Definition
The principal lengthwise structural member running through a wing or stabilizer that carries the bulk of the bending and lifting loads. In a stabilator, the main spar is the hinged structural backbone the entire control surface pivots around as it moves up and down.
Plain English
The strongest internal beam inside a wing or tail surface. It runs from root to tip and carries most of the load. On a stabilator, it's also the rod the whole surface rotates on.
Context Anchor
Seen in aircraft structure discussions, especially when describing how a stabilator is built and how it carries loads.
Derivation
Spar' comes from Old Norse 'sperra,' meaning a beam or rafter — the main timber holding a roof up. The aviation use carries the same idea: the main spar is the primary beam holding the surface together against the loads of flight.
Why Pilots Care
Any damage to the main spar threatens the entire structural integrity of the surface and can lead to in-flight failure.
Analogy
A main spar is like the main beam inside a shelf: you may not see it from the outside, but it carries the load and keeps the surface from bending too much.
Intuition Check
Do not think of a spar as just a small rod or brace. In this context, the main spar is the primary load-carrying beam inside the stabilator.
Example Sentence 1
On a stabilator, the entire surface pivots on the main spar, so the spar acts as both structure and hinge.
Example Sentence 2
During the stabilator inspection, the pilot looked along the main spar for any signs of corrosion.