Analysis of varying control inputs for a fixed wing unmanned aerial vehicle

In UAVs, autopilot substitutes the pilot and undertakes autonomous control and navigation of the aircraft. The airspeed controller is an important part of autopilot which adjusts the speed of the aircraft according to the requirement in different phases of the flight, and avoids aircraft instability during difficult maneuvers. In the design of airspeed controller, most designers implement Proportional Integral Derivative (PID) compensators by using control input from throttle only. In this paper, we present the performance-based comparison of two airspeed control schemes. One method controls the airspeed in a conventional way i.e. by throttle as an input variable; while the other algorithm uses combination of throttle and elevator for tracking the airspeed commands. In our work, a non-linear model of UAV has been trimmed, linearized and decoupled for designing the linear controllers. The controllers are then applied to nonlinear model and simulation results for both are compared. The research clearly indicates that by using combination of throttle and elevator as control inputs, better airspeed control can be achieved both in terms of transient response and payload performance. This finding may be a useful contribution towards the effective airspeed control of aircrafts and UAVs.