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F1LE r o PY NO. ? V L6D2 4 NA llONAl ADVISORY COMMI TTEE 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.
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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 expedite general distribution.
L - 749 - __________ ~ _ ~~_..J NACA LAN''!LEY J:E~ I ;ORIAL AEB01-JAUTICAL LABORATORY MEMORANDUM REPORT for the Bureau of Aeronautics, lGVY Jlepa rt ment MR No. L6D2L~ STATIC - THRUST l NVES TIGA'nON OF FULL-SCALE PV-2 HELICOPT:SH RO'I'ORS HAVING NACA 0012.6 A ND 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 Eng in.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 an d were similar in construction bu t differed in blade airfoil section - one havin g 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 inclu d ing the design rotor speed of 371 rpm .
The results of th e tests are presented as the vari- ation of torque coefficient vi th thrust coeff icien t. A comparison of the results obtaine d with the 0012 .6 rotor from the presen t tests . and fr om a previous investigation shows excellent agreement . Only s~all d ifferenc 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 cambe red blades became increasi nely better, The comparison of their performance is probably i mpai red by the poorer surface condition of the cambered rot "o r. The performance of both rotors could be substantially inproved, as indlcated by p re v i ou s 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 percen t o f t he r o t or d i amete r) wa s negl i g i ble in t he r ange o f no r ma l ho ve r ing f li ght c ondi t .i ons .
INTRODUCTION At t he r eq u es t of t he Bu ~ ea~ of Ae r onau ti 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 tu nne l t o compa r e t he p erf o r man c e of two 25 - f oo t - d i amet ~ roto r s c ons tr u 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 si mi l a r in cons t r u ctio n bu t d i ffe r ed i n their b l ade air fo il s e cti on , one ha vi ng an N AC A 00 1 2 . 6 se c tion and t he othe r us i ng . an NACA 230 12 . 6 se ct ion .
Pr e v ious sta t ic - t h r us t and fo r ward - fligh t pe r fo r mance t es t s were made at r educed ro t ~r speeds on t he roto r 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 presen t report p r esen ts sta t ic - thrus t da t a obtained for t he two r oto r s a t three r o t a ti 6n al ..
speeds , including t he design rotor speed of 3 71 rpm .
The effec t on the r otor cha r 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 percen t of t he rotor d i ame t er , was also investigated .
2 2 C'l' th r ust c oeff i cient , T p (.DR) 7TR / C t or que coeffic i en t, Q /p( OR ) 2 7T R2 R Q R r o t or r ad iu s , fee t T roto r th ru st , pounos Q r o to r t o r ~ue , foo t - pounds
o ang~ l ar ve l ocity o f ro t or , r ad i ans pe r second
p mass dens i ty o f air , sl ~g s per c ubic foo t o so l idity , b C /7TR iAR No . 16D24 b number o f r ot or b la d es c blade chord at R f ee t
4 '
AP p ARATUS A ND TESTS The roto r s tested i n t' his i nv.estiga ti on 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 solid it y of 0 . 0605 , and were three - bladed.
They are refe rr ed to by t he ir airfoil sections which were
HAC A. (,1C 12 . 6 an '~ 23012 . G , ::'. 6spcc tl.v61 J . Ot :lP, r c\-3 t u il s ~; 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 ubula r. s t ee l spar tp which wooden r i bs are atta c hed and covered wi t h fabric . which is rein-.
forced over app r o~ i ma t e l y the fo r ward thir d of the blade chord by a laye r 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 cho r d ove r the ou t er' 20:percent of the 23012 . 6 blades . The sur f ace of · t he 0012 . 6 r oto r blades has some flat spots a t the tip and ~ome depa r 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 upp e r- an d .
lower surf aces of a 11 three bl ad.e~ at approxi m ate ly 0. 04c , and just rea r warc of ' the sp r 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 ha d a diameter of 84 inches, ' rh l ch' ' is ' 20 , percen t ' of the ro t or Giia'l1eter . , , " The general a r r~ngement of t~e r o t or , mqunted in , the
f u ll - scale tunnel i s shown in figu r e 4. , The rotor was "
dr iven by an elec tr ic mo t or and t he ppwer input to the rotor was measu r ed by a s t ra i n - ga~~ torquemeter and by a pneumatic to r quemet~ r . The r otor thrus t, the rolling moment, and t he p i tching moments ware ffieasured by a~ auxiliary st r a i ri - gage balance . Fo rce r ecords were also ' obtained f tom t h~ ' conven ti onal wind - t un nel balances . A !VIR No . L6D24 more co mple te description of th e tes ' ting ' ar ra ngement and instru m entation is given in r e ference 1 .
