Definition
The directional surface texture of aircraft covering fabric, formed by the short fibers that lie along the warp (lengthwise) threads. The nap runs in one direction along the bolt of fabric and affects how the material is laid out, cut, and finished during a covering job.
Plain English
The natural "grain" or fuzz direction of the fabric used to cover an aircraft. Like the pile on velvet, the tiny fibers all lean one way, and that direction matters when the fabric is being applied.
Context Anchor
Seen in aircraft fabric-covering work, especially when inspecting, preparing, or finishing fabric-covered aircraft surfaces.
Derivation
"Nap" comes from the Middle English noppe, meaning the fuzzy surface of cloth. The same word is used for the soft pile on velvet, suede, or felt. In fabric covering, it carries that same idea — the fibers have a direction, and that direction has a name.
Why Pilots Care
When recovering a wing or fuselage, panels of fabric must be laid out with the nap running the same way. Mixing nap directions can cause uneven appearance, uneven dope or coating absorption, and visible streaking once the finish is applied.
Analogy
Run your hand along velvet one way and it feels smooth; the other way it feels rough. Aircraft covering fabric has the same kind of directional surface, just much more subtle.
Intuition Check
Nap here does not mean sleep. It means the fine fuzz or raised fibers on the surface of the cloth.
Example Sentence 1
Before cutting the panels, the technician marked the nap of the fabric with an arrow so every section would lie in the same direction.
Example Sentence 2
Reversing the nap of the fabric during covering caused uneven shrinkage after doping.