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David-aviator

Well Known Member
Yesterday I drained the fuel tanks, the reason being the only way the tank rivet paint blisters will ever get fixed it to quit flying for a while. I've intended to do this for 2-3 years and always put it off in favor of just one more flight...well there's no fuel in the airplane so I can't fly.

There are 3 ways to fix the paint blisters.

(!) Strip down and repaint
(2) Open aft tank baffle and reseal the inside joints, strip down and repaint
(3) Build new tanks

After consulting with professional pro seal consultant Rick Galati, it has been decided to build new tanks. The reason being, we do not know for sure why the blisters have occurred (although there are some strong theories) and starting from scratch has the best statistical chance of getting rid of the nuisance blisters. I figure it is about a 99% sure thing. I've had the tank kit for a couple years, why not use it?

So I am back in the builder mode, not flyer mode. So far things are moving along well, drilling, dimpling, clecoing, and making the parts not made by Vans. Good friend, Charlie Eubanks, cut the 5.25" holes in the inside ribs on his milling machine yesterday. They will be the most accurate cuts on the airplane this side of the spar attach holes. :)

The pro seal business will begin next week. (actually Flamemaster) I will use Rick's fay seal method and am confident the process will be not a big deal. The only major challenge not yet figured out is how to match drill the attach brackets to the existing holes in the wing spar skear web, but I know it has been done and we will come up with a way to do it.
 
David,

One note from my experience. Don't wipe off wet sealant from rivet heads with MEK. Wait until it dries. It'll be a lot more work, but I suspect many fuel leaks are caused by people cleaning their tanks with MEK and thereby removing too much sealant.

Just my opinion.
 
I think Vans has a procedure for match drilling a replacement tank. I almost bought an 8 that had struck a taxiway edge light and dented one tank. The owner contacted Vans and they helped him through it.
 
Progress Report.....

The assembly of the 2 new tanks was completed yesterday. I decided to let everything cure until Saturday before doing the balloon leak test.

Meanwhile a matter that has been most troublesome has been resolved.

While hemming and hawing on just how to match drill the new Z brackets to the shear web holes, it occurred to me the brackets on the old tanks could be used. They are drilled, have plate nuts installed and if I transfer them rib to rib as they were installed in the old tanks, they just might fit the existing holes.

This evening both tanks were trial fit the wings.

The old Z brackets on the new tanks are a perfect fit the wing shear web holes!! Thank you, Vans, for using incredibly accurate CNC tooling machines. The old tanks and wings were built 6 years before the new tank parts were made.

Now it is on to determining if the darn things will hold fuel. And then it is priming, painting and reinstalling.

(Another slightly bothersome question is this. Both tanks were cleaned of everything that could be sucked up with a vacuum before installing the aft baffle. However, in the course of riveting the attach brackets to the ribs ends and aft baffle after a fay seal with clecos, a #30 drill bit had to be run down through the holes to clean out partially cured sealant so the juiced up blind rivets could be inserted and set. Some junk from the clean out drilling could have fallen inside the tank.

I am wondering if running water through the tank to wash such junk out is a worthwhile effort? I've build composit tanks before that were clean and never saw junk in a filter but the need to clean out those 25 holes at each aft baffle makes me wonder if this should be done.)
 
Rinsing the tank out with water should not be an issue with the access plate removed. Rinse and slosh it good, then dry with a fan or a hair dryer.............
 
Progress report.....



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The last 4 days were spent learning how to paint (again). I've painted before but it always takes a few tries to get it right.

Fortunately, the primer was easily sanded after 3 attempts to get the gun to work right. The gun is just an el-cheapo from Harbor Freight but it works well - if it is cleaned of all junk from the last use 2 years ago. It took some MEK to do that task.

The 4th prime job and final paint today went on like a charm with no sags and little dust. I moved outside and that really helped keep dust to a minimum.

The paint and primer are Dupont Nason Urethane 2K. It is a good auto paint and has held up well on the airplane.

