REPORT No. 447

STATIC THRUST OF AIRPLANE PROPELLERS

By WALTERS. DmEL

SUMMARY

Statti thrwt dk.ta from more than 100 aiqd.une pro-peller teds are Golkcted from variom 80UXC4Sand coni-bind in working than%, from which t?w LTM.0 thnwtw@iJ.YM KTO in tb -

K.ox l). hpT,==r. p. m. X diam.

may be readily deknnined. T& avai.labk o?.alacoverpracticd?y d? types of propders and are in good agree-ment. For artreme pitch ra.tk8, or for very ho and forvery high blua%settings, tti VUlu.tXof KTO are shown todevide cm”dmbly from the generally used linearre+Wons bamo?on data at moderate pitch ra.tws.

INTRODUCTION .

The static thrust of a propeller was formerly ofinterest only in connection with proposed helicopterdesigns, but the advent of very high powers andcorresponding high performance in reoent airplanedesigns have made in necessary to consider the staticthrust as a desigu factor. At present the chief appli-cations of accurate static thrust data are in the calcu-lation of nosing-over moments and the estimation oftake-off runs.

The available methods of calculating static thrustam based on constants derived horn D urand andLealey’s tests on wooden propellers. (Reference 4.)It is the purpose of this report to revise the constantsand to extend the methods to include reoent data onadjustable metal propellem.

Warner shows in reference 1 that the thrust perhorsepower is obtained by division, from the coeffi-cient

TcT=~ (1)

(3)

In Chapt8r XIV of reference 2, Nfr. Warner stat8s:“It can be shown horn propeller theory that thestatic thrust per horsepower for a propeller is equal toa constant divided by the product of the r. p. m. ofthe propeller and its &meter, and experiments byDurand have shown that the average value of theconstant rangea from 49,000 for propellm”dmigned towork normally at a value of V/nD of 1.1 up to 79,000when V/nD for maximum efficiency is 0.5 -----The variation of the coefficient is approximatelyI.ineaxbetween the points given.”

In reference 3 the author gives the static thrustformula

TO=6,000(18.7–9 .5$) (r. pbrn~X~ (4)

Where To is the static thrust in pounds, p/D is thenominal pitoh/diameter ratio and D is the dimneter infeet. The value of the cxmstant in equation (4) wasbased on D urand and Lesley’s data and is substan-tially identical with Warner’s values as quoted above.

It will be shown that the static thrust coefficientKro in the equation

TO= %xb. hp(r. p.m.)xD

(5)

can be determined with fair accuracy for any propellerfrom data usually available or readily obtained.

DIJRAND AND LESLEY’S TESTS

In Table V of reference 4, Durand and Lesley givethe “standing thrust and power” for 67 propellem.these include a number of varktiom in blade sectionand blade form that are of academic interest only, sincepraotica.lly all propellers now in use are in the & I?2class. Table I lists the essential data including thestatic thrust ccefiioient KTO for all of the S, F2propellers. KTO is found from the relation

.K,. =33,ooo $

the conversion factor 33,000 being required for theunits of b. hp and r. p. m. in equation (5).

126

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.

126 IIEPOET NATIONAL ADVISORY COMblTITEE FOR AERONAUTICS

The valuea of .K~Oare plotted against p/D onFigure 1. The dashed line on this figure correspondsto equation (4) and maybe represented by

K~o= 112,400 – 57,000~ (6)

or

~&57,000(1.97-5) (6a)

both of which are identical with equation (4).

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FIOUME1.-St8tlo tbnwt cmfiiclentsfor 2-bladevnmlenPrwdkrwDarandand L@&stesk N. A. O. LTc&nfcal R6PRt No.33

N. A. C. A. TESTS

Three series of systematic tests on adjustable blademetil propelle~ have been made by the NationalAdvisory Committee for Aeronautics in the propellerresearch tunnel at Langley Field. (References 5, 6,and 7.) Static thrust data horn these reports aregiven in Tables II to V, inclusive, and the values ofKTO are plotted against blade setting at 0.75 R inFigure 2. There is a considerable scattering of thepoints probably due to fuselage interference effectsand ta the method of obtainrng the static vahm of CTand CPby extrapolation but the trend of the,variationis well defied. It is of considerable interest to notethe reduction in static thrust at high pitch angles forpropellers with the Clark Y section. This charac-teristic, which may be due to an early stalling of theblade sections, has been observed in flight tests to suchan extent that a separate curve is apparently reqtired

for these propellers. As shown by the data fromTechnical Report No. 351 (reference 6), given inTable III, cutting off the tips to reduce the diameterdoes not appreciably affect the static thrust coefficient.

BRITISH TESTS

A very complete investigation of propeller charac-teristics is covered by Reports and MemorandaNo. 829 of the British Aeronautical Research Com-mittee, @eference 8.) Static thrust data from thisreport are given in Tables VI and VII. The formercovers propellers having constant pitch along theblade, while the latter have the variable pitch dis-tribution obtained with the usual blade adjustment.Values of K=. are plotted against blade angle at 0.76 Ron Figure 3. The data are usually consistent due tocare exercised in eliminating interference and fallvery close to the three curves, the one for two bladesbeing identical with that given on Figure 2.

&bfode mgle, o%gees, of Q 75 RFmum 2-StatIo Unuutwaffkhts for adjustableblademeti propollora

THE CALCULATION OF STATIC THRUST

For any given set of design conditions the staticthrust may be calculated from equation (5):

&,X (b.h )‘o-~

(6)

the proper value of K= being obtained from I?igurea1,2, or 3. In the case of adjustable blade metal propellersit is common practice to specify the blade setting interms of the blade angle at the 42-inch radius. Figure4 has been prepared for obtaining blade anglea at0.75 R from the values at the 42-inch radius, for con-ventional pitch distributions. Thi.a cmrve gives the .correction Ad to be added to or subtracted from the

STATIC THRUST OF AIEPLANH PROPELLERS 127

blade angle at the 42-inch radius to obtain the bladeangle at the 0.76 1?.

