A friend just emailed me this YouTube clip. I don't know if it's been aired before but I thought it interesting enough to post for those that want a gander 
They are ridge soaring
Something I've done a lot of, though in a glider! Hugely good fun:
I was wondering for those in the know like TomW or others, if it could be explained to us lay persons of the wind dynamics created by ridges and it's effects on winged crafts? Also what are the possible safety margins (ie, maximum wind strengths / wind directions to the ridge face) or knowledge on things that could go potentially or terribly wrong? As I can recall when I first started Kiting there was a certain YouTube clip uploaded to Seabreeze of a guy getting ripped up a 100+ feet into the air off a beach near a tallish dune face and the dumped below after plummeting to the ground and people rushing over to assist the poor bugger 
It's all reasonably straight forward. An air mass travelling towards an obstacle (ie wind blowing on a hill) will be forced over the top of that hill.
If you fly in the area where the air is being forced upwards then you can stay airborne, so long as the air is ascending faster than your aircraft is descending.
Safety margins depend a lot on what you are flying and the shape of the hill. I've managed to stay airborne in a glider in about 5 knots of breeze, blowing straight on to a steep cliff. Also keen in mind that if the wind suddenly stops, the aircraft will still fly, it will just glide down to the ground. In my case (in the video) I am always within range of an airfield, just in case. Top speed on that glider is 300kph, I was doing somewhere between 200 and 250. Lots of fun
There are certainly safety issues. The leeward side of the hill is a dangerous place to be since all that air is coming back down again and can take you down with it. You should also turn away from the hill, as turning towards it can result in you misjudging and getting blown into the side of the hill!
Essay over . . .
Great vid, wouldnt do it though any kind of gear malfunction=goodnight
Its dedicated to Nicolas Kalin(unfortunatly dead, speed flying) says it all, crazy barstards
Thanks Gibbo!
Filmed in The Flinders Ranges in South Australia, an absolutely beautiful place to visit. Glider belongs to the Adelaide Uni Gliding Club, I just hire it. Takes about 10 hours flying to go solo, faster if you're a quick learner. It's not very difficult
