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RV3 Fuselage tank

navy06

Active Member
I have owned my RV3 since 2012 and have been fighting leaky wing tanks almost as long. Not eager to delve into the black Magic required to fix them I decided on a fuselage tank. My plane has too much stuff in the way for a full sized fuselage tank so I designed a cylinder shaped 17.5 gallon than that would be easy to build. I cut the 20 inch diameter end plates using my router and rolled 1/4 inch 6061 T6 bar stock to tack weld around this circular edge. Then rolled a 12 inch wide 65 inch long wrap piece and had a friend tack weld tank. Luckily I found an outstanding welder at Hi-tech fabrication in Shelbyville TN to finish weld the tank and fittings. With only a 0235 in my rv3 17.5 gallons is enough fuel. What I do need is a riveted on flat filler neck for top and unsure how to find part from vans. If anyone has a part number please post. I think all wing tanks use same part that gets riveted to tank skin. I also purchased 5052-H32 .050 aluminum from same shop at less than 1/2 the cost from AS.
 

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In my RV-3A, I used a flange similar to this: https://www.aircraftspruce.com/catalog/appages/fuelFlange.php?clickkey=17896 but it came with a plastic screw-in cap. I drilled a hole in the cap for the 1/4" vent tube. Unfortunately I could not seal it well and water accumulated in the top recess of cap after rain. Cut a hole in the top fuselage skin big enough for the rim of the cap.

I did a search but cannot find the one I used. Rather thin cap that I pretty much flush with the skin. I guess today I would probably use Vans wing tank flange and cap.

Made the tank with a combination of riveting, "magic-rod" alum brazing/welding and fiberglass. Never had a leak unlike the integrated wing tanks.

Finn
 
Jim, Be sure to fully vent (remove all vapor) from your wing tanks carefully.
Tanks that contain fuel (liquid and vapor) don't contain enough oxygen to explode.
But a tank emptied of liquid and the vapors not thoroughly removed will eventually
mix with enough air to be a hazard.
 
Thanks for the replies. I plan to leave the two wing tank vents in place and the fuel output lines open. That should quickly vent all the fuel vapors out. I have drained both tanks thru the sump drains. The installation is coming along nicely. I will be using the same fuel valve and have made a new mounting in center across main spar like before but without the electric gauges. Installed a mounting plate at initial weld up for a Scott mechanical gauge. It will be very accurate when calibrated during initial fillip but will be upper volume limited due to tank shape. When it gets to about 8 to 10 gallons it will read full all the way to true full at 17.5 gal. It’s got two welded in thru tubes with 1/4 inch thru hole for anti rotation mounting plus two SS straps on bottom like in Vans drawing. The welding on the tank is superb and was pressure tested by welding shop.
 
Boy, building that tank and mounting, plumbing ect sure seems like a lot more work than just cutting into the rear baffles and sealing your original wing tanks.. or you could send them out to someone like weep no more to fix them. Seems like a better option than nearly 20 gallons of fuel sitting in your lap! Fuel in the cockpit scares me in the event of a crash..
 
Fuselage Tank

The accident studies in Kitplanes magazine show that airplanes like the Piper J3 and Aeronca 7AC have some of the best safety records regarding fires when data is mixed with a bunch of EAB's
IIRC the early RV3's all had fuselage tanks.
I have over 4000 hours just in the Pitts and Wittman Tailwind. I stopped worrying about fuselage tanks a long time ago.
I think fires are related to electrical system and fuel system plumbing mush more than to tank location.
If you crash a high wing airplane with typical wing tanks you are likely to compromise the fuel lines and there is no way to shut off a break between the tank and fuel selector.
 
I feel your pain on the leaking wing tanks. A poor design in my opinion(let the flaming begin), built a 3,4 and currently rebuilding a 6. I put a third fuselage tank in the single seat 4 that was basically a copy of a Pitts tank, it never leaked. I plumbed it in as an Aux tank using the 4th port on the stock valve.

As JRS said, many fuselage tanks never give trouble and there's something to be said for a tank protected inside structure during a crash, the wing tanks are definitely not protected, less plumbing too.
Combine that with a center tunnel that houses the hard fuel lines, boost pumps, and batteries with gascolators that hang below the firewall is ripe for a fire in a sudden stop when things shift and bend.
Its alarming to me how many RV 4 crash images show fires.
Mike
 
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