Flight Tests of Trajectory Energy Management Systems Using a Vertical Takeoff and Landing Vehicle

The rise of new aircraft propulsion methods, the increased use of automated and integrated flight control systems, and the envisioned use of personal Vertical Takeoff and Landing (VTOL) vehicles in urban environments leads to novel technical and regulatory challenges for aircraft manufacturers, certification authorities and operators. Of primary concern is operational safety, and closely connected pilot situation awareness and workload. A particular safety factor for operating VTOL vehicles that depend on propulsive lift for the majority of their operations and that are operated over urban terrain, is the management of energy and power needs along with power and energy reserves. These reserves are highly sensitive to the environment (mostly temperatures), and with VTOL, where the aircraft cannot simply glide to an emergency landing, management of energy reserves is not sufficient. This generates the need for thorough Trajectory Energy Management. This paper provides flight test results of the Trinity F9 drone developed by Quantum-Systems. Prescribed trajectories were flown based on operationally-relevant scenarios. Battery usage for the various flight segments was quantified. Results were compared to analytic models. A preliminary list of safety-of-flight parameters was developed to aid aircraft certification authorities. This research is intended to define some requirements for energy management such that the pilot can safely accomplish an intended profile and land with enough energy reserves to satisfy the intent of operation rules 91.151 (VFR reserves) and 91.167 (IFR reserves). In the context of trajectory energy management, there is a spectrum of automation tools that may assist the pilot. For example, common avionics systems with moving maps display range rings that help the pilot manage fuel state. These systems make assumptions based on current ground speed, fuel flow and fuel reserve requirements. Requirements for similar tools for VTOL aircraft that employ electric propulsion do not yet exist and must be defined based on prototype algorithm development, simulation results, and flight test data. For higher levels of automation, the Trajectory Energy Management System must be able to define an optimum trajectory for a VTOL aircraft and then couple to an automatic control system to execute that nominal trajectory. This system would need to account for disturbances and off nominal conditions. This project provides solutions and data to help the FAA develop performance estimation tools, flight safety assessment tools and the associated means of compliance for Trajectory Energy Management Systems. For the flight test program an operationally relevant reference mission profile was developed and flown using a tilt rotor aircraft in 14 flights and total flight time of 2.5 hours. Vertical flight was found to use about 5 to 7 times more power than in horizontal flight. Vertical takeoff and landing used about 60% of the total flight energy in a fraction of time spent in cruise. Therefore vertical flight is most concerning for operational safety. Finally, lessons learned through the execution of the Trinity F9 flight test program are documented in this paper.