Chapter 7 - Step 1

Step 1 involves the building of the NACA scoop on the bottom of the fuselage.

NACA Scoop Template May 7, 2000. Here is the template for the outline of the NACA scoop used to draw the shape on the fuselage bottom.

Rough Cut Foam May 7, 2000. The 2" and 1" Urethane foam has been cut to size and placed into position. The NACA scoop outline still needs to be cut.

Plywood from Outboard May 11, 2000. This shows plywood pieces A, B, and C set into position on the lower longeron. The beveled edge can be seen matching the curve of the bulkheads.

Plywood from Inboard May 11, 2000. Here are the same pieces from the inboard view. The inside edges are flush with the 6 layers of BID done at the end of chapter 5.

Weighting NACA Foam May 13, 2000. Gluing the foam into place for the NACA scoop involved a lot of interesting weighting. The 2" foam needed the most effort to adhere to the curve. Once sanded down the stress will be much less.

Update: Do to a little sag in the bottom, the 1" and 2" foam on the right side of the fuselage had a big gap between it and the fuselage bottom. I discovered this after shaping everything. I had to cut part of the urethane foam off, apply a thick layer of flox, and replace the foam.

Lots of Weights May 13, 2000. The full view of all the weights keeping the NACA scoop foam in place on the fuselage bottom.

Outboard Foam May 13, 2000. Here are the plywood pieces floxed into place with the 1" foam microed to them. The bulk of this foam gets carved away when the corners are rounded.

Inboard Foam May 13, 2000. A view from the inside.

Plywood D - Outboard May 13, 2000. Here is plywood piece D floxed into place. The bevel matches the curve of the bulkhead and lines up with plywood piece C.

Plywood D - Inboard May 13, 2000. To get everything to match up, this plywood piece isn't quite level fore and aft. Hopefully this doesn't matter later.

NACA Sanded Smooth May 14, 2000. The 1" and 2" urethane foam has been sanded smooth to form the NACA scoop. You can see some popsicle sticks were used to keep the 1/8" lip above the bulkhead. I glued the stick in place with a few small dabs of 5-min. epoxy.

2 inch Foam May 14, 2000. After applying the 2 ply BID layup to plywood piece D I added the 2" block of urethane foam. Here you can see all the foam in place before being shaped.

3/8 inch Foam May 14, 2000. The aft portion of the NACA scoop is made from 3/8" PVC foam. If you look real close you can see the forward edge of the PVC foam is exposed 1/8" to help form the lip for the landing gear cover.

When doing this area I did some of the work in a different order from the plans. I found it easier to do the 3/8" PVC before doing the 2" urethane foam. This allowed me to cut the 2" foam to the shape needed to fill the area exactly.

Joggle May 14, 2000. The 3/4" by 1/8" joggle has been cut into the foam at the forward bulkhead. This was done simply with a razor blade.

Joggle End May 14, 2000. One of the big questions is "where does the joggle end?" For now I have chosen to end it about where plywood piece A reaches the bulkhead. I'll figure out how this works later when the rounding process begins.

Mounting Holes May 14, 2000. Once the joggle was made I proceeded to make the 1/2" by 1/4" holes for the aluminum mounts for the landing gear cover. I layed a piece of scrap PVC foam over the NACA foam to prevent accidental damage. The urethane foam is soft and it doesn't take much to damage it.

I made the holes with a 1/4" wood chisel. My wife was using the drill to work on our deck so I had to improvise. It actually worked pretty well.

Aluminum Mounts June 4, 2000. Here are the 16 aluminum mounts floxed into place.

Joggle Hell June 9, 2000. Here is everybody's favorite part - glassing around the landing gear cover joggles. I made a BIG mistake that made this even harder than it normally is. I didn't round the edges of the bulkheads. The plans don't explicitly say to do this but it does when glassing the bottom.

My setup here involved putting some 3/4" inch boards in the joggle and then a big board on the faces of the landing gear bulkheads. These held the glass that wrapped around the face and held the 3/4" boards in tight against the joggle.

Another View June 9, 2000. Here is another view of my setup.

Grand Champion Rube Goldberg Setup June 9, 2000. Here is the final version. This is basically the previous two pictures with weights added to hold down the boards in the joggle. Scarey, huh!