How to Install the Ariel Replacement Fin on Your Rocket

Quick Answer

Installing the Ariel replacement fin requires you to remove the damaged fin, prepare the root edge, and bond the new fin with epoxy. Use a fin alignment jig to keep it straight.

Step-by-Step Fin Installation

1. 1. Remove the Damaged Fin: Use a hobby knife or Dremel tool to cut away the old fin and any remaining epoxy. Sand the area smooth and wipe with isopropyl alcohol. Don't rush this step — leftover epoxy lumps will prevent the new fin from seating flat.
2. 2. Dry-Fit the Ariel Replacement Fin: Place the new fin into the slot or against the airframe. Check that it sits flush and matches the rocket's curve. Mark the root edge with a pencil. If the fin rocks or has gaps, sand the root edge lightly until it sits evenly.
3. 3. Prepare the Bonding Surfaces: Rough-sand the inside of the slot and the root edge of the fin with 80-grit sandpaper. Clean both surfaces with acetone or alcohol. Skipping this step reduces bond strength by up to 50%.
4. 4. Mix and Apply Epoxy: Use a high-strength epoxy rated for high-power rocketry (e.g., 30-minute or 60-minute cure). Apply a thin layer to the slot and the fin root edge. Too much epoxy creates a weak, brittle joint. A thin, even coat is what you want.
5. 5. Position and Clamp the Fin: Insert the fin into the slot. Use a fin alignment jig or a square to ensure it's perpendicular to the airframe. Clamp in place with spring clamps or masking tape. Check alignment from both the nose and tail ends — a fin that looks straight from one side may be twisted.
6. 6. Apply Fillet Epoxy (Optional but Recommended): After the initial bond cures, apply a fillet of thickened epoxy along both sides of the fin-to-body joint. Use a rounded tool to shape the fillet. Fillets dramatically increase the fin's impact resistance. Don't skip them on high-performance rockets.
7. 7. Let Cure and Inspect: Allow the epoxy to cure fully according to the manufacturer's instructions (usually 24 hours). Remove clamps and check for any gaps or movement. If you see any light between fin and body, reapply epoxy and clamp again.

Product Facts

• Fantom 438: The LOC Precision Fantom kit includes through-the-wall fin construction and a pre-slotted airframe for easier alignment. If your rocket uses a similar through-the-wall design, the Ariel fin will seat more securely and align naturally with the slots.