Definition
A joint made by tapering the ends of two pieces of material at matching angles so they overlap along a long, sloped surface, then bonding them together to form a single piece. In aircraft structural repair, scarf joints are commonly used to splice wood spars and to repair composite skins, where the long taper distributes load across a wide bonded area rather than concentrating it at a square joint.
Plain English
Two pieces are shaved to long matching slopes, then glued together along that slope so the join blends smoothly and carries load across the whole tapered surface instead of meeting at a single edge.
Context Anchor
Seen in aircraft structural repair instructions, especially when repairing wooden parts, plywood skin, or other bonded aircraft structure.
Derivation
From an old shipbuilding and carpentry term meaning to cut a long sloping end on a piece of timber so it could be joined to another. The same idea carried straight into aircraft work: a long taper gives a strong, smooth splice.
Why Pilots Care
On wood and composite structures, a properly cut scarf joint restores close to the original strength. A poorly cut or too-short scarf is a structural weak point and a common reason a repair is rejected at inspection.
Analogy
Think of two pencils sharpened to long flat points and glued together along the slanted faces. The bonded surface is far longer than the pencil is thick, so the join is strong and barely visible.
Intuition Check
“Scarf” does not mean a piece of clothing here. In aircraft repair, it means a long sloped joining cut that lets two pieces overlap and bond securely.
Example Sentence 1
The technician cut a 12-to-1 scarf joint into the damaged spar before bonding in the new section.
Example Sentence 2
A six-to-one scarf ratio was used when repairing the fuselage longeron.