REPORT 1012 -

INVESTIGATION OF THE NACA 4-(5) (08)-03 AND NACA 4-(10) (08)-03 TWO-BLADE PROPELLERSAT FORWARD MACH NUMBERS TO 0.725 TO DETER- THE EFFECTS OF CAMBER ‘.

AND COMPRESSIBILITY ON PERFORMANCE 1

By JAMES B. Dmmo —

SUMMARY

.-% part of a general inratigation of propellen at high forwardspeeds, tests oj two-blade propellers hating the NACA-H5)(W-03 and .%?+W.44–(10) (08)-03 blade dew”gnsweremadein the Lungley 8-foot high-speed tun nel through a range of bladeangle from 20° to 60° for forward Mach numberg from 0.166to 0.70 to determine the e~ect of camber and compredbility onprope[[er charactem”stics. RewLlt.9 prwiowdy reported for~im ilar tests o-f a tuw-bliuie propeller han”ng the A’.4.CAJ-(3) (08)43 blade de~”gn are included for compam”aon.

Biades of high design camber were more ej%ient than bladesqf low de~ign camber for operation at high power loading~.Tile blade of highest camber gare ejtct”e-ncie~15 to 25 percenthigher than the e~ciencies of h ho-camber and medium-camber blades for high power loadings at adrance ratios cor-responding h tuke-oj and climb at low Wach number~. The.3TACA +(5) (08)-03 propeller generally ,~ce peak qfo”enc-ies2 to 6 percent higher than those for the .h’.WlA +(S) (08)-03propeller and 3 to approximdely Ig percent higher than tho~eforthe .3’.MA 4–(10) (08]-03 propeller. These h ighw qj%iencies

were due. mainly to reduced compres~”bi~ity losses. At thede~ign blade angle of 45°, the em”tical tip Mach numberfor mazimum ej%iency waa 0.01 higher for the A’ACA+(5) (08]-03 propeller than. for the AT.4C.4~+?] (08)-03 pro-peller, which began to ~how compressibility losses at a tip ilIachnumb(r of approm”mately 0.90. The A’ACA 4–(10) (08)-03propeller began to show compret?m.bility losses at a tip Machnumber a~ [OWas 0.70 but? because of the large pincer-absorbingcapacity ~f tlis propeller, produced about 46 percent morethrust than the ATAPA.$-(5) (08)-03 propefler for a high-speedop~rating condition corresponding to a tip Mach number of0.86, a forward Mach number of 0.53, and an admnce ratioQf .2.48.

INTRODUCTION ‘

Man~- airplanes now take off and climb with propellersat least partly stalled, and the tendency to use increasingpowers may ag~vate a condition that is already serious.FIight at high ahitudes also may necessitate propelleroperation at hi@ lift coefficients, dich would increasepossible stall and compressibility effects and result in areduction of prope~er efficienc~.

The h’atiomd Adviacq Committee for Aeronautics hasattempted to improve propeller performance by conductinga general investigation of propeUers at high forward speeds.

This investigation includecl the effects on propeIIercharacter-istics of compressibility, blade solidity, and bIade-sectioncamber. The research program included tests of propellersof a sticient range of blade forms to make possible thestudy of changes in blade shapes that might be required asa consequence of compressibility effects.

The effects of compressibility and solidity on performanceas determined from tests of the N’ACU 4–(3) (0S)-03 andNACA 4-(3) (0S)-045 tvro-blade propdlem (reference 1)constituted the initial phase of a general imw.tigation ofpropellers at high forward speeds. The effects of camberand compressibility on performance as determined fromtests of the NACA 4-(5) (0S)-03 and NACA 4+0) (0S)-03two-bIade propellers constituted the second phase of theinvestigation and are presentecLherein. These resuki are comp-ared tith results of referent ,- ,for the A’AC..+4-(3) (0S)-03propeller, in order to indicate the effects of section designcamber for propellers operating over a tide ra~me offorward Mach number. These three blade desigg ccrrerthe practical range of blade section camber.

