"Attached is a picture, taken in 2003, of an Ali tank which I believe was made for Nigel Graham."
Ian Rickard
Y9-07-15
I'm a bit late getting back on this one but as others have said, I built a tank out of 5251 quarter-hard magnesium alloy.
It weighs 7850 grams and has a capacity of 110 litres.
I incorporated internal baffles, and breathers with proper AN fittings to accommodate alloy pipework. It is also fitted with a full length capacitive probe and four solid-state optical fuel level sensors.
nigel_graham@m-tecque.co.uk
Y13-11-11
The only advice I would offer is: allow yourself a long time to make and perfect your cardboard templates - the fuselage is partly conical in section so the development will be an interesting shape. Choose a welder based on his ability to weld alloy and don't fall into the trap I did of restricting yourself to a CAA approved welder whose self-belief exceeded his ability!
Nigel
Y13-11-12:
Hi Bill
If you are serious about constructing your own alloy tank, here are some of the issues that I considered carefully before embarking on what turned out to be a lengthy project.
Capacity
If you want to maximise capacity, the tank shape will be complex to take advantage of the available space. I went "full span" and put seamless tubes through to accommodate pitch control and rudder cables. Since you have sawed off the top of your cockpit module, there is now room to extend the tank vertically up by about 100 mm (to the door sill), this should give you an extra 18 litres. Restore the strength of the CM joint using standard "good composite practice".
This should not compromise the seating or baggage-bay access.
Mounting
The tank cannot sit on the bottom of the fuselage but should be clear. Incorporate supporting brackets to spread the (considerable) load to the front and rear of the cockpit module (seat back). Design in some method of allowing the tank to expand and contract - sitting it on a rubber or cork mat for instance.
Breathing
Use considerably larger breathers than were originally fitted - to prevent pressure build-up and blow-back while filling. If possible use two, one on each side of the tank. I routed mine up and then down, venting under the fuselage, to prevent siphoning or fuel dumping in the event that the aircraft ever flipped over.
Fuel Return
I pondered the ideal configuration for the fuel return line (discussed ad-nauseum since!) and opted to return it to the top of the tank. A vertical cross-drilled pipe inside the tank allows the fuel to dribble down without vapourising or having to contend with the back-pressure of a full tank.
Fuel Level Monitoring.
There are now far more options available to accurately monitor the fuel contents. Capacitance level sensors work well but are sensitive to fuel type, if you only ever use one type of fuel, this won't be an issue. They can be used with a "lookup table" to linearize the readout giving an accurate indication of fuel contents. Float switch stacks are the next option, (as supplied by Europa) they are reliable and not fuel sensitive but give a non-linear indication. I opted for the former but included four optical sensors to give an independent indication of fuel contents at "Full", 2/3 1/3 and "Reserve" and chose to delete the standard "stand pipe", which, without any method of isolating, I considered a safety risk.
Maintenance
Now is a good time to include an inspection hatch. Machine a large diameter "weld-in" ring with matching cover, tapped for at least six bolts. Include a groove to accept a Viton "O" ring to seal the joint. This cover also makes an ideal mount for the fuel level sender.