2. Migratory bird flight a) When geese fly south for the winter, one typically o

Question

2. Migratory bird flight a) When geese fly south for the winter, one typically observes a formation of geese flying in a V-shaped pattern. Based on your aerodynamic knowledge of wingtip vortices that are shed from the tips of finite-span wings generating lift, what can you say about why the geese tend to fly in this formation when flying long distances? (Be sure to explain using vortex filament theory.) b) Based on your aerodynamic knowledge of the effect of aspect ratio (AR) on lift curve slope for finite wings, and the Bruguet range equation, what can you say about some bird wings vs others, and which wing planform types should be more efficient for long-range flight?

Explanation / Answer

Part-A

The formation of the birds in the V shape essentially improves the efficiency of flying birds, particularly over long migratory routes. Every birds of a flock, except the first bird fly in the up-wash from one of the wingtip vortices of the bird ahead. The up-wash 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. According to a study, in a V formation of 25 members, each bird can achieve a reduction of induced drag and as a result increase their range by 71%. 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.

part-b

Firstly we discuss about high speed wings,

They are short and pointed wings that when combined with a heavy wing loading and rapid wing-beats, will provide an energetically expensive high speed. The speed will be at the expense of high energy. This type of flight is used by the bird with the fastest wing speed, the peregrine falcon, as well as by most of the ducks.

Now about high aspect ratio wings

High aspect ratio wings usually have a lower wing loading and are far longer than they are wide, are used for slower flight. This may take the form of almost hovering or in soaring and gliding flight, particularly the dynamic soaring used by seabirds, which takes advantage of wind speed variation at different altitudes (wind shear) above ocean waves to provide lift. Low speed flight is also important for birds that plunge-dive for fish.

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