Now it is let the paint cure for a few days and then install the tanks. Here's hoping they hold fuel. They did hold air for 6-8 hours with the balloon test. With any luck at all, the beast will be flying again next week end. I may even make it to OSH. :)
 
144 screws, 42 bolts....

If I counted corrected, there are 144 #8 screws and 42 AN3 bolts attaching the fuel tanks to the wings. They all went in yesterday and I slept better last night than for a long time.

What was most troubling, even though a trial fit indicated the "Z" brackets would match the spar sheer web, was the possibility one or two would not. And then what? I did not have a plan B. The effort has established that if the old brackets can be salvaged and installed as removed from old rib to new rib, they will match the sheer web holes.

They did fit, very well. Of the 42 bolts going in through from the access holes, only one was a bit contrary. I could not see it but could tell the edge of spar web hole was off a tiny bit and while the bolt went through the hole, it would not catch the plate nut thread. I finally got a small electric screw driver in the area with a hex head 3/8" drill bit and took the edge off the hole and problem solved.

The tanks each had 5 gallons of fuel over night. The fuel supply, return and vent lines are hooked up and fuel is flowing from tank to FM200 and back to tank - leaks so far. :)

More work getting it back together today.
 
Good fix Dave, thanks for the update. Not that it matters, but I think you made the right choice just to replace the tanks. Once the painting gods are upset it seems like it best to replace it, or live with it! ;)

No LEAKS! :D
 
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David-aviator said:
There are 3 ways to fix the paint blisters.

(!) Strip down and repaint
(2) Open aft tank baffle and reseal the inside joints, strip down and repaint
(3) Build new tanks
.
Click to expand...

I tried stripping the paint on my tanks and repainting. I laid a thick coat of epoxy primer before laying down the base clear. Blisters came right back. You cant imagine how upset I was. I do not consider your #1 to be a viable fix. I do not know if anyone has had success with that method.

I ended up building new wings. Not to cure the blisters, but for other reasons.
 
Kahuna said:
......I do not consider your #1 to be a viable fix......
Click to expand...
Unfortunately, Kahuna learned that painful lesson the hard way. Stripping and repainting will do absolutely nothing to address and fix the underlying problem. You are not going to stop fuel or its fumes from eventually intermingling with that fresh coat of paint if the proseal that is designed to seal the tank from the inside does not meet acceptable standards. In your case Dave, I have little doubt that your correctly built fuel tanks are up to the task and in all likelyhood, the paint blistering problem that plagued you for so long is history.:)
 
7DD flying again...

I finally got everything buttoned up yesterday and launched today. Its been a long dry spell, the last flight being April 12, but the trusty Lycoming came to life instantly as always. There were a few TRW's around but none near enough to cancel the flight. First stop was at KSET for fuel, topped the tanks and so far no fuel stains. I keep my fingers crossed on that one.

If anything can be said in summation regarding old paint blisters and new tanks, its this - I hope it works.

As many of you know, building fuel tanks is not quite as dreadful as some have cracked it up to be. I like Rick Galati's method a lot and would have been stressed out doing the riveting the same day.

Total flame master sealant used was 1.3 qrts plus three of the 3.5 oz tubes. Doing it again, I would use a bit more on the rib flanges so there is plenty of stuff available for the filet seal.

The tanks were painted off the airplane and the screw dimples got loaded with primer and paint. That resulted in the screws not sitting down quite as deep in the dimple as they should. Live and learn on that one.

As previously mentioned, the Z brackets are transferrable from old tanks to new tanks, just be sure they go in the same ribs they came out of. Of the 42 AN attach bolts, only one was a bit contrary.

The aileron push tubes have to be disconnected and moved outboard in the wing to get at all the attach bolts. While the airplane was apart, a long ago purchased aileron trim kit was installed. Also, a rudder trim kit was installed so I now have 3 axis trim. I like that, the airplane can be trimmed sweet. I tried it this morning and both work. The rudder is in trim at about 120 knots, above that speed left rudder was required. Now I just turn that little knob and the ball slips back in the center. The rudder trim kit came from Robby Knox who was cleaning out his hangar a few weeks ago. It was intended for a RV-10.

