Investigation of the NACA 4-(3)(8)-045 Two-blade Propellers at Forward Mach Numbers to 0.725 to Determine the Effects of Compressibility and Solidity on Performance

NATIONAL ADVISORY COMMITTEE

FOR AERONAUTICS

REPORT 999

INVESTIGATION OF THE NACA 4-(3)(08) -03

AND NACA 4-(3)(08)-045 TWO-BLADE PROPELLERS AT

FORWARD MACH NUMBERS TO 0.725 TO DETERMINE

THE EFFECTS OF COMPRESSIBILITY AND

SOLIDITY ON PERFORMANCE

By JOHN STACK, EUGENE C. DRALEY. JAMES B. DELANO, a nd LEWIS FELDMAN For sa le by th e Superintendent or Documents, U. S. Government P rintin g Office, Washington 25. D . C. Yearly subscription. $3.50; for eiin, $4..50; single copy price "aries according to size - - - - - - - - - Price 30 cents AERONAUTIC SYM BOL S 1. FUNDAMENTAL AND DE RI VE D UNITS Metric English Symbol Abbrevia- Unit Un it Abbreviation tion m eter __________________ Length ______ foot (or mile) _________ I m ft (or mi) second _________________ Time ________ second (or hour) _______ t s sec (o r hr) Force ________ weight of 1 kilogram _____ F kg weight of 1 pound _____ lb Power _______ hors(' power ___________ horsepower (met ri c) _____ P hp ---------- {kilometers per hOllL _____ miles per hOUL _______ kph mph Speed _______ V feet per second ________ meters per second _______ mps fps 2. GENERAL SYMBOLS

w Weight=mg v Kinematic viscosity

p D ensity (mass per unit volume) g Stanuard acceleration of gravity=9.80665 m/s 2 4 2 or 32.1740 ft,/sec Standard density of dry air, 0.12497 kg_m- _s at 15° 0 and 760 mm; or 0.002378 Ib-ft-4 sec W Mass=- m g Specific weight of "standard" air, 1.2255 kg/m or I Momen t of inertia=mk • (Indicate axis of 0.07651 Ib/cu ft, radius of gyration Ie by proper subscript.)

Ooeffieient of viscosity 3. AERODYNAMIC SYMBOLS Angle of setting of wings (relative to thrust line)

s Area

Angle of stabilizer setting (relative to thrust Area of wing S'" line) G Gap Q Resultant moment b Span n Resultant angular velocity e Ohord . b R Reynolds number, p Vl where l is a linear dimen- A Aspect ratIO, S J.I.

sion (e.g., for an airfoil of 1.0 ft chord, 100 V True air speed mph, standard pressure at 15° 0, the corre-

q Dynamic pressure, ~ p V2

sponding Reynolds number is 935,400; or for an airfoil of 1.0 m chord, 100 mps, the corre- L Lift , absolute coefficient Gr, =:S sponding Reynolds number is 6,865,000) Angle of attack

D Drag, absolute coeffici ent G D = ~

Angle of downwash Angle of attack, infinite aspect ratio

Profile drag, absolute coefficient GDO=~

Angle of attack, induced Angle of attack, absolute (measured from zero-

Induced drag, absolute coefficient GDi=f~

lift position) Flight-path angle

Parasit.e drag, absolute coeffici ent C = ~S

Dp

Oross-,," inJ. force, absolute coefficient C = q~

G c

REPORT 999

INVESTIGATION OF THE NACA 4- (3)(08)-03

AND NACA 4-(3)(08)-045 TWO-BLADE PROPELLERS AT

FORWARD MACH NUMBERS TO 0.725 TO DETERMINE

THE EFFECTS OF COMPRESSIBILITY AND

SOLIDITY ON PERFORMANCE

By JOH N S TA CK, E GENE C. DRALEY, JAME S B. DELA NO, and LEWI FELDMAN Langley Aeronautical Laboratory Langley Field, Va.

ational Advi ory Comnlittee for Aeronautic

H eadquarters, 1724 F tre et NW., Wa shington 25, D. C.

Cr e ated by act of Congres approved March 3, 1915, for the supervi ion and diT ect ion of the cientific tudy of the problems of flight (U. . Code, Litle 50 , ec. 151 ). It member hip \Va increased from 12 to 15 by act approved March 2,1929, and to 17 by act approved May 25,194 Th e member are appointed by the Pr e ident, and serve as such without co mp en ation.

