Definition
A composite laminate in which the ply orientations and materials are arranged as a mirror image about the centerline of the laminate stack. For every ply at a given orientation above the midplane, there is an identical ply at the same orientation and the same distance below the midplane.
Plain English
A stack of composite layers built so that the top half is a mirror image of the bottom half. Each layer above the middle is matched by an identical layer the same distance below the middle.
Context Anchor
Seen in composite aircraft structure, composite repair instructions, and maintenance drawings that specify how layers of fiberglass, carbon fiber, or other composite cloth must be laid up.
Derivation
Symmetrical comes from the Greek 'symmetria,' meaning 'same measure on both sides.' Laminate comes from Latin 'lamina,' meaning 'thin plate or layer.' Together: layers arranged with the same measure on each side of the center.
Why Pilots Care
A symmetrical layup keeps the part dimensionally stable. An unsymmetrical laminate can warp or twist as it cures or as temperature changes, which matters for control surfaces, skins, and any repair work where the part must stay true to shape.
Analogy
Think of stacking colored sheets of paper so the order above the middle is mirrored below the middle. If the stack is red-blue-green-green-blue-red, it is symmetrical around the center.
Intuition Check
Symmetrical does not just mean the finished part looks even from the outside. Here it means the internal layer pattern is mirrored through the thickness of the laminate.
Example Sentence 1
The repair was built up as a symmetrical laminate so the panel would not warp after curing.
Example Sentence 2
Because the laminate was symmetrical, the cured part remained flat and required no additional shimming during installation.