Cyclic Blade Pitch Control Without a Swashplate for Small Helicopters

Abstract

This paper presents the design, dynamical model, and experimental investigation of an articulated rotor that affords cyclic pitch authority in small unmanned air vehicle rotorcraft without requiring either a mechanical swashplate or blade pitch actuators. An offset flap hinge coincident with a skew lag-pitch hinge is used to impose a positive lag-pitch coupling on one rotor blade and a complementary negative lag-pitch coupling on the other. The motor torque driving the propeller is electronically modulated to excite a lead-lag motion with controlled rotational phase and amplitude; the ensuing once-per-revolution variation in blade pitch obtains the conventional control response and flapping character of fully actuated cyclic systems. The governing nondimensional lag-flap equations including a nonconstant speed hub are shown. The experimentally measured motor torque, the hub speed variation, the cyclic blade lag-pitch response, and the cyclic blade flapping response are compared with model predictions.