Definition
The cylindrical metal sleeve of a reciprocating aircraft engine cylinder inside which the piston travels up and down. The barrel is typically made of steel, has a hardened and finely finished inner wall to resist wear from the piston and rings, and is usually fitted with cooling fins on its outer surface. It mates to the cylinder head at its top end and to the crankcase at its bottom end.
Plain English
It is the round metal tube that the piston slides inside in a piston engine. The piston goes up and down within this tube to produce power.
Context Anchor
Seen in piston engine descriptions, maintenance discussions, and inspections of aircraft engine cylinders.
Derivation
Cylinder comes from the Greek 'kylindros', meaning a roller or round body. Barrel comes from the Old French 'baril', meaning a wooden cask. Together they describe a hollow round tube — which is exactly what the piston rides inside.
Why Pilots Care
Cylinder barrel condition controls compression, power output, and engine reliability; wear or damage can cause power loss or failure.
Intuition Check
Do not think of barrel here as a storage container or gun part. In this engine context, it means the hollow round sleeve that the piston moves inside.
Example Sentence 1
During the overhaul, the mechanic measured each cylinder barrel for wear before deciding whether to hone it or replace the cylinder.
Example Sentence 2
Proper lubrication keeps the piston moving smoothly inside the cylinder barrel during flight.