hipps_76 asked in Cars & TransportationAircraft · 8 years ago

# On a turbine (jet) engine, what does the "N" mean when monitoring engine speed?

(e.g. Monitoring N1% and N2% speeds.)

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• 8 years ago

Nxxx% means xxx percent of a nominal full-thrust rotational speed defined for the engine by the manufacturer. It typically is not the maximum speed the engine can produce, but it is often at or near the maximum continuous speed that the engine can tolerate in extended cruise flight. It's essentially an arbitrary number defined by the manufacturer for each engine specifically. Usually it is uncorrected, meaning that the N% does not exactly track the actual thrust produced by the engine.

Most engines have compressors and turbines mounted on two or three concentric spools or hubs. The innermost spool is typically called N1, and the others are numbered consecutively outwards. So for a typical two-spool turbofan engine, the innermost spool—which drives the large front fan—is N1, and the outermost spool is N2. The N2 rotational speed is usually much higher than the N1 speed, and since both spools spin freely and independently, there's no precise correlation between N2 and N1 speed, although there's a fairly close relationship between them when the engine is running normally.

N2 (or N3, on three-spool engines) speed is important for starting the engine and for monitoring engine health, but the N1 speed is more closely related to thrust, especially on turbofans where the N1 spool contains the front fan (which itself provides about 80% of total thrust).

My guess is that N stands for "nominal," but I've never seen an explanation of its origin.

• chitty
Lv 4
3 years ago

N1 Jet Engine

• 8 years ago

"N" is a variable used to represent the "specific speed" of a pump (a jet engine is pretty much a big air pump). "Specific speed" is the RPM at which a pump is at maximum efficiency.

So in an engine at an N1 of 50%, the fan would be rotating at half the RPM at which the it would be most efficient as an air pump.

• Anonymous
8 years ago

What is it like on a turbine jet engine what does the N mean when monitoring engine speed. Are they exactly the same?

Source(s): www.mariobrothersonline.com/robot.php
• 8 years ago

N is a compressor Spool.. On Turbofan engines.. N1 is the first stage compressor spool.. or in simple terms 'The big Fan at the front'

N2 is the second stage spool..

On my current aircraft we have NH and NL... High pressure spool and low pressure Spool