Schempp-Hirth water Ballast Cap vent Mod

[Paul M. Cordell]

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/show-album.asp?albumid=5&currentpos=32

http://www.gliderforum.com/photos/show-album.asp?albumid=5&currentpos=34

http://www.gliderforum.com/photos/show-album.asp?albumid=5&currentpos=35

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

[Gary Emerson]

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/show-album.asp?albumid=5&currentpos=32
>
> http://www.gliderforum.com/photos/show-album.asp?albumid=5&currentpos=34
>
> http://www.gliderforum.com/photos/show-album.asp?albumid=5&currentpos=35
>
> I have to give credit to Jackie Payne for this mod.

[Udo Rumpf]

"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

[Andreas Maurer]

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

[Tomas]

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/show-album.asp?albumid=5&currentpos=32
>>
>> http://www.gliderforum.com/photos/show-album.asp?albumid=5&currentpos=34
>>
>> http://www.gliderforum.com/photos/show-album.asp?albumid=5&currentpos=35
>>
>> I have to give credit to Jackie Payne for this mod.
>
>

[[email protected]]

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

[John Galloway]

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/show-album.asp?albumid=5&curren
>>>>tpos=32
>>>
>>> http://www.gliderforum.com/photos/show-album.asp?albumid=5&curren
>>>>tpos=34
>>>
>>> http://www.gliderforum.com/photos/show-album.asp?albumid=5&curren
>>>>tpos=35
>>>
>>> I have to give credit to Jackie Payne for this mod.
>>
>>
>

[Andreas Maurer]

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

[John Sinclair]

My Nimbus 3 had vents in the filler plugs AND tip vents
that I believe ran inside the wing all the way to the
root rib area. If one vent were blocked the other vent
would still provide adequate venting of the wing. This
can be tested by blowing into the filler hole. No resistance
= tip vent is open.
JJ

At 23:00 24 May 2005, John Galloway wrote:
>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/show-album.asp?albumid=5¤
>>>>>tpos=32
>>>>
>>>> http://www.gliderforum.com/photos/show-album.asp?albumid=5¤
>>>>>tpos=34
>>>>
>>>> http://www.gliderforum.com/photos/show-album.asp?albumid=5¤
>>>>>tpos=35
>>>>
>>>> I have to give credit to Jackie Payne for this mod.
>>>
>>>
>>
>
>
>

[[email protected]]

I've heard it in the air.

Gary

T o d d P a t t i s t wrote:
> Andreas Maurer > wrote:
>
> > As John already
> >pointed out, you need only a small differential positive pressure to
> >blow up your wing.
>
> According to the manual, my Ventus wing will withstand an
> overpressure of about 3 feet of water or roughly a tenth of
> an atmosphere. That's about a pound and a half per square
> inch. My vent hole is roughly 0.2 inches in diameter, or
> only 0.03 square inches in area. Thus, the plastic should
> burst when .045 pounds or about 3/4 of an ounce of pressure
> is applied to the area of the small vent hole. Otherwise,
> I'd be outside the manual limit on overpressure. I doubt
> the ZipLoc plastic is that weak.
>
> OTOH, it's not clear how good of a seal you get with air
> attempting to escape. Perhaps a small hole in the plastic
> would assure minimal leakage of water when the "one-way"
> valve is sealed and still allow rapid dumping.
>
> I heard a wing crack during water filling (from a hose)
> without adequate pressure relief. It's a pretty sickening
> sound. As much as I like the nifty design here, I'd really
> hate to hear it on something I owned while I was in the air.
>
> >I'd strongly suggest to email Shempp Hirth about this topic - you
> >should get a reliable answer quickly.
>
> It would be nice to get a solid answer, but I doubt they're
> going to say "Sure go ahead." without some reasonable
> testing, and that costs money. You're more likely to be
> referred to the manual that already has overpressure
> guidelines related to filling the ballast tanks.

[[email protected]]

I was working on a 300K speed triangle record out of Parowan, Utah and
had reached Richfield, some 75 miles to the North, conditions were good
and I had made the turn at Richfield airport and was at the top of a
rapid 1000 fpm average thermal at 17,000 feet when I heard or felt a
loud thud. My immediate reaction was that the water ballast had frozen
in my vertical stabilizer and blown apart. (Graham Thomson had caused
this apprehension by discussing the issue while putting anti-freeze in
his tail ballast). I moved the controls and still had control of all
surfaces and attitudes. I then looked at my right wing and saw about
a 2 foot split on the leading edge about 2 feet out. It looked as if
it were a foot wide also and I immediately dumped all water ballast and
the split reduced to no more than 1/4 inch. Stew Tittle in his LS6 and
Dale Bush in his Nimbus were close by as I announced my situation and
decision to head home. As I slowed to below 70 kts and headed home we
discussed the situation. I had reduced my performance on the computer
by 15 % and had enough altitude to make it back in my Pegasus. Dale
and Stew continued to shepherd me as I slowly made my way home. As I
arrived in the Parowan Valley and with still about 4000' over the
ground I determined to try the spoilers to see if this had any adverse
affect on the split, it didn't, I continued on to a safe landing at
Parowan and subsequent repair. Dale continued on South to the North
Rim of the Grand Canyon and return.

[[email protected]]

In trying to decide what had caused this problem, I remember trying to
fill my tank (Smiley Bags) with a water house and having a similar
result, this helped me in my decision to fly home as I knew that these
wings are built in halves and epoxyed together. Now I fly gliders
because they have fewer things to go wrong with them. I am not a
mechanic, engineer or technician, I just enjoy flying them and as John
Sinclair says I have a slow learning curve. Needless to say, however,
I don't want this to ever happen again. I called John Sinclair to
discuss what caused it, how to avoid it again and what to do next. I
had seen many people place water tanks on the roof of their motor
homes and fill their tanks that way.....my tank was a closed system
with no vents as I am sure many are. John informed me that that
practice put too much of a head (pressure) on the water going into the
wing and that even 5 lbs. pressure is too much. I had undoubtedly
weakened the structure and that coupled with a probable air bubble
entrained in the tank and the rapid (10 kt.) climb and altitude
pressure reduction (17,000 ft.) all combined to cause the problem.

The fix: 1) Fill one wing at a time.
2) Have a relief valve in the hose coming from the
motor home, no more than 1 meter above the wing.
3) Place a vent in the water bag system in thE glider.