water wing tank venting

Has anybody experience with central venting like an ASW 24 but with a hard
tank. I am preparing the internals of the wings and I would like to vent
three tanks in on wing independently and join the three vents lines
at a manifold at the root rip and then with a single line up to the deck.
Comments please.
Regards
Udo

Hi Udo,

Yes, the Zuni has a vent line running from the outboard end of the
tank, back through the tank, and exiting the bottom side of the wing,
near the leading edge, ahead of the dump hole. This is not exactly as
you had asked about, but very similar. It does provide good venting of
the tank. It does have a drawback in that if the tanks are full and
the plane is slightly wing low (sitting with the wing wheel on, for
example), water will tend to siphon from the low wing out the vent
hole. This vent is about 5/16th diameter on my Zuni.

Also, the HP-18 built by my father, Robert Leonard, and now owned by my
brother, Ron Leonard, has a vent tube running the length of the wing.
It also exits the underside of the wing, but near the trailing edge,
just outboard of the root rib. I believe this vent tube is 1/2 inch
tygon tubing. His dump system comes out of the stock Schreder dump
port on the front face of the spar, goes through a 90 degree elbow to
go outboard, through a dump valve, and exits through the bottom of the
wing, one or two foam ribs outboard of the root rib. The intent of
this system was to keep the water plumbing all in/on the wing. That
way, there would be no leaks into the fuselage.

When building this HP-18, he had considered adding an extra ballast box
in the first bay ahead of the spar. His plan was to put an isolation
valve on this tank so he could either fly with half water (fill the
spar only) or full water (by openning the valve and filling both
tanks). He decided against this, and just stuck with the stock water
capacity. Is this similar to what you are planning to do, but with one
tank ahead of and one behind the spar?

But, yes. Vents back to the root do work. Oh, yes. You can set a wing
down and not worry about loosing your water! But you will fill the
vent lines and then drain at least part of that water overboard when
you level the wings for takeoff.

If you do tie all vents to a common manifold, you wil probably not be
able to be assured that you will not get some water into a tank you did
not fill. Amount would likely be vent line volume. Maybe a bit more
or less, depending on how you fill the system. My suggestioin would be
to keep each tank vent seperate.
Steve Leonard
Zuni II
HP-14
Too many others to mention ;-)

Hi Udo,

Interesting ... seems like most hard integrated tanks fill from the top
and dump through a separate valve controlled exit out the wing bottom
or through the root through the fuselage. The top mounted cap is
vented to let air out of partially filled tanks as you gain altitude
.... or let air in as you dump. On 27Bs we increase the vent
openings/capacity to support quicker dumping. The top vent is a
problem unless you keep the wings level when you have water. Having a
root vent could eliminate this ...

Lte's see ... soft tanks use a tube vent that is held well above the
tank ... typically to an external outlet ... probably needed as water
sloshing in the bladder can create hydralic pressure ... squirting the
water out of the tank. The vent tubes are typically small ID. Since
the soft tank just collapses when you empty, you don't have to worry
about moving any air back through the vent into the tank to reduce the
vacuum.

So, will a hard tank with a vent potentially have a slow dump rate?
Probably not if your vent tubes/system is large enough. And do you
nave a potential to have air trapped at one end of the tank creating a
high PSI bubble as you gain altitude?

I know you have already figured this stuff out ... :-)

Happy new Year ...

KK






Udo Rumpf wrote:
Has anybody experience with central venting like an ASW 24 but with a
hard
tank. I am preparing the internals of the wings and I would like to
vent
three tanks in on wing independently and join the three vents lines
at a manifold at the root rip and then with a single line up to the
deck.
Comments please.
Regards
Udo

BEGIN:VCARD
VERSION:2.1
N:Rumpf;Udo
FN:Udo Rumpf

REV:20050103T195453Z
END:VCARD

wrote in message
oups.com...
It does provide good venting of
the tank. It does have a drawback in that if the tanks are full and
the plane is slightly wing low (sitting with the wing wheel on, for
example), water will tend to siphon from the low wing out the vent
hole. This vent is about 5/16th diameter on my Zuni.

Steve,
I should maybe manifold all three lines at the turtle deck that would
prevent siphoning.
I believe also the 5/16" vent tube will be enough, as each tank is
relatively
small and all will have a separate dumb valve.
The centre tank is 2 x 8 gal. front 2x 6 and the back 2x5gal.

one or two foam ribs outboard of the root rib. The intent of
this system was to keep the water plumbing all in/on the wing. That
way, there would be no leaks into the fuselage.
Is this similar to what you are planning to do, but with one
tank ahead of and one behind the spar?

I was planning on placing the valves in the front and back tank
and stay with a standard 2 ball valve set-up for the spar tank.
Tank you
Udo

Hi Ken,
I am planning on filling the tanks from the tip independently.
My intent is to have good control over the water.
Also I like the idea of being able to put the wing down without it running
out or having to seal it and then forget to remove the seal on take off.
Your old ASW20 is being put to good use buy the new owner.
Hop to see this year at one of the contests.

