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

[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.

typo. brainfreeze. yes.  yes, you're right.
> 
> ...... 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.

The beauty is, it's never slack. Embedded with chord-wise fibers, so virtually 
no flagging.
> 
> 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.

I'm not shooting for similar drag ratios. Simply less drag. And really, drag is 
not the issue while running in this taxon, not as big a deal, as every step is 
another unit of thrust. And the uropatagia become wings when lateral. 

The key to this thread is long legs (longer tibia than femur) = cursor. Not 
sure about leaping, other than that last arboreal fling before becoming 
airborne. All sister taxa tracks (Rotodactylus) indicate narrow-gauge, often 
bipedal, proximal phalanges elevated along with metatarsus-type locomotion.

> 
> 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)