Hatz Biplane Association

Hi Guys,
My CB-1 has a tank done like the Classic. I made it so it fills the hole in the center section with only a 1/16" space at the bottom. I will be using strips made from a closed cell polyethylene foam or felt to support the tank bottom since the bottom of the center section is quite strong. The ends of the tank and the two baffle ribs transfer a good percent of the fuel weight to the overhang that sits on the top. My cad program says it is good for about 25 gallons.
Al

I recently removed a fuel tank from a Cessna 172. The tank rests on stringers capped with a resilient hard rubber. That got me thinking about my tank and should it be supported on some type of stringer. The Makelan plans sheet shows a small gap between the bottom of the tank and the plywood floor but no support mechanism. I think a little space is good for drainage, ventilation etc. and with drain holes forward of the rear spar in each stringer bay provides an escape path for condensation and an early warning system for leaks. Thanks all!

The 1x1x2 blocks we added are located on the inside top edge of the plywood end ribs. These have screw anchors in them. We added them just to provide more
hold down screws for the tank. We had about 3/8 inch clearance between the tank bottom and the bottom plywood so I glued in some 3/8 thick felt pads in each
corner and two in the center to help support the tank.

Hi John and Ebby!

Can you post any pictures of the additional blocks added? On our set-up with Makelan built tank we don't have a large cap between bottom tank panel and centersection bottom plyfloor! We just screwed the tank as per plans with 11 threaded inserts each set in wooden members glued in front of the fron and rear of the rear spar. Does anyone finds this unsuffiecient?

Hans & Sam, H.C.#78, Switzerland

Hi Ebby,
We added three 1x1x2 blocks on each rib and used three more screws on each side to hold the tank down. We didn't seal along the ribs but we did drill and varnish
two 3/16 drain holes in the floor of the center section in front of the rear spar in case any moisture worked its way in. It should also give you a little warning if your tank starts to leak rather than having the leak fill up the tank cavity before you know its leaking.
John Hanson

I did not see anything in the Makelan plans sheets regarding support for the fuel tank from the bottom. There is up to 1" of open space between the bottom of the tank and the plywood 'floor' of the center section. Did any builders who completed their tanks have a gap and add some type of support to the floor of the center section? On the other hand perhaps I short changed my fuel tank capacity by not matching the walls of the tank to the interior dimensions of the center section. Either way it looks to me to be prudent to support the bottom of the fuel tank in some way. Just wondering if others have a gap under the tank and how they dealt with it.

Second item, the left and right sides of the center section are 1/4" plywood. Again the plans do not show it but I was thinking of adding a piece of wood, perhaps 3/4", along the top edge of each end to provide a better bearing surface and allow for the addition of a seal. Decent idea? Waste of time? Opinions always welcome.