[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: vaulting pterosaur launch, questions

----- Original Message ----- From: "Erik Boehm" <erikboehm07@yahoo.com>
To: <jrccea@bellsouth.net>
Cc: <DINOSAUR@usc.edu>
Sent: Monday, June 16, 2008 12:21 PM
Subject: Re: vaulting pterosaur launch, questions

I think the physical requirements for a standing/leaping launch are greater than a running launch.

What is your evidence?

(ok, birds don't ALWAYS do it, but I'd say 99% of the time any appreciable wind is present)

Given a bit lower percentage, I'd agree. :-)

I question the applicability of this example, due to the large differences in scale, weight/wing loading, airspeed, and landing aparatus (feet vs wheels).

My actual point was that it is a pilot's choice, whether the pilot be a bird, or a human. A bird's downwind takeoff might be due to the desire to escape from a predator, for example.

I can gaurantee the preferable landing direction in an HG would be into the wind - even in no wind, properly executed technique results in 0 ground speed when your feet touch the ground.

This presumes the ability to generate vortex lift.

> 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.
But archeaoptyrx could sustain flight, the problem was getting airborne and the trouble it would have flapping its wings on the ground, right? a running start into a head wind could be sufficient to get airborne to allow for weak flapping to do the rest.

Since leaping would be an easier way to reach a cruise speed where the poorly developed supracoracoideus would not be a major factor in flapping, it is likely that leaping would require less total energy and achieve the desired goal in less time.

True, but I think any animal that does a leaping takeoff from the ground, is already adapted for flight, I have a hard time beleiving it is the basal launch technique

What's your evidence? :-)

I'm not talking shear here (30 knots consistent straight in is at my limit, if not just above it), but smooth laminar flow over elevated coastal terrain.

How do I get that in the Mississippi delta? I'm from 600+ miles upstream of the mouth, and only 140 feet above sea level. Here (with the exception of Crowley's Ridge), we use either shear or convective flow to extract energy from the atmosphere. We don't have much smooth laminar flow over elevated coastal terrain here.
More seriously, it seems to me that you are hypothesizing that all vertebrate flight originated on a seacoast. That's possible, but I've not seen any evidence to support it over other viable alternatives.

At Marina beach, I can cruise for dozens of miles along the ridge exerting almost no energy, the dunes are only a 100' climb to relaunch should I find myself landing on the beach for whatever reason- I often spot miscilaneous washed up dead things on the beach.
Like seabirds today, the seashore has a lot to offer, and the ability to traverse it with little energy expenditure does have a lot of value

It does. We can do that here along the west face of Crowley's Ridge, except for the coastal stuff.

Coastal lift is the most consistent lift I know of, and presents in my view the lowest barrier to controlled flight. This doesn't mean thats how it happened, but I wouldn't be surprized if controlled flight arose from pterosaurs or therepods living near the beach, or consistent wind.

I wouldn't be surprised at that either, but then nor would I be surprised if flight arose in other locations. Easy doesn't equate to "that's how it happened".

I should note there are ridges in the Utah desert that also have very reliable and consistent wind for ridge soaring - of course I see such an environment as less likely to host the first flying animals because of the much lower availability of any food source.

Water too. On the other hand, such harsh conditions might give a vertebrate just the drive needed to force evolution toward a mechanism that allowed high speed, long distance travel. Let's keep the lid on our box open so we can look outside it.

However, as with the Wright brothers, you can't very well have powered flight until you can have controlled flight.

Actually, you can, but it leads to a lot of kersplats. What it would more likely lead to, is very stable flight modes in the earlier forms of flying vertebrates. Long tails, etc.

The transition form has to be viable, and I think a coastal soaring unpowered flight form is viable.
At least more viable than something clumsily flapping to extend its glide between trees.

It is viable; just not exclusive. Personally, I think flight origins were probably neither trees down nor ground up, but rather a mixture of making use of all energy sources available.

Among human foot launched flight, a lot of the time all you need to do is walk to the edge of a coastal dune with a neutral/negative angle of attack, and then increase angle of attack at the edge, and away you go- no leaping or running required at all. It should get even easier as it is scaled down.

That's true. What technique would you use for foot launching here? (it's so flat that we give names to the tallest cotton rows.... :-)

A an early bird or pterosaur need not neccesarily run or leap at at all, just waddle up to the edge and unfold its wings

And I'm sure that they would, given the nearby presence of one. I can visualize an early pterosaur waddling (actually, they were quite effectively mobile on the ground and didn't need to waddle) a couple of hundred miles to the nearest cliff so he/she could launch away from that predator that was chasing him. I don't think they could generally afford to take that hit in performance and expect to survive as a species.

All the best,