Definition
Short exhaust stacks fitted to a reciprocating aircraft engine that vent each cylinder's exhaust gases directly overboard with minimal length and no muffler or collector system. They are typically used on aerobatic, racing, and agricultural aircraft where weight savings, simplicity, and a slight thrust gain from exhaust gas velocity are valued over noise reduction.
Plain English
Short pipes that let each cylinder's exhaust escape straight out the side of the engine cowling, without being routed through a muffler or joined into a single tailpipe.
Context Anchor
Seen in aircraft engine and maintenance discussions, especially when describing older or simple piston-engine exhaust arrangements.
Derivation
Stack' comes from the old use of the word for a vertical pipe or chimney that carried smoke or exhaust away. The term was carried over from steam engines and early industrial machinery to describe the exhaust pipes on piston aircraft engines. 'Short' simply distinguishes them from longer collector or muffled exhaust systems.
Why Pilots Care
They can increase engine power output but raise noise levels, exhaust gas temperatures, and the risk of heat damage to nearby components.
Intuition Check
Do not read “stacks” as piles of objects here. In this aviation use, stacks are exhaust pipes, and “short stacks” are short exhaust pipes on the engine.
Example Sentence 1
The Pitts Special was fitted with short stacks, giving it a sharp exhaust note and saving a few pounds over a full collector system.
Example Sentence 2
During preflight the pilot examined the short stacks for cracks and loose clamps.