JEROME C. HUN SAKE R, C. D ., Ma s achu set t I nstitute f T e chnology, Chairman ALEX AN DER WETMOR E, C. D ., ec r et ary , mitb so nian In t i tut i on, Vice Chairman D ETLEV W . BRONK , PH. D ., Pr esid ent, J ohns Hopkins Univer- Do , ALD L . P UTT, i\Iaj or General, United tates Air Force , s it y. Dir ect or of R e e ar ch and D eve lopm ent, Office of the Chie f of J OHN H . CASSAD Y, Vice Admiral, United tate I avy , D eputy Staff, D eve lopm e nt .

Ch ief of aval Op e rations. ARTHUR E. RAYMOND, 8c . D ., Vice Pr esid ent, Engin ee ring, EDWARD U. C ONDON , P H. D. , Dir ect or, National Bur e au of D oug la s Air c raft C o., In c.

tandards. FRAN CI W . R EI CHELDE R FE R, C. D., Chie f, nited ta tes Ho , . THOM AS W . . DAVI , A i stant ecretary of Commerce . We ather Bur e au.

JAM ES H. DOOLITTLE, C. D., Vice Pre s id ent, he ll Union Oil Ho . D EL OS W . R EN TZ EL, Admini st r ator of C ivil Ae rona ut ic, Co rp. D epa r tment of C ommerc e.

R. M . HAZE ,B. ., Dir ecto r of En ginee ring , Alli on Divi sion, GORDON P. 811. V ILL E, M ajor General, United tate s Air F orce, General 1\Iotors Cor p . D eputy Chief of S taff- D e,·e lopment.

WILLIAM LI TTLEWOOD, 1\ 1. E., Vi ce Pr esid ent, Engineering, WI LLIAM W EBSTER, M. ., hairman, R ese ar ch and D eve lop- American Airline, In c.

m ent Boa rd , D ep artm ent of D ef en e.

THEODORE C. LON NQUEST, R ea r Admi ral , United tates Navy, TH EODORE P . WR IGHT, C. D ., Vice Pr esid ent for R esea rch , D e pu ty and A i t ant Chie f of the Bur eau of Aeronaut ics. Co rn e ll niversi ty.

H UG n L. DRYD EN, PH. D ., Director JOHN F. VICTORY, LL . D., Executive S ecret ary JOHN W . C ROWI , EY, JR. , B. ., Associate Director Jor Research E. I-I. CHAMBERLIN, Executive Offi ce r H ENRY J . E. R E ID, D. Eng., Dir ecto r, Langl ey Aer o nau tical Labora to r y, Langl ey Fi e ld, Va .

~!lTH J. D EFR ANCE, B. S., Dir ecto r, Ame s Ae ronau t ical Labora to ry, Moff ett Field, alif.

EDWARD R. HARP, C. D ., Dir ecto r , Lewis Fligh t P ropulsion Laborator y, Cleveland Airpor t , Cleveland, Ohi o TECHNICAL COMMITTEE A ERO DYN AM I CS O PERATING PRO BLEMS PO WER PLANT S FOR AIR CRAFT I NDUSTRY Co SUL TIN G AIRCR AFT CONSTRUCTIO Coordination oj Research Needs oj Milita?'y and Civil Aviation Preparation oj Res earc h P ro gra ms Allocation oj Problems Prevention oj Duplication Consideration oj Inv entions L ANG LEY A ERONAUTICAL LABORATORY, LEWIS FLIGHT P ROPULSION L ABO RAT O RY , AM ES AE RO AUT I CAL L ABORATORY, Langl ey F ield, Va. Cl eve land Airp ort, Cl evelan d, Ohio Moffe tt Field, Calif.

Conduct, under unified con t Tol, Jor all agencies, oj scientific research on the Jundamental pr obl ems oj flight O n'ICE OF A ERONAUT I CAL IN TELLIGENCE, W ashington, D. C.

Collection, classification, compaation, and dissemination oj scientific and technical inJormation on aeronautics II

REPORT 999

INVESTIGATION OF THE NACA 4 -( 3) ( 08 )- 03 AND NACA 4- (3) ( 08 )- 045 TWO-BLADE PROPELLERS AT FORWARD MACH NUMBERS TO 0.725 TO DETERMINE THE EFFECTS OF COMPRESSIBILITY AND SOLIDITY ON PERFORMANCE 1 By JOR T A K , E GENE . DR ALEY, JAM ES B. D ELANO, and L EW I S FELDMAN SUMMA R Y Available airfoil data arc essen tially two-dimensional and when applied without co rr ect i on for three-dimensional As part oj a general investigation oj p1'op ell e1's at high e ff ects, as at a tip , and withou t co rr ect ion for tunnel-wall j01'wa1'd peeds, t es ts oj two 2-blade propellers ha vin g the N A 'A.

e ff ect , which at high Ma ch number are till un cer ta in , 4-(3) (08 )-03 and NAOA 4- (3) (08) - 045 bl ade designs ha ve may give unduly pessimi tic r es ults. On the other hand , been made in the La ngley 81 00t high-speed tu nne l through a exi st ing prop eller data obtain ed at high tip speeds but low range oj blade angle jrom 20 ° to 60° jor j01'wa1'd - .Mach num - forward peed are noncon ervat i ve wh en applied to co m- b el' j1'om 0.165 to 0.725 to esta bl is h in detai l the chang es in pu tat ions for high forward peeds because the var ia tion propeller characteristics du e to compressibil it y effec t. Th ese of Ma ch numb e l' along the blad e is inc orr ec t. Pl'opeller propelle1' differed primarily only in blade olidity, one pro- e ffici en cy at high forward speed est ima ted by the u e of pelleT havin g 50 pe1'cent mOTe olid it y than the other.

these data is too high. ome fligh t t est data hav e been Serious lo s es in propeller efficiency were jound as the pro- obtain ed by variou expe rim e nt s which how cr iti cal tip peUer tip ]vlach num b er exceeded 0 .91, i1'respective oj jorward Ma ch n umbers of O. to 1.0. 80m of the 1' e ult are speed 01' blade angle. Th e magnitude oj the efficiency lo ses qu es tionable because of the pr act i ca l impo si bility of obtain- va Tie d jrom 9 percent to 22 peTcent peT 0 .1 incTease in t ip ing adequate ly controlled te t cond ition. Furthermore, lYlach num b eT ab ove the cTitical value. Th e range oj advance non e of th e flight data per mit an eva lu ation of the co mpr ess- ratio JOT peak effic iency decrea ed ma1'lcedly wi th incTea se oj ibility losses beca use the blade- ection speeds are in the jOTward speed. Th e general j01 'm oj the changes in thrust c ompr e ibility range even for th e lowe t peeds in vest i gate d.

and power coefficients was jound to be imilar to the changes eve ral year ago the AOA, r ecognizing the el'iousne s in aiTjoil lift coefficient wi th chang es in Ma ch num b er. Effi- of the probl m , in tituted a long-range re ea r ch pro gram to ciency losses due to compressib ility effect decrea ed with l ea d to the developmen t of improved propellers at high increase oj bla de width. Th e Tesults in dicated that the high forward speeds. Early pha ses of this work were airfoil level oj pTopeller efficiency obtained at low speeds could be tudie that led to the design of ections havin g ru o- h critical maintained to jorwa Td sea-l evel speeds excee d in g 500 miles Ma ch numb er (refer e nc e 1). Exi sting prop eller dynamorri- per hour.

, eter were un sui tab le because of inad equate power for I TR OD CTION this extensive r esearch, and the building of new and ade- Limitation s of th e scr ew prop eller as a propul iv e elem e nt quat ely powered dynamom eter was al so und e rtak en.

for aircraft du e to adv erse co mpr e ibility e ff ect hav e b ee n hor tly after this prog ram was in tituted , the defen e pro- r ecognized for ev e ral yea r s. Airfoil and prop eller inv e ti- gram and l ater the war emergen cy aro e and many delays gations ha ve s hown th at mark ed decr ea e in prop eller in the procureme nt of blad es and equi pm ent were e n- e ffi cie ncy ar e en c ount er ed a blad e- ect ion peed approach co unt er ed becau e of priorit ies as igned to other work.

th e speed of sound. ome exi ting information ha ceen R ecognizing the need for prop eller development and for int e rpr eted a showing that screw prop ellers might become tudy of co mpr e ibili ty phenomena as related to propeller, impracticable becau e of c om pre ibility 10 es at sp ee d the Langl ey L abor at ory propo ed an emergency investi- slightly high er t han C Ul'r e nt blad e- ect ion peeds. Oth er gation with imm ediately ava ilable equipment to stu dy information ha been interpreted a c on tra dictory of this par ticularly th e c()mpre sibili ty ph enomena.

conclu ion. T wo dedu ct ions that appear to be clear ar e : Th e pr esent r e earch con i st of in vestigations of two- Fir st, the Lrue magnitude of the 10 i re l at i ve ly unknown bl ade propeller over an extensi ve range of ' Maeh number and , second, th e 10 se are of ma g nitud e ufficient to r equire and blade angle and includ e, in addition to th e e ff ects of con ide rabl e r esear ch leading to the developme nt of im- co mpr e sibili Ly, the c fl' eeL of olidity and blade- ection pro ved propeller if c urr en t efficiencies are to be maintained. cam ber . Th e flr st re ul ts of thi invcstio-ation which are I Thi s repo rt co nl a in s ma lerial originally issued as A A ACR 4AIO and ACR 4B1 6 in Ja nu a ry and February 19 44, wbich until r ece ntly bavo b ee n subje ct to ec urity r eg ul at ions.

REPORT 99 N ATIO AL ADYISORY COM MITTEE FOR AERON A TI S A PPARATUS AND ME'l ' HOD related to lhe efrecl of com pr e sibility and oli dity on propeller performance arc pre en led in this report for two Th e inve ligation \\ ' :1S co ndu cted in lh e Lang ley -foot propellers having lat e-critical-speed blade section and hi gh-sp eed tunnel. Th e propell er-model configuration in- differing essentially only in so lidity. One propeller ha vestigated is sh own in flgm e 1.

conventiona l olidity and the other prop eller ha s 50 percent Propellers .- Tw o 2-blacle prope lle ]' were u ed in t hi s greater de ign so lidity.

inv est igat ion . Th e e propellers are d i gnat d a th e AOA 4- (3) (0 )- 03 and the N AOA 4- (3)(0 )- 045 blade de ign .

SY ' lBOL S T he desiO'nation numb er de cribe th e propellers. T he b blade \\i cll h, feel, number ( or number) of t he fir t group i t he diameter in Cl blade -section design lif t coefficient fect; the number (o r numbers ) of the econd group (e nclosed d wi thin the fi r st et of par ent he es ) i the de ign lift coe ffi-

C p power coefficient (pnfD s )

cie nt (in tent h ) of the blade section at the 0. 7-radiu statio n ; thc number s of t he third group (enclo cd within

C thrust coeffic ient (p J D 4 )

T the seco nd set of pa rentheses) arc th e L hi ekne ratio of the blade section at th e 0.7-radius sta tion ; and the n umb er of D prope ller diameter, feet the fomth group arc the blade so lidi ty expre sed as the ratio biD blade ",idth ratio of the blade eh orcl at the 0.7- radiu s tation to t he circumfer- h maximum lhicknes of blade seclion, feet ence of t he circle haying a rad ius 0.7 of the propeller tip h/b blade thickne s ratio radius. Th e • A A 4- (3 ) (0 )- 04 5 prop ell er thu ha a

J advance ratio (V o/ nD)

diameLer of 4 feet and t he blade section at the 0.7-radius JJ tunnel - dalum (forward) ::' Iach number (tunne l- tat ion ha a design lift coefficie nt of 0.3 , a thi ckn ess ratio empty ::'Iach number uncorrecled for lunnel- of 0.0 , and a blade 01iclity of 0.045.

wall cons l rain t)

lvf, he lical lip :\f ach number (:M-Jl +(5Y )

~ \J ,,, critical tip :\fach number propeller roLa lional peed, revolutions pel' second n p pOI I'er absorbed by the propeller, fooL-pound pel' second pOll 'er di k-l oadil1O' coefficient ( P ) 1 V - p 0 R propeller tip radius, feet r blade-seeLion radius, feet

D 2 )

propeller disk area, sq uar e feet 7r 4

s

(

propulsive thrust of prope ller, pound T

thru t disk-loading coe ffi cient (p ;;: D 2 )

Ca) Win g-fuselage m ode l.

tunnel - datum velocity (tunne l- empty ve lo city uncorrected for tunnel-ll'all con traint) , feet pel' second e quivalent free- air velocity (tunne l-d atum velocity cOl'l'ectecl for tunnel -wall constraint), feet per second blade- ection tation r/R section blade angle, degrees {3 section blade angle at 0 .75 tip radiu , degrees (3 0.7S R

propulsive efficiency ( g: J)

7J maximum propul ive efficiency at 10 1\ ' tip ::'I ach number ( J1 , ,,,, 0.25) relative maximum efficiency maA'imum propulsive efficiency 7Jm ax air density, slugs p e l' cubic foot FI Gt: HE I.- Installa tion for prope ll er investigation in Lan gle), 8 -f oo i hig h, speed tullo e\.

