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Jaime A. Headden wrote:
> and Colin McHenry (cmchenry@westserv.net.au) wrote:
> <Any structure can provide lift under certain circumstances. I can make a
> brick fly if I propel it fast enough at the right angle of attack.  A
> facetious point, but worth remembering.>
>   Lift in any tossed object is one thing, throwing something, including
> oneself, with effects designed to catch air rather than those that do so 
> accidentally, such as a brick, are another.

That isn't what he was referring to.  He can indeed get a brick to
generate respectable lift if he stabilizes it in an appropriate

> I guarantee that I could make it fly (by shooting it out
> of a cannon, for example

That isn't the process he was referring to.  As an aside, I personally
have no opinion about whether Longisquama could fly -- haven't been
interested enough give it the thought I expect it deserves.  On the
other hand, Sharovipteryx could fly, and durned well, too.

> a better question would be whether it could 'fly' - either by powered
> flight, or by gliding/parachuting from an elevated surface - in a way that
> might have been realistic biologically (not to mention non-fatal).

He was actually referring to mechanisms that generate lift, not saying
that a brick could do so at a speed such that it wouldn't injure itself
upon landing.

>   I have proposed, to my credit perhaps, that models be tested on the
> aerodynamics of a structure and system as is found in *Longisquama*'s
> holotype.

I don't know which of you said that, but it is a good idea in my

> The problem here is a radiating, non-overlapping set of vanes
> with little assymmetry and distal inflection that correspond to no known
> flight structure. This does not mean they couldn't fly, but that
> conventional theory doesn't hold for them,

Oh, conventional theory would hold for them.  Aeronautical and
structural theory, as opposed to paleo theory.

> and any true testing should be mechanical and practical in nature.

I'd agree with that.

> However, I was trying to say that the
> basic design is flawed in that more than their structure, they are not
> anatomically sound, and the idea of them as flattened, venate
> "parafeathers" requires data we do not have.

I have a hunch that if they were flight surfaces, the 'vein' layout
pattern would loosely resemble that in dragonfly wings.  Do they?

> <<Studies in flying snakes show that the skin flabs allone (integument) do
> virtually nothing but impose drag on the snake,>>

What about the counter-rotating longitudinal vortices above the snake?

> I mean, just because it's called a flying snake, surely
> no-one was seriously suggesting that it moved through the air by
> lift-based powered flight?>

Sounds reasonable to me.  Gravity powered, lift based flight.  In an
updraft equal to its sinkrate, it could even maintain level flight. 
Granted, that'd be a pretty healthy updraft.

>   It's not drag that makes something fly, in the sense of a bird anyway,
> but the powering of the structure that produces drag to increase the
> resistence by forcing it down and backward, thereby impelling the
> structure, increase presure, and exceed thje pull of gravity and create
> positive upward/forward movement, rather than reducing rate of falling.

We in the paleo world often have a profoundly different understanding of
how fluid drag and resistance work than do those who deal more often
with fluid mechanics.  I must admit some prejudice in favor of the
opinions of the latter, though they tend to be profoundly lacking in
anatomical knowledge.

> All a flying snake ...... Snakes
> also "throw" themselves brick-like from trees

Not at all brick-like.  They generate the same type lift forces as a
dirigible, using the same mechanisms (excluding that portion of the lift
due to hydrogen, helium, or hot air).

> *Longisquama* has several different sized, largest in the middle or
> rear-trunk, slats that radiate rather than forming a single membrane; in
> thisd they resemble the birds primaries, yet these act differently
> aerodynamically from a membrane since they are designed to allow air to
> flow through them.

That doesn't mean that they act differently from a membrane in all
aerodynamic regards.

> <Now, I can't resist observing at this point that feathers are excellent
> structures for producing drag, and lots of it :-)...>

Yes, and they are also excellent structures for minimizing drag, and
lots of it........
>   Yes, but feathers do more than generate drag, they have an assymetry in
> the outer tail and wings that are designed to produce pressure variants
> above and below, and work in a flapping motion by twisting during the flap
> so as to produce minimal drag on the upstroke, maximum drag and maximum
> pressure on the downstroke.

These are not the entire functions of the asymmetry.

> I beleive only soaring birds use their wings
> as more of a gliding mechanism due to absence of a regular flapping
> because they move from thermal to thermal, as does a human glider.

Actually, most human gliders are not capable of moving from thermal to
thermal.  Many human pilots, encapsulated in an appropriate flying
machine, can.  Although unencumbered human gliders can achieve a fairly
respectable glide ratio, the associated sink rate is quite substantial,
and the 180 mph landing is prone to be awkward...