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Re: pterosaur take-off analog



Good news about the hang gliders. Just goes to show it doesn't take much ground 
speed when everything else is right.

Back to pteros:
Knowing that the sharks came in from hundreds of miles away to feast during the 
two-week period of albatross fledglings going for their little swim before 
flying, let's give them credit for good timing. 

Similarly knowing that pterosaurs were successful over 100 million years, but 
did get eaten occasionally, can we also give them credit for hypothetical good 
timing and: 

1. Knowing when and where to land
2. Knowing to land in trees tops when the ground was "busy"
3. Knowing to land on deserted islands or flotsam when trees weren't around. 
4. Knowing when the breezy parts of the day occurred to land and take-off. 
5. Landing somewhere with a ten-foot drop off nearby (probably a traditional 
site)
6. Climbing up a nearby tree or vertical surface to launch (not exactly like 
WAIR, but maybe)
7. Or simply launching in some sort of springy fashion if all else failed.

While the recent animation on pterosaur arm launches is an interesting look at 
engineering and dynamics, it depends on a worst-case scenario of a flat surface 
and no breeze. Given any other scenario, other solutions may be more tenable 
given the lesson of the fledglings. There's still the problem of no clear 
metacarpal IV impressions, only digits I-III. So there may not be a lock and 
recoil mechanism. And the problem of what to do with that giant wing finger 
rotating straight down at the moment of launch is still vexing. 

Best regards,
David

---- Erik Boehm <erikboehm07@yahoo.com> wrote: 
> Of course take offs into the wind are easier.

But what would these animals have done when on the ground, in no wind, when a 
predator approaches?
If they needed wind to takeoff, they would be lunch far too often, particularly 
since there would probably be a strong correlation between lulls in wind, and 
when they would be on the ground.
Unless these pteros would just constantly flap to stay off the ground in light 
winds, knowing once they landed they couldn't take off again until the wind 
picked up.

If the wind is blowing above their stall speed, they need only spread their 
wings, its very simple - hardly worth study in my opinion.

If they were feeling particularly "lazy" and the wind was strong enough - they 
could probably lie on their stomachs, and just lift their wings up (making a 
shallow " V " like silhouette when viewed head on)

You see effortless launches into the wind in hanggliders:
(warning, 1 &3 set to bad music, but they only last a few seconds)
http://video.google.ca/videoplay?docid=6344681486819194061#
http://video.google.ca/videoplay?docid=958254119070263198#
http://video.google.ca/videoplay?docid=9211273983270502855#

Hanggliders have 30-40 foot wingspans, aspect ratios of 5.5-12, weights 
(including pilot) from 100-200 kilograms, wing loadings of 1-3 lbs/square 
foot), very comparable to some of the large pteros (at least some of the HG 
variants- the early ones from the 70's and 80's, or the gliders for beginners, 
have much lower aspect ratios and would compare very unfavorably in terms glide 
ratio).

So a large ptero with much greater control over its wings would surely have 
very little trouble taking off with wind like in those videos.

But in general, to be a viable animal, they would need to be able to takeoff 
when lacking that wind, or live in an area with extremely consistent winds, or 
only land on islands free of predators.
(Im sure albatross, given their extremely long flights while dynamic soaring, 
have both very consistent wind, and safe places to land)

--- On Mon, 10/5/09, jrc <jrccea@bellsouth.net> wrote:

> From: jrc <jrccea@bellsouth.net>
> Subject: Re: pterosaur take-off analog
> To: davidrpeters@charter.net
> Cc: dinosaur@usc.edu
> Date: Monday, October 5, 2009, 6:32 AM
> 
> ----- Original Message ----- From: "David Peters" <davidrpeters@charter.net>
> To: "Mike Habib" <mhabib5@jhmi.edu>
> Cc: "dinosaur mailing list" <dinosaur@usc.edu>
> Sent: Monday, October 05, 2009 6:40 AM
> Subject: pterosaur take-off analog
> 
> 
> > Pterosaur wings were like those of sailplanes (when
> properly reconstructed). Maybe calculations involving
> take-offs should be modified to reflect different wind
> conditions.
> 
> Paul McCready and John McMasters were doing that as early
> as 1983 .... :-)
> Both Mike and I have done it for the quad launch as
> well.. I looked at it for the quad launch as early as
> February 1999, over 10 years ago, and for other launch modes
> a couple of years earlier than that.
> JimC 
> 
> 



> 

--
David Peters
davidrpeters@charter.net