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


Tim Williams wrote:

> But surely the fact that there is a non-continuous lift surface across the
> body (as a result of the substantial gap between the distal wing and torso)
> means a *lower* lift-to-drag ratio.

Please explain why?  And note that I didn't say it wouldn't be lower, I said it
wouldn't take a substantial hit.

>  I have modern patagial gliders (flying
> squirrels, colugo, etc) in mind when suggesting this.

My ignorance is showing here -- do any of these have a substantial gap between
the distal wing and torso similar to the one suggested in this thread?  As an
aside, I have doubts that archaeopteryx had such a gap, but don't consider it to
be a 'go-no go' in terms of flight capability.

>  > and the high wing loading would also make the animal
>  > glide at a relatively high airspeed, which would increase the
>  > territory covered per unit time, which I take as an advantage.
> But for improved maneuverability to be the major selective advantage behind
> the development of the primordial wing, a *slower* airspeed would be better,
> wouldn't it?  The aim is not so much to travel a long distance but to land
> with greater precision - i.e. for the theropod to land upright on top of the
> prey, rather than to land on its fanny with the intended prey laughing its
> little head off.

The higher airspeed doesn't increase the gliding range -- it just reduces the
time required to get there, which increases the territory covered per unit time
-- not quite the same thing as increased gliding range.   Why would a slower
airspeed be better?    A slower airspeed doesn't seem to me to be compatible
with the developing wing because of the probably higher wing loading in the
developing wing.   And why would the theropod want to land upright on its prey?
I'd expect it to want to make contact feet first.  One way to accomplish this
would be to use the wings to rotate the feet forward just prior to impact.  Note
that I use the word 'impact' rather than 'land'.  When landing, I'd expect the
animal to use active vortex shedding with momentum reversal in a manner similar
to the 'fast-start' mechanism in fish, rather than a steady-state gliding
configuration with its inherent limitations in CL max.    Wouldn't you?

> In other words, for both lift *and* maneuverability to be selected for,
> wouldn't you expect to see (1) feathers along the inner wing to meet the
> torso (to provide a continuous lift surface across the body, a la modern
> gliders); and (2) feathers along the outer wing (the wing-tip) to provide
> maximal leverage against the air (to provide optimal orientational
> stability).

No, I wouldn't particularly expect to see those features selected for in early
avian flight.  If I'm not misinterpreting you, they seem to make presumptions
that flight developed through a gliding stage rather than through active
flapping., and they seem to make the presumption that increasing stability is an
advantage, when all flying animals seem to develop toward decreasing stability
as their brains evolve to handle the requirements of flight.   Even current
aircraft design is trending toward decreasing stability as computers become more
capable.  They also appear incorporate the assumption that the production of
flight forces is similar to the production of forces by rowing, and that is not
at all the case.

All the best,