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Report No. 658 , Tests of Two Full-Scale Propellers with Different Pitch Distributions, at Blade Angles up to 60 °, by David Biermann and Edwin P. Hartman. 15 pages, illustrations, 23 X 29 cms. Washington, Government Printing Office, I~39. Price IO cents. Two 3-blade lo-foot propellers were operated in front of a liquld-cooled engine nacelle. The propellers differed only in pitch distribution; one had normal distribution (nearly constant pitch for a blade angle of I5 ° at 0.75 radius), and the other had the pitch of the tip sections decreased with respect to that for the shank sections (blade angle of 35 ° for nearly constant pitch distribution). Propeller blade angles at 0.75 R from 15 ° to 60 °, corresponding to design speeds up to 50o miles per hour, were investigated.
The results indicated that the propulsive efficiency at a blade angle of 6o ° was about 9 per cent. less than the maximum value of 86 per cent., which occurred at a blade angle of about 3 o°. The efficiency at a blade angle of 60 ° was increased about 7 per cent. by correcting for the effect of a spinner and, at a blade angle of 3 o°, about 3 per cent. The peak efficiencies for the propeller having the washed-out pitch distribution were slightly less than for the normal propeller but the take-off efficiency was generally higher.
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