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

Re: pterosaurs, bats, flying theropods



Jim Cunningham () wrote:

<If I remember correctly, the Peregrine falcon is the fastest of all
birds.  What is the shape of its tail?>

  The fastest birds in the world, including falcons and swifts, all have
tapered tails that are longer than broad, even distally, and have a V-cut
in the trailing edge; this is also true for several hummingbirds.

<What about Frigate birds?>

  Frigate birds also have wing and tail designs for high-speed flight.
They appear to be secondarily adapting to distance soaring, but their wing
design and habits still preclude, I think, a distinct evolution to soaring
as in their relatives, but instead towards aerialism and flaying above the
surface of the water or short plunge-diving stints.

I had written:

<<The mechanic to soaring is in the wing proportions, which minimizes wing
effort with loading,>>

and Jim asked me:

<Would you translate this for me please?>

  I was trying to say that during wingloading, the shape and length of the
wing minimizes effort to keep flight stable, so that flapping is reduced.
This is enhanced by the feathers taking on the wing shape no matter the
stroke position, meaning that bird does not have to "try" to keep the wing
fixed during soaring flight. I may be mout on a limb here.... 

<The largest bird in the world that flies by means of continous flapping
is a male Whooper swan called 'JAP'.  He is far larger than a goose and
each year migrates between Iceland and Scotland (sometimes Ireland).  As
an aside, about ten years ago, during a gale on the North Atlantic, 'JAP'
made one of the most extraordinary emergency flights I've ever heard
about.  Geese also fly by means of continuous flapping and flap at a
faster rate than 'JAP'.  When did geese become soarers?>

  I had seen geese soar locally, but just the other day a few flocks with
costant flapping made me revise my opinion on this. I take my statement
back.

<Odd.  That's usually taken as one of the definitions of soaring.  Riding
orographic lift and wave shear are a couple of the other energy extraction
mechanisms used for soaring.>

  This may be true for human flyers. Riding thermals is performed by many
birds. For birds with anatomical adaptation to soaring, as I tried to list
in the previous post, thermals are only an aid and should not be the
definition to avian soaring. Rather, a mechanical fixed-wing design with
the wing design itself should be, and many of the human-powered,
one-seated gliders I have seen have used the design of the fixed,
narrow-chorded wing.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

__________________________________________________
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
http://mailplus.yahoo.com