p INVES ' fIGATION OF THE EFFECTS OF COMPR ESSIB IL ITY A D SOLIDITY 0 PRO PE LLER PERFORMANCE 3 Th e propeller we re origu la lly designed and eon t r uct ~ d ec tion was a modified ACA 66 - eric ection of 9 perce nt for u e in an extensive and genera] inve t io-ation of propel- thi ckness and 2 0- in ch chord, The critical Ma ch nu mber of lers at high forward 1Iach numbers . Th e blade of the e the model exceeded 0.75. Th e highe t forward Mach propell t' rs we r t' design d for a three-bl ad e propell l' to number at which th e e inv (' tigation w re conducted was pro luce minimum indu ce d ener gy los es (pro fi le drag 0.74. I n some of the pr eli minary run , oxces iv e vibration assumed e qual to ze ro) at a blade angle of approxi mately of the model wa e ncounter ed at orne p ee d and was 45 ° at the 0.7- radiu tation, Th blade ect ions arc late- eliminated by a vertical t reamlin support that ec ur ed the cri tical-speed section of the NACA 16 se ri es (referenc e 1 ); tail of the mod el to the ba lan ce rin g outside th e tunnel.

met h od and pr in ciple e mp loyed in the de i gn of th blade This u pport h ad a c riti al Ma ch numb er of 0,80.

arc di crssed in referen ce 2, The bladt' diller primarily T ho propeller hub wa c ontain ed within the lllller s pinn er of th o cowli ng and the portions of tho blad e b et w en the only in blade widt h , ( Th e NACA 4 -(3)( 0 )- 03 bl ad e is of inn er and outer cowlings Wer e shielded from the air flow by convention al wi dt h .) Bl ade-form curves for the propellers cu ff s secured to the pinn er ( fig . 1 and 4). Th e ou t iele te ted arc pre e nted in fi glu' 2.

The blad es wer e mad e of duralumin and were con tructed diam eter of the cowling at the propeller plan e wa s one-third in the Lang l ey hops, Th e blade section and other general of the propd le l" diameter ; hen ce, only the bJ ade sections having good aerodynamic form wcre expo se d to the air st ream.

dim en ions \\ ":re accurate within 0.002 inch. A photograph of th blad e i hown a figure 3. Th ere wa s a small ga p between the prop 11 er a nd the outer Wing-fuselage mod e l. - Th e mo leI ( fig. 1) was es p ecially pinner at Lh tation where Lh e blad es proj ected through the pinner. Th i gap wa ealed by a kip of ponge rubb er de igned to have a high critical Ma ch nu mbel. The NACA E cO ld i ng , which Ins designed for high critical )I ach number cemen ted Lo th e bl acl ( fig. 4) Lo pr eve nt radial outflow from ba ic tu lie of ai l' in l et in a t reamlin e body (referen ce from the cowling, 3), was used. T hi pa rt ic uJ ar co wling was origi na lly tested Dyna mo met er ,- T. h e dynamometer was completely e n- in a gencral tudy of p ur u it -air plan e performance (reference elo ed by the f ll elag e. Dynamomet er d eta il ar e shown in fig- 4). Th e wi ng of th e model extendrd through the tunnel lire 5. Th e motor wa 10 inches in diamet er and 30 in ch es long, wa ll and II-as fa tened to the ba lance ystcm. Th e ail'fo il It wa rated aL 200 hor epower at 4, 900 rpm for }~ hour of .18

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(b) (a) CO o 32 o .3 .4 .5 .6 .7 .8 .9 1.0 .3 .4 .5 .6 .7 .8 .9 1.0 Blade-section st at io n, r i El Blode-section station . r i ff.

(a) ACA 4-(3)(08)-03 propeller. (b) r A CA 4-(3)(08)-045 propeller.

F , GU RE 2.- Dlade-f orm cur ves.

REPOR' I' 99 XATIONAL ADVISORY COM MI TTEE FOR AERONAUTICS FH';URE 4 .- Prop cllcr huh and spinner.

