Most people think of surfing as something that's done on water, but the Air Force Research Lab (AFRL) is trying to use vortex surfing -- a technique similar to what bicycle racers and migrating birds do when they cluster in groups to draft off one another -- to help aircraft conserve fuel by flying close together in formation.
Using C-17 aircraft in tests on Sept. 6 and Oct. 2, the AFRL determined that it can save 10 percent on fuel on long-haul flights by allowing two or more aircraft to fly together for a reduced drag effect.
The Air Force is formally calling the concept Surfing Aircraft Vortices for Energy ($AVE), Dr. Donald Erbschloe, chief scientist for the Air Mobility Command, said in a press release.
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)
The tests involved two C-17s, one of which trailed the other, surfing its vortex and staying in position on its updraft to maintain lift without burning extra fuel. Flying this way also reduces wind resistance on the aircraft. This method could save the Air Mobility Command -- which flies an average of 80,000 flights a year -- millions of dollars in fuel costs, Erbschloe said.
The Air Force used C-17s because their size and mobility make it easier to maintain formations, and they don't need to trail too closely behind another plane to achieve vortex surfing, according to the AFRL. "The test flights were flown at longitudinal separations of 4,000 or greater," William Blake, one of the developers of the program, said in the release.
Engineers were able to modify the C-17s' formation flight system software to maintain proper flight position using the auto-pilot and auto-throttle systems. This allowed the planes to hold their position "extremely well -- even close to the vortex," Capt. Zachary Schaffer, one of the test pilots, said in the release. "The flight conditions were very safe; this was as hands-off as any current formation flying we do." However, pilots reported different levels of ride quality, leaving room for improvement, according to the AFRL.
Another test pilot, Maj. Eric Bippert, said in the press release that the lab will continue to analyze data from the flights to try to find the correct balance between a smooth ride and optimized fuel efficiency before employing vortex surfing in missions.
The US military has been exploring numerous ways to make its vessels -- especially those running on fossil fuels -- more efficient. For example, the Navy recently said it was exploring a way to turn seawater into jet fuel. And the Army is working on a number of ways to use alternative energy sources.
Agreed, Greg. Given some of the issues with air traffic control and the ungodly backlog of planes at US hub destinations, we don't need to throw vortexing into the mix to complicate aircraft safety.
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.
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.
Definitely a well-known trick in the world of racing and bike racing. We did a post on a CFD study conduced by Eindhoven University of Technology in The Netherlands, to analyze the drafting effects of cyclists in more detail. Specifically, they were examining the air resistance on the leading rider.
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?
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.
Yes, that's exactly the scenario I'm thinking of. And yes, my Dad used to say exactly that - at least two minutes pause on the tarmac prior to positioning for the take-off.
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 :)
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.
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