A Study on Transient Performance Characteristics of the CRW Type UAV Propulsion System During Flight Mode Transition

A propulsion system of the CRW (Canard Rotor Wing) type UAV (Unmanned Aerial Vehicle) was composed of the turbojet engine, exhaust nozzles including some tip jet nozzles and a main nozzle and the duct system including straight ducts, curved ducts and master valve. The CRW type UAV has three different flight modes such as the rotary wing mode for take-off and landing, the high-speed forward flight mode with the fixed wing and the transition flight mode between the previously mentioned two flight modes. In order to evaluate transient performance characteristics of the CRW type UAV propulsion system during flight mode transition, the propulsion system was modeled using SIMULINK^®, which is an user-friendly GUI type dynamic analysis tool provided by MATLAB, in this study. Considering area variation of the master valve and the main exhaust nozzle simulated the transition flight mode between the rotary wing mode and the fixed wing mode. In order to verify acceptability of the main turbojet engine model, performance simulation results using SIMULINK^® were compared with results using the commercial program GSP. Moreover the performance characteristics of the propulsion system were investigated depending on position angle variation of the master valve at both the rotary wing mode and the fixed wing mode. In the transient performance behaviors at the rotary wing flight mode, the more turbine inlet temperature over shoot occurs and the net thrust at tip jet nozzles, decreases rapidly at initial condition then increase fast to the converged steady-state condition. Therefore, the fuel throttle should be slowly performed for safe operation of engine. During flight mode transition from the rotary wing mode to the fixed wing mode, rotary duct pressure was fell down to atmospheric pressure, but main duct pressure was mostly kept due to very small friction loss. Total net thrust was oscillatory increased. During flight mode transition from the fixed wing mode to rotary wing mode, rotary duct pressure was rapidly increased, but main duct pressure was mostly kept. Total net thrust also was oscillatory decreased. Through this investigation, it was found that severe thrust fluctuation should be considered for safe flight during flight mode transition even though operation of the master valve is slowly scheduled. Therefore a solution for improving the thrust oscillation will be suggested later.