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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."
Drafting.. nuff said.
Works for cars, bikes, motorcycles, swimmers, why not planes?
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What about the lead aircraft? Does he run out of gas first and crash and burn, leaving a new lead to continue the cycle?
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I wonder if you could start using something like this for commercial aircraft. With careful scheduling, you can have aircraft flying in adhoc formations when they are traveling the same corridors.
What could go wrong?
(They were actually sparrow scratches, but never mind that.)
I wonder if they realize that "Apocalypse Now" was not a documentary, and not filmed in real time?
In order to expand our pool of aeronautic expertise, the USAF is offering research positions to those with experience at bicycling long distances. ...Or something like that.
Been there, done 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...
Depends on how the first to file/first to invent law gets interpreted once it goes into effect. Birds never filed AFAIK. (They found it "obvious.")
I see folks at the DoD have been watching Mythbusters. As well they should.
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We're caught in his jetwash! Flame out! We're going in a flat spin! Eject! Eject! Hightway to the danger zone!
Migrating birds have been doing this for years
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.
Drafting is also used in racing leagues that turn right and have drivers and fans educated enough to read.
how Goose died in Top Gun?
Clearly, you have an eagle eye, to have spotted that.
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It also works for swimming. Swimmers do it, dolphins do it...even educated, bees, oh never mind.
Sorry, I was just making a joke. Didn't mean to step in your pet shit pile.
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.
It's first-to-file, not first-to-fly.
systemd is Roko's Basilisk.
Automation. Drafting isn't safe if you depend on your own reaction times and vigilance. But with automation, it should be safe for both cars and airplanes.
Besides, airplanes tend not to slam on their brakes like cars and trucks do.
Have gnu, will travel.
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I still have more fans than freaks. WTF is wrong with you people?
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.
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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Because it would take longer so the airline would not be able to charge as much for tickets. Also, the crew would have to be paid for more hours for each flight. Maintenance would also cost more per flight as each flight would involve logging more air time. And I would feel bad for the air traffic controllers - their job would get significantly more difficult.
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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This thread needs to go the way of the Dodo.
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Interesting, I didn't realize that the reduction in air density at height greatly offsets the cost to get there. I assumed it would be similar to how gunning it to 130 MPH in a car and then costing down to 55 will kill your fuel economy.
...
racing leagues that turn right and have drivers and fans educated enough to read.
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They've been talking about doing this for years.
But then you'd be robin us all of the joy of these puns.
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>
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
...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?"
Actually, aerospace engineers (civi and military) have been working with birds for some time. My guess is that they're now testing the idea because it's been a very difficult problem to solve. Turbulence is complex and chaotic, and perhaps the technology for monitoring, measuring and reacting to a lead plane's waves is just now getting to the point of viability.
If you recall the movie Top Gun from 20+ years ago, getting caught in the jet wash of another plane was something that happened twice at pivotal points in the movie; Goose (Tom Cruise's wing man) died because this jet wash thing caused a crash, and the review proceedings cleared Tom of any wrong-doing, saying that there was no way to foresee the jet wash or something like that. So as of 20-odd years ago, sitting on another plane's tail was apparently considered a dangerous and unpredictable thing to do.
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The effect can be really pronounced, easily in the double digit percents. If you're curious look up "True Air Speed" and "Density Altitude" and then take a look at the runway lengths of a place like Denver, and San Francisco.
A true racing fan would be educated enough to not watch NASCAR.
FTFY
Is 1563649 a prime number?
i couldn't be bothered googling, but surely there's a "someone's law" to the effect of "he who uses 'illiterate' in a sentence will invariably misspell it"
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.
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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Operation Guillotine is in effect.
You get the most savings at distances that would probably be dangerous due to turbulence. But even further out, you still realize some savings from the formation.
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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.
I would not assume that aerospace engineers had never thought of this before.
That wasn't what I meant to imply. Oops.
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vorticity is conserved. The flow over a wing is a rotation superimposed on a translation which results in the slower flow underneath and faster on top.The rotation, usually called circulation, embodies a certain value of vorticity which can't disappear. Where it goes is it turns 90 deg at the tip and trails back behind the a/c all the way to the tarmac (vortexes have to terminate at a boundary...the ground).
