The calculator
Runs in your browser. Inches or millimetres at the top.
How it works
A fillet laid along the edge of a lap is a right triangle in section: area = ½ × W × H. A 1/4 × 1/4 in fillet is 0.031 in². A round bead is π/4 × d².
Volume = area × seam length, divided by (1 − waste) for what stays in the nozzle and comes off when tooling. One US fluid ounce is 1.805 in³ (231 in³ per 128 fl oz).
AC 43.13-1B mentions fillet sealant beads along fastener rows, and the FAA Airframe Handbook's repair figures call for fillet and head seals to the SRM. The bead size is the SRM's or the drawing's.
Worked example
20 ft (240 in) of fillet, 1/4 × 1/4 in, 6 fl oz cartridges, 20 % waste.
- Area = ½ × 0.25 × 0.25 = 0.03125 in².
- Sealant = 0.03125 × 240 / 0.8 = 9.38 in³ = 5.2 fl oz.
- Cartridges = 5.2 / 6 = 0.87: one cartridge.
One 6 fl oz cartridge, with little to spare. Make the fillet 3/8 in and it takes three.
Limits — when NOT to use this
- Fillet size is a specification. The SRM or drawing sets the fillet dimensions and the sealant; this only counts the material.
- Application life. Mix only what you can lay within the sealant's application life at your shop temperature.
- Fay-surface and brush coats are areas, not beads; use the film thickness calculator.
Questions people actually ask
Why does a slightly bigger fillet need so much more?
The section grows with the square of the size: a 3/8 in fillet holds 2.25 times the sealant of a 1/4 in one.
Sources
- Geometry of the bead, and the US fluid ounce (1/128 of 231 in³) — bead size, cartridge content, waste and application life are inputs from the SRM, the cartridge and the sealant data sheet.
- FAA AC 43.13-1B CHG 1 and FAA-H-8083-31, Chapter 4 — fillet sealant beads and fillet and head seals made to the SRM.