IanJ
Well-Known Member
So, I'm contemplating building a Fisher Celebrity (1230 lb gross, 600 lb empty all wood two-place 100 HP biplane). As I understand it so far, the Celebrity is equipped with three fuel tanks, for a total of 13 or so gallons. It has two wing-root tanks, and one main tank aft of the engine, where you'd expect it.
I was pondering how I would make this system easy to use when I had a thought.
How about an automatic system?
The way it would work is that each wing tank would be plumbed into the main tank. The main tank would feed the engine. Normal so far. The twist is to put a float on an arm at each wing tank inlet.
The idea is that when the float is submerged in gasoline, it floats up and blocks off the wing tank, effectively becoming an automatic valve. As the main tank drains, the floats float down, opening the inlet, and the wing tanks automatically refill the main until they're empty. The wing tank inlets would have to be situated about half-way down the main tank, so it wouldn't overfill in uncoordinated turns or other odd attitudes. On a fuel gauge (if it read just on the main tank) you'd see normal fuel usage down to 1/2, then it would hang at half forever, then it'd start to go down once the wing tanks were empty. Not that I'd only have one fuel gauge, I'm just pondering how the system would "look."
The obvious downsides are:
* Mechanisms can stick
* Floats stop floating after a while
* Access inside a fuel tank is severely limited unless it's radically overdesigned
* Radically overdesigned tanks are more apt to leak
However, the fuel-management ease would be fantastic. Safer/more automatic fuel management strikes me as being quite a worthy goal. The system is basically foolproof, and gravity never fails (it's not an aerobatic plane, so that's not a factor)
I can imagine two access plates being built into the tank, on which are mounted the wing tank inlets and the float mechanisms. Drain the tank and unbolt these plates, and you'd have easy access to the float mechanism. A simple pivoting arm design could be built without much trouble. The valves would have to be inspected annually for float degradation and free movement.
You could even mount a switch on one or both of the float mechanisms to set off a flasher in the cockpit once fuel dropped below the half-tank point (I'm guessing there are sealed switches suitable for immersion in gasoline). Each wing root tank would have its own shutoff valve, intended to be used for maintenance and when the plane is parked.
What say you, assembled home-builders? I've never dealt directly with fuel system design before, so I may be blowing so much hot air. I suspect this has been thought of and implemented before, but isn't in widespread use because it's pretty specific to a gravity-fed multiple tank system like this. I'd appreciate any input.
I was pondering how I would make this system easy to use when I had a thought.
How about an automatic system?
The way it would work is that each wing tank would be plumbed into the main tank. The main tank would feed the engine. Normal so far. The twist is to put a float on an arm at each wing tank inlet.
The idea is that when the float is submerged in gasoline, it floats up and blocks off the wing tank, effectively becoming an automatic valve. As the main tank drains, the floats float down, opening the inlet, and the wing tanks automatically refill the main until they're empty. The wing tank inlets would have to be situated about half-way down the main tank, so it wouldn't overfill in uncoordinated turns or other odd attitudes. On a fuel gauge (if it read just on the main tank) you'd see normal fuel usage down to 1/2, then it would hang at half forever, then it'd start to go down once the wing tanks were empty. Not that I'd only have one fuel gauge, I'm just pondering how the system would "look."
The obvious downsides are:
* Mechanisms can stick
* Floats stop floating after a while
* Access inside a fuel tank is severely limited unless it's radically overdesigned
* Radically overdesigned tanks are more apt to leak
However, the fuel-management ease would be fantastic. Safer/more automatic fuel management strikes me as being quite a worthy goal. The system is basically foolproof, and gravity never fails (it's not an aerobatic plane, so that's not a factor)
I can imagine two access plates being built into the tank, on which are mounted the wing tank inlets and the float mechanisms. Drain the tank and unbolt these plates, and you'd have easy access to the float mechanism. A simple pivoting arm design could be built without much trouble. The valves would have to be inspected annually for float degradation and free movement.
You could even mount a switch on one or both of the float mechanisms to set off a flasher in the cockpit once fuel dropped below the half-tank point (I'm guessing there are sealed switches suitable for immersion in gasoline). Each wing root tank would have its own shutoff valve, intended to be used for maintenance and when the plane is parked.
What say you, assembled home-builders? I've never dealt directly with fuel system design before, so I may be blowing so much hot air. I suspect this has been thought of and implemented before, but isn't in widespread use because it's pretty specific to a gravity-fed multiple tank system like this. I'd appreciate any input.
