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Honeycomb Panel Floor Boards

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  • Honeycomb Panel Floor Boards

    Managed to get my hands on some sheets of 1/4" 2-ply fiberglass nomex core honeycomb panels, 3lb core. I plan to use this for the floor boards and possibly the aft bulkhead. Compared to .032" 2024 I calculated the weight for the sandwich panels at 1/2lb heavier over a 4x8 sheet, so fairly close in weight. I also plan to leave them unfinished, with thin carpet over them, and I'm thinking about neoprene edge trim to close out the open core along the periphery (via McMaster). Between the frames the panels rest on I'm considering neoprene again, but I'm concerned about vibration and wearing through the fiberglass, I just don't know yet.

    My reasons for doing this are:

    -Sound absorption, the sandwich panel will provide greater noise protection than the aluminum sheet without having to coat it with something heavy.


    -Stiffness, I've seen some excellent examples of beading the AL floor boards. While this looks very nice it's something I'd rather not have to do. For actual flooring you usually see 9lb core, but the 3lb seems quite stiff enough for this application. No high-heel punch through to worry about in my BH

    I'm debating whether I want to pot thru-inserts or just blow clearance holes through the panel to attach them. I think I'll need some blind inserts to attach things so if I'm doing that I might as well pot the others too. Anyone have experience using these in GA, or for my application specifically? I'd love to hear your thoughts about this, I only have experience in commercial interior monuments but these seem like a fine alternative.

  • #2
    Based on my experience maintaining a Grumman that was built with Nomex-core honeycomb panels, you want to keep water away from them if you're in freeze/thaw country. Here in TX we don't worry about it much, but any part where the panel is vertical and water even "might" get in is worth sealing carefully along all the edges. If water gets into those panels (doesn't take much at all) then freezes (expands), the system can begin the delamination process. I would also definitely use some kind of "thru-inserts" as you called them, because the skins (and honeycomb inserts) can be easily torn. (I'd probably seal the heck out of that hole, as well, since you could be getting in with muddy/snowy boots, allowing water in.)

    I hope to find a reasonably inexpensive honeycomb panel source and use it to line the entire baggage compartment. I might even use that corrugated plastic stuff they use to build model airplanes – assuming I can determine the burn characteristics are OK. I'm not planning to line the rest of the cabin, but my plans for the plane include using it for Pilots N Paws rescue flights, and I'd hate for some pup to claw through the Oratex covering...
    Jim Parker
    Farmersville, TX (NE of Dallas)
    Patrol Quick-Build Serial # P312


    • #3
      Good call on the water intrusion, that's definitely something I was thinking about in closing out open core. I think edge pot would be too brittle in this application so capturing the edge with trim and some sealant is what I'll do, maybe RTV, maybe structural epoxy, we'll see.

      For the inserts one ditches out the core some distance from the hole before potting it in so there's basically a slug of epoxy around it, should seal it out nicely.

      Thanks Jim!


      • #4
        If the mounting holes are near the edge, just dig out the core and inject some thickened epoxy. Farther away from the edge you can drill through one skin, take a Brad nail or piece of steel wire and put a 90 degree bend in it. Put that in a drill and put it in the hole and tear out the core. Inject (syringe) thickend epoxy. When it hardens, drill through. Doing 20 holes only takes 2x the time as doing 1.

        Thickened epoxy is good to seal the edge. A syringe helps, but a small ziplock bag with a tiny hole cut in one corner (bakers bag style) works great.


        • #5
          Hmm, that certainly would be easier than messing with NAS inserts. This would only work for through inserts though, anything I wanted to attach would still need a blind insert.


          • #6
            Yeah the epoxy "plug" is the proper way to mount hardware in cored fiberglass boats. You don't want to get the core wet, and the core can't hold the compressive loads of the bolts. The manufacturers used to use plywood at hardware bases but these always failed after 10-20 years. They didn't know fiberglass boats were going to last forever.

            I am going to use some kind of sandwich panels for the floors and interior panels in the baggage area. The ones I have seen so far are a bit expensive. Flat ones are easy to make, and I think I can make them just over 1/2 the weight of .03 aluminum sheet.

            I am going to use the thinnest kevlar cloth for the skins, and foam core, probably 1/4 inch if it will fit.
            Last edited by svyolo; 12-05-2017, 01:03 AM.


            • #7
              Ah I see, yeah I'm not used to marine applications. I'm fortunate to have acquired my panels as scrap, otherwise it wouldn't be worth it to me.