Re: Conway's Velociraptor (and pterosaurs)

["James R. Cunningham" <jrccea@bellsouth.net>]

Jaime Headden wrote:

> <So that the hindlimb could play a more active roll in providing yaw command 
> authority as the length of the tail diminished?>
> 
>   Ah. As in the digit providing a form of "elevator"?

No.  As in enhancing the ability of the entire foot to serve as a trim
servo for the hindlimb itself.


> This would make sense, to some degree, except how pterodactyloids, lacking a
> long tail or the digit, managed good yaw control if the digit and tail of 
> "rhamphorhynchoids" conferred better yaw control.

The ramphos didn't have 'better' yaw control.  They had more stable yaw
control.  Which is an advantage for early flyers whose brains are not
yet fully adapted to flight, but a disadvantage for more advanced
flyers.  That's why F-18's are more unstable than my Cherokee.
> 

>   Then this is why I am concerned, as the art illustrated suggests (perhaps 
> due to the view) that the pes faced ventrally given the
> angle of the drawing's view; from above or below, the pes is fully exposed on 
> its broad plane, digits radiating in a fore-aft
> direction with, as Jim notes, some apparent twist in John's work as well as 
> Luc's. This was not apparent to me before, but this
> "twist" in the ankle orientation does not appear to pull the pes above 30 
> degrees of a horizontal body plane, which is why I
> perceived it to be "flat."

The pes isn't pulled up on a plane. The aftward toes displace relatively
further aft than the forward toes so that a cambered surface develops. 
The camber shifts the zero lift aoa well negative.  In cruise flight,
the feet aren't lifting -- they are at near zero lift, but can be
quickly shifted to provide either a substantial download or a very
slight upload.  Since there is a range of low CL's that the uropatagium
can't achieve due to aeroelastic constraints on flutter (or the lack
thereof), the pes may help the aerodynamic tail complex generate loads
within that constrained range.

> This also makes me curious as to the horizontal orientation of the fifth 
> pedal digit in nearly all illustrations offered, though to my knowledge the 
> fifth metatarsal was largely linear with the other metatarsals and did not 
> allow
> the phalanx (or phalanges) to point caudally and thus provide a horizontal 
> flight surface for the hindwing, given the orientations
> of the pes as illustrated. Am I missing something here?

I can't really address the illustrations of others, but in life, the
chordline of the surface is not quite horizontal and the camber makes it
far from flat.  Insofar as I know, Quetz is the only species for which
the skeleton of the foot has actually been assembled in that position,
but it does so with no forcing whatever.


> Would the phalanges or the metatarsal be twisted so that the pes, if largely
> oriented "pads-caudally,"

The pads are not quite caudal, because of the orientation of the tibia
as seen from the side. But to answer your question the phalanges and
metatarsals are not twisted along their long axis.

> to create this surface? The elements largely orient in the direction of the 
> pads in preserved specimens,

I agree.


> so that a spread pedal "fan" or foot as illsutrated would operate in a 
> different, and perhaps occlusionary, plane than the hindwing, if present.

In Quetz, extending the ankles spreads the metatarsals, but not quite so
much as John and Aspidel have illustrated.  The foot as airfoil does
indeed operate in a different plane than the inboard portion of the
hindwing, but that's to be expected both because it has a different aoa
of zero lift and because it doesn't fly at the same local CL.
> 
>   Though I've heard a webbed foot as proposed for the few pes known to be 
> surrounded in skin thanks to excellent preservation in the
> Solnhofen, Chaoyang/Liaoxi, and Fergana Basins, I would wonder if the foot 
> did not operate pads down how they contrubuted to the
> flight surface, whether the metatarsals' preserved "spread" was not actual 
> but preservational, and that the webfoot was rather the
> dessicated skin of a normal, non-membraneous foot. So what does having a 
> broad, fanned, webbed foot

You don't want it to be all that broad -- just broad enough to get the
fineness ratio into a range appropriate to minimize the drag while
providing enough surface to do the job.


> that is oriented largely so that
> the first toe was ventral, the fourth dorsal and slightly aft actually gives 
> the leg when in flight?

I'm not sure what question you are asking.  Please elaborate.

> Mobility of the foot as in
> gulls and boobies appears to operate largely in the same plane as the tail 
> during slow speeds for landing postioning,

Foot mobility in gulls and boobies isn't serving the same purpose as in
pterosaurs, so I'm not sure that I would expect them to operate
similarly in flight.


> and the very
> long digits (longer than the tarsometatarsus) permit the plane to shift in 
> roll directions [okie, so bad terminology, meaning around
> the long axis of the fuselage, or or around a parallel to this long axis]. 
> Pterosaurs do not seem to have a similar pes with long,
> extremely mobile digits, so I am rather curious.

Well, the foot wouldn't need to generate forces that are significant
with respect to the gross weight of the animal.  Only significant with
respect to the weight (and moment of inertia) of the hindlimb.  And to
minimize drag during those transient periods when one would want it to
be minimized.  Most of the time they wouldn't be generating much force
at all, since they would be expected to serve as a trim servo rather
than as a flight surface per se.