Seminars

Rapid investment by industry into manned electric vertical takeoff and landing (eVTOL) aircraft has led to a diverse aircraft ecosystem due to the challenge in discerning the optimal propulsion system topology to meet design goals. A subject of significant debate is whether the weight reductions and simplicity of speed-controlled rotors justify the reduction in thrust control bandwidth versus pitch control. Therefore, the goals of this work were to quantify the thrust performance and power requirements of speed-controlled rotor systems and to develop and assess the performance of a new thrust control concept possible with electric propulsion: thrust control via stacked rotor index angle. This involved electronically phasing a pair of coaxial, co-rotating rotors to control system thrust. Thrust variations of 18% with changes in the index angle of 9◦ were observed, suggesting a low magnitude, high bandwidth thrust control method which may be useful for attitude stabilization and disturbance rejection. A comprehensive experimental and numerical study was conducted on two-meter diameter rotors at 950 RPM to compare and contrast the performance of single and stacked rotor electric powertrains. Notable findings showed that controlling the index angle of a stacked rotor reduces the peak torque required for small amplitude, quick changes in thrust versus speed-controlled rotors. Thus, if fixed-pitch simplicity is required, index angle-controlled stacked rotors are a useful option to overcome control bandwidth limitations stemming from the available motor torque.