It is great to have a flying airplane again....I am sure eternal punishment for a pilot who does make the grade will be sitting looking at an airplane he can not fly. Sort of like the cowboys in the old song Ghost Riders in the Sky. :)
 
David,

You mentioned that you installed an aileron trim kit when you were completing your fuel tank re-build. Is that an electric trim with a small 'deflector' on the aileron itself, or the standard 'two springs and a servo' as supplied by Vans?

Allan
 
David-aviator said:
Yesterday I drained the fuel tanks, the reason being the only way the tank rivet paint blisters will ever get fixed it to quit flying for a while. I've intended to do this for 2-3 years and always put it off in favor of just one more flight...well there's no fuel in the airplane so I can't fly.
Click to expand...

David, were your original leaking tanks QB from Vans.
 
Allan Christer said:
David,

You mentioned that you installed an aileron trim kit when you were completing your fuel tank re-build. Is that an electric trim with a small 'deflector' on the aileron itself, or the standard 'two springs and a servo' as supplied by Vans?

Allan
Click to expand...

It is the 2 spring device from Vans but not electric. There is a small lever between the seats to set trim.
 
Captain Avgas said:
David, were your original leaking tanks QB from Vans.
Click to expand...

Yes, built in 2001 or 2002.

They have been opened at the aft baffle with a 5" hole saw and inspected. The sealant used in construction was not what we use but what appears to a light tan colored brush-able product. Both Pro-seal and Flame Master have thinner brush-able versions of the stuff.

It was a very neat job and I do not know why there were so many blisters except the tanks I just completed have much more sealant everywhere than the QB's.

Most of the blisters were along the aft baffle flange top and bottom, both tanks.
 
The Galati method

To remind everybody, the method taught to Dave and myself by master builder Rick Galati made tank building a non-event. Instead of mixing Pro Seal, I went with a 2-part sealant that was encapsulated in a cartridge that fits in a pneumatic caulk gun. All ya gotta do is break the inner capsule and mix the two parts together...no mess, no measuring, and no fuss. I buttered the sealant on all faying surfaces and clecoed the ribs into the skin using a cleco in EVERY HOLE. A week later, I took the clecos out and riveted all the ribs to the skin. After that, I applied a fillet of sealant all along both sides of each rib, sealing each rivet's shop head. Make sure you've roughed up all surfaces with a brass wire brush, cleaned them off with naphtha, and wear gloves.

I did this many years ago, and now the tanks are full with no leaks (at least not yet).

Dave, it's good to know you're still flying. My RV will be flying just as soon as the stupid rain quits for a while.
 
David-aviator said:
Yes, built in 2001 or 2002.

It was a very neat job and I do not know why there were so many blisters except the tanks I just completed have much more sealant everywhere than the QB's.
Click to expand...

David, Van's QB tanks have an appalling track record for leaks. There is a HUGE amount of information in the archives on this....many disgruntled builder over many years.

Vans has a history of not caring too much about the quality of products produced by their subcontractors (just look at their fibreglass components). It's obvious that price has taken precedence over quality in many areas.

Unfortunately the tanks are an area where there needs to be SERIOUS quality control in the construction and obviously Van's subcontractor in the Philippines has been left to his own devices.
 
Tanks appear OK

Seven days with nearly full tanks, no blue stains anywhere. I am beginning to breath easier. The watch for blisters is on.

Man, is it HOT in the midwest, just about like Texas. Took 4 hours to install a couple upper gear leg fairings and could feel heat exhaustion setting in.

Today it's manufacturing 3 EAA tie down anchors for OSH. Total investment in parts is about $14 - what a deal!!

We need all the good deals we can find these days with avgas at $5.13 locally.

Hey, Rick Galati, thanks again for all the good advice on building fuel tanks.
 
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