The effect of high tip speeds on the performance of aeroplane propellers

Abstract

SUMMARY. Thrust, Torque, Efficiency, Thrust Grading and Blade Twist have been measured for a model airscrew running at tip speeds up to 1300 ft. /sec. i.e. 1.2 times the velocity of sound.CONCLUSIONS. (1) There was found to be a considerable loss of efficiency when the blade tips were run at speeds exceeding 75% of the velocity of sound.(2) The lift coefficient of s blade section' was found to increase rapidly as its velocity rose from 60 to 80% of the velocity of sound.(3) At high tip speeds the designed thrust distribution along the blade is liable to serious modification by blade twist.(4) As the velocity of a blade section approaches that . of sound the centre of pressure moves back and the drag coefficient increases.(5) There should be no difficulty as regards strength in constructing wood airscrews to run at tip speeds up to the velocity of sound.