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RESEARCH MEMORANDUM

FLIGHT TESTS OF A CURTISS NO. 838-1C2-18 THR;EE-BLADE

PROPELLER HAVING TRAILING-EDGE EXTENSIONS

BY

John J: Gardner

Langley Memorial Aeronautical Laboratory Langley Field, Va. .

Restriction/Classification Cancelled

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Restriction/Classification Cancelled

2 EACA RM Eo. LwlO

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b blade- section chord . - . . - . . '. .. :;.- ........ . . . . . . . . . . . :. . . . . . .

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propeller-section Mach . . nurmber . . . . . . . . . - . . . . . I . .

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Blede-form curve8 of the test propeller are preeented in figure 1. 331 figure 2 is Shawn a c l o ~ ~ u p view and in figme 3, a fltght viov,of the t e s t propeller and survey rake installed on a Republic P-47D-28 airplane

Teet equipment, test p&cscluro, and method. of data reduction are eimilar t o those deecribed in reference 1.

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- Ih figure 8 &ro presented thrust-grading curves obtained in war emergency power climb c-dftlon. There is no evidence in these -surveys of loss in thruflt near the tlp usually associated with high-tip Mach nlrmbers. It ehonld be' noted a% khla pofnt that the large thrmst difference between left and right. a u r v e ~ s and t h e l a t e ra l shift In the aurveys near €he t ip station (xS2 = 1,O) are the result of .pitched anB yawed candftions, .reqpectively, of the thruat axis and. are not to be E L S S O C T ~ M , w i t h the effectE of compressibtlity. The effects of pitch and. $aw.:axe dewribsd more completely in reference 3.

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. 6 mACA RM No. L'TDlO

Effect of extensions i n climb .- For a gimn power-absorption requirement, increasing propeller solidity, in t h i a instance by addition of trailing-edge extension, reduces the operating lift '

coefficients of the blade sections. Since it is generally known that blade geotions operate at hightlift coefficients in the olimb condition, any reductfon in operating aqctiw lift coeflicient hae a beneficfal effect on propeller efficiency fmm two stand- p i n t a . fir&, the eections operate nemr their optfmum-lift coefficiente f o r ~lta~dmum LID ratios. seccad, operating at 3ower- lift coaf'fioients raises eection cri t lcal epaede, thus delay- t he oneret of compressibility effects.

Although the t e s t propelLer is not operetfng at maximum eff lciency, it appears to be operating mar enough to maximum . efficlenog.so that the data of reference 4 may be usad in this andysi s .

If -the assumption is made that the rate of change of efficiency with power indicated i n figure 7 f& the propeller Nith extensions if3 also applicable t o .the propeller without extens9on8,. the. offect on efficiency of an incroase of 20 percent in Mwer abeqptfon of the propeller without exte~siona can 'be estfmatsd. ,For, exatnple,' ,'

figure '7 Bhowa that at an advance-ratfo of l ' .O incrpaslng +&e . propeller power coefficient from o .13 t o o .156 (a 20-peroent . ' I

incresee) decreases the efficiency by about- 2 percent. This indicates that, i n addition. to the increase In axial-energy loss, other losses have also been increased by a small amount. .

It i e now possible to estimate the amount by which the ext;enslons increased t he propeller'climb efficiency. If the increarre - fn power is absorbed without a change in sol idity, the efficiency 1088, ae akove, .is about 2 percent.. If trailing-edge exteneions equivalent t o ths percent increase in power are added, then only the added axial-energy loea of 0,5 to 1 percent is h c m d . Therefore, the riet.reeu3.t is an improvement i n efficiency of 1 t o 1.5 percent attributable t o the addltion of extensions.

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&ardna.tion of the efficiejncy c m e s of figure 1.4 indicates a gradual drop in effrcfency at the lower speeds.as.the power coefficfent is raised. This is in agreement with the trend in the climb teats of figure 7. -At the higher speeds, a reverse trend is ObEeXTed. An increase in power coefficient results la an increase in efficiency. From figure 14 it is noted that at an afrplane Mach number of 0.7 increasing the power coefficient per blade from 0 .OB to 0 a82 results in 4 gain fn efffciency of approxfmately.7 percent. A further increme to 0.092 r e d t s In an additional efficiency ga,in of 2 percent.

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be decreasgd about 2 percent. Exgrgi3eed as a loss in top speed of the airc.raf"t, t h i s would be 3 to 4 miles per hour.

