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Re: pteros have lift-off

----- 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.


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)