Bill daniels 2012-08-10 02:28:29
My Nimbus 2C has a rotating shaft that passes through the root rib into the
integral wing tank. This shaft operates the dump valve. This shaft has
about 1mm radial play and appears to be leaking water at a slow rate. I
detect no axial play. I find that the closing spring can be gently turned
off the shaft without damage but this doesn’t expose anything resembling a
seal. The shaft appears to turn in the carbon fiber composite although
you’d think they would have used at least a bronze bushing.
One other Nimbus 2 pilot suggested that there may be a rubber boot on the
inside of the wing that is supposed to seal the shaft. Maybe, but I would
suspect an O-ring or gland seal. Is there a quick fix for the leak? I
really don’t want to cut into the wing during the soaring season. The
maintenance manual is completely silent on the subject.
Trying a test case on the workbench proves that I can force silicon grease
into the space between a shaft and journal with low air pressure.
Alternatively, if there is a natural rubber O-ring it might be made to swell
by soaking it in denatured alcohol.
Any useful insights folks?
Jjglider 2012-08-10 02:28:32
Bill, I have seen 3 little holes drilled at 120 degrees around that shaft. Then
with a micro-grease gun, grease is forced into and around the shaft. Works for
a few flights. The alternative is, as you say, to open the wing. I would go
with the above, as you will find an awful mess inside the wing consisting of
rusted spring, rotted off rubber boot and no real fix to your problems. If
memory serves me, there is a brass sleeve in the root rib, which is now too
loose——new oversized shaft? Wait how long for one of those? Pay someone to
open your wing, fix things, close wing.
Honey, where’s my micro-grease gun?
Bill daniels 2012-08-10 02:28:36
Thanks, JJ but I solved the mystery.
I was suspicious of the water tank integrity from the beginning and this led
me down the wrong path. I had found water in the fuselage after the first
flight with the ballast tanks filled and jumped to the conclusion that I had
a leak. The radial play in the shafts added to the confusion. This was
re-enforced by the fact that the flapper valves leaked profusely when the
tanks were first filled.
Silicone grease smeared on the valves then pulling them closed with the tail
rigging tool fixed this leak but I continued to suspect the shaft seals.
BTW, the valve closing springs are on the outside where they can be adjusted
or replaced – neat!
I just completed a intensive leak check of the wing tanks and they are fine
with no leaks at the shafts or anywhere else. However the tests make it is
clear that any water spilled on the top surface of the wing will run into
the gap seals and then to the fuselage at the flap torque tube where it
pours into the fuselage. I’m now sure that’s where the water in the
fuselage came from.
I will have to be really careful while filling the ballast tanks not to
spill any water on the wing. Every drop goes right into the gap seals.
Chris 2012-08-10 02:28:44
I have opened up a Nimbus 2 wing tank to repair just the problem you
describe, inside there is a concertina type rubber boot seal which clamps to
the outer guide tube and the rotating shaft, the problem with the Nimbus I
repaired was that there was corrosion on the outside of the guide tube
which was allowing water to pass between the guide tube and the root rib,
this appears as water dripping out of the tube when viewed from the outside.
Universal Plastics P/L
Jjglider 2012-08-11 00:01:25
I went through the same drill with my Nimbus-3. Fixed everything, but on each
landing, I would have an inch of water in the belly. Finally found it was
caused by dumping with the gear down. The 2 wing dump valves are located in
just the right place to feed a vortex shed by the lowered gear and the vortex
sucks up some water into the wheel well. Sounds far-out, but I stopped getting
any water in my fuselage when I started dumping with the landing gear up.
My Nimbus had springs inside the wing and also on the dump shaft.
Bill daniels 2012-08-11 00:01:29
Now that’s interesting. I’ll give it a try.
With the external spring removed, there is no evidence My 2C has a spring
inside the tank. The shaft rotates easily and just stays where you put it.
With the spring installed, the valve closes with a fairly light force. I
have to grease the valve and pull it closed with the tail assembly tool to
prevent leaks. I may make some springs with 1/16″ piano wire to replace
the 1mm wire the original springs were made of to get a little more closing
Bert willing 2012-08-11 00:02:41
I have the same thing with my ASW20 – about half a glass of water sitting
under the wing root beams in the fuselage. No way that the water can come
from the tubing (everything is dry there), so the only explanation is that
it is sucked through the taped sealing of the wing root.