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Pilot's Handbook of Aeronautical Knowledge
Aircraft Systems
Turbine Engines

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




The fourth common type of jet engine is the turboshaft.
[Figure 6-26] It delivers power to a shaft that drives
something other than a propeller. The biggest difference
between a turbojet and turboshaft engine is that on a
turboshaft engine, most of the energy produced by the
expanding gases is used to drive a turbine rather than produce
thrust. Many helicopters use a turboshaft gas turbine engine.
In addition, turboshaft engines are widely used as auxiliary
power units on large aircraft.

Turbine Engine Instruments
Engine instruments that indicate oil pressure, oil temperature,
engine speed, exhaust gas temperature, and fuel flow are
common to both turbine and reciprocating engines. However,
there are some instruments that are unique to turbine engines.
These instruments provide indications of engine pressure
ratio, turbine discharge pressure, and torque. In addition,
most gas turbine engines have multiple temperature-sensing
instruments, called thermocouples, which provide pilots with
temperature readings in and around the turbine section.

Engine Pressure Ratio (EPR)
An engine pressure ratio (EPR) gauge is used to indicate the
power output of a turbojet/turbofan engine. EPR is the ratio
of turbine discharge to compressor inlet pressure. Pressure
measurements are recorded by probes installed in the engine
inlet and at the exhaust. Once collected, the data is sent to
a differential pressure transducer, which is indicated on a
flight deck EPR gauge.

EPR system design automatically compensates for the effects
of airspeed and altitude. Changes in ambient temperature
require a correction be applied to EPR indications to provide
accurate engine power settings.

Exhaust Gas Temperature (EGT)
A limiting factor in a gas turbine engine is the temperature
of the turbine section. The temperature of a turbine section
must be monitored closely to prevent overheating the turbine
blades and other exhaust section components. One common
way of monitoring the temperature of a turbine section is
with an EGT gauge. EGT is an engine operating limit used
to monitor overall engine operating conditions.
Variations of EGT systems bear different names based on
the location of the temperature sensors. Common turbine
temperature sensing gauges include the turbine inlet
temperature (TIT) gauge, turbine outlet temperature (TOT)
gauge, interstage turbine temperature (ITT) gauge, and
turbine gas temperature (TGT) gauge.

Turboprop/turboshaft engine power output is measured by the
torquemeter. Torque is a twisting force applied to a shaft. The
torquemeter measures power applied to the shaft. Turboprop
and turboshaft engines are designed to produce torque for
driving a propeller. Torquemeters are calibrated in percentage
units, foot-pounds, or psi.

N1 Indicator
N1 represents the rotational speed of the low pressure
compressor and is presented on the indicator as a percentage
of design rpm. After start the speed of the low pressure
compressor is governed by the N1 turbine wheel. The N1
turbine wheel is connected to the low pressure compressor
through a concentric shaft.

N2 Indicator
N2 represents the rotational speed of the high pressure
compressor and is presented on the indicator as a percentage
of design rpm. The high pressure compressor is governed
by the N2 turbine wheel. The N2 turbine wheel is connected
to the high pressure compressor through a concentric shaft.
[Figure 6-27]

Dual-spool axial-flow compressor.
Figure 6-27. Dual-spool axial-flow compressor.

Turbine Engine Operational Considerations
The great variety of turbine engines makes it impractical to
cover specific operational procedures, but there are certain
operational considerations common to all turbine engines.
They are engine temperature limits, foreign object damage,
hot start, compressor stall, and flameout.

Engine Temperature Limitations
The highest temperature in any turbine engine occurs at the
turbine inlet. Turbine inlet temperature is therefore usually
the limiting factor in turbine engine operation.