"A California man has set a world speed record for RC aircraft by using an aerodynamic oddity to push his glider to 548 MPH. Spencer Lisenby used a technique called dynamic soaring to whip his heavily reinforced composite glider to almost Mach levels over a mountaintop near Los Angeles on Jan. 19. The Santa Anna winds were blowing at 65 MPH up the slope of Parker Mountain, setting up the correct conditions for dynamic soaring. By performing loops that exploit the boundary layers of the moving air, the pilot can use the energy of the wind to accelerate the aircraft to speeds much higher than the wind itself. With every loop, the action adds far more energy and speed to the aircraft than it loses in climbing back up the hill and the result is a head-snapping series of climbs and descents."
Article continues... video is amazing.