Advanced servo flap rotor using variable blade index angle control

Abstract

This paper presents an advanced servo flap rotor using variable blade index angle control (VBIAC) combined with optimally designed servo flaps to achieve high performance in hover and low vibration in high speed forward flight. The variable blade index angle control can automatically change servo flap control position in flight. There is approximately 9% hover performance improvement achieved when the blade index angle is changed 30°. This system can also increase blade stall margin with a trade-off by slightly increasing the blade acceptable vibration level. Aircraft airspeed, vibration level, and pilot control positions are used in the design to feedback the index angle change requirement needed to achieve the design goal. High torque, low speed and high precision motion control actuators are used to move the blade when the aircraft has a vibration level higher than desired. The variable blade index angle control is designed in parallel with the main rotor flight control system. This approach is a sound and safe concept which has very little risk for future advanced servo flap controlled main rotor system design.