Management of primary control surface failures on a high-performance aircraft

Two main aspects have been analyzed in this thesis: first the effects of a primary actuator failures on the aircraft have been fully investigated in term of stability, handling criteria and trimmability in failed condition; then a reconfiguration mechanism following the failure of the rudder has been developed. All the analysis has been limited to the approach phase therefore only the Landing Gear Down Mode of the Control Law has been considered. Initially all the factors that can lead a primary actuator to engage the Fail Safe Mode are reviewed and the probability for each actuator to engage the fail safe mode quantified. The aircraft simulation environment has been modified to include the Fail Safe Modes. Analysing the effects of different Fail-Safe conditions (HT, AIL, RUD) on the aircraft it has been observed that there is a single major degradation, the loss of controllability of the directional axis following the failure of the rudder. The failures generally cause an increase in Gain Margin due to the reduction of the control power derivatives. A reconfiguration scheme has been developed for the case of rudder failure. Two possible approaches are developed and then joined together into the final reconfiguration mechanism. The first approach exploits the redundancy provided by the independent use of ailerons and differential horizontal tail to produce a limited yawing moment. It has been evidenced how that solution is not a good solution to generate large AoS while is a viable solution to restore a limited authority but efficient yaw-damper. The second approach used for the reconfiguration makes use of a single aileron like a spoiler in order to increase the amount of available yawing moment