Classic 320
Fuselage construction overview
- .050" carbon-fiber (CF) rod reinforcement at each corner.
- Forward of the timer-mounting area, the cross-section transitions into a circle to mate with the round firewall.
Firewall and engine mount
The round plywood firewall, with blind or T-nuts installed (for radially mounting your engine), is glued to a square balsa block. It is important that the grain of this balsa block (or plug) runs fore and aft (that is, the firewall is attached to the end grain of the plug). For additional security and peace of mind, run a flat-head #4 wood screw through the plywood and epoxy it into the balsa block.
Build in 3° of downthrust into the firewall/engine mount. Built-in side thrust is optional. During flight testing I often end up with approximately 2° of left thrust; you can build this in now or add it later with flat washers between the engine and firewall as testing and trimming dictate.
Timer-mount area reinforcement
Reinforce the timer-mount area with:
- 1/32" plywood on the inside of the balsa side, and
- 1/64" plywood on the outside.
Install the .050" corner rods from the aft end forward, but do not glue them in place forward of the timer area yet.
Square-to-round transition
With the round firewall and square balsa plug glued between the fuselage top and bottom and between the fuselage sides, cut grooves into the corners of the area forward of the timer. These grooves allow the CF rods to be bent inward to attach to the outer edge of the firewall. Carving and sanding will accomplish the cross-sectional transition from square to round.
This completes the basic fuselage construction except for the installation of the stabilizer mounts. Glue a blind nut into the aft fuselage plug to facilitate the later addition of tail ballast, if flight testing indicates any is required.
Covering and finishing
- I cover all open framework with Polyspan; other options are tissue or silk. Whatever you choose must be a material that shrinks and therefore can provide torsional "skin strength" to the wing and stabilizer.
- All structure that will contact the covering material (top and bottom of each rib, half rib, leading edge, crossbrace, every spar, the LEs and TEs, and the wing and stabilizer tips) should receive two coats of thinned nitrate dope and a final coat of unthinned nitrate dope.
Covering application:
- Apply the covering material with unthinned nitrate dope; this assures good adherence on spar and rib bottoms (for proper undercamber) and on the tops of the 7/16" ribs, where the covering tends to pull away as it shrinks and tightens.
- After shrinking and tightening the covering material (with heat, if using Polyspan), apply two coats of thinned nitrate dope.
If you use all-white Polyspan, you can trim with tissue of any color, shape, or design by applying it directly over the Polyspan with very thin nitrate dope. The all-balsa surfaces of the vertical tail and pylon should be sealed and doped similarly before finishing.
Transcribed from original scans by AI. Minor OCR errors may remain.
