Hi Simon,

I don't think the issue is how much pressure the outside air pressure can
put upon the outside of the canopy. The issue is that the suction cup is
shaped like a ... well... a cup. It has enough force to pull the canopy to
form to the shape of the inside of the cup. That causes local stresses on
the canopy. It may or may not be a visible deformation.

Paul Remde

"Simon Taylor" wrote in message
...
Hokey science alert:

I'd reason that the most pressure the atmosphere can
exert on the outside of the canopy, even with a true
vacuum in the suction cup, is atmospheric pressure
- about 1kg/cm^2. A fingertip has about 1cm^2 of area,
so to gain a feel for the scale of what we're talking
about, try pressing down on kitchen scales with one
finger until the scale reads 1kg ( 2.2lb / 35oz / 5.47
standard Hungarian apples). Not inconsiderable, but
(I would have thought) not enough to risk damage of
any kind.

To test this theory more thoroughly, you could try
wandering over to a glider on the flight line and exerting
the same pressure with a finger on the canopy. I'd
wager no localised distortions will be inflicted -
at least, not on the canopy.

Simon

PS As a disclaimer: My entire knowledge of physics
is based upon observations I made watching hollywood
movies.

PPS Steven Seagal movies.

At 01:48 12 April 2007, Paul Remde wrote:
Hi Bernie,

I doubt it would crack a canopy. My fear (founded
or unfounded) is that the
localized deformation of the canopy would lead to internal
crazing -
especially in extremely hot or cold conditions.

I just wouldn't want to risk a $2000 to $5000 glider
canopy.

Paul Remde

'Bernie' wrote in message
roups.com...
Has anyone ever seen a canopy cracked by a 'lever-action'
suction
device? You've got me worried now ..........