Definition
On a two-speed supercharged engine, the lower of the two impeller gear ratios, used at lower altitudes where the air is denser and less compression is needed to maintain rated manifold pressure.
Plain English
The slower of two speeds the engine's air-compressor can spin at. It is used down low, where the air is already thick enough that you don't need the compressor working at full speed.
Context Anchor
Seen in discussions of supercharged piston engines, especially when managing engine power as the aircraft climbs or descends.
Derivation
Blower' is an old aviation nickname for a supercharger — the device that 'blows' extra air into the engine. 'Low' refers to the lower gear ratio that drives it, not to low power.
Why Pilots Care
Selecting the proper blower setting prevents overboost damage while maintaining adequate power as altitude increases.
Grounding Statement
At lower altitude, the outside air is already dense enough that the engine usually needs only the lower blower setting.
Intuition Check
“Low” does not mean weak or wrong here. It means the supercharger is operating at its lower speed, which may be exactly the correct setting for the altitude and power needed.
Example Sentence 1
Below the critical altitude, the engine is operated in low blower setting to produce rated manifold pressure without overboosting.
Example Sentence 2
During the climb the checklist directed a switch from low blower setting to high blower once the aircraft passed the critical altitude.