Mach number virtual sensor for civil aircraft extended guidance navigation and control

This paper proposes an airspeed virtual sensor to extend the guidance navigation and control functions of an aircraft. The main idea is to exploit the indirect measurement of the aerodynamic forces applying on a control surface which are clearly related to the aircraft airspeed. Focusing on those aircraft equipped with a Fly By Wire system, at least one actuator is installed on each of the control surfaces; the actuators operate the surface by fighting against the aerodynamic forces. Generally speaking, aircraft are designed with a minimum set of control surfaces (one elevator, one rudder and two ailerons) but there are lots of examples of aircraft with redundant control surfaces. To the best of authors' knowledge, the proposed "Least Squares - Sliding Mode" estimator is new and it merges two concepts: the least squares, which exploit the available redundant actuator-surfaces systems to minimize the errors, and the sliding mode, that, in finite time, pushes the aircraft airspeed estimation toward the actual value. The algorithm has been applied to real Airbus aircraft flight data set leading to very encouraging preliminary results.