Control Design for Carefree Maneuvers in High Performance Fighter Aircraft

Flight envelope protection for a high-performance aircraft poses a challenge to the designers and involves a time-consuming procedure to verify the provided protection. In this research work, the departure is divided into two broad problems to be solved. The first problem considered is design of an automatic low speed recovery mode to protect against departure arising out of loss of airspeed and hence dynamic pressure. The second problem considered is that of loss of control due to the application of short duration rapid pilot inputs which may either result in exceeding the aircraft parameters and rate limits. In this research work, a novel design approach for low-speed recovery of a highperformance fighter aircraft is presented to address the first problem. It is shown that the phugoid mode has an important bearing on the problem of low-speed departure. Based on the analysis of the phugoid mode trajectories, a novel low-speed protection algorithm is presented. The proposed low speed recovery is achieved in three phases. These phases consist of detecting the incipient departure first followed by the application of suitable recovery controls in the second phase and finally in the third phase ending with the transfer of controls to the pilot. Performance of the ALSR-FP is demonstrated using the high-performance fighter aircraft ADMIRE model which has a delta wing configuration, canards and multiple redundant controls. The second problem has been addressed by a design approach to protect the aircraft from departure by a command path limiter for a rate command attitude hold controller in both the pitch and roll axes. The maximum and minimum rates are scheduled as a function of the dynamic pressure on the basis of the open loop aircraft capabilities. It is augmented with a novel angle of attack protection that comes into play only when the pilot inputs cause the aircraft to exceed the incidence on the positive or negative side (one sided protection), while maintaining the rate command attitude hold behavior within the normal operational bounds of angle of attack. A unique multi-modal search using genetic algorithm is developed to verify that this command path protection is able to achieve carefree maneuvering of a fighter aircraft in its entire flight envelope