Maximum Endurance of Hybrid-Electric Aircraft in Cruise

This paper, for the first time, the optimal airspeed that maximizes the endurance of hybrid-electric aircraft in cruise flight. The optimal control problem is formulated using energy-depletion dynamics and solved using Pontryagin’s Maximum Principle (PMP). The solutions show that the optimal cruise airspeed is the single positive real root of a quintic polynomial. One important result is the computation of the proportion of the aircraft’s thrust stemming from electrical energy such that all fuel and electricity are consumed for maximum endurance. The paper shows that this value depends on the ratio between the initial electrical and the initial fuel energy. Furthermore, the results indicate that the maximum endurance flight time is also influenced by the cruising altitude. Simulations illustrate the proposed methodology.