Reliability assessment of actuator architectures for unmanned aircraft

Governmental organizations are currently developing standards for civil unmannedaircraft to operate safely in the national airspace. A key requirement for aircraft certification is reliability assessment. Traditional reliability assessment methods make assumptions that are overly restrictive when applied to unmanned aircraft. This paper presents a step-by-step, model-based, reliability assessment method that is tailored for unmanned aircraft. In particular, this paper investigates the effects of stuck actuator faults (a common failure mode in electromechanical actuators) on the overall reliability. Several candidate actuator architectures, with different numbers of controllable surfaces, are compared to gain insight into the effect of actuator placement on reliability. It is assumed that a fault detection algorithm is available and affected by known rates of false alarms and missed detections. The overall reliability is shown to be dependent on several parameters, including hardware quality, fault detection performance, mission profile, flight envelope, and operating point. In addition to being an analysis tool, the method can help understand aircraft design tradeoffs.