Carbon Skin/Nomex Core sandwich panels are one of the world’s best strength to weigh materials. And it’s affordable. However,

- the edges of sandwich panels can be easily damaged.

- the panel itself is not good at handling point loads.

- the skin can peal from the Nomex with enough force.

- the edges are also not aesthetic,

But all of these issues can be fixed (see below photo).


There are several approaches to edging Nomex Sandwich panels:

o Edge, by bonding on a flat extruded carbon or plastic bar or C-channel

o Edge with caulking for lightest weight or epoxy adhesive for highest strength

o Use solid balsa core that doesn’t need edging

o Get over the sex appeal. go functional, don’t edge


But sometimes you have to edge for functional reasons:

o Drill a hole that must supports a load, like a bar going through it, so the hole has to be solid

o The area around a hole or edge has to support a side load

    … can use a washer if the load is light enough to be spread over the washer

   … if the load is high, then edging is required

o The edge is facing an impact zone or wear zone

o The edge needs to be softened (carbon on edge can be sharp)

o The skin is subject to peal forces.


In this example, a Vibration Dampened Electronics Platform (VDEP) is being built to sit within the frame of the ship (motor masts, spars, rotors, and prop cooled ESCs). The VDEP needs to hold the electronics, battery, and camera; approximately ½ a kilogram. That load goes through four holes in the Carbon/Nomex panel.

Two carbon extruded rods (axles) connect the VDEP (think car body) to the frame (think car frame and motor)  by going through via four Lantern Style dampers laid sideways (think shocks or struts)  that are part of the frame and through four holes in the VDEP. Thus the holes need reinforcement because they carry a load that is too high for Carbon/Nomex material. See photo below.  


To reinforce the holes and make the edge aesthetic and bomb proof in crashes, the edges of the VDEP were filled with epoxy adhesive (Scotch-Weld EC 2216). Note that there are many different types of fillers. And many different types of processes. This is the Ditch Route process.


Step 1: Ditch Route the shapes into the Carbon/Nomex Sandwich Panel. But first drill locating holes so the piece can be put back under the 3-axis router again for a final route and be sure to not turn the router off or save the zero point. Route through the top skin and the Nomex, but not the bottom skin. Leave the bottom skin to make it easier to fill the “ditch” with the filler of choice.


This photo shows the ditch for an inner cut-out, and outside profile, and a hole.


This photo shows light shining where the ditch is coming through the skin on the far side, which in this case is only a single ply of carbon.


Step 2: Cut the Nomex flags. The flags will interfere with the filler penetrating the cells along the edge of the cut. This goes a lot faster than it looks when using the right tool.


Step 3:  Fill the ditch with the filler of choice. Focus on the side of the ditch that matters. Cure the filler (I used an oven at 200F so the 2216 would cure in 30 minutes).


Step 4: Route the filler and panel all the way through. Use the locating holes in the panel to set the workpiece back under the router. Set z to go all the way through the panel.


And that’s one way to build a light weight and extremely durable 250 FPV flyer.


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  • What happens if downside isn't ventilated? 

    • MR60

      if a naked ESC isn't ventilated by the props, then you will want to fly

      - one esc naked

      - the rest of the esc as they come from the factory (OTS)

      - fly it hard for about 4 minutes in a safe location, quickly land it and then touch the ESCs

      - then make an appropriate decision

      • thank's, good idea.

  • Would it be a easier and cheaper to use simple epoxy infusion resin instead of the Scotch-Weld EC 2216 glue ?

    A resin like this one (for example):!/resin-gel-silicone-adhesive/epoxy-resin/epoxy-infusion-resin.html

    will be more of a more fluid form, hence easier to fill all the gaps in the ditch and when it fully cures you just put the whole thing back to the router.

    You can even add a couple of black-colored pigment drops in the resin and the result will be with a nice black-tinted finish edge.

    BTW, I've been following you for some time now Forrest and I have to say that your work is amazing...!

    • MR60

      definitely try-storm different materials. you are probably onto something. something that you can add color to would make an interesting sex-appeal effect (red, white, a glowing green)..

      Boeing and Airbus, on floor panels, would use a light weight white calk. it might be SkyFlex 

      • I have worked on composite materials and panels in aerospace for some time.

        We like to use ATR 1000 and ATR-355.  The potting life is better (30 min vs 5 min) for these potting compounds than for the 3M 2216 epoxy.

        My 2 cents.  Not worth much . . . 

        • MR60

          thanks Tony. that's the stuff i was trying to remember. i can still see workers in Spokane WA putting the putty in the base of their hands and deftly and quickly forcing it into the edges of floor panels, it forms a light weight solid edge.

          so i assume you are with Boeing?

        • Looks good.

          Another possible alternative is black epoxy repair filler!/resin-gel-silicone-adhesive/epoxy-resin/black-epoxy-repair-filler-for-carbon-fibre.html

          To reduce the weight it may be possible to add glass bubbles to the mix

    • MR60

      Epoxy resin would be too fluid to fill honeycomb cells. You need an epoxy (or 3M2216) that is thick enough not to run like water.

    • I tink it would be too heavy because it will fill all the open honeycomb cells. With a more viscous adhesive you have more control over the depth of the infill.

This reply was deleted.


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