Fundamentals

M15
GAS TURBINE ENGINE
Rev.-ID: 1SEP2014
Author: DaC
For Training Purposes Only
ELTT Release: Sep. 19, 2014

M15.3
Inlet

EASA Part-66
CAT B1

M15.03_B1 E
Training Manual

For training purposes and internal use only.

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GAS TURBINE ENGINE EASA PART-66 M15
INLET
M15.3

M15 GAS TURBINE ENGINE

M15.3 INLET
FOR TRAINING PURPOSES ONLY!

FRA US/O-5 DaC May 23, 2013 ATA DOC Page 1

Lufthansa Technical Training
GAS TURBINE ENGINE EASA PART-66 M15
INLET Compressor Inlet Ducts
M15.3

COMPRESSOR INLET DUCTS

Engine Air Intakes

Air enters the engine via the engine air intake.
The air intake has:
S an intake nose and
S an inlet duct.
The air inlet duct gets wider. This shape is named divergent.
You probably remember from the Bernoulli Principle that this shape increases
the static pressure of air that is moving through the duct. This is an advantage
for the engine as we are going to see later in this lesson.
FOR TRAINING PURPOSES ONLY!

HAM US/F SwD 01.04.2008 01|Air Intakes|L2|A/B1 Page 2

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INLET Compressor Inlet Ducts
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Figure 1 Engine Air Intakes

HAM US/F SwD 01.04.2008 01|Air Intakes|L2|A/B1 Page 3
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INLET Compressor Inlet Ducts
M15.3

Engine Air Intakes cont.

The intake nose also helps to smooth the airflow.
This stops air disturbances from entering the inlet duct, which would reduce
engine efficiency.
However, air disturbances can be caused by damage to the intake nose, by
ice−build up or even by crosswinds during low speed aircraft operations.
As the aircraft moves through the air, all air enters the engine from the front.
This is because of the ram air effect at high airspeeds.
FOR TRAINING PURPOSES ONLY!

HAM US/F SwD 01.04.2008 02|Air Intakes|L2|A/B1 Page 4

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Figure 2 Airflow Changes at the Engine Air Intake

HAM US/F SwD 01.04.2008 02|Air Intakes|L2|A/B1 Page 5
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INLET Effects of Inlet Configurations
M15.3

Engine Air Intakes cont.

If the engine is running and the aircraft is not moving, there is no ram air effect.
In this situation, air is also sucked in from the side of the engine. This is very
dangerous if maintenance must be done to an engine which is running.
Equipment, tools or yourself can be sucked into the engine.
To reduce this danger, limit maintenance to a minimum on an engine that is
running.
If you must work near an engine that is running, move carefully and wear a
safety lanyard.
A red stripe on the engine cowling and a warning placard tells you not to get
into the danger zone.
Do not stand anywhere in front of this red stripe or you may start to fly all by
yourself.
FOR TRAINING PURPOSES ONLY!

HAM US/F SwD 01.04.2008 03|Air Intakes|L2|A/B1 Page 6

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INLET Effects of Inlet Configurations
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Figure 3 Danger Zone at Engine Air Intake

HAM US/F SwD 01.04.2008 03|Air Intakes|L2|A/B1 Page 7
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INLET Compressor Inlet Ducts
M15.3

Supersonic Engine Inlets

The air entering the compressor section of a jet engine must be slowed to
subsonic velocity.
The slowing down of the air must be accomplished with the least possible
waste of energy.
At flight speeds just above the speed of sound we only need slight
modifications to the ordinary subsonic inlet design to produce satisfactory
performance.
At higher supersonic speeds the required modifications are more complicated.
The inlet design must slow the air with the weakest possible series or
combination of shock waves in order to minimize the energy losses caused by
temperature increases.
FOR TRAINING PURPOSES ONLY!

HAM US/F SwD 01.04.2008 04|Supersonic EngineInlet|L2|A/B1 Page 8

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Figure 4 Supersonic Engine Inlet

HAM US/F SwD 01.04.2008 04|Supersonic EngineInlet|L2|A/B1 Page 9
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INLET Effects of Inlet Configurations
M15.3

EFFECTS OF INLET CONFIGURATIONS

Supersonic Engine Inlets

Here you see 1 of the least complicated engine inlet designs:
a normal shock diffuser inlet.
You can see that this type of inlet employs a single normal shock wave at the
inlet to slow the air to subsonic velocity.
This type of inlet is suitable for low supersonic speeds where the normal shock
wave is not too strong.
It is not suitable at higher supersonic speeds because the normal shock wave
is very strong and causes a great reduction in the total pressure recovered by
the inlet.
FOR TRAINING PURPOSES ONLY!

