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Re: chriropteran upstrokes and flight take-offs



StephanPickering@cs.com wrote:
> 
> Darren's question re: take-off (which
> is related to the biomechanics of locomotion, unless I am mistaken)

It is.

> A nonbipedal bat on the ground would...jump up rather than
> begin flapping wings, or would the launch be in tandem, i.e., with a
> few seconds of jumping up, additional lift would be provided by
> flapping?

For bats, a fraction of a second of jumping up, followed by a forelimb
upstroke, then standard flapping.  For pterosaurs (probably the small
ones too, but I've been excluding them in  discussion because I've
concentrated on Qsp and Qn), the leap is more forward than up, with just
enough upward component to allow adequate ground clearance for the first
downstroke should it be needed. In pterosaurs, often it wouldn't be
needed depending upon available atmospheric lift and/or the animal's
intent. Qsp can launch and glide horizontally 150-175 feet in calm air
without ever bothering to flap, and in rising air might not have to flap
at all.  Flapping, if it occurs will tend to occur in short bursts of 2
to 20 anaerobically powered wingbeats followed by soaring (these animals
operated as motor gliders, with intermittent, occasional flapping,
usually one or two beats at a time followed by a period of soaring). 
The same is true for Qn, with a somewhat longer initial non-flapping
glide available to the animal.  Launch becomes much more difficult with
increasing mass, and is the maximum size limiter for pterosaurs as in
birds. Birds may have an additional max size limiter in the probable
upper limits for feather length.  I speculate that maximum bird wingspan
is on the very loose order of 27 feet, and maximum pterosaur wingspan is
on the very loose order of 43 feet.  Pterosaurs tend to be more
span-loaded than birds, and span-loading allows an increase in wingspan
because of the consequent reduction in spar stresses.

> Perhaps the reasons small, ground-foraging bats jump up is
> related to why larger bats do not spend much time (that I am aware of)
> on the ground: energy costs of launching related to larger body size.
> SP