Pawnee Fuel Tank Question

[Larry Ruggiero]

Hello folks, did a little searching on past posts related to Pawnee tanks and came up empty handed, so here goes: ours is a C model with the bladder/liner equipped fiberglass fuselage tank. It's developed a leak at the bottom that I'm digging into. Discovered a poorly done previous repair that attempted to secure what the manual describes as a vent tube adjacent to the outflow shutoff valve. Except it's not the tank's primary vent, but appears instead to be a drain for fuel that might accumulate between bladder and tank in case of a leak. It's about a half inch aluminum tube that further mates to a tube out the bottom of the fuselage. Anyhow, it was glassed in place at the tank bottom and the repair has delaminated and loosened. Before further surgery, I want to verify that's its function. We removed the oval access panel on the top of the tank and sure enough, the tube does not penetrate into the bladder/liner. If I could post a pic here I would, but hopefully someone will know.

I've looked through the POH and service manuals; they only show one vent. The tank's primary vent line takes air from the sight gauge opening at the top and exits via a smaller tube out the top front of the tank, through an exit tube at the fuselage bottom. Thanks in advance.

Larry Ruggiero
Carolina Soaring Assoc
Spartanburg SC

[Bob Youngblood]

I have a bit of experience replacing the fuel bladder in the Pawnee. The bladder can be repaired, the leak is probably coming from the area close to the bottom valve area. Contact Johnson Aircraft and they can give you datails on the bladder repair. Bob

[[email protected]]

www.johnstonaircraft.com/

[Larry Ruggiero]

Thanks. It’s all torn apart now, tank off the airplane, and I suspect fuel’s been leaking around the outflow hardware, based on some slight corrosion (from accumulated water in fuel) and absence of much sealant on the threads. Original bladder looks pretty good. The original drain mast must’ve broken off at some point and a poorly fabricated one grafted on. Leaked fuel helped debond the fiberglass patch holding the drain on. We’ve fabricated a much better replacement drain. Will bond that on, reassemble, and leak check before reinstalling.

Larry Ruggiero

[Charles Longley]

This probably doesn’t help you. One of the Pawnee’s I work on has an aluminum tank. It’s a one time STC that some Boeing engineers came up with. I’ve done one repair on it. It’s a pretty cool design!