Chapter 7

Chapter 7 - Fuselage Exterior

In this chapter I will make the NACA-scoop on the underside and shape and glass the fuselage exterior.

NACA-scoop:
Starting with the NACA-scoop which is the intake for cooling-air for the engine. There are many ways to cool an engine, this way is the plans way, so it's well proven. Since I plan to use a water-cooled-engine (as pr. March 2010 i.e.!) the cooling is a bit easier than for the regular air-cooled aircraft-engines. I will follow the plans and as usual call out if I divert from the plans. So - here we go!

First I cut out the drawing of the NACA-scoop from the large-size-drawings. I then marked the outline on the foam and trimmed off some millimeters from the bulkheads to make it fit inside. Normally I don't like to cut in the drawings but since I have the original drawings there was no problem this time. As one can see the bottom foam has some dents and scratches from the supportive frame that was bondoed ontop of it in chapter 6. I will fix this with dry micro when I am ready to glass the bottom.
On my work-table is my 1/4-scale Cessna 182. The snow is melting and soon I can start to fly my model-airplanes. Had to do some service on the model to make it ready for the season! Read more about the Cessna here (sorry - only in Norwegian). I used to beleive that the Cessna was big. Not so anymore when I compare it with my Cozy :-)

Next step was to cut four blocks of urethane (2" and 1" thick) and place them like the picture shows. Then I draw the shape of the NACA-scoop and cut it out on my jigsaw. The blocks are then microed to the fuselage-foam, the landing-gear-bulkhead and to each other. Then it is weighed down and let to cure.

After cure I placed two plies of BID on the brace overlapping the aft LG and the FW. While still wet I microed blocks of urethane ontop of this. I will later knife-trim the glass so it follows the contour of the bulkheads.

Three pieces of 3/8" H45 is then floxed between the aft LG and the firewall.

According to the plans I should make a 3/4" flange (joggle as they call it in the plans) in the foam on both sides of the cavity for the landing-gear. In chapter 9 I will make a cover over this hole, and the cover will then be made to fit in the flange to make a nice surface without bumps. I will instead follow Wayne Hicks method and drop this flange.

After reading some builders blogs and looking at my own construction it is clear that sanding the urethane according to the plans will create an angle approx. 8" aft of the landing brake instead of a straight line. The ruler at the picture shows a gap if I place the end of the ruler at the aft position of the landing brake.

The gap is almost 6mm (1/4"). I don't know how visible this will be when the fuselage is finished, but it's easy to just add some more urethane in front of the existing foam and sand it down together with the other foam.

And finally the inside of the scoop is glassed with 2 plies of BID. The white speckels are mainly the micro I used to fill the voids in the foam. However - there was some air-pockets in this layup. I fixed this by drilling small 1.5mm holes through the glass and inject raw epoxy with a thin syringe. Worked very well!
A tip: I made micro-corners between the walls and the bottom of the scoop to get the glass to lay down properly. This is no problem for the functionality of the scoop. The important thing is that the corner between the fuselage bottom (not the scoop-bottom!) and the vertical walls of the scoop are square. They will be this when the bottom is glassed later on.

Contouring the sides:
Next step is to contour the sides. First I will shape the bottom corners and glass the bottom. Then I will turn the fuselage and contour the top longerons and glass both sides.

The plans are rather weak in telling how the end-result of the next steps will be, so I read through all the builder-logs I found and collected pictures and descriptions of how other did it. Then I started...

The first corner-cut is according to the plans a 45° cut into the lower longeron exposing 1/4" inch of it. I drew a couple of help-lines on the bottom-foam and the side-foam and used my saber-saw instead of the jigsaw recommended in the plans. I also deliberately avoided to cut into the longeron. I will instead use my belt-sander to trim of the final millimeters. Using the saber-saw was a walk in the park. I've seen numerous blogs where the builders invents special-tools, jigs and whatever to do both these cuts and making router-jigs to shape the NACA-scoop using several HOURS on a task that just takes some minutes to do on freehand. These corner-cuts are not rocket-science. The main thing is to get both sides as symmetrical and esthetic pleasant as possible.
Bonus: Had to buy a new power-tool: The belt-sander. Didn't have this in my collection!
Bonus2: Since I used Divinycell instead of the plans Last-a-Foam as spacer-material (the grey foam in the picture), cutting, sanding and shaping the countors was easy since both materials have the same density and properties.

On the sides and aft of the landing break (which is temporary glued in place) I built up a 1/16" high and 1" wide strip of duct-tape. Took 6 plies to get it flush with the landing-break. The reason for doing this is beeing explained in chapter 9 (at least that's what the plans tell me)...

Antennas
I have read a lot about antennas and landed on the simple solution that has been used by many builders. I tried to contact RST Engineering as recommended by many, but they refused to ship the parts outside US (!). I ended up buying the stuff I needed from Aircraft Spruce (copper-tape and ferrite-torroids) and coax-cable locally.
The info needed is on Marc Zeitlins Cozy-website. I also gathered very useful information from Charles ... website.

The coax-cable ends up just ahead of the instrument-panel. Remeber to make a transition between the hole and the cable-channel so the cable exits with a gentle radius. I drilled the hole pointing slightly forward as well.

I routed space for the torroids. I had to carve out some more foam where the copper-tape meets the coax to get the soldered ends to be hidden inside the foam. I later filled the channel with wet micro to secure the cable and stuff.

The soldering was easy, altough I had to remake the glide-slope antenna once since the copper-tape broke when I bent the wire too much. It's delicate stuff. There are no need for recessing the copper-tape into the foam as it's very thin.

Finally - the antennas are in place. The next step is to fill the channel and depressions I made with some wet micro to ensure that the coax, torroids and soldered ends will stay in place and be protected. I also remembered to measure where the cut-outs for the wheel will be so that the routing of the cable avoids this.

Before glassing the underside it's neccessary to route a groove in the scoop since we will have a glass-to-glass-bond between the underside and the NACA-scoop. Remember to do the same in the aft part of the scoop. This groove is to be filled with flox when glassing the underside.

Finally the underside is glassed and peel-plied. My wife helped me in this stage. It's very useful to have a helper when placing the glass on such big surfaces. She did a great job in squeeging and stippling and brushing!
The things ontop of the fuselage is placed to weigh down some wooden strips I placed in the depression for the landing-break to hold the glass firmly down.

Finished contouring the fuselage sides. I started by marking the various positions where the templates should start and end. Then I marked on the longeron and the foam how much material to remove. Used my saber-saw to cut of most of the foam and parts of the longeron. Then I used the bandsaw to do the shaping according to the templates. I finished with a small delta-grinder with 120-grit-paper. Took about 1 hour pr. side. Again - use the hand to feel any bumps.

Before glassing the sides I made the rottisserie and mounted the fuselage into this. It's basically made according to the plans. I chose to drill holes through the firewall and through F22. Have to repair them later but that's no big deal. One difference from the plans is that I mounted castoring wheels under the frame. In this way I can move the tub freely without needing to ask for help.