Chapter 7:  Fuselage Exterior


 

Chapter 7 is the first major milestone and everyone looks forward to this moment. Yeah, we DID sit in the fuselage and make the obligatory varoom noises! Geaux Tigers!


(Addendum:  June 1, 2002:   In the Cozy Newsletter #78, Nat Puffer clarified how the aft end of the fuselage is to be carved.  Essentially, the foam outboard of the top longerons and LWY’sis to be removed to provide for glass-to-wood bonds in the spar box area.  Also, some of the BID tapes that tie the spar to the fuselage sides are now supposed to be 5 plies.   These details were not described in the text portions of the plans, and in my opinion were not clearly depicted on the M-drawings.  Many of us that finished Chapter 7 before the newsletter were published got caught with our pants down!  Furthermore, those who have already installed the spar and strakes cannot implement these instructions without major surgery.  So… DO NOT USE my pictures or my references as fact or as being representative of the instructions and clarifications available in the plans.)

A better representation can be found here:  http://www.stealthturtle.com/cozy/chapterLogs/chapter7/chapter7_2.html


Step 1 – Building the NACA Scoop

I sized the urethane foam blocks to the plans dimensions, but fell a few inches short of being perfectly flush with the rest of the fuselage bottom. I was unhappy with this, so I added two small blocks to the front edge of the scoop and resanded flush. For reference, the scoop foam starts very near the aft edge of the landing brake cutout. I recommend laying a straight edge across the landing brake area and onto the forward landing gear bulkhead to find the dimension of the foam for your NACA scoop. There's no way to atone for this in the plans as I'm sure everyone's bottom curvature is slightly different.

Step 2 – Contouring the Bottom

Carving the fuselage bottom and sides was fun, but tough and challenging! The challenge comes in trying to get good curves in the transitions between the PVC foam and the clark foam spacers. The clark foam is sooooo soft compared to the PVC foam. After roughing in the corners with the belt sander, I used a sanding plank (4-foot long poplar board with sand paper glued to it) to finish up. I highly suggest this. The length gives you excellent control. I always focused on shaping the PVC foam first. For final shaping of the clark foam, I used a belt sander belt (suggested by one of our brilliant builders). I bought a 3x24 inch, 100 grit belt sanding belt, cut it crosswise, then used a gentle buffing motion until I got the curved shape I wanted in the clark foam. Buffing straight up and down (90 degrees to longerons) would cut deep; buffing at shallow angles resulted in good, rounded curves. I gave up trying to carve the sides exactly like Nat's curvature templates. I ended up with a "pleasing shape", not too far removed from the templates, and that's good enough for me. I've learned that Nat's plans can specify dimensions, but your mileage will vary. This is not a knock against the plans, it's just to say that in moldless construction, no two planes are ever identical. It took me about 5 hours to carve the first side and about 2 hours to carve the second side.

3. This is how my carving looks at the firewall. (DON’T CARVE YOUR FUSELAGE LIKE THIS!  Please see the addendum above.)  You can't really tell due to the lighting, but that taper extends forward of the firewall for about 4 feet. Also, note the gap between the C&D birch pieces. I should have paid more attention to how the C and D birch pieces fit together. They are supposed to touch on one edge. I used the plans dimensions instead of fit-checking first, so I ended up with a gap at the rear corner. I filled it with micro and feathered the edge into the rest of the foam. For strength, I filleted the inside corner with flox before 2-BID taping. From then on, I started making patterns and fitchecking the patterns before cutting the pieces.

4. These pictures show the A, B, C, D birch pieces, the PVC foam closeouts, and the urethane blocks prior to carving. Again, I made up patterns before cutting the pieces.

 

5.  I bought the antenna kit from Jim Wier and installed the VOR antenna per plans. The copper tape has adhesive on one side, which gets stuck to the foam. I routed out a groove for the solder joints, torroids, and cable. Like Zeitlin, the cable enters to cabin just in front of the instrument panel. If marker beacons are still around in 4 years, I'll just put one along the lower longeron (on top of skin and under final micro fill), or put it on the strake or in the wing. Note also where I've routed out the overlapped area for the landing brake. The yellow paper says, "Don't forget to do the duct tape buildups before glassing the bottom!" Addendum:  Years and years later, after the exterior skins were glassed, I decided to add another NAV antenna about 18 inches forward of the existing one that was installed in the plans location. I simply soldered up another antenna, cut a hole and a channel into the bottom skin for the baluns and the cable, filled the channel with dry micro, and glassed a strip of BID over each of the foils.  It will be covered up and hidden completely with the contouring process in Chapter 25.

 

6.  From the drawing in the plans, I was expecting the wood reinforcement piece for the step to be fairly thick. After carving out the foam, I realized that the piece for my plane would be rather thin (less than 1/4th-inch thick). It almost wasn't worth the effort and might have been easier just to fill the space with flox. Again, the thickness will vary from plane to plane.

7.  I didn't make the joggles into the bottom foam for the landing gear cover. I knew I was going to make the landing gear cover differently than plans. I'm jumping ahead here, but I glassed in some lips between the landing gear bulkheads. See Chapter 9 for how I did that.

Step 5 – Glassing the Sides

It has been suggested to sand a depression (joggle) along the length of each side to incorporate the glass overlaps without bumps. I didn't do this. Since my clark foam sanded low anyway, I just made my overlaps over the clark foam to build that area up a little.

True confession-- I can't scissor trim in a straight line worth a damn! So prior to glassing the bottom and sides, I ran a length of duct tape down the sides, wet out the cloth to the middle of the tape, then using the tape as a guide, I scissor trimmed to the edge of the tape. Then I peeled the tape away. Wetted cloth scissor trims easier than trimming dry. The tape also kept epoxy drips off the raw foam and/or completed glass work. Note the duct tape buildups for the landing brake, engine mount/landing gear reinforcing layups, and the recessed area for the Vance's fuel sight gages.


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