Udo




"Ken Kochanski (KK)" wrote in message
oups.com...
Hi Udo,

Interesting ... seems like most hard integrated tanks fill from the top
and dump through a separate valve controlled exit out the wing bottom
or through the root through the fuselage. The top mounted cap is
vented to let air out of partially filled tanks as you gain altitude
... or let air in as you dump. On 27Bs we increase the vent
openings/capacity to support quicker dumping. The top vent is a
problem unless you keep the wings level when you have water. Having a
root vent could eliminate this ...

Lte's see ... soft tanks use a tube vent that is held well above the
tank ... typically to an external outlet ... probably needed as water
sloshing in the bladder can create hydralic pressure ... squirting the
water out of the tank. The vent tubes are typically small ID. Since
the soft tank just collapses when you empty, you don't have to worry
about moving any air back through the vent into the tank to reduce the
vacuum.

So, will a hard tank with a vent potentially have a slow dump rate?
Probably not if your vent tubes/system is large enough. And do you
nave a potential to have air trapped at one end of the tank creating a
high PSI bubble as you gain altitude?

I know you have already figured this stuff out ... :-)

Happy new Year ...

KK






Udo Rumpf wrote:
Has anybody experience with central venting like an ASW 24 but with a
hard
tank. I am preparing the internals of the wings and I would like to
vent
three tanks in on wing independently and join the three vents lines
at a manifold at the root rip and then with a single line up to the
deck.
Comments please.
Regards
Udo

BEGIN:VCARD
VERSION:2.1
N:Rumpf;Udo
FN:Udo Rumpf

REV:20050103T195453Z
END:VCARD

My HP16 has a forward and aft tank in each wing for a total of 4 tanks.
on the Root Rib I have a Outlet fitting and a vent fitting for each
tank. The left wing has an outboard fill port on each tank. I have a
single Dump valve in the bottom of the fuselage that was homemade and
has two 1" vinyle hoses, connected to Each Hose is a Tee with hoses
going to the forward and aft tanks. BTW the Tanks are made 4" PVC
Tubing. I think one tank is slightly smaller maybe 3" tubing? I can
carry a total of 21 gallons.

The vent tubes are all Tee'ed together with 3/8" vinyl Tubing in an H
type fashion, Then the center of the H also has T with the 3/8 vinyl
Tubing that is looped up through a ring in the top of my Turtle deck
and then back to a 3/8 aluminum tube that is mounted in my gear well
to drain any overflow. I drill an 1/8 vent hole in the vinyl tube at
the high point of the vent system where it passes through the Ring.
This prevents water from siphoning out the vent tube.

to fill this system put the right wing down, open the fill ports on the
left wing and begin filling it does tend to burp quite a bit for the
last 5 gallons or so, so the fill rate has to be fairly slow. I usually
plug the Vent line while filling. It takes me about 20 minutes to fill
that tanks. It takes about 10 minutes to dump all the water.

The disadvantates of my system a

1. about 8 hoses to hook up after installing the wings. Much of the
time I fly dry, and just leave them disconnected.
2. The outboard end of the tank is just about he same hieght of the
top of my turtle deck when one wing is on the ground, so I have the
keep the wings somewhat raised to keep water from draining out the vent
tube.
3. if the tubing comes loose you can end up with a cockpit full of
water. It has only happened once but flying in the bathtub is a bit
annoying.

If I were designing a new system I think I would try to keep the tanks
and vents all separate or at least contained in each wing so that there
were a few connections to make as possible, after assembling the
aircraft.

The Vent From the tip back to root seems to be best solution I have
seen so far for venting, with least # of disadvantages..

Brian

Udo Rumpf wrote:
Steve,
I should maybe manifold all three lines at the turtle deck that would

prevent siphoning.

Now that I think about it a bit more, it is not so much siphoning, as
simply draining. With the wing low enough that the water is up to the
level of the vent at the outboard end of the tank, and the exit point
of the vent tube from the aircraft is below the water level in the
tank, it will simply drain. I suspect there is a point in the vent
tube that goes above the water level in the tank when it is sitting
with one wing level with the ground.

I think if you just keep them above the level of the water in the tank,
it should be OK. Manifolded together, or individually. I would make
sure it is either outside the airplane or in an area that can drain, as
if you tow the ballasted glider around a corner, you will likely push
some water into the vents, even if it was level to start with.

Steve

Udo Rumpf wrote:
Has anybody experience with central venting like an ASW 24 but with a
hard
tank. I am preparing the internals of the wings and I would like to
vent
three tanks in on wing independently and join the three vents lines
at a manifold at the root rip and then with a single line up to the
deck.
Comments please.
Regards
Udo

BEGIN:VCARD
VERSION:2.1
N:Rumpf;Udo
FN:Udo Rumpf

REV:20050103T195453Z
END:VCARD

Reply:
Put in big vents and keep 'em short. If you don't do it now, you will
later.
If practical on your installation, the best way from a dumping
standpoint is bottom mounted vent at outboard end of each tank with
check valve so air goes in and water does not come out.
Keep in mind that flow resistance through a line is inversely
proportional to the 4th power of diameter and linear with length.
Schleicher increased the venting on '27B's when we showed that flow was
choked.
UH

You need to be a bit carefull using check valves, as they also need to
be able to let air out of the tank as well.

Otherwise if the tank is not completely full as you go up in altitude
the pressure build up on the tank might damage the Tank/Wing.

Brian