Schempp-Hirth water Ballast Cap vent Mod

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...&currentpos=32

http://www.gliderforum.com/photos/sh...&currentpos=34

http://www.gliderforum.com/photos/sh...&currentpos=35

I have to give credit to Jackie Payne for this mod.

"Gary Emerson" wrote in message
m...
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...

I agree,
A solution would be a valve that positively closes as well as opens.
The mentioned flap type valve will stick and any pressure build up
will put undue stress on the tank.
In the case of vents being at the wing tips, a rolling type ball valve will
do the job. The ball is stainless steel and it will roll into position when
the wing is down, when horizontal the ball will unseat and roll back.
I made at prototype valve for my last project and I was only able to fly
with it once before I sold the glider. There was a minimal acceptable leak
when the wing was down. When the wing was horizontal I was able to see the
ball clear the seat. ( I used a clear housing to observe)
Regards
Udo

On Mon, 23 May 2005 22:26:11 GMT, 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...

This is very likely to happen. I once heard a report of a pilot (iirc
Helmut Grix) who had plugged his water drains before he went up in a
wave. The over-pressure of the air in his waterbags broke his wing
shells in the thinner air - he needed completely new wings afterwards.


Bye
Andreas

There is a great difference between thermal expansion of water
splitting the wing and trapped air (at altitude) splitting the wing,
this could happen regardless of the amount of water (air is the
significant factor). The amount of water that could heat and cause a
problem would be dependent on the wing being completely full. (I only
fill mine half way)

Gary Kemp
Andreas Maurer wrote:
On Mon, 23 May 2005 22:26:11 GMT, 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...

This is very likely to happen. I once heard a report of a pilot (iirc
Helmut Grix) who had plugged his water drains before he went up in a
wave. The over-pressure of the air in his waterbags broke his wing
shells in the thinner air - he needed completely new wings
afterwards.


Bye
Andreas

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...&currentpos=32

http://www.gliderforum.com/photos/sh...&currentpos=34

http://www.gliderforum.com/photos/sh...&currentpos=35

I have to give credit to Jackie Payne for this mod.

On Tue, 24 May 2005 14:09:09 GMT, 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.

I'm not sure if these tests are reliable.
Helmut only covered the ventilation hole of his glider with tape - and
the tape was strong enough to keep the overpressure. As John already
pointed out, you need only a small differential positive pressure to
blow up your wing.

I'd strongly suggest to email Shempp Hirth about this topic - you
should get a reliable answer quickly.


Bye
Andreas