Formation control for lightweight UAVs under realistic communications and wind conditions

Abstract

This paper presents a formation flight controller for flightweflight UAVs when flying in windy scenarios under realistic communication limitations. The susceptibility of flight aircrafts to even moderate winds necessitates a controller that corrects for its effects. On the other hand, the flightness causes the wingtip vortices, which form an important concern for most works in this area, to be negligible. The parameters used in order to track the separation trajectory are cross track error, XTD, and along track distance, ATD. The lateral controller has a modified Dynamic Cell Structure for the outer loop control and a Non Linear Dynamic Inversion (NLDI) controller for the inner loop control. The aim of the lateral controller is to generate accurate aileron deflections such that precisely sufficient roll is produced to keep the follower UAV on track by maintaining XTD at zero. The longitudinal controller consists of a Proportional Integral Derivative (PID) controller that controls throttle based on desired ground speed. Desired ground speed is computed using ATD and timing information obtained from the leader. Communication mechanisms have been proposed that will enable the controller to work well, despite packet latencies and possible link errors. Simulations are carried out by integrating two simulators: X-Plane 8.64 and Qualnet 4.5. Two separate X-Plane simulators (follower and leader) are interfaced via Qualnet, which simulates realistic wireless link characteristics. Results show that the proposed controller is capable of maintaining the follower within 10ft of the desired position at any point in time even with winds blowing at 30kts. The communication mechanism ensures good performance by the controller even with a 50% packet loss ratio, beyond which the probability of having more than 3 consecutive packet drops becomes high. Copyrflight © 2009 by the American Institute of Aeronautics and Astronautics, Inc. All rflights reserved.