Following t he t e sts of r efe re nc e 1, the pyl on was stiffe n 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 . T he static - thrust tests were made with the rotor shaft v e rtic ~l over a r ang e of i ndi - cate d blade p itch angle s from 3 t o 11 . 5 for rot or speeds of 200 , 290 , and 3 71 , r pm . The r o tor w as kept tri w~ed in roll and p itch . ' RESULTS AND DISCUSSION The static - thrust r esults obtained for the 00 12 . 6 r o tor a r e pres ente d in figure 5(a) in , terms of t he variati on of the thrust c oeffi cie n t with the torque , coeffic ien t . Similar results for the 230 12 . 6 rotor alone and in combination with the 84 - in c h discus a r e given in fi gu r es 5(b) an d 5(c) . Vfu il e t heore ti ca l co nside r ation~ migh t indicate so me scale effe ct, ' t hese r esul t s , like previous rotor t es ts made i n the ful l - scale tunnel (see r e fere n c es 1 a nd 2) , show no consistent effeq t on curves of thru s t c oef ficient against. tor que c oef fici e nt du e to chan ge s in rot a ti ona l sp eed . On l y one curve , th e r ef6 r e " was f aired through t he dat a in ea ch of t hese figures . ' The f aired static - thrust curve for the 00 12 . 6 rotor g iv en in ref e r ence 1 has b ee n inclu ded in fi g ure 5(a ) for ~he p urp ose of c' omparison with the more r e c ent results . The two sets of da ta are in excellent ag r eemen t .
The resul t s of the static - t hrus t t e sts are summarized in figure 6 . The pe rfor man ce of the 23012 . 6 r o tor become s increasin g l y bett e r t han that of the b0 12 . 6 r o tor for thru st coefficients g reater than about 0 . 0030 . The fli gh t c onditions fo r the PV - 2 h e lic op t e r corresponds t o operation at a r o t o r ti p speed of 485 feet p r second and a rotor t hr ust co eff ici ent of 0 . 00364 . At t h ts des i gn thr ust coefficient the difference in ho ~ sepowe r r equ ir ed to hover with each r o tor is l e ss th an 2 pe rc en t . It ap pea rs p robabl e that a somewh ct t lar ge r d iff e r ence :migh t hav e b~en shown we r e it no t f or the s li gh tly be tt e r surface condition of t he sJ ~me trical - sec ti on rotor~ Also , since the cambered secti on shows increasing g ai ns at thru s t coeffici en ts b eyon d t he design value up to the hi g hest value covere d by the d ata, the max i mum gains MR No . L6D2h ~btainable w ou ld presumably be realize d at still higher thrust coefficients . rr heory indicates that the maximum effect of the blade ca mb er would be reali,zed just prior to the stall; however , powe r limitations on the electric drive mp tor pre v ented obtaining data nearer the blade stall. ' , The imperfect surfa ce co nditions of the two rotors tested undoubtedly impairs th ei r static - t hrust performance .
The data of reference 2 in d ic ate that elimination of surface defo r ma t ion an d irre gu l a riti es ma y result i n an average povve r savirl g in horsepower of as, much as 10 percent.
The close rib spacing an d'doped finish of the two rot ors tested should prevent excessive d ra g l osses due to surface deformation . The el i mina ti on of the rotor blade surface irregularities , however , sh ould appreciably increase the performance of t hese rotors.
Figure 6 also shows t hat the 8h - inch- diameter discu s has no effec t on the stat ic-t h ru s t performance throughou t the ' norma l ope r atj.ng range of the rotor although it produc e s a s li ght det ri men tal e ff ec t at the lower t hrus~ coefficients .
CONCLUDING REMARKS Static - thrust tests of t wo PV~2 helicopter ro t ors in the Langley ful l - s cal e tunn e l show t he following results: 1. At the design thrust c oe ffici en t of 0 . 00364 , the 23012.6 rot o r r equi~es a ~prox i ma t e l y 2 percent less power to hoye r : than the symmet ri cal b l ades. This differ - ence would probab l y beincreai~d if the surface of the • cambered blades was as relativ~l y smooth as that of the s,yrmnetrical b la d es. At thr us 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 00 12. 6 rotor.
2 . As ind icat ed by p r evious full - sca le-tu nnel tests, improved pe rfor m anc e of bo t h rot ors can pr obably be obtained by el imi nat in g their surface dis c ontinuities.
MR No . L6D24 3 . The use of an 84 - inch - diame ter discus had no appreciable effect on the static - th ru st performance throughout tte no~ma l ,o perating 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 Schaefe r, Raymond F .: Static - Thrust Tests Qf S ix Rotor - Blade Designs on a Helicbpter in t~e LaNgley Full - Scale Tunnel .
,,}J J..CJ.. ARR Nb . L)F25b , 194) . .
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