Extreme model airplanes - without engines.
Beats my ancient experience of spinning around in a circle flying my P40 Flying Tiger.
It’s called Dynamic Soaring, or DS, and it requires some specific land and weather conditions, experience and the cojones to slice your precious RC plane through extreme wind shears. If you have a long hill or ridge and the wind is hitting it at a right angle, the air that moves over the top causes an eddy on the leeward side, a steady, spinning whirlpool of air underneath the wind shooting over the ridge.If you can hit it right, you can power the glider over the ridge and then dip it down into the torrent of air running in the opposite direction. Flip the plane 180º, over and over, and you’ll build up speed. The video above shows a glider clocking an astonishing 392mph from a wind gusting to just 45mph. Think of it as somewhere between surfing a big wave and pumping a skateboard around a half-pipe. [More] [RC = radio-controlled]
Helpful illustrated description of Dynamic Soaring here.