SYMBOLS

B number of bladesbIade width, feet

:/23 bIade width ratioc& bIade-section proflc+ckg coe5eientc1 bkde+ection lift coefficientCIH blade-section design lift coefficient

-.

c. (F)povrer coeilicient -&

c. T()

thrustcoefficient —pn2DJ

cTna maximum thrust coefficientD

.-propeIIer diameter, feet

G Goldstein tip-correction factorh maximum thickness of blade section, feeth/b blade thickness ratioJ advance ratio (T”O/nD)iv tunddatum (forward) Mach number (tunxiel-

empty Mach number uncorrected for tunneLWd.1constraint)

M,‘e’cdtipJia&nuber(”lm

n propeller rotational speed, re-roIutionaper secondP power absorbed by the propeller, foot-pounds per

secondi Sapers?desN-ACAACR L3F15,%mstfgatfon of ‘J%o-BE.dePrr@Iers atHI@ ForwardS@ in the X-AC-4E-Fwt EfIghSwed TULUWLlTI-Effeots C4Cam&r and ComprmsibOitg -

>-ACA 4-(5)(06)4’3find3’ACA 4-(IO)(C8)411BIsdes” by J- B. Delano,1945.

189

190 REPORT 101 2—NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

P.

Iir

sT

T,

v’

P

()

power disk-loading coefficient ~~ pvow.

propeller tip radius, feet “ ‘blade-section radius, feet

()rD2propeller disk area, square feet ~

propulsive thrust of propeller, pounds/m\

thrust disk-loading coefficient(J;’-)

tunnel-datum vclocit y (tunnel-empty velocityuncorrected for tunnel-wall constraint), feetper second

equivalent free-air velocity (tmmel-daturn veloc-iby corrected for t.unnel-wdl constraint), feetper second

r/R Made-section station

~f induced angle of attack, degrees

P section blade angle, degreesflo.7is section blado angle at 0.75 tip

~) ckgrees-f=t~~n-lc~

c1-JT

()propulsive efficiency ~

.P

n maximum propulsive efficiency//1azP air density, SIUWJper cubic foot

(tan-~act

ZRRjj )

radius, degrees

u total bIa&:secfio~ solidity (HJ/2m)‘#’ ncrodynamic helix angle, degrees (#JO+at)

40 - (tan-’:)geometric helix angle, degrees

APPARATUS, METHODS, AND TESTS

TIN apparatus and methods described in reference 1 wereused in tho present investigation. The investigation wascomlucted in the Langley 8-foot high-speed turuml. Aphotograph showing the model setup is given as figure 1.

Tho blaclesof the propellers investigated were designed forthre+blacle propellem to produce minimum induced energy10SSCS(profile drag assumed equrd to zero) at a blade angle ofapproximately 45° at the 0.7-radius station. TIM bladosections are late-critical-speed sections of the NACA 1!3series(reference 2); methods and principks employed in the designof the bIacles arc discussed in reference 3. The bladesdiffer only in design camber ancl are designated as NACA4-(:3) (08)+3 (low camber, reference 1), NACA 4-(5)(08)-03

FmurmI.–setup for tcst[ogpropellersInthe IarrgleyS-footbIgh-epe?dtnrmeli

(medium camber), and NACA 4-(10) (08)-03@gh camber).The designation numbers describe the proprll(~ls. TIN

number (or numbers) of the first group is the diameter infeet; the number (or numbers) of the second group (cncloscdwithin the first set of parentheses} is the clesi=mlift coefficient(in tenths) of the blade section at the 0.7-raclius station;the numbers of the third group (enclosed wit,hin the secondset of parentheses) are the thickness ratio of LhcMade sectiouat the 0.7-radius station; and the numbers of the fourthgroup are the blade solidity expressed as the mtio of Wblade chord at the 0.7-radius station to the circumfercnw ofthe circle having a radius 0.7 of the propdler tip rtdius.The NACA 4-(10)(08)-03 propeller thus hw a diamctw of4 feet and the blade section at the 0,7-rwdius station hus t]design lift coefficient of 1.0, a thickness ratio of 0.0S, finda bIade solidity of 0.03.

Blade-form curves for thepropellersareprrwmted inflgur(~2.A photograph of onc of these blades and a comptirison ofthe sections at the 0.7-radius station are given as figure 3,

The range of this investigation wus the same, within powwlimitations, m that of reference 1. The range of blade angh~and tunnel-datum Mach number is given in table 1.

REDUCTION OF DATA

The daLahave been reduced to the usmd thrust tind powwcoefficients and efficiency and have been correctWI for thcpropulsive effects of the cowling and spinner and for tumwl-vmll constraint. The tunnel-wdl constraint nwessittitcd avelocity correction to free-air conditions and a n]odd-drqjcorrectiori because of the buoyancy effect. The methodsinvolved in making these corrections arc discuescd i~~rvfcr-ence 1.

