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Re:Pterosaur wing -Part 2 - cont'd.
Chris Bennett wrote:
> I will keep your desire for active adduction in mind as I examine
> interphalangeal joints in the future.
It isn't exactly a desire. The need is there. The articulations appear
to be there. So I think the question of power source should be
addressed. Was there one? Showing that there was not a power source
would be as important a finding as finding one. Did that come out in
> What are the horizontal and vertical components of the load on the IP joints
> in flight?
It varies considerably, and the ratios vary considerably.
> I would think that the vertical component from lift and down
> flap would considerably exceed the horizontal component from tension in the
Near the tips, it tends to be the opposite (or would if the membrane
were isotonic). I believe both you and I think the actinofibril layout
keeps the membrane from being isotonic and causes a good bit of the
spanwise membrane tension to get shifted inboard to some extent before
it enters the the skeletal spar as compression, but even so, the
outboard end of the wings is lightly loaded in lift (and down flap)
while the spanwise loads are substantial even with some actinofibril
shifting. If it were not for the actinofibrils, the spanwise load would
be sufficient to fail the outer phalanges in compression. Azhdarchid
pterosaur wings tend to have an area of maximum rate of vertical bend at
about 45% of semi-span. If the wings were triangular, you would expect
that to be at about 42%, but either flapping or outboard roach will
create a need to move the region outboard. If (for purposes of
visualization only) you place the shoulder and the tip level
(horizontal) and stretch a level string between them so that you can
place a ruler perpendicular to it and measure the amount of that cupping
at the high point (at about 45% of semi-span), then the spanwise
tension will be approximately inversely proportional to the amount of
cupping, as in a catenary or an upside down suspension bridge. Halve
the cupping, and you double the spanwise tension and vice-versa. So
cupping by any mechanism can be rather important for limiting spanwise
> but I suppose it is possible the that might not be the case as
> some of the vertical load on the patagium should be converted to horizontal
> load on the wingfinger.
Almost all of the vertical load on the patagium gets converted to
horizontal loads, both in the wingfinger and in the patagium itself. The
membrane carries all loads on paths essentially parallel to its local
> My knee jerk explanation for the shape difference
> between IP joints 1 and 2 on the one hand and IP joint 3 on the other is
> streamlining. What would be the aerodynamic effect of a circular IP joint
> with diameter equal to the greater diameter of the oval 1st and 2nd IP
> joints? Turbulence and flow disruption?
The 2-D effect would be an increase in drag by something on the loose
order of tenfold. The 3-D effect (far more important) would be to shed
a second longitudinal vortex similar to the tip vortex, but very
slightly inboard. The net effect would be to reduce the span efficiency
and reduce the soaring performance somewhat. Which triggers a question
that may or may not be related. Somewhere, I've seen a paper which
describes 'blunting' structures near the wingtips of some pterosaurs,
perhaps keratinous. If these structures exist, they might be capable of
redistributing and limiting some of the tensile stresses near the tip.
I can't find my copy of the paper and don't remember who wrote it or
what journal it was in. It included some photographs. Are you familiar
with the paper and if so, can you send me the reference?
> > > > Why would the muscles not have made the same adjustment that the
> > > > articulations did?
> > >
> > > I assume they did, just following along with the rotation.
No need to follow the rotation -- the phalanges and IP joints distorted
so that they couldn't flex fore and aft. What if they didn't quite
follow the rotation? Note that I'm not saying they didn't -- I'm asking
a 'what if' question.
> > > I do not see any rotation of the phalangeal relative to the metacarpal.
Then you see the changes as an increase in the 'depth' of the phalanges
(fore & aft) relative to the 'breadth' (up & down)? The net effect
being that they lose the ability to flex in the normal direction (fore &
aft) and become thinner and more flexible transversely, that is up &
down, but retaining an upward limit so that they can't flex upward past
> > It is rotation of the metacarpal rotation the entire finger.
With a change in the cross sectional shapes of the finger.
> > Do you agree that the IP joints morphed so that they became broader and
> > fixed in the fore-aft direction while becoming narrower in the up-down
> > direction? I may not have phrased it well, but it is a sincere
> > question, not facetious.
Oops. I typed my response and question above before I saw this
> > However, I'm open to input. The joint is relatively far more robust
> > both vertically and horizontally than the more proximal joints, to an
> > extent that there must be a reason or reasons. What might some of those
> > reasons be?
> No need to streamline?
Sure. But it was still relatively streamlined, particularly if the
'blunting' structure existed. I don't have much of an opinion on the
blunting yet -- till I relocate and reread that durned paper.
That said, pterosaur wings (like all animal wings) were a marvel of
compromise serving multiple functions, not all of which were aerodynamic
and not all of which were compatible. They had lumps here and there.
> Good that you agree that I was right that it could contribute even though I
> acknowledge that a contribution to a solution is not necessarily the entire
As do I Chris. :-)
> Well you keep working on it while I look for evidence for or against active
> adduction in IP joints.
That sounds like a plan to me. Thanks.