MODULE 14

Propulsion

Pag.
 Propulsion
• 14.01 Fundamentals

15.1 Pag.
 INTRODUCTION
• A gas turbine is a thermal machine that converts the energy contained in a
flow of burnt gases to mechanical energy

• Gas turbines can be used for a large number of industrial applications.

• Gas turbines are widely used in the aeronautical field because they are
able to supply a significant thrust through the acceleration of the burnt
gases.

• A turbine does not include parts in reciprocating motion, but only rotating
parts.

• Introduction
15.1 Pag.
 NEWTON’S LAWS
Newton laws of motion say that:

1) First law: an object remains at rest unless disturbed by an external force.

2) Second law: the acceleration of a body is directly proportional to the

fraction of the force and the mass of the body.

3) Third law: for every action there is an equal and opposite reaction.

• Newton’s law
15.1 Pag. 4
 IDEAL BRAYTON’S CYCLE

• The gas turbine engine is a heat engine that uses air as a working fluid to
generate thrust

• The air has to be accelerated. The pressure energy is first increased

followed by the addition of heat energy, before final conversion back to
kinetic energy in the form of high velocity jet efflux

• Gas turbines generates the flow of gas at high temperature necessary to

produce work by operating according to a particular thermodynamic cycle
called Joule‐Brayton

• Brayton’s cycle
15.1 Pag.
 IDEAL BRAYTON’S CYCLE

• Brayton’s cycle
15.1 Pag.
IDEAL BRAYTON’S CYCLE TRANSFORMATIONS

• Brayton’s cycle
15.1 Pag.
 FADEC
• The FADEC, acronym of Full Authority Digital Engine Control, is a system that
consists of a digital computer and ancillary components that control an
aircraft’s engine it works in all the flight envelope, from engine starting to
engine shut‐off

• This electronic control system is designed to manage the fuel demand of the
engines according to the operating conditions.

•FADEC system cannot control afterburner engagement

• Other avionics systems works closely with the FADEC

• fadec
15.11 Pag.
 FADEC
A FADEC system is typically composed by the following main elements:

• The Electronic Control Unit (ECU): it receives data from various sensors,
processes them, sends electrical signals to the command. ECU is fastened to
the engine frame.

• The Hydro Mechanical Unit (HMU).

• Actuators and sensors, installed in the whole engine installation.
• The ECU optimizes operations based on data about atmospheric conditions.
• In multi‐engine installations, there is an ECU for each engine.
• Engine instruments are fitted at the centre of the instrumental panel in the
cockpit
• fadec
15.11 Pag.
 FADEC
• The throttle level position is sent to ECU via a dedicated device interfaced to the
throttle lever, named Throttle Control Unit (TRU).

• The TRU converts the mechanical position of the throttle into electrical signals.
• The HMU is the component of the FADEC which converts the signals coming from
the ECU in hydraulic pressure, adjusting the dosage of fuel to the engine ECU.

• The FADEC generally utilizes dual channel ECU units. Dual channel solution allows
having two separate and identical digital channels that are incorporated in order to
have high level redundancy

• When airplane is on the ground, if two resolvers output of Throttle Control Unit
are not in agreement, the FADEC system automatically sets engine speed to the
ground IDLE

• fadec
15.11 Pag.
 Propulsion
• 14.02 Starting and ignition systems

Pag.
15.13
 INTRODUCTION

 The systems, which, operating together, permit turbine engines to be

started are as follows:

• The starting system

• The ignition system.

The staring system as the aim to set the compressor into rotation by driving it
in the initial phase

• Introduction
15.13 Pag.
 ENGINE STARTING
The engine starting consists of setting into rotation the engine compressor
The most commonly used types of starters are :

• The electrical starters, which use electrical power.

• The pneumatic starters, which use air under pressure.

• The hydraulic starters, which use a hydraulic fluid under pressure

• The cartridge starters, which use an explosive cartridge.

• Engine starting
15.13 Pag.
 ENGINE IGNITION SYSTEM

The ignition system must be able to perform two functions:

1. Ensure that the air‐fuel mixture becomes ignited during the starting cycle
(primary function)

2. Ensure continuous relight, or relight when controlled, in flight (secondary

function) (Not all the ignition systems of turbine engines can perform the
secondary function specified)

• Gas turbine engine ignition system

15.13 Pag.
 ENGINE STARTING
 A starter‐generator includes the primary components that follow:

• One or more stator windings

• A rotating armature, connected to the gears in the accessory gearbox

through a splined shaft

• The brushes which slide along the armature collector and thus operate like a
rotary contact

• A voltage regulator.

The starter‐generator is supplied by direct current electrical power

• Electrical starters
15.13 Pag. 15
 Propulsion
• 14.03 Engine indication system

Pag.
15.14
 INTRODUCTION

The engine parameters indicating systems permit the engine parameters to be

monitored at any time.

The typical data that are of interest for the flight crew usually concern the
following:

• Temperature values
• Pressure values
• Torque
• Revolution Per Minutes (RPM) of rotating parts.

• Introduction
15.14 Pag.
 INTRODUCTION

The most commonly used definitions are: Electronic Information and Crew
Alerting System (EICAS) by Boeing, and Electronic Centralized Aircraft
Monitoring (ECAM) by Airbus.

• Introduction
15.14 Pag.
 THERMOCOUPLE

 To measure the temperature inside the engine, probes are usually used
made up of a set of thermocouples.

A thermocouple works thanks to the interaction of two different metals,

welded on the two ends, called junctions.

By measuring the electromotive force near the cold junction, it is possible to

calculate the temperature of the hot junction. The hot junction is the
thermocouple heated junction.

The JPT is the Jet Pipe Temperature

Rapid response thermocouples have a hole which is not in line with the
entrance hole
• Temperature measurement
15.14 Pag.
 THERMOCOUPLE TEST

The tests usually performed on thermocouples are:

• Insulation tests: disconnecting the conductors from the junction box and
then measuring the insulation resistance between each conductor
terminal and the ground, and between each conductor and its braid

• Short circuit tests and circuit open tests

• Resistance tests

• Accuracy tests

• Temperature measurement
15.14 Pag.
 BOURDON’S TUBE

 It is a metal tube that has a shape of a C and overal cross section

• One end of the tube is sealed, and the other is connected to the pressure
system

• A restrictor is installed in the open end of the tube to prevent damage in

case of rapid pressure changes

• When the pressure is applied inside the tube, the tube expands, hence it
uncoils. The sealed end of the tube moves upward and while doing so
drives a rotation mechanism which is made of gears and is integral with
the instrument pointer

• Oil pressure and temperature

15.14 Pag. 21
 BOURDON’S TUBE

• Oil pressure and temperature

15.14 Pag. 22
 Synchroscope

The propeller synchronization system is designed to bring all propeller

adjusting devices to the same RPM and thus reduce vibrations.

• Interaction between the propellers can be decreased by suitably

synchronizing and synchrophasing the propellers

• In some air vehicles the system includes an instrument installed in the

cockpit and called “synchroscope” and lets the flight crew do manual
adjustment.

• Vibration measurement and indication

15.14 Pag.
EXAMPLE OF SYNCHROSCOPE IN A FOUR-ENGINE
AIRCRAFT

In four‐engine aircraft, for instance, the instrument has three pointers, while in
twin‐engine aircraft the instrument has one pointer

• Vibration measurement and indication

15.14 Pag.