Aircraft

U.S. Air Force goes vortex surfing to cut fuel consumption

U.S. Air Force goes vortex sur...
Airplane creating vortices made visible by colored smoke (Image: NASA Langley Research Center )
Airplane creating vortices made visible by colored smoke (Image: NASA Langley Research Center )
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Tw0 C-17 cargo planes used in the $AVE vortex surfing tests (Image: US Air Force)
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Tw0 C-17 cargo planes used in the $AVE vortex surfing tests (Image: US Air Force)
Airplane creating vortices made visible by colored smoke (Image: NASA Langley Research Center )
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Airplane creating vortices made visible by colored smoke (Image: NASA Langley Research Center )
C-17 generating vortices in smoke trails of flares (Image: US Air Force/Tech. Sergeant Russell E. Cooley IV)
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C-17 generating vortices in smoke trails of flares (Image: US Air Force/Tech. Sergeant Russell E. Cooley IV)
Migrating geese use vortex surfing (Image: John Benson)
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Migrating geese use vortex surfing (Image: John Benson)
US Navy FA-18C creating vortices at the wingtips (Image: US Navy)
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US Navy FA-18C creating vortices at the wingtips (Image: US Navy)
Cyclists drafting (Image: Airman Nathan Doza)
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Cyclists drafting (Image: Airman Nathan Doza)
NASCAR racers drafting (Image: US Air Force/ Larry McTighe)
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NASCAR racers drafting (Image: US Air Force/ Larry McTighe)
Even spiny lobsters exploit vortex surfing (Image: Langosta Espinosa)
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Even spiny lobsters exploit vortex surfing (Image: Langosta Espinosa)

The United States Air Force (USAF) is taking flying lessons from geese and spiny lobsters. This may seem like the mother of all bureaucratic errors, but there’s actually some pretty solid science behind it. In exploiting a phenomenon known as “vortex surfing,” the USAF has found that by having C-17 cargo planes flying in formation, it can reduce fuel consumption by up to ten percent.

Vortex surfing involves the whirlwinds of turbulence generated at the wingtips of planes in flight. Because they produce turbulence and drag, aeronautical engineers do their best to minimize these. That’s the reason for the little winglets on aircraft. Now, instead of trying to get rid of vortices, the USAF is trying to exploit them to increase fuel economy.

Tw0 C-17 cargo planes used in the $AVE vortex surfing tests (Image: US Air Force)
Tw0 C-17 cargo planes used in the $AVE vortex surfing tests (Image: US Air Force)

This may be cutting edge as far as aviation is concerned, but vortex surfing has been around a long time. In fact, nature has been exploiting it for millions of years. Geese flying in formation vortex surf. The lead bird generates vortices as it flies and the other geese position themselves inside the wave of turbulence also known as a slipstream. Though the lead bird is working hard, the vortices it generates increase lift for the following birds. The lead bird has to work harder, but the net energy savings for the flock as a whole goes down.

Lobsters use vortex surfing, too. Spiny lobsters migrate in long queues called “lobster quadrilles” where the principle is the same as with the geese. The lead lobster pushes through the water, stirring up vortices, and the others line up behind to take advantage of the slipstream for an easier march.

Migrating geese use vortex surfing (Image: John Benson)
Migrating geese use vortex surfing (Image: John Benson)

Airbus has also proposed flying commercial aircraft in formation in “express skyways” to reduce fuel consumption as part of its “Smarter Skies” initiative that looks to the future of air travel. Now the USAF sees it as a way of decreasing fuel consumption over long-haul cargo flights.

As part of a program called Surfing Aircraft Vortices for Energy, or $AVE, the Air Force carried out tests in September and October at Edwards Air Force Base in California. Two C-17 Globemaster III cargo jets were used to see if what works for a goose will work for a plane big enough to carry an M1 battle tank. The tests involved two aircraft – one flying ahead while the other surfed on the vortex of the leader to gain updraft without expending additional fuel.

C-17 generating vortices in smoke trails of flares (Image: US Air Force/Tech. Sergeant Russell E. Cooley IV)
C-17 generating vortices in smoke trails of flares (Image: US Air Force/Tech. Sergeant Russell E. Cooley IV)

Unfortunately, vortex surfing involves more than just clever flying. To carry out the maneuver, the C-17’s autopilot software had to be modified to allow the aircraft to remain in the proper formation on the vortex without pilot assistance.

"The autopilot held the position extremely well – even close to the vortex," said Capt. Zachary Schaffer, commander on one of the test flights. "The flight conditions were very safe; this was as hands-off as any current formation flying we do."

The early tests showed a ten percent fuel savings over the course of the flights. The Air Force said its Air Mobility Command (AMD) conducts 80,000 flights per year, so a ten percent reduction in fuel consumption would translate into millions of dollars in savings. The Air Force Research Laboratory is now analyzing the test data and plans to adapt vortex surfing for other aircraft and missions.

Source: USAF via Dvice

12 comments
Graham R
Mythbusters already tested this and showed similar savings.
Grunchy
There are at least two competitive sports that I can think of that are directly based on the drafting concept: first one is peloton groups in long distance bicycle racing, second is Jr Johnson's drafting technique in Nascar stock car racing. In 1899 Charles "mile a minute" Murphy set a 60 mph speed record on a bicycle by drafting behind a train on tracks that had the ties smoothed over by 1 mile of plywood.
Jeremy Nasmith
A rare instance I agree with military thinking!
Panayis Zambellis
the problem i see is the safety aspect birds are feathery and pliable and can even survive mid airs !!! and they can all take off simultaneously Multiple plane formation flights on the other hand would have to be marshaled and synchronized . I .e. form up before setting of for their destination or meet up at some point in the sky to benefit from vortex surfing if they share a destination. The logistics and effort might outweigh the cost savings. I certainly would be an even more very nervous and anxious passenger watching this practice from my window while flying panayis zambellis luton uk
robin
The lead goose doesn't do all the work. The job of leader is rotated among the members of the formation. I wonder if the lobsters trade the lead spot?
Jeff Wilson
Would this work for wind turbines as well?
Gadget
Did some work on a sail design back on 2003 specifically designed to take advantage of vortices. Used the IBFV flow modeling software from Jarke van Wijk at Eindhoven UNI then did some wind tunnel testing of a rough prototype at Auckland Uni with some positive but inconclusive results. Personally I believe higher velocities are required in the 20kts + range. My modeling predicted a vortice should form approx 4 meters directly ahead of a full scale version creating very substantial additional lift. Needs more work anyone wants to take a look the drawings are on my Facebook page back in 2003. https://www.facebook.com/christoalnz
elpenguino
Why is this news? This has been known for many decades - there's a reason why WW2 planes flew in the formations they did.
Gerard Gallagher
Would this principle be more or less fuel efficient than the utilization of ground effect by WIG craft,like the "Caspian Sea Monster"?
Robert Duckmanton
Have seen this principle exploited by wind turbines in Utah canyons. On the lead bird working harder: this is true but it also the case that it is not working as hard as when flying alone, just as any one who rides in close peloton groups when cycling can tell.