Re: pteros have lift-off

[jrc <jrccea@bellsouth.net>]

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


> So at a launch angle of 25-35º ground effect is employed for a very  short 
> duration in pterosaurs?

That's not what I said.  Pterosaur climb performance is typically and 
approximately about 100-150 feet/minute (for purposes of this description, 
say 120 fpm or 2 fps). At an airspeed of  roughly 25-35 mph depending upon 
species (say 30 mph or 44 fps), that works out to a climb angle on the loose 
order of  ASin(2/44) = 2.6 degrees, roughly about 10% of the launch angle. 
The 25-35 degrees is just for launch, and only during the last 10% or so of 
the launch.  And, if the animal chooses to launch to an airspeed 
substantially less than cruise, he will likely increase his launch angle and 
then choose to level out and accelerate in ground effect, taking advantage 
of the Biot-Savart relationship until his speed builds up.  But, he doesn't 
have to do that -- it would be a deliberate choice.

> As opposed to airplanes and big birds,  which stay within a downbeat of 
> the ground or water until sufficient  speed is attained.

Again, I did not say that they don't do that.  They can do either, at will.
As an aside, when flying the J3 (O-200 engine, 100 horsepower), I just leave 
the tailwheel on the ground, let the mains lift off first, and immediately 
climb out at about 50 mph without remaining in ground effect. When flying 
the same J3 with an A-65 engine (65 horsepower), I remain in ground effect 
till speed builds to 60 mph, then climb out at 60.  Different strokes for 
different power combinations.

> > Looks like: 1) crouch simultaneous with wing unfolding and upbeat.  2) 
> > hindlimb extension simultaneous with first downbeat.

I didn't notice your 2) comment before.  No to that. Hindlimb extension is 
simultaneous with terrestrial launch, both for initial power pulse, and also 
so the uropatagium can support the weight of the hindlimbs after the pes 
clears the ground.

Back to 1), upbeat begins at the end of the crouch, which ends when the 
manus leaves the ground.  The wingfinger can be unfolded to an interior 
angle of roughly 110 - 114 degrees prior to the manus leaving the ground, 
but doesn't have to do so.  I would expect that amount of terrestrial 
unfolding under two circumstances 1) soft or slippery ground, 2) relatively 
heavy animals.  In both of those cases, the muscles that open the wingfinger 
pivot can be used to power the forward rotation of metacarpal IV while the 
manus is still on the ground thereby providing substantial additonal launch 
power.  Since the trailing edge of the wing membrane is still slack at this 
point, the membrane can be allowed to trail to a low drag configuration 
early in the lift off.  There are a number of ways to skin this cat.

> No  surprises. Probably common to most birds.

Very few birds push off from a solid ground surface with their wings, and 
some retract their hindlimbs after the foot leaves the ground, rather than 
extending them.  I don't think birds are a terribly close analogy for 
pterosaur launch.

> And mostly irrelevant to pterosaurs.

> Maybe not. That's what we're trying to understand here.

I wouldn't say "we".  :-)

> Pterosaurs came from a lineage of hind limb leapers.

That may well be true; I don't know.  Is there a consensus on that yet?

> [JimC comment] Of who's ?  Birds generate as much as roughly 90% of their 
> launch  power with the hindlimbs, depending upon species.

> Mike Habib. As a courtesy, Jim, you were cc'd. Since pterosaurs came  from 
> a lineage of hind limb leapers,

Is there a consensus on that?  Note that I'm not saying that they don't (as 
I've mentioned before, I don't know, and don't have an opinion either way).

> there was a time when  pterosaurs, or their immediate ancestors, ALSO 
> generated as much as  roughly 90% of their launch power with the 
> hindlimbs.

Consensus?

> If that  gradually decreased as evolution changed things, a change in 
> launch  mode, such as you suggest, has to be documentable.

Only if the fossil record is complete enough to allow it.  I don't think the 
fossil record is presently complete enough to demonstrate that, or to 
disprove it.

> What if someone found trackway evidence for a bipedal pterosaur  or  two? 
> Would that change your view?

If anyone were to find bipedal trackways, it would convince me that some 
pterosaurs were bipedal.  So far, I don't think such trackways have been 
found.  Note that all pterosaurs land bipedally, but they are unlikely to 
remain in that mode for more than a couple of  hops and/or stutter steps.

> It's not at all incompatible with pterosaurs -- it just has nothing  much 
> to do with them.

> I think the jury is still out. You present a good case, but it  depends on 
> quadrupedality in all pterosaurs, something that has not  yet been 
> documented. This is pertinent because they came from bipedal  ancestors.

1) It doesn't depend upon quadrupedality in all pterosaurs -- only on the 
ones that are incapable of launching bipedally, which appears to be the vast 
or perhaps, total majority.
2) Is there a consensus on bipedal anscestors?

> Final question: how much angle do you figure at the carpus to create  your 
> Z fold in the forelimb?

It depends upon wind at the time of launch and weight of the animal at the 
time of launch.  The carpal shear mechanism in the wing that I've been 
manipulating disengages at an interior angle of about 80 - 85 degrees, and 
I've been using a minimum interior angle of  about 90 to about  95 degrees 
(carpal shear is near its minimum during launch). It's not particularly 
critical, and the animal can still launch OK even if using considerably 
larger interior angles (less 'Z' bend in the arm and more shear capability 
at the wrist)
JimC