Thrust balance .- Th c t hru t wa m ea ur ed by th c tunncl (t ra g balance . Th e forc c indi cate d by Lhe dra g balan ee wa th c res ultant for ce al ong Lhe thru l ax i , th at i , th c thl'u t of the propell er m in u Lhc d r ag of Lhc mod el. Th c propu l- s ivc t hru sL w as de te rmin ed a tb c l' s ult a n t forcc in tb c thru st di recLion m inu L h e drag of th c model wi L b o ut Lh e p rop eller. Th c v ar iaLion in bod ? dru g clu c to va ri at io n in ae r odynam ic moothn ess from ru n to run wa s d ete rm ined from man y r ep eat tc L of th c bod y wiLhout th c prop ell er a nd ,, 'a found to bc Ie Lhan ± 1 p ercen t of the va l Li e of the FIr-eRE :l .- Blnclc dcsil,'11S i nw stign tcd.

propul iv c L hru st at ma x imum e ffi cien cy.

operat io n. ~om e of t be run s wc re limiLcd he ca usc of la ck Ro tat ional speed .- Th c prop cller l'ot a Lional specd wa s of pow('/" ('ven thou g b a cons ide rable ove rl oad a bo ve th e m ea ur ed by a con dense r- type tac h omcte r attac h ed to thc norma l ' ~ -holll" rat in g was e mplo.n ' ci. Cont inu o u p eed motor sh ah. A ch ec k on thc acc ura cy of t hi ins trum en t co nt rol of the inducL io n mo to r w as obta in ed by tile usc of a wa provid ed by co mparin g it s r eadi ngs wi th thosc obtained va ri ab le-f r('qu enc .\ - po wer s upp l.\-.

from known Li a j ous' flg ur es on an 0 cillo cop e on nectecl Th e motor h O ll s in g wa s m o ullted 0 11 b ea rin gs coaxial \\ ' ilb Lo an al te rnaLor on th c moLor sh aft. Genera ll y , th e r ota- L h e haf L a nd wa s ll eld from ro ta tLJl g lInde'r lite lo rq u (' tion al spee d obtained from both in L rum en t ag r eed to rcacLion b.\ ' a ca n l ile ve r s prin g. One e nd of t bi ca ntil e" ('/" within ±:3 rpm .

s pring w as r igid ly fix ed to tlte fr ame of tile model and th c TESTS ot h er e nd wa held i ll co n tact with t Lt e molor cas in g t hr oug h tor quc rea c tio n. The co n Lact b cL wee n s prin g a nd mo Lo l' Thru L , torqu e, unel roLat i onul peed wel' measu r ed cas ing wa s t hrou gh ro lkr b ea rin gs in th e e nd of th e sp l'ln g thr oughout th e ope r ati ng ran ge of th e p r ope llers. Th e and ) ('a ring plate f aste ll cd to th e moLo r cas in g.

r ange of blud a ngl cove red for each te t ::'II ach number Th e p r ope ll er torque' is the motor torque reaction acti ng is giycn in Lab lc 1.

on the can tilenr prill O". Thi s torqu e wa measu r ed by dcct ri nl l s train gages c eme nt ed to lh e ca n tileve r s prin g .

T .\ B L E 1. - TI -': ST RA NGE OF BLADE .\ XGJ,E ,\ ND :\fA ' J-[ FOUl" s Lrain gages werc us ed Lo fo rm th e a r ms 01' a , Vh ea t- X 1. ; :\ fBER sto nc brid ge . By arrangi ng two gage on each ide 01' th e pring , it wa po sibl e Lo provide tempe r atu r('-e A' eet com- Tunne l-d at um pe n sa tion a nd to o bt a in a d eq uat e se n itivit.\,. F o r rUD S at Blad e ang le at 0.75 mdius, 13 0 "R (fo rw ard ) (d eg) l\ [ ac h numher low va lu e 01' torque , a s imilar but w ea k('[' s prin g was u seclto obLai n improved accu r acy. A phoLog raph of til e spl'ln gs O. I ii.)

20 25 30 35 '1 0 45 50 55 60 .23 a 20 25 30 35 '1 0 45 50 55 60 with train g ages ins ta ll ed i sh own as fi g ur e 6.

.3.5 30 35 ' 10 45 50 55 60 . 43 35 40 45 50 55 60 Th c t r ain gages w er e ca librat ed b.\ ' app l.\ ' in g known .53 40 45 50 55 60 .60 45 50 55 60 weight aL the end of a n a rm fa Le n ed to th e moto r casin g .65 55 60 .675 55 60 an d by re co rdillg th e brid ge unbal anc(' as th e torqu e. Lineal' .70 55 60 .725 (150 a55 a60

ca libr aLio n w ere obta in ed ill w l1i (' h th e mea lIrc ci. to rqu e /-

------ va l ues w eI'(' within ± O .. 5 perccllt of t lt e app li (,d nl 1u (' .

• S ot tested fo r the -"AC'A 4 -(3 )( 0~ )-o· 1 5 prop<' ll er.

