I ORDER to properly evaluate the effect of tip speed and profile shape upon the thrust to hp. ratio of a propeller, allowance must be made for torsional deflection of the blade if such occurs. Under static conditions the effect of tip speed is greater at blade angles of 15° than at 23°. For a propeller using an R.A.F. 6 profile the tip-speed effect is noted above 700 ft. per sec, while for propellers using the Clark Y and N.A.C.A. 2400 profiles the effect becomes noticeable above 900 ft. per sec, particularly for the lower blade angles. For a value of CP of 0.06, equivalent to a blade angle of approximately 15°, and a tip speed of 900 ft. per sec, the R.A.F. 6 profile propeller gives a CT/CP ratio 4.5 percent greater than the Clark Y and 6.5 percent greater than the N.A.C.A. 2400 profile propeller. At a CP of 0.12, equivalent to a blade angle of approximately 23°, the values are, respectively, 10.5 and 15.0 percent greater. The ratio of the net static thrust on a single-engined airplane to the propeller-shaft thrust varied from 0.85 on a high-wing monoplane with several struts in the slip stream to 0.95 on a streamlined low-wing monoplane.