Propeller design to improve flight dynamics features and performance for coaxial compound helicopters

Abstract

The coaxial compound configuration has been proposed as a concept for future high-performance rotorcraft. The co-axial rotor system requires no anti-torque device, while the longitudinal thrust is provided by a propeller. A well-designed propeller can ensure both the performance and the cruise efficiency. The propeller design also influences the flight dynamics of such configuration. To design the propeller parameters of the coaxial compound helicopter, the propeller modelling and design method devised by Adkins and Liebeck is firstly introduced. A flight dynamics model of the coaxial compound helicopter is developed. Trim characteristics, power consumption results, and handling qualities features are calculated with variable propeller parameters at optimum (corresponding to the maximum flight range) and maximum speeds. The results indicate that the propeller parameters alter its efficiency and improve the performance characteristics of this helicopter. In addition, the propeller design also influences the flight dynamics characteristics and handling qualities of the coaxial compound helicopter, and consequently affect the power consumption indirectly. In this light, a design method for the propeller has been developed by formulating the design procedure into the nonlinearly constrained optimisation problem based on the flight dynamics characteristics. The method is demonstrated by evaluating propeller parameters to improve the performance in both optimum and high-speed range, which could also guarantee the handling qualities of the rotorcraft for related requirements.