Advances in optimal active control techniques for aerospace systems; application to aircraft active landing gear

The problem of runaway denial is a real threat to the Air Force. The effectiveness of a counterattack after a hostile airraid depends on the capabilities of the airbase to make rapid runway repair of such quality that safe-and-sure launch and recovery of aircraft can take place without experiencing any structural damage.; Aircrafts with conventional landing gears can operate on rough repaired surfaces under certain limited conditions within its design limits. When the surface roughness is severe, and the taxiing speed of the aircraft over the runway is high, landing gear forces start exceeding design structural limits causing catastropic failures and damages to the aircraft.; Active control landing gears present a solution to this problem. An active control landing gear can reduce landing impact loads, provide better ground handling capabilities to the aircraft, and negotiate runway damages more effectively than a conventional landing gear. These capabilities are provided by the control of an electronic controller which activates a force generating device (an actuator) or a variable orifice control valve (an active damping orifice) to achieve a desired variation in landing gear stiffness, or damping characteristics.; Optimal control techniques can be applied on active landing gears to provide the best control laws for different conditions. A performance index can be chosen to minimize the load transmitted to the aircraft and the aircraft vertical and angular motion thus improving aircraft stability and ground handling characteristics.; The dissertation starts with a discussion of active control concept, and then describes the problem of optimal control of active landing gears (semi-active concept). The problem formulation is done for an aircraft that has three landing gears (one nose gear and two main gears) and flexible body dynamics. The technique of steepest descent that is used to solve the resulting nonlinear two point boundary problem is given together with numerical results of an exemplary optimal solution.