Tomas,
What you have written so far seems to takes no account
of the structural risk to the wing of a sealed partially
air-filled tank inside the wing when flying in the
lower external pressures at altitiude. It only takes
a small differential positive pressure within the wing
per unit area to have a very large effect over the
whole area of a tank and thus on the length of the
spar to skin bond. It is this, not thermal expansion,
that is the risk. Your assertion the freezer bag plastic
will 'blow out' is a totally untested suggestion with
regard to flying at altitude and, unless there is another
vent in the tank, or firm experimental evidence that
it will reliably give way well below the critical
differential pressure, your modification is very unwise.
John Galloway
At 14:30 24 May 2005, Tomas wrote:
One of the great things about the freezer bag mod is
that there is
enough resistance to hold water in a slowly lowered
wing, but not enough
to stop the force of any signifigant pressure. I have
found that if I
lower the wing too rapidly, I get a 'blow out' of the
plastic diaphram.
I am now in my third year using this method and it
works great. I think
the supposition that this 1mil sheet of plastic is
going to create
enough resistance to split the wing is unrealistic.
I made several blow out and reset tests.
Gary Emerson wrote:
Hopefully thermal expansion will not become an issue....splitting
a wing
open because it warmed up in the sun could ruin your
day.... Your
'check valve' has the potential to allow such a situation...
Paul M. Cordell wrote:
I am always amazed at how few Schempp-Hirth Glider
owners have done
this very simple Mod to their water ballast system.
The addition of
this 1 way valve to the top cap of the ballast tank
plug will
prevent water from flowing out of the tank prior to
launch. You can
put a wing down without water flowing out of the vent.
The vent
will still function properly during the dumping process.
It�s a simple project using a screw driver, scissors
and a plastic
freezer bag. Unscrew the top cap from the rest
of the plug
mechanism. Cut a disc out of the freezer bag slightly
smaller in
diameter than the cap. Punch a hole in the center
of the freezer bag
disc of sufficient size for the screw mechanism
to reattach.
Reassemble and you are done.
http://www.gliderforum.com/photos/sh...bumid=5¤
tpos=32
http://www.gliderforum.com/photos/sh...bumid=5¤
tpos=34
http://www.gliderforum.com/photos/sh...bumid=5¤
tpos=35
I have to give credit to Jackie Payne for this mod.