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Compared to currently used chemical boosters or mechanical devices, electromagnetic catapults have special advantages on multiple acceleration profiles and highly variable velocity, which are attractive for launching unmanned air vehicles (UAVs) in several hundred kilogram range. A linear motor is usually designed as the thrust producer of the electromagnetic catapult. In this paper, we firstly give technical features of the catapult applied to the UAV of 200-kg class with an initial velocity of 30 m/s, and then make a comparison between linear synchronous motors (LSMs) and linear induction motors (LIMs). The LIM is selected and the initial characteristics (thrust, input power, efficiency, current and mass) of the LIM working under different voltages and frequencies are calculated by a T model equivalent circuit method. The calculation suggests that the LIM exhibits better properties when it works under the higher voltage or higher frequency. When superconducting wires are applied to primary coils to construct a superconducting LIM (SLIM), the motor characteristics are also calculated and discussed. The SLIM gives a favorable opportunity to reduce the input power and current. A finite element method (FEM) is employed to simulate static field distribution of the SLIM and give electromagnetic properties to verify the equivalent circuit method.
Date of Publication: June 2010