Two Air Force C-17 planes prepare to take off in tight formation as part of a test of vortex surfing. The technique is similar to bicycle racers or migrating birds forming tight groups to conserve energy. (Source: Air Force Research Lab)
It's really interesting to hear especially from the pilots about this concept. I, too, wondered about the dangers of wake turbulence, having seen some television shows and read articles about it. I imagine it's a tricky balance to maintain the right distance and formation to leverage the vortex without putting either craft in danger, as TJ pointed out. I'm not a pilot or an engineer, but I imagine, too, using aircrafts of similar weight makes this safe as well.
I'm a private pilot...planes are separated for wake turbulence. "Heavy" aircraft >300k pounds are given extra separation. If you listen to ATC radio chatter you might hear a flight call in as "United 15 Heavy". After a wake turbulence accident in Orange County involving a business jet, NASA testing discovered 757's have a very strong wake due to the high lift wing and full span flaps. (Requirement for the 757 was transcon range out of La Guardia and Orange County...both have very short runways) BTW, the 757 has the highest thrust/weight ratio of any airliner except Concorde. A full-thrust takeoff in a 757 from SNA followed by the noise abatement power cut at 1000 feet is always exciting :)
Drafting is a little different than vortex surfing, I think. The paragraph immediately after the image describes it best. Riding the vortex increases lift (think higher pressure on the lower surface of the wing).
Drafting vehicles try to avoid the vortices.
And yes, vortices from larger aircraft can be incredibly dangerous for smaller craft. Some aircraft more than others - I've read that a Boeing 757's vortices are notable and it's worth it for small aircraft to wait more than 2 minutes before taking off after a 757.
I'm not a pilot, either, JimT, but since you have a connection to the aviation world, I have a question for you: Could the phenomenon being described here also be known as "wake turbulence?" Isn't that considered dangerous?
I'm not a pilot but my Dad was; and I specifically remember him talking about dangers of flying into the turbulence of a vortex from a larger plane, particularly on the runways during T-O & L . Maybe using like-sized planes (2 C17's in this example) reduces or eliminates that danger, but I know just from freeway driving that 18-wheeler vortex's cause unseen forces on your stability. On the contrary, the NASCAR crowd often quips, "I ain't tail-gatin' – I'm DRAFTING!" -- so it's a well-known trick – now applied to the skies.
This is a great idea. Yet another advance borrowed from dynamics in nature. Geese get even more out of the system by rotating which goose has the more difficult drag and placing the weakest goose in the high glide position.