In design studies it is more convenient to work withthe V/nD for mmimum efficiency than with the blade~gle. Figure 5 is a plot of KT, against V/nD formaximum efficiency, using the data from Tablea I toVII. The points appear to fall nearer to regularcurves than when p/D or o is used as the base.

In using equation (5), the full rated b.hp and r.p.m.may be used without appreciable error since the ratiob.hp/r.p.m. is substantially constant for full-throttleoperation.

~.Q

* 4&xw

3(XMO

‘8 12 IIS. 20 24 28 32 380,blade mgf.. dqees, of 0.75 R

EIOUBE3.–Statto tbrnet cmllkientskc metal propeUem Brftisb kts, IL & M.A’o.629

CONCLUSIONS

A study of the collected data leads to the followingconclusions:1. In general, narrow blades give a h~her static

thrust coefficient than wide blades.2. Thin blades appear to give a higher static thrust co-

efficient for low pitch setting and lem static thrustat high pitch settings than thick blades.

3. Blade section may be very important in deter-mining the static thrust coefficient at high pitchsettings.

4. There is a decrease in the static thrust coefficientdue to the use of 3 or 4 blades at low pitchsettings but the curves converge into one curveat and above a blade setting of 23° at 0.75 R.

5. The effect of gearing an engine is to reduce the pro-peller r. p. m., to increase the diameter, and toincrease the pitch or blade angle required. Withlarge reduction ratios the effect of the increaseddiameter and the reduction in Km correspondingto the increased pitch may more than offset theeffect of the change in r. p. m., and thus reducethe static thrust.

FIGURE4.—Canwth h obtaining bledo auk at CL76rodfrMfrom blade f#t@ at42” shtton. PmMva (+) vfdnH cd A Oto ba added to mtthg at 42’ etafioqn-~ve (–) * to be snbtraetd to@ blede angle at 0.75IWUUS. EXWIIpIO:For 10R dh. ProP. A$=–9. L90.7~.b’4y_p

6. The variable pitch -propeller will give a large in-crease in static thrust coefficient when the avail-able blade setting change is .mi3icientto attainblade angles of 12° or less.

BUILEAU or AERONAUTICS,

NAVY DEPARTMENT,

WU=GTON, D. C. Sept., 19w?.

REFERENCES

1. Warner, Edward P.: The Problem of the Helicopter. T. N.No. 4, N. A. C. A., 1920.

2. Warner, Edward P.: Airplane De@n-Aerodynarnicc.Chapter XIV.) MoGraw-Hfll Book Co., Inc., New

$ ork Citv. 1927.3. Di~ ~ - ‘S.g.Engineering Aerodynamic. The Ronald

4. Durand, Tl? F., Ad Lesley, E. P.:%

erimental Researchon b Propellers-11 T. IL No. 30, A. C. A., 1920.

5. Weick, Fred E.: FuU-Soale Wind-Tunn~ Teets of a l?arieaof Metal Propeller on a VE-7 Airplane. T. IL No. 306,N. L C. A.. 1929.

6. Wood, Donal’d H.: Full-scale Wind-Tunnel Tests of aPropeller with the Diameter Changed by Cutting Off the

7. +a~~;!#~’B; ~$%;Y$;+;~~mhpti0R9. .T. R.

No. 37% N. A. C. L 1931.8. F e, A.: ~ck, C. N. ~. Howard R. G., and Bateman, H.:

% erunents with a $amily 0$ AiracrewE Inoluding theEffeot of Traotor and Pusher Bodies. Part I. Experi-ments with the Family of Airacraws Mountad in Front ofa Small Body. R. & M. No. 829, British IL R. C., 1922.

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128 REPORT NATIONAL ADVISORY COMMIITDE FOR AERONAUTICS

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STATIC TERUST OF AIRP.LANEI PROPELLE.R5

TABLE I TM3LE IV

STATIC THRUST COEFFICIENTS FOR WOODEN PROPELLERS-DATA FROM DURAND AND LESLEY7;WNJ, TABLE V, N. A. C. A. TECHljICAL REPOW

STATIC THRUST COEFFICIENTS FOR MXTUSTABLEPITCH PROPELLERS WITH NAVY STANDARD SEC-TION MODIFIED R. A. F.-$) N. A. C. A. TESTS,

&TECH CAL REPORT NO. 37S1 1 I

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TABLE II

STATIC THRUST COEFFICIENTS FOR MET~ PRCj~LW# N. A. C. A. TESTS, TECHNICAL REPO13

. TABLE V

STATIC THRUST COEFFICIENTS FOR ADJUSTABLEPITCH PROPELLER9 WITH CLARK Y SECTIONN. JL C. A. TESTS, TECHNICAL REPORT NO. 37S1?B~de8tatIothrnn SbMe

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TABLE III

STATIC THRUST COEFFICIENTS FOR ADJUSTABLMETAL PROPELLERS WITH CUT-OFF TIPS N. JC. A. TESTS, TECHNICAL REPORT NO. 351

U&

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130 RI)PORT NATIONAL ADVISORY COhUKFITEE FOR AERONAUTICS

I TABLE VJlTABLE VI

STATIC THRUST COEFFICIENTS FOR METAL PR(PELLERS DATA FROM BRITISH A R. C. IL & h

TATIC THRUST COEFFICIENTS FOR ADJUSTABLEPITCH METAL PROPELLERS—DATA FROMBRITISH A. R. C. 1%& M. NO. 829NO. S29

Swio dnto

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