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Re: vaulting pterosaur launch, questions



Comments inserted
JimC

----- Original Message ----- From: "Erik Boehm" <erikboehm07@yahoo.com>
To: "Tim Williams" <twilliams_alpha@hotmail.com>; <mhabib5@jhmi.edu>
Cc: <dinosaur@usc.edu>
Sent: Monday, June 16, 2008 1:46 AM
Subject: Re: vaulting pterosaur launch, questions



I would be very interested in knowing what sort of environment pterosaurs and archaeopteryx's ancestors evolved in.

As would we all.... :-)

I don't know how the later ones started flying (birds today will both do a running takeoff, or just leap into the air), but I highly doubt the first ones to begin to fly just leapt into the air.

It seems to me to be an easier mode than running, but the two are not mutually exclusive.


Going away from paleontology, and into aviation:
Birds always take off into the wind,

Like pilots, usually, but not always. Other constraints can override the desire to takeoff into the wind. As an aviation-related example, when taking off from and landing on the sandbars on the Mississippi and White Rivers, you usually have to do it downriver no matter the direction of the wind, due to the saw-tooth shape of the ripples and dunes (they will take your landing gear off if you hit them going upstream, while you jump them like jumping off a ski jump when going downstream)


a 9 mph wind would be enough to make up the difference between the 2 m/s running speed, and 6 m/s stall speed.

Only until the wind decelerates the animal so that it's 'rest' speed matched that of the wind. Steady wind can help with launch, but not with sustained flight. Orographic lift would do more good in the long run.


It can also make up the difference between a 2 m/s leaping speed and a 6 m/s stall speed (diminishing as the animal decelerates due to drag).

The local weather and terrain can dramatically effect how easy it is to fly. Perhaps this Tree vs Ground debate is overestimating the requirements for flight, and ignoring the situations where I personally find it to be easiest to fly.

Trees and ground are not mutually exclusive. Neither are convective and orographic lift processes.


Certainly, windy coastal dunes or cliffs would allow very easy flight without the need to run anywhere near flying speed, or flap.

There also has to be a purpose for the flight, and though shear can provide energy for flight, it can also make control more difficult (I can takeoff and land a Piper J3 in direct crosswinds gusting to more than 30 knots, but I sure don't enjoy it or search out the experience.


It is at coastal dunes that humans were first able to reliable practice flight- first at Kitty Hawk with the Wright brothers, and then southern california beaches with hang-gliding.

But, they were deliberately lookng for orographic lift. Birds can can and could do that as well, but it is not a requirement.


Early hang-gliders had horrendous glide ratios (like 4:1), and pretty bad sink rates- but could still soar coastal dunes with sufficient wind. If I recall, that was about the estimated glide ratio of Microraptor (which occurs after Archaeopteryx, so I'm assuming the Dromeosaur linage is secondarily flightless).

It's also about the same as the glide ratio for Archaeopteryx with non-cascaded tail. If the tail could cascade, Archie's gliding performance would improve substantially, but an ability to cascade the tail has never been studied or demonstrated.


I don't know how bats evolved, and the numerous arboreal gliding animals do seem to strongly hint that perhaps an arboreal origin is likely. How would an animal transition from gliding flight between trees, to powered flight?

One way could be by intermittent flapping, initially for control.

I wonder if there were any forests that went right up to the beach with coastal cliffs/dunes when and where pterosaurs/bats/birds evolved.

Most likely were.

Such an arboreal glider should be able to fly in the ridge lift, and could then perhaps develop further flight adaptations.

That's true, as are a number of other scenarios.

I learned to fly hanggliders at coastal dunes, flying there is super easy - I can run nowhere near fast enough to get off the ground with my glider, doesn't stop me from flying.

That's true of leaping as well. And leaping doesn't require flapping as a precursor either.


All the best,
JimC