Evaluation of helicopter flight missions with intended single engine operation

Abstract

Current helicopter power train design of light and medium class helicopters is mainly driven by safety considerations. Thus, these helicopters have two or more engines installed. However, in up to 60% of the helicopter flight mission time, the available installed maximum continuous power of the engines is not needed [1]. Hence, the engines are running most of their operation time in part load. But turboshaft engines have their lowest specific fuel consumption (SFC) at high engine loads. Taking this into account, an operational strategy can be an intended controlled shutdown of one engine. At the same time, the load of the remaining running engine is increasing, whereby the overall SFC is shifted to better values and fuel can be saved. This saving can be used either to reduce the mission-specific fuel consumption or to extend the flight mission time. Quantification of the fuel savings is the focal point of this paper. However, the intended operational engine usage strategy is limited to certain areas of the helicopter flight envelope. Hence, these areas of the envelope are specified by flight performance analysis of the helicopter in advance. Afterwards, realistic flight missions were chosen for subsequent flight mission simulations with and without intended single engine operation (ISEO). For this purpose a non-linear flight dynamics model of a reference helicopter is used. The turboshaft engine is represented by a quasi non-linear state space model and is integrated in the flight dynamics model. Finally, the resulting fuel saving potential is evaluated and details for flight mission modifications are given due to an enhanced usage of ISEO