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scutfarcus
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Flying In Formation To Save Fuel?

Wed Aug 12, 2009 5:44 am

Found this interesting - according to Stanford study if airliners flew "in formation" like birds they could save 12% on fuel. By "in formation" they actually mean at distances of 3-5 miles. I find it hard to believe that at that distance you'd save much, but that's the report. Assuming that works, would you have tons of turbulence at that distance or what?

Thoughts?

Link:
http://www.triplepundit.com/2009/08/...rds-to-green-the-airline-industry/
 
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DeltaMD90
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RE: Flying In Formation To Save Fuel?

Wed Aug 12, 2009 7:50 am

I can only see this affecting military aircraft rather than civil aviation. If there are multiple aircraft flying the same routes at the same time someone down in the route planning department didn't do a good job...
 
TruemanQLD
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RE: Flying In Formation To Save Fuel?

Wed Aug 12, 2009 7:58 am

There was discussion of this sort of thing in OZ a few years ago, I dont remember if it was for saving fuel or making it easier for ATC. The plan was that all international flights to a certain dest. would arrive and land within minutes of each other. I.e. QF SIN-BNE arrives 12:30, SQ SIN-BNE 12:35 and then even destinations nearby so CX HKG-BNE and TG BKK-BNE. The obvious problem is planes never all leave on time. It would work better on domestic for the large routes. E.g. BNE -SYD and SYD-MEL and MEL-BNE at 12:00 then at 1:00 SYD-BNE BNE-MEL and MEL - SYD. There are still problems with it though
 
Nicoeddf
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RE: Flying In Formation To Save Fuel?

Wed Aug 12, 2009 11:11 am



Quoting DeltaMD90 (Reply 1):
If there are multiple aircraft flying the same routes at the same time someone down in the route planning department didn't do a good job...

Hmm, I guess having a look at the trunk routes cross Atlantic oder Pacific Ocean, you will find that many planes are flying the same route at approx. the same time.

After all, the best (most convenient) time to leave e.g. LHR for NYC doesn't change if the airline name or the livery of an aircraft is different...
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airbazar
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RE: Flying In Formation To Save Fuel?

Wed Aug 12, 2009 11:47 am



Quoting DeltaMD90 (Reply 1):
I can only see this affecting military aircraft rather than civil aviation. If there are multiple aircraft flying the same routes at the same time someone down in the route planning department didn't do a good job...

It's much the opposite. Most airlines have planned arrival and departure banks at their hubs.

Quoting NicoEDDF (Reply 3):
Hmm, I guess having a look at the trunk routes cross Atlantic oder Pacific Ocean, you will find that many planes are flying the same route at approx. the same time.

 checkmark 
Essentially there's only one travel path between the US and Europe with hundreds of flights every day traveling within minutes of eachother. But the article suggests 3-5 miles apart but that already happens today over the N.Atlantic routes, sometimes a lot closer than that.
 
HarrisonRuess
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RE: Flying In Formation To Save Fuel?

Wed Aug 12, 2009 1:46 pm

To me this is exactly the kind of innovation that the industry needs right now.

We're in a cash strapped environment, so we can't make the investmens that we want (or need in some cases) in order to cut costs in the long run - things like newer more efficient engines, frames, etc.

Something like flying in formation in order to cut costs (and 12% lower fuel burn is not at all insignificant) is perfect because it doesn't incur huge upfront costs. Juggling a few schedules and getting things coordinated obviously would take a little time and effort (and hence a little bit of $), but it would certainly cost less than buying new planes in order to achieve similar fule burn savings.

Certainly more work needs to be done in order to see if flying in formation really would work, but this is the kind of thinking that we need. Ideas that can save us money without costing us money.
 
0newair0
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RE: Flying In Formation To Save Fuel?

Wed Aug 12, 2009 2:26 pm

I'm thinking that this isn't going to be very useful... the airlines could spend their time better, and save more money, by adding winglets and starting/continuing "aircraft weight reduction" programs for now...
That's not how this works! That's not how any of this works!
 
HarrisonRuess
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RE: Flying In Formation To Save Fuel?

Wed Aug 12, 2009 3:11 pm



Quoting 0NEWAIR0 (Reply 6):
I'm thinking that this isn't going to be very useful... the airlines could spend their time better, and save more money, by adding winglets and starting/continuing "aircraft weight reduction" programs for now...

Certainly true. I'd put those items into the same category though: Finding ways to save money without big upfront costs. And these sorts of ideas (whether it's winglets, formation flying, or weight reductions) are the key right now.