HAM US/F SwD 01.04.2008 05|Supersonic EngineInlet|L2|A/B1 Page 10

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INLET Effects of Inlet Configurations
M15.3
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Figure 5 Normal Shock Diffuser Inlet

HAM US/F SwD 01.04.2008 05|Supersonic EngineInlet|L2|A/B1 Page 11
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INLET Effects of Inlet Configurations
M15.3

supersonic engine inlets cont.

Here you can see a single oblique shock inlet.
This design employs an external oblique shock wave to slow the supersonic
airflow before the normal shock occurs.
A more complicated variation of the single oblique shock inlet is the multiple
oblique shock inlet.
This design employs a series of very weak oblique shock waves to gradually
slow the supersonic airflow before the normal shock occurs.
The normal shock wave doesn’t have to be very strong.
This combination of weak shock waves leads to the least waste of energy and
the highest pressure recovery.
FOR TRAINING PURPOSES ONLY!

HAM US/F SwD 01.04.2008 06|Supersonic EngineInlet|L2|A/B1 Page 12

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INLET Effects of Inlet Configurations
M15.3
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Figure 6 Single and Multiple Oblique Shock Inlet

HAM US/F SwD 01.04.2008 06|Supersonic EngineInlet|L2|A/B1 Page 13
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INLET Effects of Inlet Configurations
M15.3

Variable Supersonic Inlets

The optimum shape of supersonic inlets varies with the inlet flow direction and
with the Mach number.
In other words to derive the highest efficiency and stability of operation the
geometry of the inlet would be different at different angles of attack and at
different speeds.
Here you see an example of an inlet which can be varied to suit different
conditions.
You can see that it is equipped with actuator operated panels.
At flight speeds below Mach 1 the engine inlet is fully open and the aircraft flies
with a high angle of attack.
At flight speeds just above Mach 1 the actuators change the position of the
panels slightly and the inlet employs a single normal shock wave.
This is similar to the normal shock diffuser inlet.
At high Mach numbers the actuators operate the panels so that they employ 3
oblique shock waves and then a normal shock.
This is similar to the multiple oblique shock inlet.
FOR TRAINING PURPOSES ONLY!

HAM US/F SwD 01.04.2008 07|Variable Inlet|L2|A/B1 Page 14

Lufthansa Technical Training
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INLET Effects of Inlet Configurations
M15.3
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Figure 7 Variable Supersonic Inlets

HAM US/F SwD 01.04.2008 07|Variable Inlet|L2|A/B1 Page 15
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INLET Ice Protection
M15.3

ICE PROTECTION

Engine Anti-Ice
In addition to the negative effect on aerodynamics and a higher weight, the
engines can also get problems when there is an ice build−up.
Ice has 2 important negative effects on the engine inlet. These are:
S a disturbed air flow that reduces the performance of the engine and can
lead to a compressor stall and
S if the engine sucks in pieces of ice, these pieces can damage fan blades or
inlet vanes. This means that the engine will stop completely.
To prevent ice build−up on the engine inlet, all jet engines have a thermal anti-
ice system.
If an aircraft has a center engine as shown here, you must make sure that ice
pieces from the fuselage do not hit the engine.
Usually the antennas get this ice build−up and therefore they are also heated
by warm air.
FOR TRAINING PURPOSES ONLY!

HAM US/F SwD 01.04.2008 01|Engine Anti−Ice|L2|A/B1 Page 16

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INLET Ice Protection
M15.3
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Figure 8 Effects of Ice on Engine Inlet

HAM US/F SwD 01.04.2008 01|Engine Anti−Ice|L2|A/B1 Page 17
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INLET Ice Protection
M15.3

Thermal Anti-Ice System

Two thermal anti−ice systems are installed in jet aircraft:
S The wing (M11.12 / ATA30) and
S the engine anti−ice systems.
The engine anti−ice system uses hot air. The air comes from the engine
compressor. An engine anti−ice valve provides the connection.
When an anti−ice valve opens, the hot air enters the anti−ice duct.
The hot air sprays through small holes into the engine cowling.
The hot air heats up the nose cowl and prevents ice build−up.
Later, the air leaves this area through openings in the lower part of the nose
cowl.
Extreme caution is necessary during ground tests of thermal anti−ice systems
because the air is still hot.
FOR TRAINING PURPOSES ONLY!

