Performance improvement of tail rotors by dynamically extendable chord

Abstract

In order to study the performance improvement of variable speed tail rotors by dynamically extendable chord, a flight performance model is established, which includes a rotor model, a tail rotor model, a fuselage model, and a propulsive trim method. The flight data of the UH-60A helicopter is utilized to validate this model. The results show that the extendable chord has little effect on the power at hover. At cruise, some extra power is needed. At high speed flight, the power can be reduced significantly. The extendable chord is best placed inboard and close to the blade tip region to efficiently shift the lift and/or the drag inboard. The optimal azimuth angles for the deployment of extendable chord are 40°~50° and 130°~140°. The dynamically extendable chord with non-harmonic motion can obtain more power savings than the other strategies. The extendable chord is suitable for deployment on variable speed tail rotors. When the tail rotor speed is reduced by 20%, the maximum power reduction is 20.3%. The extendable chord increases the maximum thrust, which can compensate for the decrease in the maximum thrust by the reduction of the tail rotor speed.