Sample Page From Cozy IV Manual

Chapter 5

The Fuselage Sides

In this chapter you will manufacture the sides of your fuselage. You will start by making jigs to provide the correct fore to aft curvature of the fuselage sides. The jigs will first be laid flat on your work table so that the upper longerons may be laminated together with the correct curvature. The jigs will then be mounted upright on the worktable and covered with 1/8 in. masonite to provide a form for the fuselage side layup. Then 3/8 in. thick, blue, low-density PVC foam is laid in the form and cut to the correct profile. Spacers of 3/4 in. white, low-density Clark foam are glued to the top and bottom edges, landing gear-centerspar cut out area, etc. The inside surfaces are contoured, that is, the spacers are beveled, fuel sight gage areas carved, depressions carved for additional stick clearance, etc. The inside surface receives a 2-ply UND skin and, while the layup is wet, the upper longerons are floxed in position. After cure, some local beef up is added to the upper longerons, the lower triangular longerons are installed, and local beef up to the landing gear and center spar mates to the fuselage is opened. The outside foam surfaces are left bare until after assembly of the fuselage is completed in Chapter 6.

Step 1. Cutting The Jigs and Laminating the Top Longerons

For this step you will need two pieces of 1 in. x 8 in. (nominal) x 8 ft. pine board. Layout and accurately cut the fuselage jigs shown on page 2 of this chapter. Jigs FJA, FJB, and FJC will be used to laminate the top longerons to the required curvature. Lay two sets of these jigs flat, back-to-back along the centerline of your worktable, checking to see that they measure 102 in. (minimum) total length, and spread the FJAs 0.5 in. at the forward end only and the FJCs 0.5 in. at the aft end only (fig. 2). The reason for this, of course, is that the longerons will need a smaller radius of curvature than the sides, to fit inside the sieds. Fasten these jigs securely in place on your table with several nails in each jig. Apply box sealing tape to your workbench along side the jigs (so you don't epoxy the longerons to your worktable). Take 6 pieces of 0.25 in. x 1 in. x 105 in. spruce from your kit (fig. 1), mix up some some epoxy, paint the mating surfaces with epoxy, and clamp them (3 strips per side) in place tight against the jigs (Fig. 2). Don't epoxy them to the jigs! Nails driven into the table can also be used to hold the longerons in place (Fig. 2, sec.AA). If you have difficulty holding them tightly together against the jigs, you can even use wedges between the nails and longerons. Allow a smooth transition curve where FJB meets FJC, and let the excess length extend equally at both ends. After cure, take the 60 in. x 0.4 in. x 0.7 in. wood stiffners (Fig. 1), taper the ends as shown, saw cut 0.45 in. deep at 0.75 in. intervals where they will have to bend to match the curvature of the longerons. Make sure you make one right and one left. Epoxy them in place, using flox, on top of each longerons as shown, fastening them until after cure with nails (Fig. 3, sec. AA). Don't try to drive the nails into the wood, rather, predrill holes. In a similar manner, install the two 5-1/2 in. long doublers on top of the longerons at the forward end, and the two 15-1/2 in. long doublers alongside the longeron at the aft end as shown (Fig. 3). Let sure for 24 hours minimum. After cure, remove the nails with pliers.

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