Subject: Re: FW: Bird Magic
Date: Jan 10 16:27:29 1998
From: "Rob Conway" - robin_conway at hotmail.com


Tom,

I've often watched gliding birds (gulls, hawks, vultures, ravens etc.)
flying effortlessly into the wind. You're right - some of them do
"tack", but more vertically and horizontally. If you watch these guys
for a long time you'll see that they use the wind to push them "up"
(gain altitude) simply by adjusting their wings. As a matter of physics
this height gives them "potential energy" at a low cost (literally
captured from the wind or thermals, same principle). They then use this
potential energy (height) to move forward by sailing forward and
downward against the wind, using aerodynamics (gliding) rather than
physical force (flying) to move - in "up and down waves". An elegant
solution to a sticky problem. You won't see the little guys doing this
- they still have to pump like mad to move upwind - their wings just
aren't built to keep them in the sky for long periods of time - just to
get them in the air and move them from place to place. You'll see the
little guys do the horizontal tack to minimize the force a head-on wind
gives and to yep, capture some upward motion for free.


<Q) // Icarus was a waxwing;
((``// Too bad his dad wasn't a flycatcher.
||
^^

Rob Conway
Cougar Mountain, Bellevue, WA
47.551N 122.142W

robin_conway at hotmail.com
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

From: "Benedict, Tom" <tbenedict at macgwx.ghc.org>
To: tweeters at u.washington.edu
Subject: FW: Bird Magic
X-Listprocessor-Version: 8.1 beta -- ListProcessor(tm) by CREN

An acquaintance asked me this question today. Can anyone give me a
detailed
explanation of the aerodynamics of birds?

>Out my window I can see whitecaps aplenty, all heading southeast.
There's
>obviously a strong wind (20-30 mph) from the Northwest.

>There's also lots of seagulls. Flying northwest. Without flapping their
>wings! Oh, there's few half-hearted wing-flags once in a while, but
mostly
>they "glide" *against* the wind. I've noticed the same on the ferry. A
>seagull can "ride" a ferry going top speed by gliding alongside or
above it.

>I'm beginning to suspect that just as a plane achieves lift by the
>difference in pressure between the lower and upper surface of the wing,
a
>seagull achieves forward motion by a difference in pressure between the
>front and rear surfaces of its torso. Giving it thrust.

>How else can a bird glide forward against a strong wind?

>Or does the bird perhaps use a "tacking" motion. And never flies
directly
>into the wind?

Thanks,

Tom Benedict
tbenz at halcyon.com





______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com