.9

9

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Blod~stoti~ rflFIOVRE2.—Bktd&formcurves,

IIN73STIGATION OF EFFECTS OF C.AMSER AND COMPRESSIBILITY ON’ PROPEIZJI.R PERFORMANCE 191

—__ ------ .-—- —- —

. ‘Cmra b%[5)

w Ty’pled teat bltie.fbl Sections at 0.7 mdius.

FIGm.c 3.—TYPIcsJteat bladeati mmparfsonof sectionsat 0.7mdIm.

Thrust.-The thrust coefficient was determined frompropulsive thrust, that is, the net measured force minus&ag of the model mithout the propeIIer and minusthrust clue to the buo~-ancy effect (see reference 1).

thethe

the

Velocity correction- due- to t=el-wall constraint.-Theequivalent free-stream veIocity corresponding to the thrustand torque of the propeJler measured at each rotationalspeed differs from the tunnel-datum velocity (tunnel empty)bemuse of the flow constraint produced b-j the tunnel walls.

TABLE I.—TEST RIXGE OF BLADE .%XGLE .%XD lL\CHH-MBER

lpmlrmd-

f.yw(ll

lumber,M

0:&

. a5

.43

.53

.ao

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. -.

..:

.——.—

.—..J-

—

.=

The veIocitv correction, -whichhas been amdied to the calcu-“lation of ad&mce ratio,’is presented ,in &&e 4 as the ratio of .free-airvelocity to the tunneklatum -reIocity (tunneI empty)as a function of the thrust disk-loading coefficient. Thetunnel-raII correction was found to be dependent only onthe thrust disk-loading coefficient for the range of tunnelspeed and propeIIer operation used in this irmestigation.

The tunneldatum Mach number has not been correctedfor tunnel-all constraint. For the range of velocity shownin figure 4, the factors required to correct the tunneldatumvelocity and tunneI-datum Mach numbers to the free- -stream condition are essentitiy equal.

RESULTS AND DISCUSSION

The basic characteristics for the AT.*CA4–(5) (0S)-03 andNM.% 4–(10) (08)-03 two-blade propeIIe~ are presented infigures 5 and 6, respectively. For each due of the tunnel- -datum Mach number the propeller thrust coefficient, powercoefficient, ancI efficiency are pIotted against advance ratio.The -rariation of tip Mach number with advance ratio isalso included. As used in this report, the tunnel-datumMach number .Uis not corrected for the effects of tunneknllconstraint. The free-stream Mach number can be obtainedby appIujingthe tu.uneI-waHcorrections presented in iigure 4to the tunneI-datum Mach number. SimilarIy, the correctedtip Mach number can also be obtained. .... ...:=i- —

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212 REPORT 1012—NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

Effeot of camber on thrust coefficient.-The primaryeffect of using propeller blades of increased design camber(increased design lift coefficient) is to increase the powerabsorbed by the blades and consequently to increase thethrust. A typical illustration of the increase in thrustproduced by increasing the design camber is shown in figure 7in which the thrust coefficients for the high-camber, medium-camber, and low-c.arnbm propellers for a blade angle of 45°and a forward Mach number of 0.23. are compared. Thepower-coefficient curves are simih and hence are not shown.For cases in which take-off and climb performances are ofprime importance, the increased thrust produced by theblades of high design camber may determine the design;greater thrustsmay be produced with no increase in propellerweight. Tho maximum bust coefficient and the thrust co-efficient for maximum c5ciency also increase with an increasoin design camber, as shown in figures 8 and 9 for Mach

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FIGURE7,—Effeetof de.sfgrrcamberon thrustmedhht. M-O.ZI km -45°.

—Hi-H-H-H-tAcknce rof~ J

Fmti &-Efleet of dedgmcamberonnwhnm thrustcmllclmt. .W-O.1O4.

