A pressure test this morning revealed a definate tank leak around the
bung.

http://www.anjo.com/rc/aircraft/dr1/dr1.tankleak.jpg

The bung which is tightened by means of the screw (just visible between
the three tubes) was noticably slack, so even light lung-pressure on one
line caused the stream of bubbles. It would also cause a serious fuel
spill, obviously.

Why was the tank bung slack? I don't know. There is no sign of damage on
the tank mouth lip, and the bung itself looks fine. I *NEVER* put a tank
into an aircraft without giving it a good pressure test, and this tank has
not been out of the aircraft or fiddled with since. I can only assume
that time has caused the rubber to shrink a little, and become slack.

I reinserted the bung, and applied approx. 350 ft.lb. of torque to the
screw :) then pressure-tested again. After a lengthy, red-in-the-face, eye-popping, Dizzy Gillespie-style, rigorous check, I conclude that the
tank is now sealed up again.

It's a good thing that I make a habit of fuel-proofing the tank bay on my models. It saves me from the real problem of fuel-soaked wood in the
event of a leak like this. Unfortunately, the flight battery was stored
in the bottom of the bay, right under the tank, packed in with EPP foam
cut specially to shape. The foam is all fuel-soaked now, and I'll have to make up a couple new bits. The pack itself was also drenched, so I cut
away the heat-shrink and cleaned it off. When it dries I'll wipe it with alcohol, let it dry from that and put some new heat-shrink.

Hopefully, I can get it back together in time for a flight on Independence
Day (two days away).


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þ Synchronet þ Made of wood and glue, but mostly glue!

Re: Tank leak
By: Angus McLeod to Digital Man on Mon Nov 28 2005 10:15 am

A pressure test this morning revealed a definate tank leak around the
bung.

http://www.anjo.com/rc/aircraft/dr1/dr1.tankleak.jpg

The bung which is tightened by means of the screw (just visible between
the three tubes) was noticably slack, so even light lung-pressure on one line caused the stream of bubbles. It would also cause a serious fuel spill, obviously.

Why was the tank bung slack? I don't know. There is no sign of damage on the tank mouth lip, and the bung itself looks fine.

Never thought I'd see "mouth", "lip", and "bung" altogether like that in an innocuous sentance. :-)

Good news on the (relatively) easy repair.

digital man

Snapple "Real Fact" #188:
Antarctica is the driest, coldest, windiest, and highest continent on earth.

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Re: Tank leak
By: Digital Man to Angus McLeod on Mon Nov 28 2005 14:08:00

Why was the tank bung slack? I don't know. There is no sign of damage o the tank mouth lip, and the bung itself looks fine.

Never thought I'd see "mouth", "lip", and "bung" altogether like that in an innocuous sentance. :-)

Good news on the (relatively) easy repair.

I sent a query to Great Planes about the effect of fuel-spill on the glue
used to assemble the fuse, and hope for a reply tomorrow. Unless I hear something unpleasant, I will reassemble the front end Wednesday morning.
it only involves reinserting the battery and tank, and refitting the cowl
and prop. I'll have all the preparatory work (e.g: re-shrinking the
battery, cutting some new foam padding) finished tomorrow morning.


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þ Synchronet þ Made of wood and glue, but mostly glue!