Pulse jet rotor drive for helicopter

TLDR: In this paper, a U-shaped valveless pulse jet engine with an annular scoop adjacent to the lip of the inlet is used to provide fresh air to the rotors of a rotary wing aircraft at increased air velocity.

Abstract: A pulse-jet system for driving rotary wing aircraft. In a first embodiment the tips of the rotors of a rotary wing aircraft are provided with "U"-shaped valveless pulse jet engines having an annular scoop adjacent to the lip of the inlet to provide fresh air thereto at increased air velocity. In a second embodiment a pair of straight, valveless pulse jet engines are mounted perpendicular to the rotor shaft of a rotary wing aircraft so as to rotate therewith. These engines may be contained within a streamlined cowl at the opposite outer ends of which are attached flow augmenters which change the direction and increase the flow of exhaust gases from the engines by 90 DEG and eject the same in a chordwise direction. This forms a propulsion unit. When a cowl is used, air enters the cowl through an inlet disposed along the axis of the rotor shaft. The propulsion unit is adjusted angularly and heightwise with respect to the rotor blades in order to optimize the aerodynamic effects of the flow of exhaust gases over the blades. In both of the embodiments, a first control device primarily governs the engine thrust and consequently the rotor speed while a second control device can be added which supplies fuel to the engines at a frequency differing from the fundamental or resonant frequency of the engines so that engine noise is reduced. Also, in both embodiments, the engines are started by exciting them with bursts of air from a compressed air supply to be carried on the aircraft.