Modelling and Design of a High Performance Electric Drive for an Unmanned Helicopter Main Rotor

摘要

Advances in electric drive technology have meant that power to weight ratios and efficiencies have increased to a point where the practical implementation of an electric drive VTOL UAV is viable. The replacement of the existing gearbox, tail-rotor assembly and tail-rotor drive shaft with electrical drives on the main and tail rotors offers many potential benefits. The electric drive system has fewer parts, it is easily maintained and is highly reconfigurable, and hence reduces the overall life-cycle cost. The position of the main powertrain components can be configured to suit the aircraft rather than to meet the constraints of the mechanical system. In order to test the viability of the application of an electric drive for helicopter applications, an evaluation has been made for a high efficiency permanent magnet brushless motor installed as a direct drive main rotor on a Unmanned Helicopter (UMH). A representative mission profile has been selected, from which the torque and power requirements are found for the drive, thus enabling a sizing and performance study of the electrical system components. The performance of the system has been modelled in Matlab & Simulink.The parametric model of the drive is obtained from published test data indicating the losses and efficiency of a high performance brushless permanent magnet drive system. The model demonstrates that the electric drive rotor has a comparable performance to the conventional layout and is of a comparable weight. The paper goes on to investigate a novel design to integrate a direct-drive electric motor into the hub of the main rotor. This has two main advantages. It frees space within the fuselage, and by raising the C of G closer to the blade disc, it will improve the stability of the aircraft. A stationary central stator drives an integral permanent magnet rotor/hub. Finite Element modelling is used to validate the analytical design. The design is shown to achieve the performance requirements of a UMH mission profile while having comparable weight and size to a conventional mechanical drive.