Distributed electric propulsion tested on scale in aircraft

Abstract

A scaled aircraft with distributed electric propulsion was built and tested in flight. The approach for the tests, the test campaign and the results are presented. Demonstrating the benefits of distributed propulsion and identifying the risks of the development with scaled flight testing are the objectives of the tests. The scaled aircraft was first installed in a large wind tunnel to acquire aerodynamic data and to test the aircraft and the aircraft systems. The electric propulsion system with propellers was also operated in the wind tunnel to acquire thrust effects. After the wind tunnel campaign, the batteries were installed and the aircraft was tested on the ground. Regretfully, a thermal runaway of the batteries caused an incident destroying the aircraft. The aircraft was built again with modified batteries and modifications in the power distribution system. Iron bird tests preceded the ground testing of the aircraft with batteries. Lessons learned from the incident and improvements in the design of the aircraft are addressed. After stationary ground tests, the aircraft was subjected to taxi tests on Deelen Air Base in the Netherlands and eventual flight tests were on the airport in Grottaglie, Italy. The aircraft was operated from a ground control station in which pilots and test engineers controlled the aircraft Beyond Visual Line Of Sight (BVLOS). The test flights were initially attributed to qualify the aircraft for the flight envelope foreseen for the test objectives and in a second phase dynamic manoeuvres were executed by a dedicated autopilot. Accurate instrumentation was installed in the aircraft that measures, amongst others, air data, inertial data, angular position of surfaces and engine parameters. Furthermore, the electrical power system is closely monitored to reveal the condition of batteries and systems. Manoeuvres were performed with symmetric thrust on left and right propellers and with asymmetric thrust. Controllers were developed by partners ONERA and CIRA to control and steer the aircraft with differential thrust, also with the remote human pilot in the loop. The control during one-engine-inoperative conditions was also subject of the campaign. Results demonstrate the DEP technology with respect to flight dynamics and control.