Attitude Control of Micro/Mini Aerial Vehicles and Estimation of Aerodynamic Angles Formulated as Parametric Uncertainties

A recurring problem in controlling the attitude of miniature/micro aerial vehicles (MAVs) is the presence of an unknown atmospheric wind. Wind directly affects the vehicle's translational variables, namely the airspeed, angle-of-attack, and sideslip angle, all three of which are important variables in the equations that govern a fixed wing aircraft's aerodynamics. Consequently, wind exerts a major influence on the overall dynamics of an MAV. In this letter, we assume a knowledge of airspeed and describe a Lyapunov-based nonlinear estimation and control method that estimates the effects of angle-of-attack and sideslip on the vehicle's attitude, and at the same time controls the attitude to track a desired quaternion trajectory. This makes it possible to design an attitude control module that does not rely upon a knowledge of the individual components of the vehicle's translational velocity. The decomposition of the measured airspeed into the individual components is accomplished by the controller itself, in the form of an estimation of the angle-of-attack and the sideslip angle. We prove that, under quite general conditions, we can achieve asymptotic tracking of the attitude to the desired trajectory and also estimate how the attitude dynamics are affected by unpredictable disturbances in the angle-of-attack and sideslip angle.