A synthetic airdata system

A method for estimating airspeed, angle of attack, and sideslip without using conventional airdata sensors or pitot-static system is presented. The method relies on measurements from GPS, inertial measurement unit (IMU) and low-fidelity model of the aircraft dynamics which are fused using two, cascaded Extended Kalman Filters. The first filter uses information from the IMU and GPS to estimate the aircraft's absolute velocity and attitude. These estimates are used as the measurement updates for the second filter. These measurements along with the aircraft dynamics model are used to estimate airspeed, angle of attack and sideslip. Issues associated with using correlated estimates from the first filter as measurements in the second filter are discussed. Simulation and flight test results of the method are presented. Simulation results show that airspeed estimation error is less than 1 m/s RMS. The nominal error from the flight test on airspeed, angle of attack and sideslip are less than 2.5 m/s, 2 degrees, and 1 degree, respectively. Factors that affect the accuracy of the solution are discussed.