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Re: hovering diversity (was Re: Ornithurine diversity)

----- Original Message ----- From: "Mickey Rowe;893-2446" <mrowe@lifesci.ucsb.edu>
To: <dinosaur@usc.edu>
Sent: Tuesday, July 15, 2008 9:32 AM
Subject: Re: hovering diversity (was Re: Ornithurine diversity)

I'm sure the region containing updraft extends a good bit
to the leeward side of the bluffs as well, but birds never kite

It doesn't. There is a seperation bubble just leeward of the top of the bluffs and the flow turns quickly downward there and then splits at the surface to flow back toward the lip of the bluff (until it is reentrained by the rising air, thereby bleeding off energy from the rising air) and also (with a smaller velocity component) horizontally away from the bluff. There is some flow above the seperation bubble that continues to rise for a short distance, but it is too far above the top of the bluff to serve the birds' needs (it also has a severely reduced vertical velocity component).

Glad to be of service :-)

You are most welcome. After all, the alternative is working on my day job, and I'd rather do this.

} birds usually have to resort to the 'flutter' stroke to hover at
} constant altitude

Yes, I've always thought it ironic that that's by far the most common
mechanism by which actual kites hover.

They will usually only resort to the flutter stroke when no external energy source is available, because it takes a very high power input to generate and seperate the alternating spanwise vortices that they are shedding off the leading edges of their wings in order to produce the lift forces required.