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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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 .
/ 2 2
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 I. - D/mensions of a P,V-2 helcopkr rolor hlade and the discus.
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Fig ure 2.- PV-2 rotor blades tested during static-thrust investigation.
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Figure 3.- 8 4- inch discus tested during static-thrust
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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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