Trim Analysis of a Classical Octocopter After Single-Rotor Failure

Abstract

The performance of an octocopter with single rotor failure is examined in hover and forward flight conditions. The aircraft model uses blade element theory coupled with a finite-state dynamic inflow model to determine rotor aerodynamic forces (thrust, drag, and side-force) and moments (rolling moment, pitching moment, and torque). Failure of various rotors is considered in both flight conditions and an understanding is developed of how the aircraft trims post-failure in terms of multirotor controls defined for the aircraft. In hover, the baseline octocopter trims with all rotors operating at the same rotational speed. When a rotor fails, trim solutions exist that utilize the original reactionless controls of the aircraft to drive the commanded thrust of the failed rotor to zero. The combination of reactionless controls used varies depending on the position of the failed rotor. Post-failure, the primary and reactionless multirotor controls are redefined for each rotor in terms of the original multirotor controls. In forward flight, rotor failure is recovered in a similar manner to the hover case, with additional inputs required to compensate for the rotor hub moments and in-plane forces that were not present in hover. Overall, trim solutions exist for any single rotor failure in both hover and forward flight at 10 m/s. In hover, rotor failure requires an additional 10.7% increase in power to trim, in forward flight this penalty is found to range between 7.7 and 13% depending on the rotor that has failed.