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Air Force Lab Test Out "Aircraft Surfing" Technique To Save Fuel
coondoggie writes "It's not a totally new concept, but the Air Force is testing the idea of flying gas-guzzling cargo aircraft inline allowing the trailing aircraft to utilize the cyclonic energy coming off the lead plane — a concept known as vortex surfing — over long distances to save large amounts of fuel. According to an Air force release, a series of recent test flights involving two aircraft at a time, let the trailing aircraft surf the vortex of the lead aircraft, positioning itself in the updraft to get additional lift without burning extra fuel."
Just because the lead craft doesn't get to save gas, doesn't mean there is not a net gas savings for the entire system.
Change positions every so often. It's more fun that way. ;)
What could go wrong?
You can switch lead on-the-fly.
Actually, in most examples of drafting, the benefit extends to the leader as well, reducing the tail drag associated with a solo player. As I recall, the benefit generally increases as you add cars to the train as the lead drag and tail drag are spread over more units.
(They were actually sparrow scratches, but never mind that.)
Apparently things are a bit more complicated in the air...
Drafting helps by reducing air resistance (drag) and requires you to be really close, this technique is a bit more subtle in that it involves using trailing air vortices to get free "lift". The article had a handy link to explain this... http://www.av8n.com/fly/vortex.htm
Of course I'm sure that someone will draw such an analogy in a pop-science article...
I see folks at the DoD have been watching Mythbusters. As well they should.
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It's not drafting, it's flying in a V like birds. The lead bird works harder than the rest, and the lead changes when the front gets tired. Birds have "known" about this phenomenon for thousands of years (at least). But I'm surprised someone didn't patent it and charge the military for doing it.
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Well yeah, and it's been known for a long time they do this to save energy for those behind the leader, and that they trade off leaders from time to time.
Sometimes it takes a while for something in one discipline to reach another (I'm guessing ornithologists and military aerospace engineers probably don't rub elbows too often, but what do I know), and it's not always obvious that an idea in one area would apply to another (geese and airplanes are in fact different).
Still, I can't help but scratch my head that they're just now testing the idea.
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Obviously they didn't have their ducks in a row.
Firstly, this isn't drafting. Secondly, the lead would likely swap periodically, as birds have done for thousands of years. Drafting airplanes won't work for the same reason helicopters hovering can crash wile under full power (google "settling with power" for an areodynamic description of what would happen when multiple wings travel through the same air). Yes, I am a pilot.
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Drafting is also used in racing leagues that turn right and have drivers and fans educated enough to read.
Companies operating commercial aircraft have different regulations about how they fly vs the military.
If this were ever used commercially, I don't think it would be allowed with passenger aircraft, just cargo. The risk is just too damn high for so little reward.
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It also works for swimming. Swimmers do it, dolphins do it...even educated, bees, oh never mind.
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Because it costs a shit-ton of energy to get up to that high altitude. Much more than just going directly from point A to point B.
The vortices of planes last a long time. At airports when you are dealing with the big planes they have to leave minutes later so that the vortices have time to dissipate. Otherwise there is severe turbulence for the next plane. Watch a plane coming down through fog and see how long it takes for it to settle down...
No, there are strict rules for vertical and horizontal separation for planes depending on VFR/IFR http://en.wikipedia.org/wiki/Separation_(air_traffic_control) Not likely this will be changed anytime soon for safety reasons...
It always blows my mind seeing geese flying in such perfect V formations as they migrate in the spring and fall. I can't help but wonder if this is some sort of instinct that is pre-programmed into their brains, or if they can actually feel the difference and thus simply do whatever is easiest, or if there is some other aspect (maybe visual or even social?) that prompts the behavior and it just so happens that it is also more efficient.
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The Airlines should take notice.
Judging by the formations of geese and pelicans I've watched flying by in large groups, I have to assume this effect can be carried from one flyer to the next in a chain and isn't confined to just two flyers. The next question would be "Do all trailing flyers receive this 10% fuel savings, or is there some sort of diminishing return at play?"
If all of the flyers receive the savings, then the airlines might find that sending a small squadron of aircraft, say five DC-10 sized aircraft in formation as opposed to one large "super-liner", is economically beneficial both in terms of lower costs AND lower CO2 emissions. It would also relieve a common problem with current flight scheduling--empty seats. If the "flight" (I'm referring to the squadron idea) did not sell all the seats, they could simply send one less plane--it allows for options in balancing demand vs resource allocation, which would, I assume, allow the airlines to lower costs across the board including ticket prices. It would also allow the airlines to scale specific routes based on demand more accurately--if there is a sudden surge in demand on specific route, they simply increase the squadron size as required.
