Definition
A short exhaust pipe extending from the exhaust port of an aircraft reciprocating engine cylinder, designed to direct exhaust gases away from the engine and, in many installations, through a heat exchanger shroud that supplies cabin heat or carburetor heat.
Plain English
A short pipe that carries burnt gases out of one cylinder of a piston engine. It often runs through a metal sleeve so the heat coming off it can be used to warm the cabin or the carburetor.
Context Anchor
Seen in aircraft maintenance discussions of piston-engine exhaust systems, especially older radial engines.
Derivation
Named for its resemblance to a bayonet — the short blade that fits onto the end of a rifle. The exhaust stack is similarly a short, straight piece that attaches to the end of something larger (the cylinder).
Why Pilots Care
Cabin heat and carburetor heat are typically drawn from air warmed by these stacks. A cracked bayonet exhaust stack can leak exhaust gases — including carbon monoxide — into that heated air and then into the cabin, which is why exhaust system inspections are taken seriously.
Analogy
Think of it like a short piece of tailpipe that slips into a larger pipe instead of being locked solid at both ends. That small freedom to move helps it handle heat expansion.
Intuition Check
Bayonet does not mean there is a weapon-like part on the airplane. Here it describes the way the exhaust pipe fits into the exhaust collector.
Example Sentence 1
During the preflight inspection, the mechanic checked each bayonet exhaust stack for cracks before signing off the annual.
Example Sentence 2
After the annual inspection the bayonet exhaust stack was reinstalled and checked for proper seating before the next flight.