Crossfeed in LS8 wing tanks?

I have an LS8sT (from DG) which is exhibiting the same problem, leaking from the outer tank to the inner tank - its a later one (post Sn 8500), and my manual says to fill the outer tanks first.

Does anyone have any experience with these?

On Wednesday, August 6, 2014 10:30:03 AM UTC-4, wrote:
I have an LS8sT (from DG) which is exhibiting the same problem, leaking from the outer tank to the inner tank - its a later one (post Sn 8500), and my manual says to fill the outer tanks first.



Does anyone have any experience with these?

Hi,

I haven't looked at the TM library in a long time, but I have to believe it is the same problem. The tanks were not designed to cross-feed from inner to outer, and IIRC the only way for water to flow was through the venting system. Shouldn't be too hard to observe if you can put a wing partially filled with water on a saw horse and stick a cheap boroscope up against the point where the tubes run through the bulkhead/rib.

P3

I have an LS8-18. I usually fill only the inner tanks since when full I am essentially at max gross. The outer tanks will take on water and I know how it happens in my ship. The vent tubes for both the outer and inner tanks exit into a small chamber in the wing root. This chamber has a common drain on the bottom of the wing. You will identify this chamber in the wing root because there are two plastic plugs that fill inspection holes into the common drain chamber. The plastic plugs allow direct access to the drain tubes from both the inner and outer tanks. When I fill the inner tank until water drains out the vent what is happening is that the overflow from the inner tank is filling the common drain chamber in the wing root and water can back flow into the outer tank.

I am confident that this is the problem because if I am careful to slowly fill the inner tank and unplug the fill system at the first sign of water draining, there is no water in the outer tank. Also, when there is water in the outer tank after filling the inner tank I will drain the outer tank and it stays dry. If there was a leak in some kind of tube inside of the wind the outer tank would continue to take on water after I drained it.

On Wednesday, 6 August 2014 17:01:53 UTC+1, wrote:
I have an LS8-18. I usually fill only the inner tanks since when full I am essentially at max gross. The outer tanks will take on water and I know how it happens in my ship. The vent tubes for both the outer and inner tanks exit into a small chamber in the wing root. This chamber has a common drain on the bottom of the wing. You will identify this chamber in the wing root because there are two plastic plugs that fill inspection holes into the common drain chamber. The plastic plugs allow direct access to the drain tubes from both the inner and outer tanks. When I fill the inner tank until water drains out the vent what is happening is that the overflow from the inner tank is filling the common drain chamber in the wing root and water can back flow into the outer tank.



I am confident that this is the problem because if I am careful to slowly fill the inner tank and unplug the fill system at the first sign of water draining, there is no water in the outer tank. Also, when there is water in the outer tank after filling the inner tank I will drain the outer tank and it stays dry. If there was a leak in some kind of tube inside of the wind the outer tank would continue to take on water after I drained it.


I know the set-up you are referring to and I'm confident my problem doesn't reside there. If I put the wing slightly tip high in the flying attitude, put 26litres into the outer tank (nowhere near full), water gradually appears in the inner tank - no water passes through the common air vent box.

At 16:00 06 August 2014, Papa3 wrote:
On Wednesday, August 6, 2014 10:30:03 AM UTC-4,
wrote:
I have an LS8sT (from DG) which is exhibiting the same problem, leaking
f=
rom the outer tank to the inner tank - its a later one (post Sn 8500),
and
=
my manual says to fill the outer tanks first.
=20
=20
=20
Does anyone have any experience with these?

Hi,

I haven't looked at the TM library in a long time, but I have to believe
it=
is the same problem. The tanks were not designed to cross-feed from
inner=
to outer, and IIRC the only way for water to flow was through the
venting
=
system. Shouldn't be too hard to observe if you can put a wing
partially
=
filled with water on a saw horse and stick a cheap boroscope up against
the=
point where the tubes run through the bulkhead/rib. =20

P3


Having continued to scour the internet I've come across this

http://www.dg-flugzeugbau.de/Data/TM-LS/LS8/TM8012.pdf

The implication is that later serial numbers shouldn't have TB 8006
applied,
also it would seem unlikely that the design wasn't changed following a
mandatory AD.

What is that additional drain point for? Where does it exit the wing?
Presumably it is blocked off at some point?

We finally resolved the issue of water leaking from the outer tank to the
inner tank. It was a poor seal around the outer tank's breather tube where
it passed through the bulkhead from the outer tank to the inner tank. The
main problem that the repairers had was getting the resin/cotton floss mix
around the side of the tube where it was nestling up against the main spar.
Fortunately? they had already made a hole in the inner tank expecting to
have to replace the release cable gaiter (which was fine as it turned out).
However they had to remove one of the fibreglass straps holding the tube
in place so they could move the tube to get behind it. Now looking forward
to next season so I can re-start my experience of flying with water.

At 22:26 06 August 2014, Geoff Brown wrote: