Composite Sandwich Floor Panel

Somehow I convinced Scott we should try and lay-up a composite sandwich panel in place of the .032” aluminum floor in our airplane. There was nothing in particular wrong with the aluminum floor but I felt we could add a little protection from being impaled by tree branches in the event of an off field landing. Yep, we read the NTSB report on that one. It also can look really cool if you use a fancy Carbon/Kevlar hybrid. I had done a little work with composite panels and was very impressed with their strength and weight. Scott wasn’t sure about the strength so we layed up a sample panel and placed it over a 12’’ x 12” frame to simulate an open section between frame tubes on the fuselage. An engineer would test the strength of this panel with a universal test machine that applies a load and measures strain to failure. In lue of a machine like that I loaded up Scott with pizza and had him stand in the middle of the panel. Needless to say he was impressed enough that we now have a composite sandwich floor panel, and no more pizza. By the way . . . We tried the same test with the aluminum panel and it looks amazingly like the bottom of Scott’s shoe. I’ve been meaning to return that to Travis since we did not use it. 

What is a composite sandwich panel?  The best way to describe the structure of a “sandwich core panel” is to look at it like an "I" beam. Like the “I” beam, a sandwich core panel consists of strong thin skins (flanges) bonded to a core (web). The skins are subject to tension/compression and are largely responsible for the strength of the “sandwich”. The function of the core is to support the thin skins so that they don't buckle and stay fixed relative to each other. The core experiences mostly shear stresses as well as some degree of vertical tension and compression. The core material is usually lightweight and might be foam, Nomex honeycomb (fancy paper), or balsa wood. That’s right, I admit it, there is balsa in our airplane. If it's good enough for NASA [space shuttle, Apollo, etc.] it should be good enough for a Kolb! 

We created this panel using the vacuum bagging technique described previously. However there were some difficult steps that had to be added to an already complex process. Because we wanted the pretty weave of the Carbon/Kevlar material to show we needed to protect it from the sun light that will be beating in through the large wind screen. This required a clear UV resistant gel coat to be applied first to the waxed mold that would become the first layer of the lay-up. Each subsequent layer had to be added to the lay-up as the previous layer became green. Green is the state where the gel coat or resin has become cured enough to not be sticky but is not even close to completely hardened. We also did not want a super glossy surface. The gloss looks great and gives a deep finish but we were concerned about reflection in the windscreen. Our tool (mold) was a Formica covered table that had the perfect satin sheen for our purpose. 

This turned out to be quit a grueling project but I think the result is great. We are even considering making a luggage panel to go above the fuel tank.