RG~R~9.—Effeet (Mdedgnearnberon thrustK@lleknt h rndmunr etlldellcy. .M=O.W.

numbers of 0.165 and 0.35, respectively. The perwmtagc ofincrease in thrust is lees than the pwcenttigc of incrcasc incorresponding design camber. The maximum thrust coef-ficients for. the medium-camber propeller are 7 to 11 pmce.ntgreater than for the low-camber propeller. The maximumthrust &efficients for the high-camber propelIer are 4I to46 percent greater than for the low-camber propeller. Thoincreases in @ust coefficient for maximum efficiency are

INVESTIG.iTIOh- OF EFITECTS OF CAMBEE AND COMPRESSIBILITY OX PROPELLER PERFORM=K!E 213

much greater than the increase in maximum thrust coeflicieut.The thrust coefficients at maximum efficiency are 30 to 79percent greater for the medium-camber propelIer and 105to 165 percent greater for the high-camber propeLIerthan forthe low-camber propelIer.

Operation at high angIes of attack may cause the bIaclesections to become stalled or nearIy stalledso that the pro-

peller efficiencyis decreased because of increased profile-drag losses. The pressure distribution o~er these bIadesections is therefore far from optimum and has high peaksthat have a tendency to cause flovr separation or to initiatecompressibility shock. The use of bIades of high designcamber, however, makes it possibIe for the bIade sections tooperate at high section lift coefficients, which are obtainedat angles of attack much lower than for bIades of low designcamber; thus, the tendency of the flow to separate is reducedand stalled conditions me IrugeIy ehninat ed. Since thepressure distribution about the sections may closdy approxim-ate the design distribution, the profile cIragand the tend-ency for shock to be initiated are reduced.

Effect of camber and power loading on efioiency.-Theeffect of blade power Ioading on propeller efficiency for thehigh-camber, medium-<amber, and Iow-camber propeIIem isshown in &ure 10 for a forward Mach number of 0.165.Values of the power coefficient of about 0.10 for thesepropellers represent operation at high lift coefficients forvaIues of the admnce ratio corresponding to take-off andclimb. For this condition, the propeller efficiency decreases-i-cryrapidly as the power coefficient is increased because ofthe increased profle-drag losses and the faihre of the lift toincrease beyond the maximum sect-ion lift coefficient withfurther increase of angle of attack. The ideal efficiencycomputed from the momentum theory is also shown in figure10 for comparison. The divergence of the measured effi-ciency from the ideal efficiency emphasizes the magnitude ofthe profile-drag and induced leases.

The effect of design camber for constant dues of powercoefficient is shown in @e 11 for a forward Mach numberof 0.165. At Iow advance ratios corresponding to take-offand climb, increased camber giwa increased efficiency atl@h power coefficients. At these high power coefficients,the high-camber blade is 15 to 25 percent more efficient thauthe Iovr-camber and medium-camber blades. Ac Iow ad-vance ratios and for Iovr power coellicients, the high-camberblade is approximately 5 percent kss efficient than the lovr-camber and medium-cmnber bIades. These variations em-phasize the necessity for choosing the correct bIade camberto meet operational requirements. The high-camber bladeis generalIy more efficient than the Iow-camber and medium-camber bIades up to values of the ad-mnce ratio appro.ti~mateIy 10 times the value of the power coefficient. Themedium-camber blade is generaIly as much as 5 percent moreefiicientthan the low-camber blade for the same operating

rarge. These results suggest that a satisfactory compromisepropeller may be designed by proper selection of the designcamber.

Single-station a.mdysis of camber effects.-In order toshow the tied of design camber and operat&~ lift coefE-cients on propelIer section efficiency, the results of tests of .the XAC.A 16-series airfoiI sections of 9-percent thickness(reference 2) were chosen as representative of the section atthe 0.7-radius station. Since this analysis is not an attemptto eqdain or present compressibility effects, data at a Machnumber of 0.45 are used. It can be shown that the sectioneficiency is given by

tan &

‘=tan (~+~) (1)

Figure 12 shows the remdtsobtained by use of equation (1).For a given operating Iift coefficient, the induced a~~le ofattack for aII the sections is the same; hence, the efficiencyshows the effect of Iift-drag ratio. The most obvious resuhis that the sections with design lift coefficients betvieen 0.3and 0.5 are the most eficient, because these sections havethe highest Iift-drag ratios at maximum efficiency. Forsections tith design Iift coficients of 0.3 and lower, themaximum efficiency occurs at operating lift coefficientsgreater than the design lift coefficients. For sections -withdesign lift coefficients &~her than 0.3, the maximum effi-ciency occurs at operating Iift coefficients Iower than thedesign lift coefficient. The masimum attainable efficiencyat any bIade operating lift ooef3cient is represented by theenvelope of the efficiencies in &we lz. ne ~eatest effi-ciency attainabIe for operation at a given Iift coeihcientoccurs when the section has a design Iift coefficient equal tothe operating Liftcoefficient.

