Definition
The vertical structural portion of a wing spar that connects the upper and lower spar caps. The web carries shear loads imposed on the spar, while the caps carry the bending loads.
Plain English
The flat middle part of a spar that joins its top and bottom edges. It handles the up-and-down forces trying to slice the spar, while the top and bottom edges handle the forces trying to bend it.
Context Anchor
Seen in aircraft structure descriptions, maintenance manuals, and inspections of wing or tail spars.
Derivation
‘Web’ comes from Old English ‘webb,’ meaning a woven fabric or flat connecting sheet. In structural engineering it was borrowed to describe the flat connecting panel between two heavier edges — exactly what a spar web does between its caps.
Why Pilots Care
Damage or corrosion in the web reduces the spar’s ability to carry flight loads and can lead to structural failure if undetected.
Analogy
Think of an I-beam in a building: the top and bottom flanges resist bending, and the flat vertical sheet between them keeps the two flanges from sliding past each other. The spar web does the same job inside a wing.
Intuition Check
Do not read web as an internet page or a spiderweb. Here, web means the thin structural sheet that connects the main upper and lower parts of a spar.
Example Sentence 1
During the annual inspection, the mechanic found a small crack in the web of the rear spar and removed the aircraft from service for repair.
Example Sentence 2
Mechanics reinforced the web of the spar with a doubler plate after discovering corrosion.