Research Progress of High Advance Ratio Implementation Method for High Speed Helicopters

Current requirements for future helicopters proposed by some main investigation projects need helicopters to fly at a higher speed than they commonly achieve while maintaining significant hovering performance. In recent years, interests have increased in the study of high speed helicopters, for example, tiltrotor, compound and coaxial helicopter. They have overcome the flight speed of common helicopters. A main characteristic of high speed helicopters is that they have high advance ratio. The main rotor operates over a wide speed range from 100% in hover to 80% in high speed cruise. Main methods to achieve high advance ratio are variable rotor diameter technique and variable rotor speed technique. The former is realized by change the diameter of rotors. The later is realized by changing the transmission ratio or engine rotating ratio. The paper provides a summary of the research on the variable rotor diameter firstly. There are three kinds of methods to change the rotor diameter. Then, the variable rotor speed technique is described, consisting of the development history, large development plan and implementation challenge. Finally, a prospect of the development for the high advance ratio implementation method in the future is made.