The determination of realistic flight mission characteristics, such as fuel consumption and flight time, requires fuel-optimal flight trajectories where the vehicles total trip fuel converges to a minimum. Within the Stratospheric Flying Opportunities for High-Speed Propulsion Concepts research project, one of the main challenging factors is the design of artificial flight controllers for maintaining 4D fuel-optimal trajectories for the STRATOFLY MR3 vehicle. In this paper, we propose a continuous climb cruise (CCC) flight controller as well as a zoom dive (ZD) flight controller which are derived using Feedback Linearization and embedded in a MATLAB-based trajectory simulation program. This incorporates the establishment of a proper control design model, an aircraft state estimator and the limitation of the plants control inputs to ensure a bounded fast-time, forward integration of all aircraft state variables based on a 3 degrees of freedom point-mass model. Simulation results are presented showing that the CCC controller is primarily used in the hypersonic cruise phase - covering the main flight segment of MR3 - and that the ZD controller is used in the transonic region (while the vehicle reaches Mach 1), both ensuring a total decay of 2.98 % in the vehicles fuel consumption for a reference flight mission from Brussels to Sydney.
