Re: Cost in Aquatic Birds (short)

["James R. Cunningham" <jrccea@bellsouth.net>]

David Marjanovic wrote:

> > Personally, I can't
> > qualitatively reconcile the kinematics required for efficient thrust
> > production under water with the kinematics required for efficient lift
> > and thrust production in air.
>
> Is just the length of the phases different, and the power invested into
> each, or are there different phases? And is this the same among all
> underwater fliers?

Most animals are close enough to neutral bouancy (sp?)  in the water that
lift production becomes relatively minor relative to thrust production.  For
most larger animals flying in air, the thrust coefficient (ratio of thrust
to lift) varies from maybe 0.03 to about 0.3 roughly, usually averaging
about the same as the drag ratio (for obvious reasons).  For most animals
'flying' in water, the required thrust would be much greater than the
required lift and the thrust coefficient can be a rather large number, far
greater than 1.0.   This requires a different wingbeat locus for reasonable
efficiency.  Look at the motion of the forelimb of a swimming sea turtle to
get a good slow motion conceptual visualization.  The actual locus of the
motion could be expected to vary with speed in individuals, and with
morphology between species.