ww2birds

My Feedback: (14)

Hi Guys,

I could use some advice from those of you who have done multiple tank setups, especially those employing a belly tank. I have a Yellow F-15, and up to now I've been using a UAT plus the two stock 63 oz saddle tanks in parallel. It's all plumbed with 5/32" brass fittings and tygon. The tanks are connected in parallel, both feed lines and both vents are teed, the vent goes to a Slimline fitting on the belly of the plane, and the feed line goes to the UAT.

So far everything has worked well, the tanks fill and drain at the same rate, and the only peculiarity I notice is the swelling of the saddle tanks when they fill and start to overflow in the taxi tank. I assumed that was the flow resistance increasing when fuel vs. air was going thru the vent line.

In a quest for longer flights, I have added a wet belly tank, 50 oz capacity. I plumbed it in by attaching the previous vent line from the twin saddle tanks to the feed line on the belly tank, and the belly tank vent becomes the system vent. The belly tank is all 3/16" dia brass and Tygon, inside and out.

When filling the new 3-tank system, I do see some swelling of the saddle tanks (they are wide + flat, polypropoylene, so very sensitive to pressure), but it fills up nicely.

The problem comes when attempting to drain the system, using the fueling can to defuel the system. The saddle tanks begin to collapse, seemingly unable to draw fuel from the belly tank.

I am wondering if the height of the fuel draw from the belly to the saddle tank is simply too much, and the pressure difference required is collapsing the saddle tanks. I have not tried to run the turbine and see if the slower fuel draw of the fuel pump would not start to collapse the tanks, assuming something is wrong and this is too risky.

And ideas from others who may have successfully used wet belly tanks?

Thanks
Dave