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Re: avian flight



  I can't speak for Jim Cunningham, who's aeronautics and
mathematics specialty is well above mine. These comments are
also an attempt to reduce the 15 odd emails I need to reply to,
but I want to stay in my proscribed optimum limit, so, major
replies.

  David Marjanovic wrote:
 
<... parachuting, where there is no lift.>

  I strongly disagree. Lift is less than drag in a parachuter,
and there is no thrust, thus lift is directly opposed to drag.
The animal drops. Increasing integumentary structures and the
shape of them with increase drag to certain degrees relative to
mass.

<Flying squirrels, AFAIK, glide to a tree trunk hands-first,
grab that tree trunk, pull themselves into an upright position
while folding their patagia, and get rid of the rest of their
kinetic energy by clinging to the tree trunk with their feet.
Have I missed anything here?>

  From direct observation, glissant [gliding] animals such as 
flying squirrels will incline the entire body and _slam_ into a
tree full body. This is how they reduce kinetic energy, which
wouldn't happen if they just held on there, hoping for it to
bleed off, because it wouldn't. Kinetic energy has to be gone by
the time the animal reaches a null-movement state, simply
because the laws of physics say so.

<Birds, on the other hand, glide towards a tree limb, flap
vigorously to reduce their speed to zero or near, and then
stretch out their legs to perch.>

  I can't count the different ways I've seen birds land. On a
branch, take advanced crows (plenty around here to observe) who
decrease their pitch so they they incline the wings to stall
position, and _waft_ to the branch. Just reach out and grab it.
Th kinetic energy is released in the contact, which on a small
branch shakes a whole lot. Other birds (I've abserved generally
smaller birds than crows do this) will fly onto a branch above
stall speed, and use the hallux as a breaking device [I forget
the deviced used on jets landing on seacraft, but this is
directly analogous]. Automatic flexure in the avian foot will
grasp the branch without the bird "needing" it to.

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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