Active twist rotors, which utilize smart materials or structures to actively drive blade twisting and dynamically optimize spanwise and azimuthal twist distribution, have emerged as a critical technological pathway for enhancing the overall performance of helicopter rotors. This paper systematically reviews the technological evolution and research progress of active twist rotors, with a particular focus on their potential in aerodynamic performance improvement, vibration suppression, and noise control. Compared to indirect actuation methods, direct piezoelectric composite-driven blade twisting offers a more compact structure and higher reliability. Theoretical and experimental studies demonstrate that active twist technology can effectively improve rotor efficiency by optimizing aerodynamic load distribution while significantly reducing hub vibration loads and blade-vortex interaction noise through higher harmonic control strategies. Current technological bottlenecks lie in the development of high-efficiency smart materials, multiphysics-coupled modeling, and multi-objective optimization design. Future efforts must address challenges in reliability, environmental adaptability, and intelligent control for engineering applications, as well as expand cross-domain applications in next-generation rotorcraft. This technology provides theoretical support for the paradigm shift in helicopter rotor design from passive adaptation to active control, demonstrating significant engineering potential.

To study the driving rotation characteristics of a compound helicopter’s rotor undergoing the upwash in high-speed flight, a compound helicopter trim model is established on the basis of an existing helicopter flight performance model. With a helicopter example similar to X³ helicopter, the effects of lift share and variable rotor speed on the flight performance of the rotor and helicopter are analyzed in the driving rotation state undergoing the upwash. The results show that the energy absorbed from the airflow increases with the increase of speed due to the upwash, and the rotor drag power increases. The torque distribution is different from that in low speed flight. The blade elements that produce the driving torque increase significantly, and the area with larger resistance torque shifts from the retreating blade to the advancing blade. Decreasing the incidence angle of the wing reduces the proportion of the wing lift, which results in an increase in the rotor drag power. This is beneficial for the rotor to absorb energy from the airflow and improve the performance of the rotor and helicopter as the rotor undergoes an upwash flow. At 400 km/h, the rotor drag power with the wing incidence angle of 8° is 11.2% higher than that of 10°, and the lift-to-drag ratios of the rotor and helicopter increase by 35.7% and 2.6%, respectively. In medium- or high-speed flight, excessive reduction of the rotor speed causes the fuselage to pitch up, and the energy absorbed from the airflow by the rotor increases. As the flight speed is larger than 340 km/h, the fuselage remains horizontal, and the rotor drag power is reduced. Reducing the rotor speed is not beneficial for the airflow to provide energy. However, reducing the rotor speed of the compound helicopter in high-speed flight is beneficial for reducing the rotor power consumption and improving the flight performance.

To investigate the effects of lift and propulsive force shares on flight performance, a compound helicopter model is derived. The model consists of a helicopter model, a wing model and a propeller model. At a low speed of 100 km/h, the Lift-to-Drag ratio (L/D) of the compound helicopter is improved when the wing provides 20.2% of the take-off weight. At high speeds, the L/D can be improved when the propeller provides the total propulsive force. Lowering the main rotor speed increases the wing lift share, however, the maximum L/D increases first and then decreases. The maximum L/D increases with decreasing the blade twist of the main rotor. Decreasing the blade twist from −16° to −8° increases the maximum L/D by 2.3%, and the wing lift share is increased from 65.0% to 74.7%. When the main rotor torque is balanced by the rudder, the maximum L/D is increased by 2.2% without changing the wing lift share. The wing should provide more lift as increasing the take-off weight, which reduces the induced power of the main rotor and increases the L/D. When increasing the take-off weight from 9500 kg to 11000 kg, the maximum L/D is increased by 6.5%, and the wing lift share is increased from 74.7% to 80.2%.