust Tests Qf Six Rotor - Blade Designs on a Helicbpter in t~e LaNgley Full - Scale Tunnel .

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Figure 4.- General arrangement of the PV-2 helicopter rotor as tested in the Langley full-scale tunnel.

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