[mike the snake]

I'm not sure what V speeds are.

The planes are radio controlled, and use the same movable surfaces that real airplanes use, ailerons, elevator and rudder, with flaps for slowing down and landing. Some very custom mixing of controls is also used to optimize performance.

Basically, you have a ridge with the wind hitting one side, so you have one side with the air deflecting up (front side, with lift, where we launch from) and a lee side of the hill, with basically dead air behind the ridge. The wind continues on past the ridge, and there's a boundary layer between the wind and the dead air behind the hill.

If the plane is heading towards the ridge in 50mph winds, downwind, at 100mph, then the airspeed over the wings is 50mph. The plane is going 100mph groundspeed, but the wings feel only 50mph airspeed because the plane is flying with the tailwind. Once the plane crosses the boundary layer into the dead air behind the hill, the airspeed over the wings jumps to 100mph as now the plane is flying in still air, so the groundspeed and airspeed over the wings is the same. The airspeed jump over the wings is energy gained.
Crank the plane back up through the boundary layer into the 50mph headwind, and now the plane is still going 100mph, but the airspeed over the wings is now 150mph as you're flying into the headwind now. This airspeed jump over the wings is energy, and we use that energy to crank a hard turn and gain speed with that energy. Every time the plane passes through the boundary layer there'a huge jump in airspeed over the wings. Holding the planes in these circuits they wind up almost indefinitely.
You can hear the planes passing through the boundary layer in the videos, it's that "whump" right when the plane crosses the ridge, it's a totally cool sound.

Early calculations were for 10 times the windspeed, and we've surpassed that now. Aside from jet real jet airplanes and some Reno Air Race planes, there's nothing else in existance going this fast basically.

If you rearrange these circuits into big, strung out "S's", you have what albatross do, banging in and out of weather fronts to fly across ocean expanses without ever flapping.

I've radared tiny birds called Swifts at well over 100mph zooming along ridges doing the same thing. Swifts are total hotrod birds. Interesting too, they can't walk, they're latin name Apus means "no foot" and they can only cling to walls, and they fly to super high elevations and sleep while flying at night. If they land, they often cannot take off unless helped.

At our coastal site, I had an aggressive peregrine falcon follow my plane at well over 150 around and around for 6 or 7 laps, it was totally cool.

There's many vids on RCspeeds.com and youtube, check them out and crank up the sound!