Many Small Unmanned Aerial Systems (sUAS) are incapable of meeting the safety requirements to provide a sufficient low risk of a fatality while operating above populous areas or gatherings. A recognized mitigation of this risk is a failsafe system that in the event that the sUAS is unable to maintain stable flight, terminates the flight and activates an emergency parachute. This paper proposes a methodology for assessment of Commercial Off the Shelf parachutes for sUAS failsafe systems. The methodology encompasses the evaluation criteria for the selection of parachutes based on a user-defined Maximum Takeoff Weight and the failure scenario tests for assessment of reliability and efficiency. The current standard specification on parachutes for sUAS published by the American Society of Testing and Materials has inspired the failure scenario tests. These failure scenario tests consist of a bench/destructive test and a full power cut test. The multirotor used for test of the proposed methodology is a ~ 2kg hexarotor. The results suggests the use of one specific parachute. Furthermore, the deployment time and impact energy have been estimated to be 1.2s and 21J, respectively. This impact energy suggests a probability of fatality of less than 0.01. This work is the first step towards selecting and evaluating parachute systems for sUAS. The proposed next steps are the refinement of the assessment of parachutes and increase of parachutes included in the failure scenario tests. Additionally, this will lead to the development of parachute recovery systems for sUAS with manual and autonomous triggering.

This paper presents development of model-based fail-safe modules for autonomous multirotor Unmanned Aerial Vehicles (UAVs) with safety parachute systems. The module is based on the adaptive eXogenous Kalman filter for actuator fault diagnosis. We assume all states can be measured, such that the primary goal of the filter is not the state estimation from the measurements, but the accurate reconstruction of the multirotor dynamics in real-time. Numerical simulations show the proposed diagnostic filter can be used to estimate the magnitude of the actuator faults accurately. Furthermore, based on simulated and real data recorded during a hexacopter UAV flight when its actuators experiencing complete failure, the experiment results demonstrate the effectiveness of the approach.