As an aside though for comparison - Winglets usually provide a fuel savings somewhere in the 5% neighbourhood (although that does vary a bit from type to type of course) vs the 12% they're suggesting for formation flight.

How about flying in formation with winglets?  Wink
 
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Jetlagged
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RE: Flying In Formation To Save Fuel?

Wed Aug 12, 2009 10:00 pm

I'm not convinced loose formation 3 to 5 miles apart could reliably produce a 12% fuel saving. Also think of the time and fuel wasted while one/two aircraft loitered waiting for the second/third to join the formation. The co-ordination required, often between rival airlines, would be high and keeping the trailing aircraft in exactly the right position relative to the lead aircraft's vortices would be tricky when so many miles behind the leader.
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tdscanuck
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RE: Flying In Formation To Save Fuel?

Thu Aug 13, 2009 2:09 am



Quoting Scutfarcus (Thread starter):
Assuming that works, would you have tons of turbulence at that distance or what?

It shouldn't be too noticeable...they appear to have chosen that distance so that the vortex has grown enough to not have high gradients.

Quoting Jetlagged (Reply 8):
I'm not convinced loose formation 3 to 5 miles apart could reliably produce a 12% fuel saving.

It's only a savings for the rear aircraft...they're not doing the "goose-V" thing where each aircraft gets a "free" aspect ratio increase. They're just flying the aft aircraft in the upwash from one of the lead aircraft's tip vortices (which persist a lot more than 3-5 miles). That lets the rear aircraft fly at lower Cl and lower their induced drag.

Tom.
 
dragon6172
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RE: Flying In Formation To Save Fuel?

Thu Aug 13, 2009 11:38 am



Quoting Tdscanuck (Reply 9):
It's only a savings for the rear aircraft...they're not doing the "goose-V" thing where each aircraft gets a "free" aspect ratio increase. They're just flying the aft aircraft in the upwash from one of the lead aircraft's tip vortices (which persist a lot more than 3-5 miles).

We typically flew a lot closer formations than 3-5 miles when I was in the Marine Corps, but it was the wingmen who typically burned more fuel because they constantly had to adjust their throttle up and down to stay in position. May not apply as much in this situation because of the distance, but I think you would need a pretty good system to make sure the trailing plane stayed in the correct part of the vortice.
More importantly, how are you going to get multiple airlines to make agreements on who gets to be the trailing aircraft and get the fuel savings and who gets to be the lead and burn the most fuel.
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grandtheftaero
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RE: Flying In Formation To Save Fuel?

Thu Aug 13, 2009 12:31 pm



Quoting HarrisonRuess (Reply 7):
How about flying in formation with winglets?

This concept takes advantage of wake vortices from upstream aircraft. Winglets would mitigate these vortices and make this concept less effective.
 
grandtheftaero
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RE: Flying In Formation To Save Fuel?

Thu Aug 13, 2009 12:38 pm

BTW, this is not a new idea. It's not even an untested idea. Before it was en vogue to be "green" some clever engineers at NASA Dryden studied this phenomenon with a pair of F-18. Check it out:

http://www.dfrc.nasa.gov/Newsroom/X-Press/stories/103101/new_aff.txt.html

http://www.dfrc.nasa.gov/gallery/photo/AFF/index.html
 
oly720man
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RE: Flying In Formation To Save Fuel?

Thu Aug 13, 2009 1:31 pm

I'd have thought that there were too many atmospheric variables that could affect the wake to make this a viable proposition for civil operation.

And I can't really imagine the night sky with B747s or similar flying in an inverted V and then swapping places every 30 mins or so like Tour de France cyclists.

Wouldn't it be more fuel efficient to fly a bit slower and get away from the transonic drag rise, as well as not queue for take off for many 10s of minutes at major airports, not have to be stacked for arrival at the other end... Anyone got any numbers for fuel burn at say M0.75 vs M0.8?
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Jetlagged
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RE: Flying In Formation To Save Fuel?

Thu Aug 13, 2009 9:42 pm



Quoting Tdscanuck (Reply 9):
It's only a savings for the rear aircraft...they're not doing the "goose-V" thing where each aircraft gets a "free" aspect ratio increase. They're just flying the aft aircraft in the upwash from one of the lead aircraft's tip vortices (which persist a lot more than 3-5 miles). That lets the rear aircraft fly at lower Cl and lower their induced drag.

