Design, implementation, and flight testing of a stability augmentation system for coaxial ultralight rotorcraft

Abstract

This paper describes the first ever flight demonstration of a stability augmentation system using electromechanical inline actuators in a rotorcraft without hydraulic force amplification. A coaxial ultralight helicopter equipped with the stability augmentation system is used as a flight demonstrator. The paper covers the synthesis of requirements for the system, the design process and architecture of the system, technical challenges, the algorithms including the control laws, safety features, flight testing, and flight test results. The flight test campaign includes scaled down versions of well established mission task elements for handling qualities evaluation adapted from literature. Measurement data and pilot feedback indicate that the stabilization is effective and workload is reduced. The flight demonstration proves that the proposed system can be integrated safely into small rotorcraft despite the space and weight limits and the actuation force requirements. To emphasize the scientific contribution of the flight demonstration, the paper also includes a brief discussion of the dynamics of reversible control trains, a qualitative explanation of the expected actuator feedback forces, and a description of the associated challenges and open questions.