An Assessment of Heave Response Dynamics for Electrically Driven Rotors of Increasing Diameter

An examination is conducted of the effects of increasing rotor size on system heave response time and power consumption, due to the increasing rotor blade inertia. The study aims to establish a rotor size at which using an electric motor and fixed-pitch, variable-RPM rotor may no longer be feasible due to the degradation in system climb rate response time and handling qualities ratings. Several isolated rotors ranging from 1 to 8 feet in diameter are simulated, and the heave responses are examined based on Froude scaled ADS-33E-PRF requirements. A model validation is performed using data from a 28-inch diameter rotor tested on a rotor test stand apparatus. Various feedback controller designs are then considered, including proportional and proportional-derivative control laws. Pure proportional control fails to reach scaled Level 1 requirements due to the underutilization of the motor. Using proportional-derivative control, rotors 6 feet or less in diameter can meet the scaled ADS-33E-PRF Level 1 heave response requirements with variable-RPM control alone; rotors larger than this may not be responsive enough for effective operation.