Definition
The main lengthwise structural members inside an airplane wing that run from the wing root toward the wingtip and carry the primary bending and lifting loads of the wing. Ribs, skin, fuel tanks, and control surfaces are all attached to or supported by the spars.
Plain English
The strong internal beams that form the backbone of the wing. They are what actually hold the wing together and carry its load in flight.
Context Anchor
Seen in weight and balance, aircraft loading, and structural-limit discussions, especially when explaining how weight and flight loads are carried by the airplane.
Derivation
Spar comes from Old Norse 'sperra,' meaning a beam or rafter — the same idea as a roof beam in a building. A wing spar is literally the wing's main beam.
Why Pilots Care
Spar weight and location directly affect the aircraft's empty weight and center of gravity; damage or modifications here can shift balance and compromise structural integrity.
Analogy
Wing spars are like the main beams inside a floor or bridge. You may not see them from the outside, but they carry the load.
Intuition Check
Do not think of wing spars as the thin metal skin of the wing. They are the main internal beams that carry major loads.
Example Sentence 1
The fuel tanks in this airplane are built into the wings between the front and rear spars.
Example Sentence 2
The pilot reviewed the structural inspection records to confirm the wing spars had no corrosion before approving the flight.