There is the added benefit of "diluting" the severity in repercussions as a result of mechanical failures/human error--when a super-liner suffers catastrophic failure, everyone dies. In a squadron of planes, a failure on one craft wouldn't mean the death of everyone. Not putting one's eggs in one basket has it's benefits.
But I'm surprised someone didn't patent it and charge the military for doing it.
The innovation isn't in the concept of "drafting" another plane. The innovation is in the autopilot system that does it safely and automatically. As shown on Mythbusters the concept is viable, but a human is not capable of keeping the plane in the "sweet spot" safely for an extended period of time.
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Half right. It does take a lot of energy to climb, but you regain most of that on descent making it approx 0 net change. However, flying at high altitude reduces air density, and therefore, drag, resulting in a net fuel savings.
It's a bit more complicated still, propeller driven planes may lose some propeller efficiency in the thinner air. For any given plane, there is a limit on how high it can fly, and trade-offs in drag vs propulsion efficiency, lift vs weight, as well as design (pressure and operational temperature) limits. However, as a rule, the higher you can fly the plane (within it's design limits), the more fuel efficient the trip will be. Short flights may be constrained a bit because the optimal climb rate and optimal descent rates might limit the max height to less than what the optimal height the plane is capable of.
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Works for cars, bikes, motorcycles, swimmers, why not planes?
Turbulence due to the plane and it's engines. At least that is what I would assume to be a problem with drafting in the air.
I've talked to some pilots and they call it jet wash. The larger the plane the more severe it is. When I fly I occasionally listen to the air traffic control chatter. Larger planes like 747, 757, 767, 777, etc are always referred to as "heavy" after their call sign. It's to help ATC remember to keep the spacing a little further behind these planes due to more jet wash. At least that's what I've been told. I assume it's true as it makes sense.
I think it is learned behaviour of not flying in the poop-stream of the bird directly in front of you.
The reason to rotate lead would be to conserve fuel for all planes, so you can travel further on the same size tank.
Why don't they just install winglets like the airlines are doing? Winglets reduce fuel usage by minimizing the drag associated with the creation of the vortexes. You get the benefits, even if just one plane is flying.
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But isn't that because birds get tired? Planes don't get tired - the lead plane will just burn more fuel than the rest, but as long as it's got enough for the trip, why does it need to swap out?
Migratory birds like geese have insane flight muscles, composed almost entirely of red muscle, and they are not really susceptible to muscle fatigue. The main limitation for them is fuel.
So the reason planes would want to swap leaders is more or less the same reasons as the birds do: To increase the range of all members of the formation.
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This thread needs to go the way of the Dodo.
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The risk is just too damn high for so little reward
That depends on the cost of fuel vs lawsuit
racing leagues that turn right and have drivers and fans educated enough to read.
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Drafting, defined as "following someone/something in a manner to reduce your aerodynamic drag by traveling in air moving at a lower relative velocity" excludes this act.
If you feel it is drafting, please state the definition of drafting you are using, as I've not seen a definition of drafting that would include this.
It does not depend on mitigating detrimental vorticies. NASCAR drafting does, and the lead car gets the benefit from the reduced drag. This does not benefit the vehicle in the front and is the following car using a predicted vortex to its advantage, while traveling through otherwise undisturbed air. Thus "drafting" where the folower uses the lead car to "break the air" is not happening.
Rather than having to define "drafting" to a bunch of morons who are too stupid/lazzy to google, I'd rather discuss the efffect of this on commercial aircraft for the rest of us, flight lanes with airplane flocks saving fuel. Or discussions on how much the winglets affect this effect. But no, it's all a discussion of the definition of "drafting" with a bunch of google-illiterite people.
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That was made so independent planes don't crash in to each other. In theory planes flying in this formation will be working in concert and may have computer/radar control over each other. It's likely a whole new set of rules would need to be drafted for this kind of operation. Honestly it makes the most sense for cargo planes flying over the open ocean to use a system like this. They stand to get the biggest gains, and present the least amount of danger to others that way.
They've been talking about doing this for years.
