Centre of gravity movement as redundant pitch attitude control in control allocation

This paper addresses the use of centre of gravity (cg) of the aircraft by moving fuel to and fro the trim tank; this cg movement is exploited as an additional pitch control redundancy. In the high speed region of the flight envelope, the full utilization of the flight controls is not possible due to load factor limitations, so this redundancy can be used as a compensation system. Control allocation in aircraft is the distribution of settings for various control surfaces to achieve virtual control demands (i.e. pitch, roll and yaw moments, and forces). To achieve a control demand there are two or more surfaces that can be utilized. In this paper control law was designed as a multivariable proportional integral controller; the output of it (i.e. virtual control demands) is sent to a control allocation module, which distributes the demand among the control surfaces by solving a sequential least squares problem using the active set method. The control system (i.e. control law and control allocation) is applied to the nonlinear model of the Boeing 747-200. The system was also tested on a nonlinear model with changes in longitudinal aerodynamics coefficients due to the wing damage, which is based on the damage that arose on EL AL Flight 1862 accident Schiphol airport near Amsterdam. The reduced effectiveness of longitudinal control surfaces due to a loss of hydraulics in this crash is also realized in the control allocation. Nomenclature aor ! = right outboard aileron (deg) air ! = right inboard aileron (deg) aol ! = left outboard aileron (deg) ail ! = left inboard aileron (deg) eor ! = right outboard elevator (deg) eir ! = right inboard elevator (deg) eol ! = left outboard elevator (deg) eil ! = left inboard elevator (deg) ih ! = stabilizer (deg) ur ! = upper rudder (deg) dr

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