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Re: Great in the air, not so good underwater

----- Original Message ----- From: "evelyn sobielski" <koreke77@yahoo.de>
To: "jrc" <jrccea@bellsouth.net>
Sent: Friday, December 08, 2006 11:33 AM
Subject: Re: Great in the air, not so good underwater

Why is that the maximum possible wing loading for
active flight?  What are the constraints?

The constraints are a function of mass of flight muscles in relation to overall mass; you can only attach so much oomph to a sternum.

Is that indeed necessarily a limit? For example, the largest known pterosaurs are also the most heavily loaded (at about 20 Kg/S.M, similar to heavily loaded birds), and even though they have relatively less sternum for flight muscle attachment than birds, that size and loading don't appear to be anywhere near their upper limit. They've found another way to skin the cat. I have the feeling that for any flying bird, the maximum constraints on flight are usually not wing loading, they are more likely to be related to launch mechanism (and sometimes, landing). In general, the solution to any particular constraint is to evolve a way to sidestep it.

As to why - well, these are the empirical values.

Yes, but imperical values are observations, not reasons nor limits.

Interestingly, the
largest birds have wing loadings well below that, so
from a certain point on, the mass of the wing itself
becomes the limiting factor rather than the wing
loading (as in Argentavis).

Don't forget that wings are spanloaded and their mass is fairly irrelevant during soaring flight (only important during flapping) -- Argentavis is essentially a soarer. Argentavis appears to have been launch limited and I suspect Murres are as well. Wing loading for Argentavis was about 7.9 Kg/S.M., Minimum Sink was about 1.0 m/s (almost identical to a Murre, but at a lower lift coefficient), and Best Glide was about 13.1:1, almost as good as the Murre at 13.9:1

The highest wing loadings are found in galliforms, ?bustards?, and as you said
some alcids.

Kori Bustards mass about 11.9 Kg, with wing areas about 1.06 S.M, for wing loadings about 11.2 Kg/S.M. They don't use continuous flapping flight.
The largest individual bird known to fly by means of continuous flapping was a male Cygnus cygnus (Whooper Swan) designated JAP (I've forgotten his nickname -- it reflected his robust size). He massed 12.0 Kg (sometimes more), with a wing area of 0.75 S.M. for a wing loading on the order of 15.9 Kg/S.M. He was quite a performer and once made one of the most remarkable emergency flights that I know of, during a gale off the coast of Iceland. He disappeared several years ago and is thought to be dead..

It is interesting to note that the Kakapo is probably
very close to the limit - -----The flightless steamer ducks may be even
closer to the limit; ------ A slight decrease in size would allow at least the
Chubut Steamerduck to become flying again.

Limits always worry me. There are usually potential mechanisms by which limits can be manipulated. This is really the point that I'm quibbling about.
All the best,