Definitions of EPR, EGT, N1 and N2 ? What do N1 and N2 stand for?

Mostly Used Definitions in Jet /Turbine Engines and Pilot Skills How to  monitor..

Engine Pressure Ratio (EPR) is a means of measuring the amount of thrust being produced by a jet engine. … To determine EPR, pressure measurements are taken by probes installed in the engine inlet and at the turbine exhaust.

EGT, Engine Gas Temperature, the temperature of the gas leaving the gas core at the jet pipe.

N1 and N2 are the speeds of a turbofan engine, respectively the LP compressor and turbine, and the HP compressor and turbine. … It is common or N1  and N2 to be represented using a percentage of the design speed, rather than a figure of RPM.


Once the EPR’s are set at max/reduced thrust you check the N1’s, N2’s, and EGT’s to make sure your not exceeding any limitations at takeoff power. You monitor EGT’s throughout the climb. It is most critical from the time power is set until the first power reduction upon flap retraction. The most likely time to exceed parameters is when the engine is producing full rated power. 

N1 and N2  have nothing to do with the reading of how much air goes through the engin. They are  are representative of percent of maximum rpm for that engine section. it is read by an engine tach generator. If you want to know how much air is being pushed through the engine EPR is what your looking for.

Engines are designed to work safe and proper for a number of cycles. If they are to do that, they mustn’t get overstressed and pushed beyond the limits (N usually over 100% or EGT above a certain limit, at least not for a long period of time). The significant, limiting factors are:

*Temperature inside the engine (which is proportional to EGT, what we are able to measure) and
* The rotation speed, RPM (N) of the spools.

A pilot is only interested in N1 as a general rule. The only time they would be interested in N2 is during the start up procedure or if they had an abnormal indication of N2 during normal operation. Pilots do not need to compare N1 versus N2 during operation. N2 means nothing to a pilot. Engineers however use the N2 value in many different diagnostic scenarios when troubleshooting or testing an engine.


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