HAM US/F SwD 01.04.2008 01|Introduction|L2|A/B1 Page 18

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INLET Ice Protection
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Figure 9 Wing and Engine Anti-Ice Systems

HAM US/F SwD 01.04.2008 01|Introduction|L2|A/B1 Page 19
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INLET Ice Protection
M15.3

System Control
You probably remember this pneumatic schematic from the lessons of the
pneumatic system.
We will now see what it looks like with the two thermal anti−ice systems added.
The left and right wing anti−ice system uses hot air which is already regulated
by the bleed valve.
The engine anti−ice system uses bleed air from the corresponding engine. This
air comes either from the engine bleed−air system, upstream of the bleed
valve, or from a separate port on the engine compressor.
You can control the thermal anti−ice systems with switches on the overhead
panel. Here you see the push buttons in an Airbus aircraft.
The wing anti−ice system always has only one switch. This switch controls the
two sides at the same time because the system must always operate
symmetrically.
On engine anti−ice systems you find a switch for each engine installed on the
aircraft.
FOR TRAINING PURPOSES ONLY!

HAM US/F SwD 01.04.2008 03|System Control|L2|A/B1 Page 20

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INLET Ice Protection
M15.3
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Figure 10 Anti-Ice System Schematic

HAM US/F SwD 01.04.2008 03|System Control|L2|A/B1 Page 21
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INLET Ice Protection
M15.3

Valve Types
In thermal anti−ice systems you find the same type of valves as in other parts
of the pneumatic system.
Electrical motor operated valves, like crossbleed valves, are also used in some
wing anti−ice systems.
You can find solenoid controlled pressure operated valves in engine and wing
anti−ice systems.
In the two systems they operate as shut−off valves, like the APU bleed valve,
or they can be pressure regulating valves like the engine bleed valve.
All thermal anti−ice valves have a manual override function like some other
valves in the pneumatic system. This manual function is used when there is a
valve or system failure.
You can lock the wing anti−ice valves in the closed position only. This is only
allowed when there is no risk of icing during the next flight. It is also very
important to remember that you must close the wing anti−ice valves always on
both wings.
The engine anti−ice valves you can lock in the open or closed position. The
position you use depends on several conditions and is stated in the
maintenance documentation.
FOR TRAINING PURPOSES ONLY!

HAM US/F SwD 01.04.2008 04|Valve Types|L2|A/B1 Page 22

Lufthansa Technical Training
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INLET Ice Protection
M15.3
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Figure 11 Valve Types

HAM US/F SwD 01.04.2008 04|Valve Types|L2|A/B1 Page 23
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INLET Ice Protection
M15.3

Solenoid Controlled Valve

We will now look at a solenoid controlled pressure operated valve.
This valve closes by spring force when there is no air pressure available.
When air pressure is present it fills the lower chamber of the valve cylinder,
this pushes the piston up and moves the air in the upper part of the cylinder to
ambient via the de−energized solenoid. This opens the valve.
To close this valve type you must energize the solenoid.
This brings high air pressure to the upper chamber.
With equal pressure on the two sides of the piston the spring closes the valve.
We have simplified this function to make the principle clear to you. In reality,
the internal build−up of the valve is more complicated.
FOR TRAINING PURPOSES ONLY!

HAM US/F SwD 01.04.2008 05|Solenoid Controlled Page 24

Valve|L2|A/B1
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INLET Ice Protection
M15.3
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Figure 12 Solenoid Controlled Valve

HAM US/F SwD 01.04.2008 05|Solenoid Controlled Page 25
Valve|L2|A/B1
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INLET Ice Protection
M15.3

solenoid controlled valve cont.

Now we can use this solenoid− controlled, pressure−operated, shut−off valve in
an engine anti−ice system. When the pushbutton switch on the overhead
panel is switched off, then the solenoid is energized and the valve closed.
Two limit switches monitor the valve position.
This type of valve is fail safe to open. This means that it automatically opens
when there is no electrical power.
You can also find other valve types which close when the solenoid is
de−energized, for example, in Boeing aircraft. In this case the engine anti−ice
system is off when there is no electrical power.
FOR TRAINING PURPOSES ONLY!

