Fuel Weight Fraction Estimation for a Disk–Rotor Hybrid Aircraft Along an Optimal Flight Trajectory During Concept Design

Owing to the transition flight of rotor/wing hybrid vertical take‐off and landing (VTOL) aircraft, the fuel weight cannot be estimated from empirical data during the conceptual design phase. This paper proposes a method for estimating the minimal fuel weight fraction (FWF) through a strategy of trajectory optimization under a given flight profile. The typical flight profile of a disk–rotor hybrid aircraft is selected, and a dimensionless dynamic model is established for the flight mission segment by introducing the thrust–weight ratio and power–weight ratio. A trajectory optimization strategy is established with the minimum fuel consumption and flight time as the performance index, taking the dynamic model and waypoints on the flight profile as constraints. The Gauss pseudospectral method is used to solve for the minimum FWF of each mission segment, subsequently obtaining the FWF of the whole flight profile, and results are compared with those obtained from the conventional empirical Breguet method, confirming the validity of the approach proposed here. The optimization results demonstrate that the method proposed in this paper enables the comprehensive calculation of the FWF for the entire flight profile without considering the take‐off weight. Furthermore, the impacts of the general and performance‐related parameters associated with the flight profile on the FWF can be observed.