EfFect of compressibility cn maximum efficiency.-Theen-reIope efficiencies for the high-camber, medium-camber,and Iovr-camber propellers are presented in figure 13 forforward Mach numbers from 0.23 to 0.70. The values ofadvance ratio at which propeller tip Mach numbem of 0.9,1.0, and 1.1 are reached are indicated by vertical dash linesIabeIeclwith the vaIue of M,. The medium-camber propellergave the I@hest efficiencies for aU advance ratios and forforward llach numbers up to 0.53. In most cases, themedium<amber propeIIer vias 2 to 5 percent more efficientthan the low-camber propeller. The high-camber propellergave peak efficiencies 3 to apprc.ximately 12 percent lowerthan those for the medium-camber propeller; the higherefEcieney Iosses were due mainly to compressibility effects.At tip Mach numbers greater than approximately 0.90, thelow-camber and medium-camber propellers showed corn-preasibiIity losses. The high-camber propeller, hoviever,showed an appreciable compressibility loss at a tip Machnumber considerably below 0.90, but the efficiencies werestiIl abcme W percent.

—

214 REPORT 10 12—NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

I I

Lo Cp— — —C-105. --- “

/.8 t/

.35..,Y

/ {/ /

.6 ; I //

/ 1 ‘i\1i

// “ / / ~ )0

t .25“ .35

.4T / .30-/

/ /if’

.2 I/

II

(d0

Ik I

1.0— — — Cp

.8 /I ,+j / ‘/

/ /./ o “15/ r

/!s I / / i

./ ‘. 05

.10

861, !

a /

.

i / /$

/ ‘.25 / .35 ‘

k .4/ .30 /

Q I

1/

.2 tf

I -..

b)o

Lo Cp

.8 /~ ‘

/ ..& /

.6/ \f I

I /.4 I f

1 /.40 /

If ‘\

/ (4

o .4 .8 L? /.6’ 20 24 28 3.2. .36 40 4.4 48 52 56Advcmce raiicj J

iNVESTIGATION OF EFFECT’S OF CAMBER AND COMPRESSIBU.JTY OX PROPELLER PERFORWWCE ~~~

216 REPORT 1012--NATIONAL ADVISORY COMMIIT.EE FOR AERONAUTICS

.96 -

,#nw kpe .SfYiciency.94 ,,

~a ,0”r

l\ I Y\ I I I I f I

.-Sec%n operothg /i* coefficienfl q

l%IrRE 12.—Effectof designcambw on Made-wetloneffleiency,fromstndr-storlonmudyskusingNACA M-serieswctiom. ;-O.Z +-0.09: ~- 44”: .If-0.45.

The effect of compressibility on maximum efficiency isshown in figurH 14 for a blade angle of 45°. Masimumefficiency differed very little for the low-camber and medium-camber propelke with critical tip Mach numbem of approx-;mately 0.90 and 0.91, respectively. The high-camber pro-peller begins to show comprewibility loeses at a tip Machnumber of 0.70, but the rate of Ioss is less than that for thelow-camber and medium-camber propellers. The Iow criticalspeed of the propeIIw with the highest camber obviowdyexcludes the uso of this propeller for very efficient high-speedopmation. The early compressibility losses for the high-oamber propeller are due, in part a~ least, to the high powerabsorbed. If the low-oarnber and medium-camber propellemabsorbed tlmsame power as the high<ambcr propeller, thesepropellers would have to oporate M high angIesof attack; thisoparation would produce high pressure peaks and perhapsearlier and more extmsive compressibility losses.

