The calculator
Runs in your browser. Inches or millimetres at the top.
How it works
AC 43.13-1B paragraph 3-10g: “Core potting is the process of filling the core cutout with a curable paste filler material. ... if the honeycomb or foam core is damaged, it may be potted rather than plugged if the damaged area is small (1 inch or less).” Figure 3-11 shows the typical undercut: the core is cut back wider than the hole in the skin, so the cured plug locks in.
Volume = π/4 × (hole + 2 × undercut)² × core depth, plus π/4 × hole² × skin thickness, plus overfill. The AC asks you to fill slightly above the surface for an overlay repair and slightly above the core for a flush repair, then trim; the overfill percentage covers that and the paste left in the cup.
Honeycomb cells are open, so the paste fills the whole cavity. The cell walls are left in, a small share of the volume; ignoring them makes the figure slightly high, which is the right side to err on.
Worked example
A 0.75 in hole, 0.125 in undercut each side, 0.375 in of core removed, 0.020 in skin, 10 % overfill.
- Core cavity = π/4 × 1.0² × 0.375 = 0.295 in³.
- Skin hole = π/4 × 0.75² × 0.020 = 0.009 in³.
- Total = (0.295 + 0.009) × 1.10 = 0.334 in³ = 5.5 mL.
Mix about 6 mL. The damage is under 1 in, so potting is within what the AC allows.
Limits — when NOT to use this
- The SRM governs whether potting is allowed in that area, and with what compound.
- Over 1 inch the AC points to a core plug repair instead.
- Already-potted areas: the AC says a replacement core in an already-potted area should also be potted.
Questions people actually ask
Why undercut the core?
So the cured potting is wider below the skin than the hole through it and cannot pull out. AC 43.13-1B Figure 3-11 shows the typical undercut cavity.
Sources
- FAA AC 43.13-1B CHG 1, Chapter 3, par. 3-10g and Figure 3-11 — core potting, the 1 inch limit for potting instead of plugging, the undercut cavity, filling and trimming.