Reduced-Order Dynamic Modelling of the Wankel Engine Employed in the Hybrid Propulsion System of a Lightweight Helicopter UAV

This work deals with the development of a reduced-order dynamic model of a Wankel rotary engine for the propulsion of a lightweight helicopter UAV, to be used for in-flight health-monitoring. The model, which is real-time executable by the on-board electronics of the UAV, includes the simulation of mechanical power generation, intake manifold pressure dynamics, fuel flow consumption, and thermal transfer in the combustion chamber. Aiming to develop a simulator based on physical principles, a correlation analysis among the experimental measurements obtained by endurance tests has been carried out, up to select the states and the inputs of the model sections and to identify their parameters via ordinary least square method. Simulation demonstrates to satisfactorily reproduce the experimental behaviour (maxima errors are lower than 5%), when the engine works near its nominal operating conditions, i.e. at constant rotor speed, while the model errors increase (up to 30%) during the transients from/to warm-up phases.