As my current scale building project continues, I am now starting to build the Nieuport 24’s engine cowling. I barrowed my good friend John Tanzer’s technique of apply glass cloth to a foam plug and then pulling a nylon stocking over it to hold the cloth tight against the plug. The resin will then be applied and allowed to flow into the cloth. I got most of my materials from Home Depot.
The fiberglass shown here is labeled heavy duty, but I would guess it is 2oz. cloth. I made a test of three layers with resin pressed between two sheets of acrylic and the cured sample was 0.020 inches thick. So I am ordering some 6oz. cloth as well.
I used 1-inch-thick pink foam insulation board and carefully cut five 12×12 inch squares from two 24×24 inch boards using a sharp utility knife.
Next, I carefully marked each square’s center of each square.
A sharpened piece of K&S Brass tubing makes a great foam hole cutter. I used 1/2 inch diameter tubing to match the hardwood dowel I will used as the mandrel for shaping the foam.
Using plenty of spray adhesive (letting each surface dry before joining), I glued the foam squares together and weighed it down with led shot weights. The dowel is used as a guide to position each layer of foam.
Here I am checking the alignment of the dowel with the surfaces of the foam block.
Here I am adding rough cut marks onto the top of the foam block for cutting with my band saw.
I ran the foam through the band saw before gluing the dowel mandrel into place. If I had a larger band saw table, I would have made a jig board so I could use the center dowel as a pivot to cut the foam into a circle. Here the foam has been cut slightly larger than the required 11 inch diameter. Make sure to check that the saw blade is square to the table. Use a slow cutting rate, and let the saw do all the work.
I screwed a smooth plywood base plate to my drill press table and drilled a 1/2 inch guide hole that will accept the bottom of the dowel.
I used 5-minute epoxy to glue the dowel in place in the foam. Take care to make sure everything is aligned and square to minimize any wobble when the foam is spinning. I also spot glued a couple of plywood end plates to the foam to spread the torque force while spinning the foam with the drill press. The bottom plate just rests on the plywood base plate screwed to the drill press table. Test run the drill press to make sure you have the base plate properly aligned with the drill chuck.
To get the shape right, I printed out my plan’s engine cowling side view and glued it to some poster paper.
Using 80 grit sandpaper, I slowly rounded the foam to the final diameter and then rounded the top corner. It does not take a lot of pressure to shape the pink foam.
Here you see I am almost there. I just kept sanding off the points that touched the template until the entire foam plug matched.
After only about 15 minutes effort, the foam plug was finished. I used 50 grit sand paper to smooth the foam surface as shown. Here I removed the top end plate and marked off the approximate cowling opening. The next step will be covering the foam with clear food wrap and start applying the fiberglass cloth.