Aluminum Fuel Tank

[DuncanK]

Does anyone have any experience or knowledge concerning aluminum fuel tanks in Sonex?
Is an aluminum tank available for a Sonex B Model?
What are the disadvantages/problems associated with using an aluminum tank?

My request is the result of the Sonex supplied fuel tank buckling in my B model. The bottom has bowed inwards/upwards about 3 or 4 inches and the back has bowed outwards, pushing into my avionics and wiring. Last week Sonex issued an SD which says the tank can expand up to 3% and they have promised to send me a new tank. But the work to change the tank is huge because of the avionics wiring etc. I don't want to replace it once, but I certainly don't want to replace it twice. Hence I'm interested in information for an aluminum tank.

Duncan

[Kai]

Duncan,

Hm- mysterious!

There is a (milky white) thermoplastic fueltank in #0525. First flight was in 2005, and the plane is exclusively run on mogas with 5-15% bioethanol. Now, after almost 600 hours, there is no sign of buckling, deformation, walls caving in, leaks, or whatever. However, I once noticed that walls, top and bottom are surprisingly thick- I’d estimate some 5,0 to 10,0 mm.

I would be sceptical using a welded alumimium tank. There is always a little water in the fuel, and alu welds hate water. Also, should the unthinkable catastropy happen that the plane is involved in a crash, the alu tank might burst open; let go in the welds. Not good! A thermo tank is much more resilient.

Better to let Sonex supply a new and better thermoplastic tank, replace your old one and be done with it. It is going to be shitty work for sure, and I’m glad it’s not me. But there is no question that Sonex is perfectly capable of supplying a thermo tank that does not deform, so the chances are slim that you will have to do it again.

Thanks
Kai

[Area 51%]

There are at least 3 of us that have aluminum tanks that I know of. Myself, Billy Rofomoto, and garyb.
The Legacy plans allow for an aluminum tank and have a page with the specifications and material requirements.

I went with a metal tank due to fitment and potential fuel fitting issues, not distortion after installation. I ended up with a tank that was 3lbs lighter than the factory tank, and it holds 3 gallons more.

Type "aluminum fuel tank" into the advanced search box, then go to page 6 or 7 to find the thread on the matter.

You will get "extra credit points" from the DAR at inspection time if you can pull off fabrication of your own tank. It was not an easy task and took longer to construct than a wing.......but it was very rewarding.

[racaldwell]

One issue that could appear with an AL fuel tank would be a pinhole leak in a corner weld. Fortunately, there is a simple fix that could be done in the plane depending on access to the area. I did this on the AL tanks I had in my One Design. On the exterior of the tank, make some AL angle out of 0.020" or so and conform it to straddle the seam that has the pinhole. Clean everything really good with acetone and a scotchbrite pad and use Proseal or other Van's type fuel tank sealant in the angle and squish this over the edge of the tank. After a week, add fuel and the leak is no longer. After the 2nd pinhole leak in my tank, I just sealed up the entire perimeter and never had a leak in the next six years I owned that plane.

Rick Caldwell
Xenos 0057

[pappas]

I have a B model and the tank deformed during the fuel flow test prior to the first flight. Sonex suggested it might be a clogged vent. It wasn't, I knew it wasn't that when it happened. The vent was clear. But the cap was on. So what, the cap is on when we fly.

There have been enough of these tanks deforming that Sonex has stepped up and is doing something about it. I built a Legacy Waiex and the B model. The fuel tanks are of different materials. The Legacy tank never deformed.

I have been in contact with Kerry. He tells me that the replacement tank is exactly the same as the tanks that have been deforming. The difference is that Sonex is replacing the (2) one-piece lower tank straps with (2) two-piece tank straps which should allow for adjustment and perhaps less pinching effect.

Also different is the preparation for the replacement fuel tank. The instructions say to place 2 gallons of fuel in the replacement tank, seal it up with the cap on, and leave it alone for 6-weeks! Apparently, the tank will expand to its max size during this exposure to fuel, but will still fit in the space allowed in the airframe for the tank.

I also have a VERY full panel. I am not excited about deconstructing the panel and all of the avionics and wiring to make this swap. Luckily, the deformation in my tank is not serious and does not disrupt any fuel flow. I can still get about 19.5 to 19.8 gallons in mine.