# Minimalistic gas tanks

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#### rv7charlie

##### Well-Known Member
The Dragonfly (tandem wing canard) and some gyros build the fuel tank into the seat. The Dragonfly does use a header tank between instrument panel & firewall, to feed the engine.

#### Skinnybird

##### Well-Known Member
I like gravity...
Gravity is so pleased. As a "thank you" for your support you will not float off into the sunset...

#### Bill-Higdon

##### Well-Known Member
The Dragonfly (tandem wing canard) and some gyros build the fuel tank into the seat. The Dragonfly does use a header tank between instrument panel & firewall, to feed the engine.

Main fuel tank in the Dragonfly is in floor aft of the canard that your legs rest on not the seat. You can see the seat back on the right & the fuel tank on the left

#### Victor Bravo

##### Well-Known Member
Duncan, if you put small tanks between the wing ribs on the upper wing, and the tanks are close to the pivot point, they would likely not affect the stick force and control mass in flight. These would be tanks that are NOLT the full chordwise length of the wing, but are oriented more spanwise. Not a problem-free solution, but would eliminate needless fuel pumps.

Otherwise, the upper part of the fuselage in front of the windshield is an obvious and easily accomplished solution.

#### rtfm

##### Well-Known Member
I've been checking out horisontal boat tanks (polyethelene, with vented caps and fuel cock), as well as go-carts, ATV's etc. Some promising candidates - for less than $100. These would mount in front of the windshield, and could easily be removed for filling and transport. Would need to use plexiglass for the windshield though. But that's OK. For the sake of pilot visibility over the top of the tank, it would need be no higher than about 200mm or so. There are a number of candidates which satisfy this criterion - but capacity in the region of 12 litres. That equates to about an hour's flying time. Another option would be to mount two of them on either side of the fuse - at about$60 each, that's not a great cost. And double the flying range...

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#### rtfm

##### Well-Known Member
Duncan, if you put small tanks between the wing ribs on the upper wing, and the tanks are close to the pivot point, they would likely not affect the stick force and control mass in flight.
I agree - but it would simply be easier to buy a ready-made tank - I'm thinking their manufacturing process would be more reliable than mine Ha ha...

#### rtfm

##### Well-Known Member
This is the leading candidate at the moment. Two 25litre polyethelene tanks, with fuel gauge and vented filler caps. Handy recess midway down the inside for a support beam, and the handle can be used as a support for a cross-beam on top of the cowl (which is conveniently flat). No chance of using gravity, unfortunately.
On the Fleabike, they would provide some protection from colder wind conditions to the legs. Ahead of the CG, but such is life.

Another option is to see if I can get two smaller tanks fitted between the ribs in the front wing. That would be convenient as far as gravity feed is concerned, but not so convenient to fill. Mmmm. The search continues.

Airplanes are an aggregate of compromises all travelling in the same direction.

#### Victor Bravo

##### Well-Known Member
Another option would be to mount two of them on either side of the fuse - at about \$60 each, that's not a great cost. And double the flying range...

Yes, "saddle bags" on each side of the fuselage above your ankles. Narrow enough that downward visibility is not affected much, removable so you can walk to the gas pump and back with it. The off road Jeep folks have several choices, complete with twist-lock attachment brackets. All you'd need is a quick disconnect fitting in the tube coming out from the bottom of the cans.

#### wsimpso1

##### Super Moderator
Staff member
I would be inclined to build tanks to suit your spaces rather than the other way around. That way, you get a cleaner package and more fuel capacity. You can also tailor the crashworthiness to suit your risk tolerance. Materials of choice for me are PVC foam, phenolic or garolite plate for hard points and fuel lines, fiberglass cloth, and vinyl ester resin. The mold can be white polystyrene foam. This will make a fuel tank that is absolutely proof against even gasahol but fits the spaces you have, are sturdy, and can use AN hardware for all fuel and vent connections. Seat tanks and other conformal tank schemes become part of the design...

Billski

#### Skinnybird

##### Well-Known Member
Airplanes are an aggregate of compromises all travelling in the same direction.

"20,000 rivets flying in close formation."

#### Toobuilder

##### Well-Known Member
If using multiple tanks make sure there is either a positive fuel valve to isolate them, or a very, very robust gravity feed. With multiple tanks, once one finds air, fuel flow stops for all.

As for construction, materials become a compelling factor in the overall weight fraction of an airplane of this class. Plastic boat tanks might be attractive from a procurement standpoint, but come with a substantial weight penalty. A simple "double taco" aluminum tank has but a single weld seam and is easy to form. True, you are not going to get one overnight from Amazon, but...

#### rtfm

##### Well-Known Member
Just finalising the details on this. I've found two 11.7 litre "saddle bag" gas tanks, and a fuel pump. Both fuel pick-ups (which plumb to the bottom of each tank) can be joined and then led into the fuel pump intake. Would that equalise the gas in the two separate tanks?

Perhaps I could enquire to see if someone local could build me a 20 litre aluminium tank which sits in front of the windshield? Or in the wing?

Why is nothing easy?

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#### rv7charlie

##### Well-Known Member
Listen to Toobuilder on Y-ing two tanks. They never feed evenly (ask any Cessna driver), and it takes significant head to avoid sucking air when one goes empty.

#### rtfm

##### Well-Known Member
I've asked on the Aussie forum if someone knows of a reliable and reasonable person who can weld up an aluminium tank to fit into my front wing. What gauge aliminium do folks use for tanks?

##### Well-Known Member
I've asked on the Aussie forum if someone knows of a reliable and reasonable person who can weld up an aluminium tank to fit into my front wing. What gauge aliminium do folks use for tanks?
What state are you in?

#### rv7charlie

##### Well-Known Member
I've asked on the Aussie forum if someone knows of a reliable and reasonable person who can weld up an aluminium tank to fit into my front wing. What gauge aliminium do folks use for tanks?
My neighbor has scratch-built several a/c and restored or repaired probably dozens more. He just welded up an aux tank for his RV6; he used 0.050" 6061. If you're willing to use reinforcing ribs, and are willing to build with rivets & fuel sealant, you can go thinner. RV leading edge tanks are 0.032" 2024 (stronger aluminum) with ribs on ~9" centers. Of course, the leading edge is curved, which makes the skin a lot more rigid. 2024 shouldn't be welded.

(Sorry for the barbarian measurement units; I blame our government for not teaching me to think in civilized units when I was a kid.)

#### FinnFlyer

##### Well-Known Member
Listen to Toobuilder on Y-ing two tanks. They never feed evenly (ask any Cessna driver), and it takes significant head to avoid sucking air when one goes empty.
I can attest to that. Previous owner of my RV-3B removed the fuel selector and Y'd the left and right wing tanks together. Had to glide to nearest airport with 5 gallons remaining in left wing tank. Banking, skidding and slipping did nothing. I guess it's easier for a pump to suck air from the empty tank than to suck gas.

Finn

#### John Halpenny

##### Member
I can attest to that. Previous owner of my RV-3B removed the fuel selector and Y'd the left and right wing tanks together. Had to glide to nearest airport with 5 gallons remaining in left wing tank. Banking, skidding and slipping did nothing. I guess it's easier for a pump to suck air from the empty tank than to suck gas.

Finn
If the Y connection is below both fuel outlets, I can't see how it would not be full if there is fuel in either tank. If the Y is above the fuel outlets, it just seems like a bad idea.

#### rv7charlie

##### Well-Known Member
If you can't see it, you haven't seen it. ;-)

Even high wing Cessnas with the fuel selector set to 'both' draw fuel unevenly from the tanks. All sorts of things come into play, from differences in fuel line length, to number/shape of bends, to differences in the vent systems pressurizing the tanks differently. A Cessna can get away with it because the 'head' of the more-full tank will push past the Y (created by the valve) to keep at least some fuel in the line from the empty tank. If you try it with only a foot or so of 'head' from each tank, all bets are off.