Re: L'origine et l'évolution des oiseaux, with a twist

[jrc <jrccea@bellsouth.net>]

Comments inserted
JimC

----- Original Message ----- 
From: "David Peters" <davidpeters@att.net>


.........Exactly. Sharoviptyerx legs were like wires. Add uropatagia: like 
struts, or better. Same transverse width (chord),

Umh, chord is length fore to aft.  Transverse width is thickness.  You're 
off by 90 degrees.

...... less drag by extending the anteroposterior length.

A thickness/chord ratio of about 3:1 is close to optimum.  Roughly the ratio 
expected with muscles applied to the femur and tibia, but without 
uropatagium.  The uropatagium chord will increase drag relative to that, not 
decrease it.  Plus, when the uropatagium is slack, allowing the animal to 
run (if it can), then the uropatagium is free to flag, which adds even more 
drag.  Personally, I would speculate that Sharovipteryx may be more of a 
leaper than a runner.

As an aside, a strut with a thickness of about 2 inches will usually have a 
chord of roughly about 4 to 6 inches.  For the same drag, struts are a lot 
bigger than circular dragwires.

David Peters
davidpeters@att.net


--- On Thu, 1/29/09, jrc <jrccea@bellsouth.net> wrote:

> From: jrc <jrccea@bellsouth.net>
> Subject: Re: L'origine et l'évolution des oiseaux, with a twist
> To: davidpeters@att.net
> Cc: dinosaur@usc.edu
> Date: Thursday, January 29, 2009, 9:28 AM
> I didn't follow the comment below.  A circular cross
> section dragwire with a diameter of 3/16 inch has roughly
> about the same drag as a strut with a width of 2 inches, due
> to the strut's lower drag coefficient.  In normally used
> sizes, struts are far lower drag than wires.
> JimC
>
> ----- Original Message ----- From: "David Peters"
> <davidpeters@att.net>
>
> > and thus it reduces drag (think of biplane wires vs.
> struts)