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Leaking QB tank on my RV8

H

Huskyhipdoc

Member
Hi folks...feeling somewhat dejected...
MY QB wings arrived last August. I pressure tested the fuel tanks, and seemed ok. I filled them with avgas and UV fluorescent marker and no halos formed ae=round the rivets,or my flop tube installation. I pressurised the tanks and checked them under water ( senior management objected to me taking the tank into the hot tub!)
I then degreased the wings, painted with 2 pack acid etch primer then 2 pack epoxy, and put them away.
I came to move them to the hangar today as I need more space at home to hang the engine, and found 9 paint bubbles along the port lower rear tank baffle/wall seal!
I can't think of anything it might be other than a poorly sealed tank... unless anyone else has a better suggestion?
I've stripped the paint off and I'm pressure testing again... but the prospect of stripping the tank off and opening up to repair something that should have been done professionally in the first place is very depressing...
https://www.dropbox.com/s/15ytz90ramxmz9u/IMG_0992.jpeg?
[IMG]https://www.dropbox.com/s/3e3khte17hq68ld/IMG_0991.jpeg?dl=0dl=0[/IMG]
 
Haven?t built tanks myself, so no inside knowledge. Just spitballing ideas.

I get the impression the plane hasn?t flown yet, so I?m assuming it has been sitting empty of fuel, not sealed and pressurized? If so, it shouldn?t really have anything trying to get out to cause the blister. I know you said you de-greased it. But around rivets would be a place for residue to hide. Did you possibly not prep for paint quite well enough?

Mark
 
Found the previous threads..
Also checked my build log.
Tanks had 20litres fuel inside for 2-3 days, the drained and tanks left open to clear any residual fuel vapour.
Skins cleaned with isopropyl alcohol, not MEK.

Painting not done until three weeks after the tanks last had any fuel inside, and have been dry ever since.

Pressure checked in tank this morning... still no leaks.

This can?t be a fuel problem...
 
Mark,
I?d accept poor prep prior to painting if it wasn?t for the fact that the blisters are on 9 aft lower baffle seals on one wing and nowhere else on the entire airframe...
When I installed the flop tubes I checked that the pro seal fillet was good, and took a few pictures... it wasn?t pretty, but there was pro seal everywhere. The lower aft baffle has been in contact with fuel for no more than 24 hours in the past 8 months.
 
I have QB wings that are on my RV7a and flying for 4 years. It was tested with pressure , no leaks, and painted by a professional auto painter before First flight.Within a few months of flying small bubbles appeared on top and bottom rivets on both fuel tanks. I punctured these bubbles and have never found avgas stains or liquid in these bubbles. I have just compressed these bubbles with digital pressure and they have stayed deflated and no sign of leakage. The rest of the plane painted surface is perfect. The painter denies that his preparation was not adequate. When I contacted Vans , the reply was that this happened uncommonly, but it was due to vapor bubbling under inadequately prepared rivet skin area around dimples.

I have never seen staining or avgas, so you really may not have any leak that you will see, even when you prick the bugles with a sewing needle. It is disappointing, as even now after 4 years, I still find new bubbles occurring. Good luck. Jeff R Australia
 
Huskyhipdoc....had a similar problem with our quick build wings......called Mitch Locke at Vans, and he took care of the problem. They had to replace a number of rivets on the ZBrackets. The problem has NOT reoccured.
 
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