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Re: Phylogeny of Maniraptora



Graydon wrote:

> Are there any non-volant organisms that really glide, rather than
> parachuting?  Anything among the flying snakes, flying squirrels, draco
> lizards, etc. that can, frex, get energy out of a headwind to land
> higher than they started?

You realize of course, that there is no way to extract energy from a
headwind once you have reached steady state velocity after initial
launch.  On the other hand, it is possible to extract energy from wind
shears at any time.  It is possible to extract energy from a headwind
only immediately following launch and only until the drag from the
headwind brings your body into equilibrium with the wind. That happens
very quickly and is soon over with.
 
> I'm trying to get at a distinction between using aerodynamic forces to
> reduce sink rate (parachuting) and turning velocity into actual lift
> (gliding).

In oversimplification, the distinction is that in parachuting, the drag
vector is greater than the lift vector and the drag vector is oriented
mostly upward (in what is usually taken as the lift direction).  And in
gliding, vice versa and with the drag vector being oriented mostly
horizontally. The distintion is really more whether the drag vector is
primarily parallel to or perpendicular to the chordline.
> 
> I think the whole glide/flap for power thing gets tangled in this;

I don't. I do think that some of the 'explanations' get tangled in it.

> an organism doing attitude control and fall-retarding things *isn't*
> gliding, it's parachuting,

That depends upon whether the drag vector is primarily parallel to or
perpendicular to the chordline while it is doing these 'things'.  Which
is the case for the organism you describe?

> and it'll do whatever it takes to get its
> attitude on impact right, because it has to get it right.

I'll drink to that. Though I've noticed that albatrosses don't always
get it right upon landing and sometimes go fanny over teakettle.

>  You get
> something like flapping from the predatory stroke if you push a basal
> maniraptoran out of a tree; it may not do any good, but that's what its
> arms _do_ when trying to move rapidly, they're not the peculiar
> wide-range-of-motion things people have got.  If it's a maniraptoran, it can 
> flap.  (maybe not *well*, but it can flap.)

That's true.  Just as it can flap while running.  Or while standing
about or jumping up and down.

> The trick is not identifying when lift comes in; 'assisted vertical
> running' makes it clear that there *is* a nice shallow ramp for the
> utility of lift for small maniraptors, one that can't be discounted from 
> fossil evidence even if it never took place in pre-volant species.

Sorry, I miss your point (wee hours on my part, perhaps).  Would you
elaborate please? What is the trick involved?

> Somewhere, though, there's a biomechanical analysis that indicates the
> sustained load bearing capacity of the arms; it's when that passes some
> multiple of body weight that you've got a real flyer.  I'd *expect* that 
> number to be a bit over two, but that particular wild ass guess isn't even 
> sophisticated.

Doesn't that sort of depend upon the duration of the anticipated flight?
How long do you need to be able to maintain the multiple of two before
you are a flyer? Twenty seconds? Twenty days? If it weren't for gusts,
turbulence, turning forces, and safety factors, I'd expect the number to
be about 1.2 to 1.4 (optimum flapping occurs when the CL ranges by a
factor of about plus 0.2 to minus 0.2 (range 0.4) around the optimum
CL.  For an animal with an appreciable aspect ratio, optimum CL is often
about 0.8 to 1.0.  Be aware that this is an extreme oversimplification
on my part and don't hold me to these exact numbers.