If the wing is longer, for constant lift, the circulation reduces because a wider swath of air is turned downward so to give the same z-direction momentum flux the amount of "turning" is less.
By flying tip-to-tip, a/c effectively create a longer wing. Physically of course it isn't one wing but happily the highly coherent trailing vortices can be coupled by overlapping them, they rotate in opposite directions so tend to cancel each other out.
(The reason "bees shouldn't be able to fly" is that it appears to take too much energy to create the circulation around their wings every flap. It takes energy to "spin up" the air. How they do it is they slap their wings together at the top, when they separate they shed a vortex back over their wings which gets the circulation going. Not obvious.
Equine Mammals Are Considerably Smaller
By this logic, I could use metal utensils on a flight over US airspace... but I can't.
They most probably did it for millions of years but that doesn't invalidate the thousands of years. Thousands of years is simply a bit incomplete.
Well, I might have a way, but it only works on a semi spherical planet in a vacuum.
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I assumed it would be similar to how gunning it to 130 MPH in a car and then costing down to 55 will kill your fuel economy.
That doesn't kill your fuel economy. It will in fact be quite efficient. You will be using the engine at its most efficient point, full load. If you rev high while doing it, some cars will use various tricks to increase HP at the cost of fuel efficiency, but if you switch gears below 3000RPM or so, that should not kick in. Once you get to 130MPH you need to switch to neutral and ideally the engine should be stopped -- but most non-hybrids are not safe with the engine off.
Aerodynamic drag will be high for the brief time you are at 130MPH, so if you are trying this technique for fuel efficiency, you probably want to keep the speed variation a bit lower.
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Why can't large airplanes fly to a very high altitude, then turn off their engines and 'hang glide' down to some lower altitude over a long distance, then turn the engine back on and climb up again?
You can't usefully turn off the engine on an airplane. It will try to turn, causing drag. If you have a propeller you can feather it, but with jet engines you are completely out of luck.
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Very few cars are most efficient at full load or at high speed. This site even has a calculator, even accounting for the coasting distance (which isn't significantly different between 55 and 130 MPH compared to the length of the trip.)
Open wheel also has fat rednecks going in circles, they call it indy car. Another sport that looks like watching a washing machine.
The other thing that's nice about cruising at high altitude is you go faster for the same fuel burn, since the power required to overcome air resistance varies as the cube of airspeed. An airplane that's doing 90 knots at 2000' will do 120 knots at 17,000' (if it can get there.) So even though your plane has less power at higher altitude, it goes faster -- and that, too, can reduce total fuel used, since you burn a bit more fuel but spend less time on the whole flight.
And by the way, burn-and-coast is actually a viable fuel economy strategy in cars if you don't gun it: if you accelerate gradually to somewhat above your best fuel economy speed, then coast (and get free distance) you can under some circumstances exceed the fuel mileage of constant-speed driving. http://en.wikipedia.org/wiki/Maximization_of_fuel_economy#Burn_and_coast has more details.
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With cars, it's most fuel efficient to accelerate up to speed, shut off the engine, coast as long as possible, and repeat. Probably won't work as well for aircraft.
Isn't this why foursomes of fighter jets (in the movies, at least), and flocks of migrating geese, fly in a V formation?
Prior art - not patentable.
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Very few cars are most efficient at full load
Wrong. Almost all of them are most efficient at full load, assuming RPM are kept down. The effect is much more pronounced for petrol cars, but diesel cars show it too to a lesser extent. Obviously keeping RPM's down means you have to limit your top speed and coast for a while until speed has fallen sufficiently to allow for a new burst of acceleration.
or at high speed.
High speed kills your mileage because of wind resistance. If you decide to get from point A to point B within a certain time, the most fuel efficient way to do so will almost invariably involve "coast-and-burn". The one major exception is if the time allotted allows you to run at precisely the slowest speed the car can handle in the highest gear. In most cars that speed is quite low, often less than 50km/h, so that is rarely practical.
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Yes, I failed at quoting. Sorry.
Finally! A year of moderation! Ready for 2019?