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Large flock of birds when migrating usually fly in an arrow formation, which helps the birds to save energy while flying the same distance as compared to a situation when the birds are not in a group.

  1. What is the physics behind this?
  2. What is the significance of the specific flying formation?
  3. Can this be applied on airplanes (given the fact that anything analogous to engine exhaust is not present in birds)?
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  • $\begingroup$ possible duplicate of Is the V flight formation being used for commercial purposes? $\endgroup$
    – kevin
    Commented Jul 13, 2015 at 13:38
  • $\begingroup$ that question does not explain the physics behind the 'V' formation $\endgroup$
    – Victor Juliet
    Commented Jul 13, 2015 at 13:46
  • $\begingroup$ @CGCampbell I am doing some research on this right now (online ofcourse) and turns out the physics behind the planes and the birds saving enery by flying in the V formation (which I called the arrow formation) is the same. So that makes the question On Topic. Again the question is not too broad as I am asking in reference to a particular phenomenon which has a very specific answer. $\endgroup$
    – Victor Juliet
    Commented Jul 13, 2015 at 14:11
  • $\begingroup$ I reflect the same sentiment! $\endgroup$
    – Victor Juliet
    Commented Jul 13, 2015 at 14:28
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    $\begingroup$ You do realize, of course, that you are still asking 3 questions here? $\endgroup$
    – CGCampbell
    Commented Jul 13, 2015 at 14:37

2 Answers 2

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Energy saving

The wing creates lift, which is upward force on the wing. According to principle of action and reaction, there must be a downward force acting on the air. This force creates a downwash behind the wing. As the accelerated air interacts with the still air further away it turns to the sides and back up, creating a slight upwash outside of the wingtips.

Flying in this upwash adds a bit of lift on the next flying thing which in turn means it can fly at slightly lower angle of attack and have less induced drag. This recovers some energy from the wake vortex that would otherwise be dissipated as heat.

Birds

Migratory birds use the typical V formation to take advantage of this, each bird flying aft and to the side of the previous. Since the leader is not getting any advantage, the birds usually take turns in leading the flock.

Aircraft

I have however not heard of this being done with aircraft for energy purposes beyond experiments. Military aircraft usually use similar V formation, but for different reasons. They need to fly in group, because they need to provide mutual defence. And then the V formation is used during cruise to and from target area simply because in it the wingmen see the leader while remaining clear of their downwash and wake turbulence.

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  • $\begingroup$ Really interesting, could you elaborate on this specific angle: I had the feeling that the first animal/object was doing some work for the benefit of the others (the upwash stream), but actually it seems the total quantity of work is decreased. How can that be? Thanks. $\endgroup$
    – mins
    Commented Jul 13, 2015 at 14:54
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    $\begingroup$ @mins: The leader is doing exactly the same amount of work that they would if they were alone. What happens is that the followers are able to recover some energy from the wake vortex that would otherwise be dissipated as heat. $\endgroup$
    – Jan Hudec
    Commented Jul 13, 2015 at 15:16
  • $\begingroup$ "provide mutual defence" Lessons learnt during WWII would disagree with that. The RAF paid a heavy price to learn that flying in formation requires skill and concentration that could be better spent searching for the enemy. $\endgroup$
    – Aron
    Commented Jul 13, 2015 at 18:31
  • $\begingroup$ @Aron: The formation is mainly used for flight to and from the target area where the pilots need to be aware of each other so they don't break up. In the actual fight the formation is broken and each plane manoeuvres on its own, the offensive/defensive roles only governing their choice of targets (speaking of fighters; bombers don't fly in formations much any more). $\endgroup$
    – Jan Hudec
    Commented Jul 13, 2015 at 18:41
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    $\begingroup$ @aron - the RAF learned that the "Vic", a tight 3 ship formation V formation, didn't work well. They quickly learned that the looser "Finger 4" four-man (two pairs of wingmen), however, allowed a great degree of flexibility and ability to cover each other. The British 3 man formation worked well pre-WWII in lower speed aircraft, it just needed to be loosened up with faster aircraft, and 2 pairs made more sense at that time. $\endgroup$
    – Jon Story
    Commented Nov 6, 2015 at 11:22
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Canada Geese are famous for taking advantage of this phenomenon-- they use the wingtip vortices caused by the bird right in front of them, to decrease drag during flight.

You can see wikipedia for some information regarding "V" formation and aviationweek for a relevant USAF experiment involving C17 aircraft.

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