Definition
A lengthwise split or crack in a piece of wood that runs along the grain, usually between or through the annual growth rings. In aircraft wood, a shake is a defect that weakens the material and generally makes it unacceptable for structural use.
Plain English
A long crack inside a piece of wood that follows the grain. It's a flaw that can make the wood too weak to use in an aircraft.
Context Anchor
Seen during inspection or repair of wood aircraft structures, such as spars, ribs, plywood, or other wood parts.
Derivation
From Old English 'sceacan,' meaning to move back and forth or split apart. The wood usage refers to the way the fibres have separated, as if the tree had been shaken loose internally.
Why Pilots Care
Recognizing this sensation provides an early warning to reduce angle of attack before a full stall develops.
Analogy
Think of a stack of thin sheets starting to separate along one layer. The outside may still look mostly intact, but the inside bond is no longer solid.
Intuition Check
Do not read “shake” here as trembling or vibration. In this maintenance context, a shake is a split or separation in wood.
Example Sentence 1
During the annual inspection, the mechanic rejected the replacement spar after finding a shake running along the grain.
Example Sentence 2
The pre-stall shake gave the student pilot a clear cue to lower the nose before the wing stalled.