I VESTIGATIO OF THE EFFE '1'S OF COMPRESSIB ILI'l ' Y AND OLIDI'l 'Y 0 PROPELLER PERFORMANCE -;"" '\ /"";;;;/ \ (/ \ \ \ \ \ \ '- D \ \ \ \ \ \ \ \ \ ) / \ / / / / / I / I / I I I " I /~----.,..

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\ \ \ ) \ ",," ,/ A pinn r (sec fi g. 1 (b» E Ba ll bearin g I T erminal block for strain gage B Motor sh aft F JI ardened b em in g plat e J Motor casi ng C lIfain housing G 1 'o rQlle spring (see fi g. 6) K Fu selage D Pr o! e ll ~ r H H ardened roller L \I ' ing FI Gl' H>: 5.-Dynamometer details.

or the power of th e propeller drive motor. For the low blad angle, the propeller-rotational-speed limit of 5,000 rpm wa the principal restriction and , for the hi gh blade angles, pow I' l:ilnitation of the moLor was the principal 1' e triction. Th e data obtained, however, are ad quate for detennination of max:ilnum efficiencie and the hap e of the propeller-efficiency curve for th e advance ratio requu'ed for zero thru t to advance ratios Ie than those requu'ed for max:ilnum fficien y. The normal operating range of ~I ach number and advan ra tio for each blade angle thus G \Va overed.

E RED CTIO OF DAT A L 31362 Th e data have been reduced to the usual thru t and power A prin g E Il arde ned roller B train gages F Bearing pl ate co ffi ci ent and efficien y and have been correcLed for the C T e rmin al block G Dearing pla t propul ive effects of the owling and spinner and for tunn 1- D F elt in sula tion H De a ring phlle I Roller r eta in er wall const raint . Th e tunnel-wall constra int nece itat ed a 1'1 ,cnE 6. -Cm llil e\·er sp rin gs with s tr ai n gage .

v lo city correction to fre -au' conditions and a model-drag correction becau e of the buoyancy e ff ect.

The Le t procedure con i sted in etting the blade angle T hrust ,- Th e thl'u t coefficient \Va del rmined from the at the de ired value and rai ing the Lunnel aU 'speed to the propul ive thn l t. Th e force actually mea ured during the desired tunne l-da tum 11ach number with the propeller propeller te t wa the net force in the drag direction. Th e wUldmilling. T he range of advance ratio \ya then covered tm'u twa then letermined as the net mea med force minu by increasing the prop eller rotational speed while the tunne l- the drag of th e model without the propeller and minu the datum Ua ch numb er wa h e ld co n tanto Th e range of tlu'u t due to the buoyan cy effect. Th e model wa so advance ratio and t unnel-d atum ' Ma ch numb er were limi ted mount ed that a lif t coefficient of approximately 0.1 wa by either one of two factor , the propeller ro tatio nal peed attained at the highe t forward peeds. Th e thl'll tax is REPORT 99 NA'l'IO TA L ADVISORY COM iv fI TTEE FOR AERONA TIC S \Va therefore inclined at a mall angle, slig htl y 1 ss than 1 1. 02 ~ to the direction in which lh e drag force was mea ur ed by the ~ ba lan ce. Th c co ine correction, however, i in ignifica nt ~ and therefore h a not been applied. --......

~ 1.01 Power.- Th e power coe ffi cien t was determined from the ~ ~ :--.- o~ read in gs of lh e calibr ate d strai n gages. ome diffi c ult y wa :;:: ~ e ncounter ed with the stra in- gaO'e operation and freq u ent '--- 21.00 ca libration were made. Wh en ch anges in calibr al ion were :----..

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found , repeat te t of the propeller were always mad e. 'u r===:::..

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Nose -blower t hru st and power .- Th e nose-blower co wling s .9 9 cont ributed b oth thrust fLncl torque to th e mea m ed tbl'u t and torque. Th e c uff , which hi elded the propell l' hank s within the cO \\ 'lin g, acted a blower blades and were de igned .2 4 .04 .08 .12 .16 .20 to opera te at ap pr eciable values of lift coefficie nt in thc low Th r u st disk. - load i ng coeff ici ent, Tc advance-ra li o range and gra du a ll y lo approach operation F WUR F.. i. -' I'unncl-wall int e rf erence co rr ection.

at zero lift coe ffi ci ent in the high advance-ratio range. Th e prope ll er thl'u t and torq ue coefficie nt hav e been correded ran ge of "elocily ra tio hown in figure 7 the facLor required for the effect of th e blower. Th e e correction were deter- lo co rr ect lhe lunnel-da tum velocity 0 1' ~Ia c h number to mined from le ts of the blower alone ope ra ted througb a fr ee- st ream condilion is e sent ially the same a lhe velocity- wide range of advance ratio at each test ~ I ac h numl cr .

co rr ection factor.

