Definition
A description of a supercharger arrangement that compresses induction air in two successive steps, typically using two impellers in series, to achieve higher manifold pressures than a single compression stage can produce. Each stage adds compression to the air already compressed by the previous stage, allowing the engine to maintain rated power at higher altitudes.
Plain English
Two stage means the air going into the engine is squeezed twice instead of once. The first squeeze raises its pressure part of the way, and the second squeeze raises it the rest of the way, so the engine still gets dense air even at high altitude.
Context Anchor
Seen in descriptions of superchargers and induction systems, especially when comparing engine power at different altitudes.
Derivation
From 'two' plus 'stage,' where 'stage' comes from the Latin 'stare' (to stand) and came to mean a step or level in a process. In aviation, each 'stage' is one step of compression — so 'two stage' simply means two steps of compression done in sequence.
Why Pilots Care
It lets the engine maintain sea-level power well above the altitude where normally aspirated engines lose output.
Intuition Check
Two stage does not simply mean two settings or two speeds. Here it means two separate compression steps: the air is compressed once, then compressed again before entering the engine.
Example Sentence 1
The radial engine on this aircraft uses a two stage supercharger, allowing it to maintain full power well above 20,000 feet.
Example Sentence 2
During climb the pilot monitored the two-stage system to ensure the intercooler was cooling the air between stages.