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Re: pterosaur take-off analog



> Only very special gust
> scenarios will launch mid-size pterosaurs, and it is almost
> impossible to launch a large one by gusts alone 

I just want to be clear about terminology:
By a "Gust scenario", do you simply mean "strong winds"
Or do you mean "A rapid change in wind velocity", which is how I interpret 
"gusts"

> (easy to
> lift it off the substrate very briefly, but that's not
> sustainable).

Well, does it need to be sustainable? Say the ptero is sitting on the ground, 
in a wind 5+mph over its stall speed, it spreads its wings, and lifts up (and 
backwards), within a second or two, its at its highest point above the ground, 
and with no further action, it will lose altitude and land back on the ground 
behind where it lifted off.
This assumes level ground, even a slight slope could produce enough ridge lift 
to keep it in the air.
All it needs to do is start flapping before it starts to settle back down.

So then the only question is how much height does it need to get in an 
effective "flap", and what wind velocity is needed to get the ptero to that 
height, assuming when it spreads its wings it adopts the optimum AoA?


> Because mid to
> large pterodactyloids could not biped launch effectively
> without special conditions, it is very, very unlikely that
> they were biped launchers - if they were, we would expect
> them to be able to manage it without gusts, even though they
> might use them when possible.  And, in fact,
> gust-assisted biped launches are still not feasible for most
> species.  Gusts do help the quad launch, however.

I think with sufficient wind, biped vs quad becomes a non issue, as the animal 
won't need to "locomote" in any fashion along the ground, just spread its wings 
and flap, this of course assumes it can get its wings high enough above the 
ground that the air isn't slowed too much due to the boundry layer/wind 
gradient.


By the way, what sort of power output do you calculate a large pterosaur needed 
to sustain flight?

A typical hangglider needs about 5 hp to maintain level flight.
However, I would assume the pterosaurs wing flapping is much more efficient 
than a relatively small diameter propellor (which moves a small volume of air 
fast, rather than a large volume slow).
I could easily see a ptero being 2x as efficient as a micro-light prop.
And even the huge pteros I think were in general lighter than a typical 
human+glider+ motor combination, and probably had better sink rates.
So my first guess at how much a Quetz would need to maintain level flight in 
still air:
1.5-2 horse power or 1,200-1,500 watts if you prefer (perhaps as low as only 1 
hp, or ~750 watts).

Given that most humans have a peak horsepower output of over 1 hp, and cyclists 
such as Lance Armstrong can sustain an output over 1 hp for pretty long periods 
of time (and that the peak horsepower output of a horse is in fact far greater 
than one horsepower), I think this guess is in the ballpark- as I'd think a 
large ptero could put out at least 2 hp for at least a minute or two.
But this does seem rather high for a creature that only weighed as much as an 
adult male human, so I'd also guess they didn't like flapping much, and like 
hawks, probably sat on an elevated point when there was insufficient lift to 
maintain unpowered flight.