Propellors in high-speed dives

Abstract

The performance of a variable-pitch, 3-bladed propellor has been calculated for conditions of fixed power absorption, fixed rotational speed and varying advance speed. Curves of efficiency and power-loss ratios are given to a base of V/a (advance speed/velocity of sound, Fig 1), together with thrust, torque grading and compressibility loss curves to a base of (radius) squared (Fig. 2). Increasing values of V/a (up to 0.85 or 600 m.p.h. at 21,000 ft.) representing the conditions of a high-speed dive, are accompanied by marked decreases in efficiency and under these conditions the thrust becomes negative over the tips of the blades.