Abstract:
As part of the U.S. Army Aviation Development Directorate (ADD) sponsored Multi-Role Rotor - Adaptive Performance (MRRAP) program, Boeing explored a novel reconfigurable rotor concept that utilized two actuators to change blade twist and effect multi-cyclic blade pitch, respectively. Development activities included design studies for a 49-foot diameter rotor, fabrication and testing of full-scale components, and two wind tunnel tests. Testing on full scale key components, namely the torque tube used for blade twist and the actuator used for blade pitch, showed that the overall concept was feasible. Wind tunnel testing of Mach-scale rotors characterized the hover and cruise performance benefits of changing blade twist. The present paper addresses the development of an electro-mechanical actuator for multi-cyclic blade pitch control, including actuation requirements and trade studies of actuator/hub integration, and focusses on actuator design, fabrication, and testing. Results of the trade studies led to selection of electro-mechanical actuators using a rotary actuator integrated into the hub arm for quasi-static blade twist control (STC) and a linear actuator in place of the pitch link for individual blade control (IBC). This provided a compact and mechanically simple solution with no active components in the rotor blade. Design of the STC and IBC actuators was completed. The IBC actuator rate and duty cycle requirements were outside the normal design space and posed substantial thermal management and mechanical wear challenges. A Breadboard and improved Prototype IBC actuator were fabricated and tested. The development of the IBC actuator has shown that a high bandwidth actuator can be built with the capability to meet the stringent requirements. IBC actuator controller capability at high rates was proven during testing which was one of the key goals of this program. The roller screw design was capable of operating at the high frequency without load applied. The Prototype actuator was built as a development unit and has not been optimized. Further study on methods or design improvements to reduce the size and weight of the actuator and improve thermal management, as well as testing under load are recommended.