IFR lets aircraft fly through clouds wherein visibility extends no farther than the windshield. You could not pay me enough to be the trailing pilot flying through a cloud formation close enough behind a plane to draft/wingtip vortex surf. I get tense enough IFR in the clouds without also worrying about colliding with another plane.
>
Besides, airplanes tend not to slam on their brakes like cars and trucks do.
No, but the sky is capable of doing scary shit...
http://en.wikipedia.org/wiki/Vertical_draft
The air resistance of the second is the same as the first. The savings come from reduced induced drag, not reduced aerodynamic drag of passing through the air. In that sense, this is unrelated to the term "drafting" where the benefit is from the folllowing object having lowered aerodynamic drag (and in most drafting, the lead vehicle gets a benefit as well, which doesn't happen with this vortex optimization).
This is "drafting" like a skateboarder holding on to the back of a bus in city traffic is "drafting." There is a benefit, but it is not from reducing air resistance.
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I'm sure that it's instinctive, "learned" through generations of selection. Birds that developed to flock over long distances developed the instinct for V-formation flying at the same time; the ones who stayed in formation stuck together for longer distances and had better choices of feeding/mating grounds. The individuals who didn't got left behind and didn't mate.
But there are other kinds of flocking behavior: think of starlings, who make those big, pulsating clouds that are so mezmerizing to watch. I don't know if those are for feeding or protection or what, but they're certainly not optimized for distance as geese are. Maybe those are the descendants of the birds that couldn't stick to the formation and stopped their migrations in different places, met like-minded fowl and created their own flocking legacy.
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"thousands of years"? Come on, at least give me "tens of thousands of years". Modern birds have been around for 150,000,000 years; even if it took 99.9% of that time to develop this flocking behavior, we're beyond "thousands of years".
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...not jetwash. Jetwash is the turbulent stream of air behind a jet coming from out of the back of the engines. That is mostly dangerous while on the ground, when there is a small, light aircraft sitting behind the jet.
Wake Turbulence comes off the wingtips of *all* airplanes in flight, while the wing is generating lift. It's like horizontal tornadoes spinning off the wingtips. It can flip another airplane upside down Lots of pictures of what it looks like here.
I almost got rolled 90 degrees on short final while landing at EAA Airventure in Oshkosh, WI a few years ago landing behind a P-51 Mustang. I was in a Van's RV-8, which fortunately is very aerobatic and has a quick roll rate. It took full right stick to get the aircraft rightside up again and the whole event was over in a split second, and I landed normally. but with quite the adrenalin dump flowing in my bloodstream, and almost experienced a brown smelly dump flowing in my pants! As soon as I touched down, the tower controller said, "Nice job RV.... Uh, sorry bout that..... (sheepishly) Uh, caution wake turbulence?"
Then someone needs to fix Wikipedia. It's broken. "Drafting or slipstreaming is a technique where two vehicles or other moving objects are caused to align in a close group reducing the overall effect of drag due to exploiting the lead object's slipstream."
The definition does not include acts outside the slipstream. But then they do include acts outside the slipstream later, as you note. The definition in Wikipedia agrees with me that you are wrong, but the examples of that definition do not agree with me.
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The important things to remember, are
1) No matter how big your plane is, it's tiny in comparison to the air;
2) There is a mind-blowingly huge amount of energy in the atmosphere, especially around thunderstorms and changes in the land. It can be beneficial (see gliders and updrafts) or detrimental (low level wind shear & downdrafts), and you must pay constant attention to it.
Birds in formation do that periodically.
I remember an airplane crash near Pittsburgh in the early 1990s, when a plane got too close to another plane and got caught in the wake, causing the plane to plunge.
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They've been testing this for awhile. AFF (Autonomous Formation Flight) from 2001 is the first project I know about. The challenge is in the guidance and control system - it must be able to keep the trailing aircraft within inches of the desired position (12 inches for AFF) and maintain position through maneuvers and disturbances.
Not really true - I do it occasionally in my 19" skiff in heavy water - I'll tail a bigger fishing boat like a 60 -70' seiner. He's bouncing around at 10 - 15 knots and not having a care in the world. In such seas, I would be limited to 7-8 knots and the boat (and my back) would be getting clobbered. I sit about 100 feet back in the wake and as long as the wind isn't blowing so that I have inhale his diesels, it saves fuel, my back and gives me a speed boost.
The nice thing about water is you can see the wake 'vortex', no additional software required.
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