  We present a novel controller for fixed-wing UAVs that enables autonomous
soaring in an orographic wind field, extending flight endurance. Our method
identifies soaring regions and addresses position control challenges by
introducing a target gradient line (TGL) on which the UAV achieves an
equilibrium soaring position, where sink rate and updraft are balanced.
Experimental testing validates the controller's effectiveness in maintaining
autonomous soaring flight without using any thrust in a non-static wind field.
We also demonstrate a single degree of control freedom in a soaring position
through manipulation of the TGL.
