65.26 Turbine Engine Indicating and Instrumentation

65.26.2 Describe the following types of turbine engine indicators and instrumentation including their function and basic principles of operation:

(a) engine rpm

The engine RPM indicator shows the rotational speed of the engine’s rotating assemblies, such as the compressor, gas-producer turbine, or power turbine.

Depending on engine design, RPM may be indicated as:

• N₁ or Nᵍ — gas-producer speed; and

• N₂ or Nₚ — power-turbine speed.

RPM is commonly displayed as a percentage of the maximum governed or rated speed.

The signal may be produced by a tachometer generator or electronic speed sensor.

(b) engine torque

Engine torque is the twisting force produced at the engine output shaft.

The torque indicator provides an indication of the load being transmitted by the engine to the transmission or rotor system.

Depending on the engine design, torque may be measured by: