Re: pteros have lift-off

[jrc <jrccea@bellsouth.net>]

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


> Do your figures take into effect 'ground effect' flying?

Yes.  That's why the numbers I quoted the other day specified 5' HAG.  That 
together with the span and the Biot-Savart rule specify the ground effect 
drag reduction.

> I mapped sequential photos of a pelican taking off (I can send this  via a 
> non DML email). Although the pelican is airborne immediately,  the 
> acceleration over a half dozen frames is easy to measure while  flying in 
> ground effect. Maybe, like pelicans and herons the  availability of ground 
> effect means pterosaurs don't have to reach  cruise speed within a second 
> after take-off?

Pelicans, herons, and pterosaurs don't have to reach cruise speed at any 
time, if they don't want to.  That choice has nothing to do with the 
Biot-Savart law (ground effect drag relationship).  I took the pterosaur to 
cruise speed during the terrestrial part of the launch simply because that 
gives the most extreme terrestrial loading.

> Perhaps a trajectory in  big pteros lower than 30º would be equivalent (i. 
> e. ultimately  ading to flying at cruise speed)?

As I have said over and over again, launch is at about 25 to 35 degrees.  25 
degrees is lower than 30 degrees.  35 degrees is higher.  The animals can 
adjust  the launch angle at will, though larger animals do tend to go out at 
a lower angle.  I suggest that birds of any species are not necessarily a 
particularly close analogy for terrestrial pterosaur launch since they do it 
so differently.

> Looks like: 1) crouch simultaneous with wing unfolding and upbeat. 2) 
> hindlimb extension simultaneous with first downbeat. No surprises. 
> Probably common to most birds.

And mostly irrelevant to pterosaurs.

> So, I'm gathering from the video that a large amount of thrust is 
> generated by the wings along with thrust from the hind limbs. Which 
> seemingly relieves the hindlimbs of a large amount of duty -- which  was a 
> major concern of yours.

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

> And this is incompatible with small and large pterosaurs because...?

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