Design and implementation of high 'G' control law for an unmanned aircraft

Vertical gyroscope is used to measure the pitch and roll attitude of the aircraft with respect to local vertical. Since it provides the state feedback for the basic stabilization loop, the error in the vertical gyro may destabilize the flight control system. The erection mechanism of a vertical gyro is based on mercury level bubble/electrolytic level sensors. The spin reference axis is driven to vertical by erection servo loop. But, during forward acceleration and horizontal acceleration, spin reference axis is driven to false vertical. Such vertical gyroscopes are used for controlling the roll, which helps to make the turns tighter. But it leads to wrong pitch indication, which affects the altitude holding capability of the aircraft. During high 'g' maneuvers (2g and beyond) even small tilts can make the turn to be more oscillatory ie., normal acceleration to be oscillating a lot. Normal acceleration, also known as load factor, is a nonlinear function of roll angle. To take care of these higher oscillations, control law has been designed.