Fuel Tank Compartments

How do you go about building a fuel tank compartment for a full fuselage stunter? Do you build a hatch, and leave room for adjustments? Or do you seal it up like King Tut's tomb? What do you use for packing around the tank, top, bottom, back, and front?

Start with a mount crutch that is extra solid. A half-inch balsa spreader with the grain "across" the span and dowelled to the bearers is a good start, although I like a hardwood "ladder" with bearer wood across the main beams, attached wit wood screws.

Totally eliminate the forward firewall so that the compartment is open to the front, behind the engine. Use tanks with all of the tubes out the front end, so they can be slid in and out. Close in the compartment on the other five sides, and seal it with finishing resins.

Kiwi

P. S. Wedge it in place tightly with closed cell foam rubber padding while determining whether it needs to be shimmed up or down, then add a few dabs of silicone seal near the front of the compartment when you are ready for a "permanent" mount. This is easy to cut with an Xacto if you ever do need to remove the tank, or replace the foam padding.

Make the tank compartment as above. 1/4 inch or 1/2 inch balsa cross grained between the motor mounts, with the mounts going all the way back to the wing. We make the crutch this way before gluing it to either fuselage side. We have found no need to add dowels or screws. This becomes the "bottom" of the tank compartment. Mount the engine on aluminum or phenolic pads. We use 1/8 inch pads (2 pieces of 1/16 phenolic together). Then make a "top" of the tank compartment out of 1/8 inch balsa and mount it between the fuselage sides 1 1/4 inch above the "bottom". That will give you 1/4 inch of adjustment--1/8 inch in either direction.

We than use balsa shims as follows: one 1/8 inch to use on one side of the tank (top or bottom) and a stack consisting of one 1/16, 0ne 1/32, two 1/64 (plywood) on the other side of the tank. If you need to move the tank up or down, use the stack on the side in the direction you need to move the tank, and take one shim out and move it to the other side. You can thus adjust in 1/64 inch increments.

If you wedge the tank in tightly, it won't move foward or backward. You can put a styrofoam block in the back of the tank if you want, but it is not needed. If you need to move the tank is smaller increments, or wedge it tighter, add business cards to the stack. You want to wedge it in absolutely tight so that it won't vibrate and cause foaming.