Definition
An exhaust stack on a reciprocating engine in which the exhaust gas exits through a narrow, tapered, slot-shaped outlet rather than a round pipe. The shape accelerates the exhaust flow, which can be used to provide a small amount of jet thrust and to help draw cooling air through the engine cowling.
Plain English
A flattened, blade-shaped exhaust outlet on a piston engine. The narrow shape speeds up the exiting gases, giving the aircraft a tiny push forward and helping pull cooling air through the engine.
Context Anchor
Seen in aircraft engine exhaust system descriptions, inspections, and maintenance instructions for piston engines.
Derivation
Named after the bayonet — the long, narrow, blade-like weapon fixed to the end of a rifle. The exhaust outlet has a similar long, slim, slotted shape, which is where the name comes from.
Why Pilots Care
On engines fitted with bayonet stacks, the shape contributes a small amount of thrust and assists cowling airflow for engine cooling. Damage, cracking, or distortion of the stack can reduce cooling effectiveness and is a finding worth catching during preflight or maintenance inspection.
Intuition Check
Bayonet does not mean a weapon here. It means a locking style where the part fits in and is secured by its shape, a turn, or a collar.
Example Sentence 1
During the walkaround, the technician noted a small crack forming at the weld of the left bayonet stack and wrote it up for inspection.
Example Sentence 2
Bayonet stacks were reinstalled after the cylinder compression check was complete.