[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Pterosaur arm supination (getting long)




----- Original Message ----- From: "Michael Habib" <mhabib5@jhmi.edu>
To: <dinosaur@usc.edu>
Sent: Tuesday, January 15, 2008 10:47 AM
Subject: Re: Pterosaur arm supination (getting long)



It might get close; I'll have to look into it. The gap is pretty big in many cases, though.

Yes, but consider that the aspect ratio of the individual tip slot feathers can be quite high, and their induced drag is low. Consequently the gross induced drag can be low (accent on the 'can' as opposed to 'will' ). August Raspet commented on this in a paper back in the 50's if I remember correctly.


It does seem that the sharp transition, and the subsequent high pressure eddy formation, would also tend to promote flow separation from the wing at high lift coefficients, though.

Undersurface, yes. At all lift coefficients above the bistable aeroelastic flutter limit. It is a case where flow seperation works to the advantage of the animal. Turbulent attached flow ain't always the ideal condition, and turbulent seperated flow isn't always bad (on top of the wing, it is bad :-(


If there was indeed an air sac system under control of the animal, with components posterior to the r/u, then the effect could obviously be mediated at low speeds/high lift coefficients as need be.

Low speed/high lift coefficients are when you want it to occur. It's a lift enhancer.


Otherwise, I might expect that the contour was kept smooth continuously.

Impossible in Azhdarchids behind the humerus. The rate of curvature can be smooth and probably is, but it is very high rate (sharp curves). There will be a seperation, and in this instance, it is a good thing.


Another aside. I've noticed differential preservation immediately behind the elbow in some pterosaurs, leading me to speculate that some of them may have had 'nacelles' faring the volume immediately behind the thick, protrusive elbow -- either fat pockets, or air sacs. I consider that to be highly speculative though.
JimC