Archive for February 6, 2011

Why do birds fly in a “V” shape?

February 6, 2011 Leave a comment
Why do birds fly in a "V" shape?
      Scientists who have studied formation flight believe that birds
      fly in this way for two reasons.
      The first reason is that the shape of the formation reduces the
      drag force that each bird experiences compared to if it were
      flying alone. This decrease in drag occurs thanks to the formation
      of wing-tip vortices.
      Creation of trailing vortices due to a difference in pressure
      above and below a lifting surface
      These vortices are generally undesirable because they create a
      down-wash that increases the induced drag on a wing in flight.
      However, this down-wash is also accompanied by an up-wash that can
      be beneficial to a second wing flying behind and slightly above
      the first.
      A bird flying in one of these up-wash regions essentially gains
      free lift so that it can fly at a lower angle of attack. As angle
      of attack is reduced, the induced drag is also lowered so that the
      bird does not need to flap its wings as hard or as often to
      generate the thrust needed for forward flight. Flapping the wings
      less often means that the bird's muscles do not work as hard and
      its heart rate drops. As a result, the bird does not tire as
      quickly and is able to fly farther.
      Other studies have estimated that a flock of 25 birds in formation
      can fly as much as 70% further than a solo bird using the same
      amount of energy.
      Theoretical investigations further support these observations of
      birds in formation flight. By spacing themselves apart properly,
      birds can achieve optimum positions that reduce the drag of every
      bird in the formation. However, not all birds benefit equally.
      Even though the V formation benefits all of the birds, the bird in
      the lead position has to work the hardest. When this bird tires,
      it will drop out of the lead position and fall further back into
      one of the lines of the V. Another bird from further back will
      rapidly move forward to take the leading position and maintain the
      formation. The two birds in the furthest trailing positions also
      tire more rapidly than those in the middle, so these positions are
      also rotated frequently to spread the most fatiguing locations
      throughout the flock. This cyclical rearrangement gives all birds
      the responsibility of being the leader as well as a chance to
      enjoy the maximum benefits of being in the middle of the
      formation. This sense of teamwork comes naturally since even the
      youngest members of the flock rapidly realize that it takes less
      work to fly in a V formation than it does to fly alone.
      Another theory as to why birds fly in formation is that this
      orientation allows the birds to communicate more easily. The V
      formation provides the birds with good visual contact of each
      other to keep the flock together. This communication minimizes the
      possibility of losing birds along the way as the formation crosses
      vast distances during migration.
Categories: Technical