Fuel Tank Construction Log, page 2
3/23/98; 2.25 hrs; redimpled right tank skin with Cleaveland Tank dies; prepped tank parts with welder's brush.
3/25/98; 2.25 hrs; riveted filler flange, drain flange, stiffeners, and nose reinforcements to right tank. (Photos will follow shortly....it is hard to handle Pro-Seal and a camera at the same time....once you pick up the camera, it is hard to put it down!?!....)
All the surfaces that will receive Black &$@*%!^? get scuffed with a stainless steel welder's brush.
The stiffeners get buttered with %&^@*#?!
Man, this stuff is the stickiest mess this side of gorilla snot.....
Here the stiffeners have been riveted to the skin. A dollop of Pro-Seal is slopped onto each rivet shop head.
The filler flange after it is violated with goop. It sure isn't pretty, but I hope it is fuel-tight....The little clip will secure the vent line.
3/26/98; 3.5 hrs; left tank components redimpled with Cleaveland tank dies; stiffeners, filler flange, drain flange, nose reinforcements riveted and glopped to left tank skin. Both tanks now ready for ribs.
3/28/98; 6.0 hrs; riveted ribs to both fuel tanks.
3/30/98; 4.0 hrs; sealed inside of both tanks; attached fuel sender plate nuts to inspection covers; installed vent and pickup els.
I recently helped a friend close a wing on his RV6 QuickBuild kit. The sealing of the fuel tanks was unusual in its neatness and technique. It almost appeared as if the sealer was painted onto the rib flanges and considerable effort was taken to mask the flanges for clean edges.
I decided to thin some sealer (MC-236) with MEK to see if I could "paint" with it. A small amount of MEK turned the sealer into a creamy goo that could easily be handled with a brush. The secret of quickly sealing the inside of the tanks was at hand!
The bristles of an acid brush are trimmed so the brush is stiff enough to "push" the sealer into confined areas of the tanks.
You could get real fancy by masking the flanges with masking tape. Did I? Naw.....I don't really care how the tank looks inside. All that really matters is that the stuff inside the tank doesn't get outside at the wrong places. The thinned sealer brushes easily over the rivet shop heads.
The acid brush quickly lays down a fillet at the intersections of the ribs and skin.
Not bad! Really beats using a stick to daub globs of goo on each rivet head. Both tanks were sealed in about 2.5 hours.
We will know in a few days if this technique works!
Detail showing fuel pickup and sender. The pickup is the optional item available from Van's. Notice the relief that had to be cut in the end of the stiffener for the pickup to clear. The vent line will attach to the fitting near the nose of the rib.
3/31/98; 1.25 hrs; Installed vent lines; checked fuel senders with 12v battery and fuel gauges. Both sets worked as advertised!
Getting ready for the final session (hopefully!) of tank sealing, installation of the rear baffles. First step is to get all the bits and pieces together.
4/1/98; 1.75 hrs; riveted rear baffle to right tank. Sealer was applied to the ends of the ribs and the inside surface of the skin. The baffle was then slid into place.
Rear baffle on right tank has been riveted in place. Wood clamps apply pressure to skin/baffle joint.
4/2/98; 5.0 hrs; fabricated and installed corner gussets; riveted rear baffle to left tank; installed tank inspection covers.
I was concerned about how well the corners of the end ribs would seal. Unfortunately, I didn't address this area until after the right tank was closed. I cut gussets to fit in the corners and riveted and sealed them in place. They should go inside the tank, but since the right tank was closed, those gussets were installed on the outside of the end ribs.
Burning the midnight oil! Once you start on a fuel tank, you can't quit until the job is done...
4/3/98; 3.0 hrs; cleaned both tanks and mounted to wings.
Fuel tanks are completed, mounted, and ready for pressure test.
4/9/98; Pressure tested tanks; A plate with a valve stem was bolted over the fuel sender hole, and balloons were slipped over the fuel outlet and vent fittings. Pressure was applied with a bicycle pump. The original plan was to inflate the balloons to 4-6" diameter, leave them overnight, and see if the tank held pressure.
This is not how the test unfolded, however. With only a a tiny amount of inflation of the balloons, the tank began to swell and occasionally pop and creak. At this time I decided there was no point in destroying a perfectly good tank! I left the tank for a couple of hours, and returned to find that the balloons were loosing pressure. Rats!! Double Rats!!
I suspected that the test rig might be the source of the leak. The tank came off the wing, some dishwashing liquid was mixed in a spray bottle, and the test repeated. This time I sprayed the entire tank with the soapy water, looking carefully for bubbles. Slight leakage was noticed at the filler cap, and one of the balloons was leaking at the fitting. There was NO leakage from the tank itself! The same test was run on the left tank with similar results. I feel quite confident that I have good tanks, but the proof will be in several months when they are called upon to contain avgas.......
Some thoughts concerning the tanks:
I highly recommend the tank dies from Cleaveland Aircraft Tool. If I had used conventional dies, the rivets would have had to been shaved or dressed in some way. As it was, a good rubdown with a lacquer-soaked rag was all the rivets needed to end up nicely flush with the skins.
So don't despair to the point that you put off the tanks until the last minute; Go ahead and grab those things by the throat and get it over with! Working with gloves is not all that bad, the sealer doesn't stink anything like that stuff the "airplane in a tube" guys use on their epoxy wonders, and the same skills you used in assembling the leading edges will serve you well with the tanks (I strongly suggest you do the leading edges first to gain the experience you will need on the tanks).
Total time fuel tanks: 50.5 hrs.