Variable-Speed Rotor Helicopters: Performance Comparison Between Continuously Variable and Fixed-Ratio Transmissions

Variable-speed rotor studies represent a promising research field for rotorcraft performance improvement and fuel-consumption reduction. The problems related to employing a main rotor variable speed are numerous and require an interdisciplinary approach. There are two main variable-speed concepts, depending on the type of transmission employed: fixed-ratio transmission and continuously variable transmission rotors. The impact of the two types of transmissions upon overall helicopter performance is estimated when both are operating at their optimal speeds. This is done by using an optimization strategy able to find the optimal rotational speeds of the main rotor and turboshaft engine for each flight condition. The process makes use of two different simulation tools: a turboshaft engine performance code and a helicopter trim simulation code for steady-state level flight. The first is a gas turbine performance simulator (called TSHAFT), developed and validated at the University of Padova. The second is a sim...