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What do N1 and N2 stand for?

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Aerodynamics, Aircraft Systems, Commercial Pilot

Hello Pilots! I see in turboprops and jets N1 and N2 inside cockpit, what do they stand for??

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1 Answers

  1. Wes Beard on Feb 16, 2012

    This answer is specific to a turboprop and not to a turbojet or turbofan engine.  Although the same principles apply, the N1 and N2 speeds are taken in different places on the three types of engines.
    The N1 is a speed sensor inside the combustion chamber measuring the rotational rate of the turboshaft and not the propeller speed.  On some turboprop aircraft it is labeled as a N1 or a Ng (gas generator).
    The N2 is a speed sensor measuring the rotational rate of the propeller shaft.  It can be called N2 or Np on different turboprop aircraft.
    There is also two different types of turboprops.  There is a fixed shaft design where the turboshaft and the propeller shaft is directly connected through a gearbox.   The second type is a free turbine where the exhaust gas from the turbine section is routed to the front of the engine where it passed through a fanbox which is directly connected to the propeller shaft.
    Also on some turboprop aircraft the N1 and N2 are represented as a percentage instaed of a RPM rate.  This is easily done by dividing the current rotational rate by the maximum rated rotational rate.

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