Flight dynamics aspects of path control

Active control of the flight path is a common task performed by the flight control systems of unmanned aerial vehicles. Whereas many research and implementation efforts currently focus on control theory issues like feedback or gain design methodologies or on aspects concerning higher level supervisory logics, this publication concentrates on flight path control dynamics considerations. Based on an analysis of the path dynamics of the aircraft, physically motivated approaches are presented to overcome stability issues and problems related to input saturations at various levels of concatenated control loops. Competing objectives for multi variable control are resolved by means of clearly interpretable prioritizations that ensure deterministic and rational behavior of the control effectors and safely keep the vehicle within its operational envelope. First, a total energy related concept is adapted to a reference model based dynamic inversion control system structure. Then, a new approach is presented, a total force control approach that represents an abstraction of the total energy principles to force generation and distribution of control authority between the horizontal and vertical plane. This approach has also been implemented within the dynamic inversion framework. The path control approach presented assumes that the pitch and roll axes inner loops control the rate of change of vertical and horizontal path angle, corresponding to normal and lateral load factor. Simultaneously the remaining control variables of airspeed and sideslip angle are also controlled to their desired targets.