Fabricating the Belly Panels

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I decided to experiment with a material used in the display business called Alucabond.  It is a 6mm panel consisting of two .020″ aluminum skins thermo bonded to a solid polyethylene core with an overall thickness of 6mm or 1/4″.  It is a very durable material and easy to form. I chose the 6mm thickness to fit the standard 1/4″ set back of the “Z” channels however in retrospect I should have used the 3mm thickness and remade custom 1/8″ “Z” channels instead. The thinner panel would have been easier to form and be less weight. 

My shop was not equipped with a metal forming machine so I designed my own contraption to form the bends.   I used a cardboard tube from my local Home Depot that is used for making footings for decks.  These come in various diameters and I used a slightly smaller diameter to compensate for springback. I filled the tube with concrete to make it as ridgid and hard as possible. A 1.5″ thick plywood panel was hinged at the edge of the work bench and was used for bending the Alucabond around the concrete filled tube.  As crude as it sounds, this fixture worked amazingly well.  There were of course a few R & D bends that did not fit right but I eventually developed a method that worked.  Fitting the panels to the airframe was also a trial and error process.  My only regret was that I did not make an extra set of panels. Ground looping the airplane during flight testing damaged two of the panels that I would later replace using an altogether different material and forming method that I will describe in a later post.

Removable Belly Panels

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The plans called for a fabric encased belly which means that once the fabric is attached, I would have to cut it open to get inside the belly or tear out the complete interior and remove the floorboards to get at what I need to, which is an equally bad idea . . . and there’s no way I’m going to use inspection rings in the fabric because I’ll never place them exactly where they should be and they are just too small to ever get any work done.

Because it’s the belly, it’s an area that is likely to get a lot of abuse including water, dirt, stones, rocks and worse. I decided to divide the belly up into four removable panels with fixed sections between them. At each fuse tube crossover point I welded a pair of channels approximetely 10 inches apart.  These channels would be used to rivet fixed aluminum skins to.  In-between these fixed sections I would fabricate removable panels shaped with the same belly contour as the fixed sections. Using the rotisserie, I welded the channels and pre fitted the fixed skins.  The channels were actually “Z” channels that had an edge that would provide the removable belly panels a lip to fit up against.  The next question was, what material should I use to make the belly panels from. They have to be sturdy, light weight, follow the contour shape of the belly and be easily fastened.  On my next post I’ll describe what I used.