Tests of Two Full-Scale Propellers with Different Pitch Distributions, at Blade Angles up to 60 Degrees

Two 3-blade 10-foot propellers were operated in front of a liquid-cooled engine nacelle. The propellers differed only in pitch distribution; one had normal distribution (nearly constant pitch for a blade angle of 15 degrees 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 degrees for nearly constant pitch distribution). Propeller blade angles at 0.75r from 15 degrees to sixty degrees, corresponding to design speeds up to 500 miles per hour, were investigated. Propeller blade angles at 0.75r from 15 degrees to 60 degrees, corresponding to design speeds up to 500 miles per hour, were investigated. The results indicated that the propulsive efficiency at a blade angle of 60 degrees was about 9 percent less than the maximum value of 86 percent, which occurred at blade angle of about 30 degrees. The efficiency at a blade angle of 60 degrees was increased about 7 percent by correcting for the effect of a spinner and, at a blade angle of 30 degrees about 3 percent. 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.