WM James Davis wrote:
>
> To anyone who can help:
>
> When I took ornithology class some years ago, it was explained that the
> lift generated from a bird's wing (secondary feathers) during gliding
> flight was due to the same forces that lift an aeroplane's wing........
It is quite a while since this was posted and unfortunately the thread does'nt
seem
to have got off the ground. Flight in birds is more difficult to break down
than in
aeroplanes because the lifting devices also act as propellers. The case is
similar
when gliding at which time the bird presents an aerodynamic surface at a
certain
angle of attack to a relative air flow.
At that time lift is explained by Newtons law that action and reaction are
equal
and opposite. The behaviour of the air around the wing is explained (
reasonably
well at speeds attained by birds ) by Bernoulli's theorem, Total energy in a
steady
streamline flow remains constant. This can be used to explain why pressure is
reduced above a good airfoil in flight.
But the short answer is that birds and planes stay up cos their wings deflect
air
down.
Robert Berry.
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