Longitudinal autopilot controllers test platform hardware in the loop

This paper presents the design, simulation and real-time implementation of an aircraft longitudinal control system using a test platform constituted of a dedicated microprocessor and the X-Plane flight simulator. Initially, the concepts of longitudinal motion of a rigid body are studied. The dynamic equations of aircraft were determined using the aerodynamic stability coefficients and the longitudinal derivates. With the aircraft dynamic equation, the altitude and vertical speed continuous controllers were designed using the inner loop pitch attitude and pitch rate feedback and the forward speed controller was designed using an engine throttle model. The continuous controllers designed were discretized. Then, the digital controllers were implemented in the microprocessor. Using the X-Plane flight simulator and the algorithm implemented in the dedicated microprocessor, the digital controllers were tested and validated into the model similar to real aircraft, minimizing risks and increasing flexibility for design changes. Basically, this experimental framework employs the microprocessor running the digital flight controllers to be tested, and a PC running the X-Plane flight simulator contained the aircraft to be commanded. These resources are interconnected through data buses in order to exchange information. The interconnection between autopilot hardware and the X-Plane host is made through data communication bus based on network protocol, Uniform Datagram Protocol (UDP) available in both systems. The X-Plane has the built-in capability of transmitting flight parameters and receiving command for aircraft flight control surfaces over Ethernet using UDP. The results show that the developed system structure is appropriate to test the longitudinal controllers. Matlab environment was used to visualize the values of the updates pitch attitude, altitude, vertical and forward speed in graphics plotted in real time. It permites to observe that the designed controllers impleme- - nted in experimental framework reaches the specified requirements successfully.