In order for the Iow-camber and medium-oamber propellersto absorb the same power as the high-camber propeller andstill operate at high efficiencies, a considerable increase insolidity would be neeessary. The large power-absorbingcapacity of the high-oaxuber propeller, however, makes ituseful for conditions of operation at which large vahws ofthrust are required, even at high speecls. For example, theinfluence of design camber on maximum efficiency and onthe power absorbed at maximum efficiency is presented in

figure 15 for an advance ratio of 2.48 at forward Xluch nun~-bers of 0.23 and 0.53 (tip Mach numbem of 0.37 and 0.86,respectively). For these conditions, the high-camber pro-peller shows a compressibility loss of 8 pcrcrmt. TIN high-camber propeller absorbs 55 percent mom power than thcmedium-camber propeller and 75 percent moro power thunthe low-camber propdler tit a forward Mach number of 0.53.The corresponding differences in efficiency arc reductions of9 and 10 percent, which result in net thrust,incwuses of 4CJand 65 percent, respectively, for the high-camber propel]cr;in addition, th-e increases in thrust are ob[ained with noincrease in propeller weight.

Effect of compressibility and power disk loading on maxi-mum efEciency.-The effects of power disk-loading co{’~cientP, anclcompressibility on maximum effic.imcy me shown in@ure 16. The curve for the ideal efficiency obtuintxl fromaxial-momentum consiclerations is dso shown. TIIe idealefficiency deviates from 100 percent solcIy bwau~c of thcinduced loss duo to increasing the ~~ial velocity of the air inthe slipstream. The additional losses for an actuul pro-poller, however, are due to profiledrag and rotational inducedlosses. The induced lossesfor these propollcrs arc small, mNlthe differences shown between the ideal and the mwtsuwdefficienciesare principally duo to blade clragloss. At a giw!nvalue of the folward Mach number, increased values of P.cm-respond to loadings at Iow values of the advance ratio.

IIW_ESTIGATIOX”OF EFFECTS OF CAMBER &WD COMPRESS ~~ ON PROPELLER PERFoRw91mEl 217

Advmce mtiq J Admce ru~ J

I*) M-().23. (e)M -0.wIh} M=.OM. (f) .lf=o.O&ICI M-U.4S.id! .Yf-o.E3. l%’) %%%

FWXUE13.—Hfect of desfg enmber ond compmlbllity on etwelop+erndewy.

.- —

fip Mach number, Aft

FIGK%JI14.—Ef?wIof eom~~btiry on maximumWIcieney.&ma-43’.

. . .-“-—.A

y-

. .-

,.-:

.-.-ti----.F,

-.

.:- .-,.—

.-

1

——

.—

FO;I.-RE15.—EUect of bfnde-s@ctiond4m M eMFident on maximum efltdencysnd power absorbed at maxhmun efllciency. J-24.

213~i—Xi-—l3

218 REPORT 1012—NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

.—

-f5)fV8J-03 1 .-

.8+0~08~03

t Ideal efficiency—-— . -.

(4.7

0 .0/ .02 .03 .04 .05” .06 .07 .08 0 D! .02 .03 .04 .05 .06. .07 ..08Power disk-/ooding coeffitin~ P=

(a) 3f-o.23.(b) M= O.S5. A

(e M= O.05.

(c) Ji=o.43.(d) M=-O.69.

&, gyJ.

FIGCBE16.—EffectLMpower & lading and wmpressfbilltyon maxlmnmaiiciency.

.4t low values of the forward Mach number (fig. 16 (a)), forexample, the maximum-efllciency curves for the three pro-pellers are parallel for high values of P. and are re~ative~yclose to the ideal-efficiency curve. This agreement is ex-pected, because these propelle.ra have approximately theoptimum pitch distributions for these valuea of Po and be-cause the profile-drag and induced losses are not expected tochange very much. Since at a constant forward Mach numberthe high valuea of P. for each curve correspond to opera-tion at the highest tip speeds for that condition, compressi-bility losses would appear at the high values of the powerdisk-Ioading coefficient. No compressibility losses appearfor the low forward Mach numbers. For all propellem,large losses begin to appear at a forward Mach number of0.53 and are most severe for the Iow:camber propeller and

least severe for the medium-camber propeller. At a Machnumber of 0.65, the high-camber propeller appears ta bo momefficient than the other propellers for operation at the highpower disk-loading coefficients. Of particular interest is thegreatly reduced range of power disk-Ioading coefficient forwhich the maxim~ efficiencies obtained at low Mach num-bers can be maintained at high forward Mach numbers.SimiIar remdls are shown in reference 1. At forward Machnumbem of 0.53 or greater, the range of power WAoadingcoefficient that gives high efficienciesfor the low-camber pro-peIIer is greatly reduced because of compressiliIity 10SSCS,Previous results (reference 1) have indicated that the rangeof power disk-loading coefficient for high efficiency may beselected by change of blade solidity. The results reportedherein also indicate that the same effect can be produced by