Tom, I'm well aware why this works in theory so I don't need a lesson in aerodynamics. Nor did I say the lead aircraft got a fuel saving, so why point that out?

In practice keeping in the correct position relative to the leader's wake would be tricky, and the two trailing aircraft would have to be laterally very close. Keeping proper formation at night and in turbulence would be difficult too.
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grandtheftaero
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RE: Flying In Formation To Save Fuel?

Thu Aug 13, 2009 10:02 pm



Quoting Jetlagged (Reply 14):
In practice keeping in the correct position relative to the leader's wake would be tricky, and the two trailing aircraft would have to be laterally very close. Keeping proper formation at night and in turbulence would be difficult too.

Jetlagged, check out the NASA pages I posted earlier. The crux of that study wasn't so much aerodynamics but an experiment to see if they could get the automatic pilot control to stay in formation with the lead A/C.
 
tdscanuck
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RE: Flying In Formation To Save Fuel?

Fri Aug 14, 2009 12:42 am



Quoting Jetlagged (Reply 14):
Tom, I'm well aware why this works in theory so I don't need a lesson in aerodynamics. Nor did I say the lead aircraft got a fuel saving, so why point that out?

I was basing my comments from this:

Quoting Jetlagged (Reply 8):
I'm not convinced loose formation 3 to 5 miles apart could reliably produce a 12% fuel saving.

I read that as some combination of not believing the effect could work at 3-5 miles and/or that the reduction % was too large.

My point was that the effect they're exploiting does last over 3-5 miles and that the reduction they specified wasn't for all the planes in the fleet, so it's not as large (overall) as it might first appear. I obviously misinterpreted the original quote, sorry about that.

Tom.
 
pilotpip
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RE: Flying In Formation To Save Fuel?

Fri Aug 14, 2009 12:55 am

I'd love to sit in somebody's wake turbulence for a couple hours to save some gas. Not.
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dxing
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RE: Flying In Formation To Save Fuel?

Fri Aug 14, 2009 4:43 am



Quoting Airbazar (Reply 4):
Essentially there's only one travel path between the US and Europe with hundreds of flights every day traveling within minutes of eachother.

There are actually 5 different tracks between the U.S. and Europe every night. There is also no rule against random routing outside the established tracks.

Quoting Dragon6172 (Reply 10):
More importantly, how are you going to get multiple airlines to make agreements on who gets to be the trailing aircraft and get the fuel savings and who gets to be the lead and burn the most fuel.

Therin lies the rub.

I'd be amazed if given anything other than a perfect weather night you could realize anything near a 12% fuel savings.
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EcuadorianMD11
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RE: Flying In Formation To Save Fuel?

Fri Aug 14, 2009 12:09 pm

How often does this happen............that you visually chase another plane?
They obviously don´t fly an identical speed at all times, so what if plane A is about 10 knots faster than B and due to her schedule needs to overtake B?
Do both planes talk to each other or is it the traffic controller that sends one of the planes to a higher or lower altitude. I mean around airports the traffic controller is very much on the ball but is this the same while crossing the ocean??

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Mir
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RE: Flying In Formation To Save Fuel?

Fri Aug 14, 2009 2:27 pm



Quoting EcuadorianMD11 (Reply 19):
Do both planes talk to each other or is it the traffic controller that sends one of the planes to a higher or lower altitude. I mean around airports the traffic controller is very much on the ball but is this the same while crossing the ocean??

ATC still has control over the aircraft over the ocean.

-Mir
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UAL747
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RE: Flying In Formation To Save Fuel?

Fri Aug 14, 2009 4:00 pm




Just a neat image.

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Jetlagged
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RE: Flying In Formation To Save Fuel?

Fri Aug 14, 2009 8:06 pm



Quoting Tdscanuck (Reply 16):
I read that as some combination of not believing the effect could work at 3-5 miles and/or that the reduction % was too large.

I accept why you might have thought I might not understand but I wasn't questioning whether the vortices would persist over that distance, rather whether trailing aircraft could be flown accurately enough in the upwash region to get the theoretical benefit. If you are in close formation with the lead aircraft it's clear where the upwash will be. 5 miles back and it's not so clear. All aircraft would have to be on the same flight plan, same speed. If not the same type then they may not all be at their most efifcient cruise speed.

Would this be compatible with RVSM, given that the trailing aircraft may well need to be at a different altitude to be in the leaders vortices, thus the formation would need a range of cleared altitude, not just a single level.
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