Influence of control strategy on forward flight performance of coaxial rigid rotor high-speed helicopters

The coaxial rigid rotor high-speed helicopter based on the forward blade concept has a high maximum flight speed, but the cooperation of the coaxial rigid rotor and the propellor brings the problem of handling redundancy. To improve the flight performance of the high-speed helicopter, this paper carries out the analysis of the influence of the rotor/thrust blade control strategy. Firstly, a high-precision Computational Fluid Dynamics (CFD) method for predicting the aerodynamic forces of coaxial rigid rotor, propellor and fuselage is established. Secondly, a robust trim method for redundant control of coaxial rigid rotor/propellor is proposed based on CFD-Surrogate Model (SM) -Genetic Algorithm (GA). On this basis, the influence of control strategies such as rotor/propellor forward thrust distribution, rotor lift offset and fuselage attitude on the flight performance of high-speed helicopter is analyzed, and the control strategies that can effectively improve the maximum forward flight speed and practical lift limit of high-speed helicopter are obtained. The results show that with fixed fuselage pitch angle, the maximum horizontal flight speed of the high-speed helicopter can be increased by 10.78% when a small part of the forward thrust is distributed by the rotor. When flying at sea level, the helicopter has the maximum forward speed when the lift offset of the rotor is 0.3, and has the maximum service ceiling when the lift offset is 0.2. When the fuselage pitch angle is -1°, the high-speed helicopter has the maximum forward flight speed and service ceiling. If the fuselage pitch angle is too large or too small, the forward flight performance will be reduced.