About this calculator
The splice rule of AC 43.13-1B par. 4-58g applied to a doubler: the width of damage the load must go round, times the rivets per inch of the table for your skin and rivet, times the joint factor. Then the rows, pitch and edges that fit, and the size of the doubler.
Runs in your browser. Measure the damage after clean-up with the corners rounded. Inches or millimetres at the top.
How it works
Rivets each side = W × rivets per inch × joint factor, rounded up. W is the damage width across the load. The rivets per inch come from AC 43.13-1B Table 4-9, 4-10 or 4-11 for the skin alloy, its thickness and the rivet diameter; the notes allow 75% for a single-lap sheet joint, 80% for stringers and 60% for intermediate frames.
The rivets of one edge go in rows parallel to that edge, the end rivets 2.5D past the damage. The calculator takes the fewest rows (up to four) that keep the pitch at the multiple of D you choose, never under the 3D minimum of par. 4-57c. Rows sit 75% of the pitch apart and at least 2.5D apart (FAA-H-8083-31A p. 4-35); the first row is 2.5D from the cut, the doubler edge 2.5D past the last row.
With load in both directions, the two other edges get their own count from the damage length.
The AC's own example (par. 4-58g): 2017 / clad 2024 sheet 0.032 in, 10 in wide, 1/8 in AD rivets: 4.9 per inch × 0.75 = 3.7, 37 rivets, two rows of 19.
Limits — when NOT to use this
- Approved data governs. If the SRM gives a repair for this area, use it. A repair outside the SRM in primary structure is a major repair needing approved data.
- The tables are for 2117-T4 (AD) protruding-head rivets in aluminium sheet in tension. Countersunk rivets, other rivet alloys, pressurised skins and fatigue-critical areas need the manufacturer's data.
- The doubler is sized for the load path round the damage, not for buckling, sealing or aerodynamic smoothness.
- Skin thicker than 0.128 in is outside the tables.
Sources
- FAA AC 43.13-1B CHG 1, Chapter 4 par. 4-57 and 4-58, Tables 4-9 to 4-11 — rivet count per inch of width, joint factors, edge distance and pitch minimums, doubler material.
- FAA-H-8083-31A Aviation Maintenance Technician Handbook, Airframe Vol. 1, Chapter 4 — transverse pitch 75% of the rivet pitch, not under 2.5D (p. 4-35); drill speeds (p. 4-17).