On Tue, 19 Aug 2003 07:17:43 -0700, "TIM WARD" wrote:


"Martin Gregorie" wrote in message
.. .
On Mon, 18 Aug 2003 10:53:46 -0700, Eric Greenwell
wrote:
snippage
Rising air comes from beneath the wing, and increases the AOA.

Kindly draw the vector diagram before continuing. You'll see that the
sinking speed velocity vector points down and the rising air vector
points up. Simple vector addition says that the rising air velocity is
subtracted from the sinking speed because their directions are
opposite.

Martin, you are using the wrong frame of reference. The "sinking speed
velocity" you are using is relative to the ground. Relative to the glider,
the air it is sinking through is rising past it. As the glider flies into
"lift" (relative to the ground) the vertical velocity of the air rising past
it is _increased_ by the velocity of the lift. So the AOA is increased
momentarily.


I'm using the air mass as the reference frame - hence my reference to
a change of reference frame as the glider moves from neutral air into
rising air. If I was using the ground or the glider as reference frame
I would not have mentioned a change of reference frame.

The air mass is the usual one for discussions of stable flight - as in
the periodic circling in a wind discussion.


--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :