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An estimation model is key in the design and development of an unmanned aerial vehicle's control system. This work presents a complete methodology for modelling the dynamics of a fixed-wing UAV for aerobatic maneuvers. The UAV dynamic non-linear model considered uses total variables instead of a nominal values and perturbation values about certain trimmed conditions for conventional flight envelopes. Such modelling allows the expansion of the flight envelope of an unmanned aerial vehicle to cover the full range of the angle of attack. The quaternion formulation is used since it eliminates the nonlinearity of the aerodynamics due to Euler angles for high angle of attacks. The objective is to have a complete and accurate representation of a highly dynamic fixed wing UAV capable of making aerobatic maneuvers without encountering singularities. A set of controllers are then designed for the inner and outer loops for attitude control using nonlinear dynamic inversion in cascade with a PI controller. Simulations carried out show robust tracking of reference attitude angles.

This paper presents the estimation of stability and control derivatives of an unmanned aircraft. The aerodynamics are described using regressors composed of velocity, angular rates, flow angles and control surface deflections. The flight data is generated from numerical simulation of postulated equations of motion describing the aerodynamics model. Least squares based on the equation error method is used to estimate the parameters representing the different force and moment aerodynamic coefficients. Statistical analysis is done on the estimates to determine the accuracy and adequacy of the estimates to describe the aerodynamic model. A dynamic simulation based on the identified aerodynamic model is used to improve the parameter estimates through regression of the errors between the flight data and the model response. The aircraft under consideration is a scaled Yak-54 fixed wing unmanned aerial vehicle.

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