Wing vs Fuse fuel tank for Corvair powered Piet

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auburntsts
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Joined: Fri Nov 08, 2019 11:32 am

Wing vs Fuse fuel tank for Corvair powered Piet

Post by auburntsts » Wed Nov 13, 2019 1:53 pm

Title kinda says it all, but what are the pros and cons of each? Is there a majority that favors one over the other? Bear in mind I don't even have a set of plans yet so this is just one of a million questions that I have after spending hours on various Air Camper forums, web sties, and YouTube.
Todd Stovall
PP ASEL-IA
RV-10 N728TT
War Eagle!

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taildrags
Posts: 285
Joined: Tue Mar 07, 2017 10:39 pm

Re: Wing vs Fuse fuel tank for Corvair powered Piet

Post by taildrags » Thu Nov 14, 2019 12:25 am

auburntsts;

I'll chime in with my take on this. I do not have a Corvair powered Piet, but considering that the carb on my Continental A75 is probably in just about the same location as the one on a Corvair Piet might be, I'll just address the fuel tank question without implicating the differences between the engines.

I have a 16 gallon fuel tank up front in the cowling, just behind the firewall. I can fill it almost all the way to the brim if I'm careful with the fuel filler at the pump (air pocket at the top corner when in the 3-point configuration on the ground prevents it from getting completely full), but I will not fly the airplane down into the last 4 gallons except in level flight and in dire circumstances because I've found out the hard way that in a steep climb or in the 3-point landing configuration, there will be insufficient head to keep fuel flowing into the carb bowl through the gascolator by gravity when the level in the tank is that low. That means that there are a couple of gallons of fuel up there that might be great to keep the nose down and maybe enable me to keep flying for another 30 minutes in level flight before the engine starts sucking air, but it's not really usable fuel. Trim-wise, when I fill the tank on my airplane and fly it solo, I've got to hold aft stick pretty good to keep it level for awhile, then it gets gentle at about half a tank. So I guess the plus factors for a tank in the nose are that you can get a pretty good sized tank up there and the fuel piping will be relatively short and simple, and the tank is easier to fill than a wing tank might be, but you've essentially got a lot of fuel in the cockpit on the passenger's legs and feet if something starts leaking, and you can't use it all for flight anyway. One last positive is that fuel level indication is ridiculously simple... a float in the tank with a rod sticking out of the top of the fuel cap, like a J-3 Cub.

With a wing tank, the CG won't shift appreciably as the fuel burns off and it will almost always feed the carb by gravity reliably if you've built the sump right. I like the wing tank approach better, myself. The negatives are the additional fuel piping to get the fuel down to the engine, the possibility of fuel leakage from that piping and fittings in normal operation or in a crash, and having to get up to the top of the wing to fill the tank (no different from every Cessna that I've ever flown, however!). If you use the conventional Piet airfoil, the center section isn't really big enough to hold a lot of fuel unless you build in a deeper sump or a DeHavilland-style 'hump' above the normal top surface of the wing- maybe 10 gallons? But my nominal 16 gallon nose tank really only holds about 12 usable anyway. Indication of fuel level in a wing tank can be done by using a Stearman-style clear tube protruding out the bottom of the tank with a float and lever in the tank, or a dial type indicator. I don't consider either of those to be as simple as the Cub-style float-and-rod, but they aren't very complex either.

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power

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auburntsts
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Re: Wing vs Fuse fuel tank for Corvair powered Piet

Post by auburntsts » Thu Nov 14, 2019 7:10 am

Thanks for the info Oscar! Are you aware of anyone running some type of fuel pump vs a pure gravity fed system?
Todd Stovall
PP ASEL-IA
RV-10 N728TT
War Eagle!

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