The re ults of these data were r ed u ce d Lo thru st and pow er Buoyancy correction to t hrust .- Owin O' to the contraction coeffi c ient.

of the propeller slip lr eam in the presence of lhe t Ullll el wall, Veloc it y correction due to tunnel -wall constraint .- Owing th e air ou tside of Lhe lip st r cam undergoe an increase in to lhe con traint of the tunnel walls, the equivale nt free- stat ic pr essure wi th cli tance clown t l' eam from the propel- st ream velo city co rr es ponding to the thrust and torque of ler. Thi s in crea e in stat ic pr e s ur e giv es ri e Lo a buo yancy the prop 11er mea ur ed at each ro tational peed d iffers from fo rcc on til mod el. Th c buoyancy forcc was eva lu ated the tunne l-d at um velocity (t unnel empty). Th e CO IT cction from simultan eo us m ea urem ents of th e tati c pres ur e at to lh e tunnel -d atum ve lo city was eva lu ated by urveys of orifice 6 inches apa rt in a circular tube exte ndin g to lo ca- the tota l and tatic pre ure in three planes: 12 inch e in tion ahead of and behind thc fu e la ge a nd in t< Hed approx- front of and 3 and 12 in eh behind th plan e of the propel- imat ely 6 inche from the wall of th e tunn 1. Th e e mea me- ler. Th ese urvey exte nd ed radially from the tunnel wall me nt s per mitt ed eva luation of the buoyancy for e from to the tip location of the propeller. Th e veloci ty cO lT ection chan ges in th e longitudinal pr ess ure g ra cli n t (p roduced by was then eva lua ted by the m et hod of reference 5. Thi c han ges in prop eller tbru t) in which th e mod el wa located.

correction , whi ch ha been app lied to th e calcul at ion of It was found t h. a t t h. e buoyan cy for cc \Va approximately adva n ce ratio, is pr e e nt ed in fi g ur e 7 as the ratio of fr ee -ail' 2 per cc nt of th e propul ive thrust fo r all operating co n litions vel oc ity to the tunnel-datum velocity (t ullllel e mpt y) a a of the tunnel and propeller s. Thi s co rr ec lion ha been funct ion of the t hru st di k-loading coe ffi cie nt . Th e tunnel- applied to tbe thru st r es ult pr esented h erein.

wall co rreeti on wa found to be depe nd ent on ly on the thru t R ESU LT S A D DI SCUSS IO I disk-loading coe ffi cie nt for the ran ge of tunnel pecd a nd propeller operation used in th e e inve tigation .

Th e ba ic c hara cte ri tic for the N A A 4- (3) (0 )-03 and Th e results pr ese nt ed in fi g ur e 7 how that, for the ze ro 4 -(3) (0 )- 045 two-blade propellers are pr e e nt ed in figures t hru st co ndit ion, a co rr ecti on of 2 perce nt is required to the and 9, r es p ectiv ly. For each value of the tun nel-da tum tunne l-datum ve lo c it y. Thi s c orr ection is du c to co n- ~I ach numb er, the prop eller th ru st coeff LC ient, power co - tri ct ion of flow produc ed by thc model al on e in the pre en ce efficient, and effic iency are plot ted against advance r at io.

Th e varia tion of tip Mac h nu mb er with ad va n ce ratio is al so of the t unn el wall. Th e veloci ty c orr ection re quir ed beca use the propeller is operating in tbe pr esence of th e t u nn el wall include d. A u sc 1 in th is repo rt, the tunnel-datum Ma ch i zero for the above condition. Consequently, th e chan ge numb er M is not c orr ected for the e ff ect of t unn el-wall in the ve lo ci ty c orr ection hown in figur 7 are du e entirely con st rain t. Th e free- st re am M ach number can b obtained to propeller operation in th e pr e encc of thc tunnel wa n . by applying the tunnel-wall co rr ection pre en ted in fi gure 7 The t unne l-datum Ma ch number ha not been corrected to the tunnel-da tum ~ 1a c h numb er. \ imilarly, the co rr ected for tunnel-wall con tra in t. I t an be shown that for the t ip :\1ach numb er can al 0 be obtained.

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