.—

i

EWESTIGATION OF EH?FECTS OF C.=ER ANm COM2BESSIBHJTY OX PROPELLEE PERFORMA.SCE 219 __

change of camber. This effect is particuldy pronouncedfor forward Mach numbers of 0.53 and 0.65 (figs. 16 (d) and16 (e)). The medium-camber and high-camber propellerscan operate more efEcientIyat high values of the power disk-loading coefhiemt, but compressibility effects have con-siderably Iomered the efficiencies. Chmging the designcamber thus offers another possibility of operating at highpovier disk loadings without too much Ioss in maximumefficiency.

The power disk-loading coefficient for which lovi-speedefficiencies may be maintained at high speeds can also beincreased by using a grea~ number of similar blades, aswas pointed out in reference 1. For operation at,very highspeeds, particular consideration must therefore be given to theaerodynamic design. The design of a propeller then ap-proaches the design for a specific condition of operation toobtain high efficiencies because of the reduced range ofwkIabIe power disk Iowling.

CO~CLUSIO~S

Two-blade propellers designated the NACA 4-(5)(08)-03(medium camber) and the NACA 4-(10)(08)-03 (highcamber) propellers have been investigated in the LangIey8-foot high-speed turmeI through a range of blade angIesfrom 20° to 60° for forward Mach numbers bm 0.165to 0.70 to determine the effect of camber and compressibilityon propeller characteristics. The results of these tests andcomparison with results obtained from previous”tests of theNACA G(3) (08)-03 (LOWcamberl propeIIer indicated thefoIIowing conclusions:

1. PropeIIem of high design camber were more eflicientthan propellem of low design camber for operation at highpower coe&ients. The propeller of highest camber gaveefficiencies 15 to 25 percent ~eater than the efficiencies ofthe low-camber and medium-camber propekrs for highpower coefllcients at advance ratios corresponding to take-off and climb at low Maoh numbem.

2. The medium-camber propeller generalIy gave peakefficiencies 2 to 5 percent higher than the Iovi-mmber

propeller and 3 to approximately 12 percent higher than thehigh-camber propeIIer. The tigh<amber propelIer wasoperating at much higher povrer coefficients, which led toearIy compressibfity effects.

.—

3. The critical tip Mach number for mtium efficiencyat the design bIade angIe of 45° was 0.01 higher for themedium-camber propeller than that for the Iow-camber .. ~propeller, -which began to show compressibility Iosses at atip Mach number of approzdmateIy 0.90. The high-mberpropeIIer, which was operating at higher power coefficientsthan the other propellers, shored the Iargest compressibility ‘-”lows. The compresaibiIity losses for the high-camberpropelIer began at a tip Mach number as low as 0.70 butefficiencies of more than 82 percent were still maintained.

4. For a forward Mach number of 0.53 and an advanceratio of 2.4S (tip Mach number of 0.86), the high-camber _propeller showed a compressibility loss of 8 percent inmaximum efficiency but, bemuse of the large power-absorbqcapacity of this propelIer, produced about 65 percent morethrust than the lore-camber propeller and 46 percent morethrust than the medium-camber propeIler.

5. The range of power disk-loading coefficient over which ‘—high efEciencies could be obtained Tas greatly reduced athigh speeds.

LANGLEY 31EJIOW AERONAUTICAL LABORATORY,

h’ATIONAL kmsoBY COmmTTEE FOR AERONAUTICS,

LWWLEY FIELD, J-A., May 7, 1$?45..

REFERENCES

1. Stack, John, DraIe~,EugeneC., DeIano,JamesB., and Feldman,bti=: Investigation of the ~AcA 4+3)(08)+3 and NAC-44-(3) (0s)-045Two-BladeprO@kS at ForwardMach Num*

to 0.725 to Determine the E&da of CumpressibiIity and SoIidity

on Performance. NACA Rep. 999, 1950.2. Stack, John: Tests of Airfoils Designedto Delay the Compremi-

biIitF Burble. XACA Rep. 763, 1943.

3. Hartman, Edwin P., and Feldw, Lwh: -bod~~~ ROble~ ..-.in the Design of Eficient Propellers. >-ACA ACR, &. 1942,