Implementation Details and Flight Test Results of an Autonomous Soaring Controller

*Using only the initial energy from a 140m launch, an autonomous soaring glider covered over 48km and stayed aloft for over 1.5hr by actively searching out and using naturally occurring convective air updrafts (thermals). North Carolina State University and the U.S. Naval Research Laboratory have designed and implemented this novel convective air updraft locating and guidance algorithm for glider-based unmanned aerial systems (UAS). The local air vertical motion is estimated using the vehicle energy rate of change and the vehicle speed polar. Next, updrafts are initially geo-located with a centroid-based center estimator acting on the local air motion estimates. Then, an adaptive grid of nodes is constructed in real-time, the nonlinear regression correlation coefficient for each node computed, and the highest correlation node chosen, yielding much improved center estimation. Vehicle commanded speed has been optimized using MacCready Speed-to-Fly theory, coupled with a Speed Ring to increase cross-country performance. The effects of wind-drift correction, no-phase-lag filtering, and nonlinear updraft-parameterization are demonstrated with samples of flight data.