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Fuel syste for Hummelbird with header and wing tanks.

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12notes

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Fuel system for Hummelbird with header and wing tanks.

I'm currently building a Hummelbird, carbureted 1/2VW engine, with a header tank and leading edge tanks in the outer wing sections. The wing tanks have been done before, but there are no plans for them. I'd appreciate a second (or third, or twentieth) set of eyes on what I'm doing and have a couple of questions.

The header tank is going to be around 8 gallons, with a gravity feed -04 AN stainless steel & teflon flex hose line to a firewall mounted gascolater. The wing tanks will be used to refill the header tank when it gets low. The wing on the Hummelbird is in 3 sections, the center, which is straight, and the two outer wings, which are inclined at 3 degrees. I am planning on venting the the header tank to the two wing tanks, and the wing tanks to outside air.

I have not built the wing tanks yet, so I have options here. I'm close to closing the leading edge of the center section of the wing. What I have in place on each wing center section are:
-Fuel: -04 AN bulkhead fitting on the fuselage with 18" long 1/4" OD aluminum fuel line run unsupported through the center of the front rib rear lightening holes (tube has an "S" bend for any flexing) to a mounted Facet fuel pump with integral check valve and positive shut off. The input side of the pump has a -04 AN 12" SS & teflon flex hose which will be connected to the wing tank. The Facet pump inlet and output are 1/8" NPT, so adapters to -04 AN are in place.
-Vent: -03 AN bulkhead fitting to a 3/16" aluminum fuel line run unsupported through the center of the front rib front lightening holes (also with an "S" bend) to a bracket with another -03 AN bulkhead fitting, and a SS & teflon flex hose which will be connected to the wing tank*.

All lines from the fuselage bulkheads to the header tank will all be aluminum with AN fittings going into the header. Vents will be in the center top of the tank, fuel input to the rear middle top of the tank.

The cruise fuel burn of the 1/2 VW is about 2 gallons per hour, so a failure of the refilling system from the wing tanks should never be a critical problem, however, I'll probably make an automatic refill function tied to the fuel level sensor, pumps on at 5 gallons, off at 7. If it fails, I'll have 2.5 hours to land.

I am planning on using the sealant type that you apply when assembling it, rather than the Proseal slosh when done type. I have the closed end rivets already, but have not yet decided on which sealant to use.

*Since the wings are inclined, the vent line from the header will need to run all the way to the wing tip, correct? Is there a way to route it inside the tank, or should I run it behind the tank/spar? To prevent sloshing in turns, the only holes I planned for the outer wing front ribs were a 3/8 hole at the bottom for fuel flow. I'm thinking with the wing flexing, outside the tank is the only way to do it, but maybe I'm missing something.

I'd like to put a finger strainer inside the wing tank at the pickup point, but it would be difficult to access if there were ever any problem with it. Is there an easy way to put an access port on the side of the fuel tank, the innermost wing rib? This would ease any maintenance, but I don't know of a method of sealing it reliably. A small access port on top maybe? This would need to be accessed if a slosh type sealant is ever needed.

Fuel level sensors are also wide open, but I'd like sensors rather than switches. I like this type: http://www.beliteaircraftstore.com/liquid-level-fuel-probe-system-with-1-8npt-probe/ , if I could find the sensor itself without the calibration/translation box, I'd like to get the data from the sensor directly. I'll see if they'll sell the sensor by itself (I'd need 3, $750 is way too much to spend on it), but if anyone knows of something comparable and cheap, that'd be great. Header tank would have a sealed float and wire mechanical backup.

Edit: I currently only have one shut off valve in the system on the bottom of the header tank. I assume I need them for the outer tank, or will the positive shut off feature of the pump suffice?

Anything crazy about this, other than the absurd amount of fuel this little plane could carry?
 
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