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Re: Pterosaur Lift Off (was Pterosaur Bipedal Challenge)



In the pterosaur species that I work on (in short, oversimplified
version and temporarily omitting the usual caveats using words like
seemingly, it appears, probably, and such), the technique is to crouch
quadrupedally and go out at about a 25-35 degree angle to the
horizontal.  First part of the launch is powered by the hindlimbs while
the forelimbs are being loaded into adverse mechanical advantage with
the front feet (hands) on the ground initially well in front of the
shoulders.  As the force curve of the hindlimbs begins to fall off, the
shoulders have moved forward and slightly up, and the forelimbs are
coming out of adverse mechanical advantage and begin to take over the
force production with the animal swinging over the front feet (hands)
sort of like a pole-vaulter on a gradually unfolding pole. The hindlimbs
leave the ground first and immediately start spreading to carry some of
the hindlimb weight in flight (they don't necessarily carry all of it
because you may electively want to create a tail download until you
stabilize, and perhaps thereafter, partly to increase your flight speed
and partly to compensate for the pitching moment of the wing). After the
fore limbs clear, an upstroke is started (pretty much standard from the
wingfinger pivot inboard, but with the wings still folded).  As the
wings come high enough for the tips to clear the ground, the outer wings
are unfolded and a standard flapping motion is begun if required (a
large fraction of the time, no flapping is required). For the species
I've done the numbers for, average acceleration is just a little over 2
g's and maximum skeletal loads are aligned with the maximum skeletal
bracing (which isn't aligned with maximum flight loads).  Unlike a bat,
and perhaps unlike some smaller pterosaurs, a really big pterosaur
doesn't want to go out vertically for a couple of reasons.  First,
because going out semi-horizontally increases the escape velocity
relative to an approaching predator. Even in a dead calm, at the time
their hands leave the ground, Q species an Q northropi have both
achieved a ground speed greater than their stall speed and seemingly
greater than the groundspeed available to any of their likely predators.
In other words, if a predator approaching from the approximate rear
hasn't grabbed them by the time their hands leave the ground, he isn't
going to.  Second, they went out semi-horizontally because they couldn't
go out vertically without falling flat on their tummies at the end of
the leap due to not being able to generate enough power to launch in
that mode.
All the best,
Jim
P.S.  When I said this was the short version of the launch description,
I wasn't kidding.  I've left out almost all of the detail.  For quetz,
the omitted details seem to be internally consistent.  Perhaps some
other pterosaurs used a similar technique too.

MarkSabercat@aol.com wrote:
> 
> At least some families..(bats)..., the technique is to crouch down in a 
> quadrupedal position and spring into the air almost vertically, gaining the  
> time and space to begin
forward flapping motion.