Reliability Assessment of Actuator Architectures for Unmanned Aircraft

Abstract

A reliability assessment framework is presented for small unmanned aerial vehicles. The analysis considers several candidate architectures with different numbers of controllable surfaces and servos. It is assumed that a servo fault detection algorithm is available and affected by known rates of false alarms and missed detections. The aircraft flight envelope is analyzed to determine the fault levels for which the aircraft can still be flown at a trim point. For these "flyable" fault levels, it is assumed that the flight control law can be reconfigured to safely land the aircraft. Finally, the probability of catastrophic failure is estimated based on the histogram of (pre-fault) control command distributions, mean time between failure of the individual servos, and missed detection and false alarm rates. In applying the framework to assess the reliability of the candidate architectures, several interesting observations on design trade-offs are made.

Comparison of fault detection and isolation methods for a small unmanned aircraft

“…Stuck faults impose constraints on the flight envelope of the aircraft. Section III of Venkataraman et al (2017) shows one example of the impact of stuck faults on the allowable flight envelope of a fixed wing aircraft. In par-185 ticular, there may be fault magnitudes where it is not possible to trim the aircraft in the conventional sense, e.g.…”

Quantifying Risk of Ground Impact Fatalities for Small Unmanned Aircraft

“…In [27] the same group showed how a dedicated reconstruction of the aircraft based on a fault tree analysis could theoretically reduce the failure rate by a factor 20, and they were able to implement changes to the physical aircraft to achieve a catastrophic failure rate of 0.76 per 100 flight hours. Actuators and control surfaces are investigated in [30] and [31] where the probability of having an uncontrollable aircraft is modeled using a servo fault detection algorithm.…”

Mass threshold for ‘harmless’ drones

“…29 A group of students 30 has conducted a reasonably detailed investigation into the reliability of a specific small RC model aircraft, an Ultra Stick 120, a 4-5 kg aircraft, concluding a MTBF around 50 flight hours. And in Venkataraman et al 31 using the same aircraft stuck actuators are investigated both in terms of consequence and probability. Actuation failure modes are investigated in Freeman and Balas 32 using FMEA (also using the Ultra Stick 120 at 7.4 kg).…”

“…And in Venkataraman et al. 31 using the same aircraft stuck actuators are investigated both in terms of consequence and probability. Actuation failure modes are investigated in Freeman and Balas 32 using FMEA (also using the Ultra Stick 120 at 7.4 kg).…”