A V formation (sometimes called a skein) is the symmetric V-shaped flight formation of flights of geese, ducks, and other migratory birds. V formations are also used on military flight missions.
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The V formation greatly boosts the efficiency and range of flying birds, particularly over long migratory routes. All the birds except the first fly in the upwash from the wingtip vortices of the bird ahead. The upwash assists each bird in supporting its own weight in flight, in the same way a glider can climb or maintain height indefinitely in rising air. In a V formation of 25 members, each bird can achieve a reduction of induced drag by up to 65% and as a result increase their range by 71%.[1] The birds flying at the tips and at the front are rotated in a timely cyclical fashion to spread flight fatigue equally among the flock members. The formation also makes communication easier and allows the birds to maintain visual contact with each other.
Visual contact is why V formations (and the asymmetric echelon formations) are also commonly adopted by flights of military aircraft engaged on a common mission.
The basic flight formation for military aircraft in many air forces during World War II was a V formation. In the U.S. Army Air Forces, the most basic formation for bombers was a three-plane "V" called an "element". Stacks of these elements were configured to form a defensive bombing formation called the "combat box". The standard fighter unit, early in World War II, for the British Royal Air Force was the V shaped "vic". This involved one lead plane and two wingmen, with the wingmen flying very close to the sides and slightly behind the lead plane to form the V shape. Typically four vics would fly together one after another to form a squadron. The problem with the vics were the formations were so tight that the wingmen had to constantly be watching the lead plane or risk running into them. This left only the lead plane to search the skies for enemy planes. After many complaints from the British pilots of the vics not being the optimal flying formation, the RAF Fighter Command changed the squadron formation so the fourth vic would weave back and forth theoretically giving them a better field of view. This resulted in the "weavers" as they were called being picked off because the German fighters could attack them and get away before the rest of the squadron could leave formation and be ready for a counterattack. The Germans called these vics Idiotenreihen ("rows of idiots"). Later in the war the RAF Fighter Command abandoned the vic formations in favor of the Finger-four formation that the German Air Force (Luftwaffe) used.[2]
The V formation is also common in ceremonial flyovers and airshow flights.