Flight tests of a remaining flying time prediction system for small electric aircraft in the presence of faults

Abstract

This paper addresses the problem of building trust in theonline prediction of a battery powered aircraft's remainingflying time. A series of flight tests is described that make useof a small electric powered unmanned aerial vehicle (eUAV)to verify the performance of the remaining flying timeprediction algorithm. The estimate of remaining flying timeis used to activate an alarm when the predicted remainingtime is two minutes. This notifies the pilot to transition to thelanding phase of the flight. A second alarm is activated whenthe battery charge falls below a specified limit threshold. Thisthreshold is the point at which the battery energy reservewould no longer safely support two repeated aborted landingattempts. During the test series, the motor system is operatedwith the same predefined timed airspeed profile for each test.To test the robustness of the prediction, half of the tests wereperformed with, and half were performed without, asimulated powertrain fault. The pilot remotely engages aresistor bank at a specified time during the test flight tosimulate a partial powertrain fault. The flying time predictionsystem is agnostic of the pilot's activation of the fault andmust adapt to the vehicle's state. The time at which the limitthreshold on battery charge is reached is then used to measurethe accuracy of the remaining flying time predictions. Accuracy requirements for the alarms are considered and theresults discussed.