' The =&m3.ysis of the climb and high-speed teats have indicated , .

that the exbeneiuns improves. climb efficiency at the expense CXP ,

high-aged efficiency. For the normal .lo@ing condition of a Republtc P-4m28 airplane (appmximately'13,000 pbUnd8) it i S estimated me resulting fncreaee in rate-o#-climb is of, the order of 100 feet per *Ute,. ' The decroase in %ob speed is difflcult. to accurately determihe ?$it it 'is.,likely that it is not more than 4 miles..per hour. In adtiltion, these tests' haye demonstrated that the propeller l e considerably underloaded ,et high speeds. This cadit ian could be correctecl bg.increaering the power available, reducing blade; solidity, or changing the propeller-engine Gear ratio, .but all of these methods would result in reduced: 'clinib efficiencies. However, a twu-epeed propeller-engine gee ~ystem would permit efficient propeL1ar.operation at both climb and high- speed conditions. The neea f o r . such a dyetem will'become more eviaent as the gap be-en t h e mx~Lnnnn a p e d and' climbing speeds of ai.rcraft ftru;the'r +den&.

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3 . For'airplaae, Mach ~l~rmber~ qf 6.6 t o 0.7,. peak efficiency " .. ... ,

will be 'reachod'uat a power coeffic$ent per. 'zilide of appron.ltely 0 -12. . . . . . .. . . .

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Figure 2.- Republic P-47D-28 airplane equipped with a Curtiss No. 838-1C2-18 - three-blade propeller and survey rakes.

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Figure 3.- Flight view of Republic P-47D-28 airplane equipped with a Curtiss No. 838-1C2-18 three-blade propeller and survey rakes.

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Figuse 4.- normal pousr alimb at an indioated afrsgsed of 165 m q e a per hour. Ourtima EO. 833-la2-18 three-blade propeller on Republia pJc7D.28 airplane.

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Figure 5.- Military p m r olimb at an indioated. alrmpeed of lb5 milee per hoar. (lurtias Blo. d j d - l e - 1 8 threbblade propelleu ar Republlo p-47D-26 alrplana.

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PIguxe 7.- Effect of power loading OD efflolenoy i n the climb oondltlm. Ourties lo. p,g- 1'22-18 three-blade propeller an Regublio p-47D-2g airplane.

NACA RM No. L7D10 Fig. 8

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Figure 8. - T h r ~ t - g r a d i n g QUTVBS for climb at w a r emergency power. Indloated airspeed, 165 miles per hour. Curtfsa No. $38-lC2-18 three-blade propeller on Republio P-47b-26 airplane.

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Figure 8.- Oonclluded.

Fig. 9 NACA RM No. L7D10

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+- Point taken f m m aired curves o f the Military hber-Cl im b tests.

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Figure 9.- Variation in propeller efflolenuy with airplane Mach number a t aonstant blade-loading oonditlon. Power ooefflclent per blade approxl- mate15 .06; 2700 engine r p m . Curtis8 Bo. g3d-le-18 three-blade propeller 04 Republlo H7D-28 airplane.

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Figure 10.- Variation in propeller efficlenog with airpltW3 Maoh number at omstant blade-Io.ading oonditlon. Power ooeffiaient per blade approxi- mately, .a2; 2 00 engine rpm. Ourt lse No. g38-l@-lg three-blade propeller on Republic P- z ?I!-28 airplane.

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Figure 11.- Variation in propeller effiolenay with airplane Maoh number at oonetant blade-loading oondition. Power ooeff iolent per blade approri- mate15 .M5; 2 00 engine r p m . Ourtiss EO. 838-162.18 three-blade propeller on Republio P 1 7D-28 airplane.

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figure 12.- Variation in propeller effioiency with airplane MR& number at oonstant bla8e-loading condition. Pouer ooeffiofent per b l e e approxi- mately, .O92; 2 00 engine rpm. Ourties No. 83I3-102-lg three-blade propeller on Republio P- k m 2 8 airplane.

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Airp iane Mach number. M Ffgvre 13.- Variation in propeller effiolenoy with airplane Maah number at oonetant blade-loading oanditfan. Power ooeffiolent per bUdg apprcrxi- Isately, .le; 2 00 engine rpm. Ourties BO. 838-1U2-18 three-blade propeller on Republio P- c 7D-28 airplane. ,

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Figure 15.- Oomparatlve thrust-grading ourves for several blade loading oondltlons. Advanoe-ratio approximately 2.5, airplane Mach number approximatelp, 0.7. Ourtise Bo. g3€?-1@-18 three-blade propeller on Regublio P-47D airplane.

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Figure 16.- Seotian lift coeffioient for d u r t f s s No. 832L102-1$ three-blade propeller on Republio P-47D airplane for m i l i t a r y and war emergenoy powers at altitude. !

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