Definition
In a dual-spool turbine engine, the N2 compressor is the high-pressure compressor — the second, inner compressor section that further compresses air already pressurized by the low-pressure (N1) compressor before it enters the combustion section. It is mounted on its own shaft and is driven by the high-pressure turbine, forming the high-pressure spool. N2 is also used to refer to the rotational speed of this spool, expressed as a percentage of its rated maximum rpm.
Plain English
The inner, high-pressure compressor in a two-shaft jet engine. It takes air that has already been squeezed once and squeezes it again before it reaches the combustion chamber. The same name is used for how fast that compressor is spinning, shown as a percentage on the cockpit gauge.
Context Anchor
Seen in turbine engine maintenance, engine start procedures, and cockpit or test-cell indications that refer to N2 speed.
Derivation
The 'N' stands for the rotational speed of a spool (from engineering notation for shaft speed), and the '2' indicates the second, inner spool. So N2 simply means 'speed of the number-two spool,' which carries the high-pressure compressor.
Why Pilots Care
N2 speed directly affects thrust output, fuel scheduling, and engine health monitoring; abnormal readings can indicate compressor issues or impending failure.
Grounding Statement
Air entering a turbine engine is squeezed in stages, and the N2 compressor is the higher-pressure squeezing section before the air is burned with fuel.
Intuition Check
Do not read N2 compressor as simply “compressor number two” or the second blade row. In this context, it means the high-pressure compressor section tied to the N2 rotating shaft.
Example Sentence 1
After motoring the starter, the technician waited for N2 to reach the minimum value before introducing fuel.
Example Sentence 2
After the bird ingestion, maintenance inspected the N2 compressor blades for damage before clearing the aircraft for flight.