Author: B. Evans
Edition: Model Aviation - 1981/06
Page Numbers: 36, 37
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Firewall Finesse

Most fiberglass fuselages come either with the firewall installed or with the installation left to the builder. Pre-installed firewalls may require blocking or shimming to provide proper spacing between the spinner and fuselage. A fuselage that comes without the firewall in place can easily be adapted to fit your engine if you use a technique that will assure proper alignment. Here's how.

Materials

  • Engine and engine mount
  • Spinner, backplate and prop
  • 3/16 in. plywood for firewall template/disc
  • Hot Stuff (CA glue) or equivalent
  • Filament tape
  • Long drill rods
  • Drill and appropriate bits
  • Baking soda (for filler)
  • Epoxolite (or equivalent epoxy)
  • Sanding/trim tools

Procedure

  1. Trace the spinner pattern onto the 3/16 in. plywood firewall material.
  2. Cut the plywood 1/32 in. inside the traced line (to allow for the thickness of the fiberglass fuselage).
  3. Set the engine and mount into the fuselage. Slide the plywood disc over the rear hub (a few drops of Hot Stuff will hold the disc in place).
  4. Mount and tighten the spinner backplate and prop. Center the backplate on the plywood disc and fuselage front, then tape the components together (filament tape works well). This establishes uniform alignment.
  5. With the engine and mount in place, drill the engine-mount holes through the firewall. Long drill rods are helpful and obtainable at many hardware stores.
  6. Trim the firewall as necessary by trial fit so it fits loosely and rests flat against the engine mount.
  7. Tack-glue the firewall in place. Use baking soda mixed with Hot Stuff as a filler where needed.
  8. Apply Epoxolite to the rear of the firewall where it meets the fuselage. Apply Epoxolite to the front of the firewall as far as possible with the engine in place.
  9. When the Epoxolite sets, remove the engine and touch up any missed spots. Avoid getting Epoxolite where the engine mount attaches.
  10. Bolt the engine and mount in place. Check for a good fit and even clearance between the fuselage and spinner.

Job complete.

Transcribed from original scans by AI. Minor OCR errors may remain.