A modified total energy control scheme for unmanned aircraft
The paper focuses on safety and simplicity of unmanned aircraft longitudinal control and proposes a new combination of total energy control (TECS) and conventional control. The introduced new modified total energy control (TECSMOD) method applies IAS priority all the time. IAS is controlled through the elevator while the total energy of the system and so the altitude is maintained with throttle. Neither engine fault or stall detection nor switching logic is required while stall is prevented keeping the solution simple and safe. To prove the viability of the new concept it is compared to a conventional multiple zone PI controller and the TECS solution in simulation and real flight tests. First, the six degrees of freedom simulation model of the Sindy test UAV (developed and built in Institute for Computer Science and Control, HUN-REN, Hungary) is verified comparing its inputs and outputs to flight results. Then a simulation campaign is done for all three controllers with special test cases which can be critical according to the literature. Finally, real flight test comparison is done considering IAS and altitude tracking and engine fault handling. The new method was the best in IAS tracking with acceptable results in altitude tracking and successful stall prevention upon engine fault (without any fault detection or switching). Future improvements can be fine tuning for improved altitude tracking with the price of decreased IAS tracking performance and the introduction of a glideslope tracking mode for landing scenarios.