Aerodynamic Performance of a Coaxial Rotor System for Micro Air Vehicles

Abstract

Recent advances in electric motors and lithium polymer batteries have led to development of several different types of Micro Air Vehicles (MAVs). The ability to hover is an important mission requirement for this class of vehicles. The coaxial contra rotating rotors with a stabilizer bar are considered superior in terms of performance, stability and control in design analyses. In this experimental study, a coaxial helicopter model was used to characterize its rotors. The performance of the rotors was evaluated in independent and in the coaxial state. It was observed that there is a significant loss of total thrust for the coaxial configuration. The dependence of thrust loss with respect to RPM and other geometric parameters was studied. The thrust efficiency of the lower rotor is significantly influenced by the upper rotor. The single rotor configuration was found to perform better in terms of thrust per unit power consumed, than the coaxial configuration. The theoretical estimate of power, using low Reynolds number drag coefficients, was found to agree with measured input power. It was observed that a significant amount of power is consumed by the control circuitry of the helicopter rather than the rotors, reducing endurance of flight.