Helicopter Horizontal Tail Incidence Control to Reduce Rotor Cyclic Pitch and Blade Flapping

摘要

This study examines the possible reductions in rotor flapping and rotor cyclic pitch requirements in trimmed level flight due to the introduction of auxiliary pitching and rolling moments in the non-rotating system using collective and differential incidence control of the left and right halves of the horizontal tail. Reduction in blade flapping would reduce blade dynamic stresses, and reduction in rotor cyclic pitch requirements would reduce the cyclic eleven deflections required in a swashplateless design to levels possible with current piezoelectrically actuated flaps. Simulations were carried out for a medium-weight, articulated rotor helicopter (similar to the UH-60), and a lightweight, hingeless rotor helicopter (similar to the BO-105). Results show that at moderate to high flight speeds, modest horizontal tail collective incidence settings that produce nose-down pitching moments on the aircraft are able to eliminate the longitudinal cyclic flapping. If the collective incidence settings are further increased (to generate larger nose-down pitching moments), the rotor longitudinal cyclic pitch requirements could possibly reduce to zero, as well. The nose-down pitching moments introduced through the horizontal tail (to reduce longitudinal cyclic flapping and rotor cyclic pitch) result in a large nose-down pitch attitude of the aircraft. A combination of collective and differential settings could result in zero total blade flapping and cyclic pitch. The horizontal tail size and longitudinal position of the vehicle center of gravity are shown to be important parameters that can significantly influence the problem.