Propeller Factors Tending to Limit Aircraft-Engine Powers 380152
THERE is a strong trend toward increasing airplane gross weights inasmuch as larger sizes simultaneously result in structural economy and aerodynamic improvement. The concurrent demand for larger powerplants may be limited by the propeller since, at constant tip speed and velocity, its weight is proportional to the 3/2 power of the horsepower.
By assuming a specific engine-weight curve for increasing powers and adding the propeller weight, specific-weight curves for the powerplant group are obtained. These curves show minima in the vicinity of 2500 and 6000 hp. for 250 and 450 m.p.h. design speeds, respectively, at sea level. Multiblade propellers and very high design speeds tend to reduce the weight penalty, so there is no ultimate limit to engine powers.