A Compound Helicopter Rotor-Propeller Phase-Locked System Without a Mechanical Gearbox

This paper tests and validates an electric rotor-propeller phase-locking system to emulate a mechanical gearbox for lift- and thrust-compound helicopter configurations. A comprehensive control scheme is designed and integrated into the UMD compound rig to rotate the main rotor and pusher propeller at desired gear ratios with known azimuthal positions. Wind tunnel testing is completed with the system to validate the mechanically decoupled, phase-locked rotor and propeller using time-accurate camera imaging. Flowfield measurements are collected to examine longitudinal velocity variation at multiple rotor phases and gear ratios. The objective of this study is to demonstrate the feasibility of an electric gearbox-less coupled rotor-propeller system for high-speed compound helicopter wind tunnel testing.