HAM US/F SwD 01.04.2008 06|Solenoid Controlled Page 26

Valve|L2|A/B1
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Figure 13 Solenoid Controlled Engine Anti-Ice Valve

HAM US/F SwD 01.04.2008 06|Solenoid Controlled Page 27
Valve|L2|A/B1
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INLET Ice Protection
M15.3

Pressure Regulating Valve

Now we will look at a more complicated valve.
It is a shut−off valve which also has an additional pressure regulation function.
This pressure regulation is needed if pneumatic system air pressure is too high
for the anti−ice system.
This valve stays closed when you activate the pneumatic pressure. This is
because the pressure is not only in the lower valve chamber. It also goes, via
the pilot valve, to the upper chamber, when the solenoid valve is de−energized.
When you energize the solenoid the pressure in the upper valve chamber
decreases because it releases to ambient.
This permits the pressure in the lower chamber to push the piston up and open
the valve.
When the valve is open you get pneumatic pressure downstream of the valve
which goes to the wing anti−ice ducts.
This pressure is also connected to the pilot valve and moves its piston to the
right.
The result is that the pressure increases in the upper valve chamber. This
moves the valve in the closing direction.
The valve motion stops when the downstream pressure has the correct value
of about 20 psi, because the pilot valve then has a balanced situation.
FOR TRAINING PURPOSES ONLY!

HAM US/F SwD 01.04.2008 07|Pressure Regulating Page 28

Valve|L2|A/B1
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Figure 14 Pressure Regulating Valve

HAM US/F SwD 01.04.2008 07|Pressure Regulating Page 29
Valve|L2|A/B1
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M15.3

pressure regulating valve cont.

This system is monitored by two pressure switches, which are found
downstream of the valve, and one valve limit switch.
The fault light illuminates when you switch on the wing anti−ice pushbutton but
the pressure does not reach 14psi.
It also comes on when the pushbutton is switched off but the valve is not fully
closed.
You get a special situation when the aircraft is on the ground.
As you already know, the wing anti−ice valves close automatically when the
aircraft lands. You do not need to switch the wing anti−ice pushbutton off at
this moment.
When the pressure decreases below 14 psi you will not get the fault light. This
is because the ground sensing switch opens the circuit.
The blue on−light stays on as long as the pushbutton is pressed.
FOR TRAINING PURPOSES ONLY!

HAM US/F SwD 01.04.2008 08|Pressure Regulating Page 30

Valve|L2|A/B1
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Figure 15 PRV Operation

HAM US/F SwD 01.04.2008 08|Pressure Regulating Page 31
Valve|L2|A/B1
M15.03 B1 E

TABLE OF CONTENTS
M15 GAS TURBINE ENGINE . . . . . . . . . . . . . 1
M15.3 INLET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
COMPRESSOR INLET DUCTS . . . . . . . . . . . . . . . . . . . . . 2
ENGINE AIR INTAKES . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
SUPERSONIC ENGINE INLETS . . . . . . . . . . . . . . . . . . . . 8
EFFECTS OF INLET CONFIGURATIONS . . . . . . . . . . . 10
SUPERSONIC ENGINE INLETS . . . . . . . . . . . . . . . . . . . . 10
VARIABLE SUPERSONIC INLETS . . . . . . . . . . . . . . . . . . 14
ICE PROTECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
ENGINE ANTI-ICE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
THERMAL ANTI-ICE SYSTEM . . . . . . . . . . . . . . . . . . . . . 18
SYSTEM CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
VALVE TYPES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
SOLENOID CONTROLLED VALVE . . . . . . . . . . . . . . . . . 24
PRESSURE REGULATING VALVE . . . . . . . . . . . . . . . . . . 28

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TABLE OF CONTENTS

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M15.03 B1 E

TABLE OF FIGURES
Figure 1 Engine Air Intakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Figure 2 Airflow Changes at the Engine Air Intake . . . . . . . . . . . . . . . . . . 5
Figure 3 Danger Zone at Engine Air Intake . . . . . . . . . . . . . . . . . . . . . . . . 7
Figure 4 Supersonic Engine Inlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Figure 5 Normal Shock Diffuser Inlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Figure 6 Single and Multiple Oblique Shock Inlet . . . . . . . . . . . . . . . . . . . 13
Figure 7 Variable Supersonic Inlets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Figure 8 Effects of Ice on Engine Inlet . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Figure 9 Wing and Engine Anti-Ice Systems . . . . . . . . . . . . . . . . . . . . . . . 19
Figure 10 Anti-Ice System Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Figure 11 Valve Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Figure 12 Solenoid Controlled Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Figure 13 Solenoid Controlled Engine Anti-Ice Valve . . . . . . . . . . . . . . . . 27
Figure 14 Pressure Regulating Valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Figure 15 PRV Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

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TABLE OF FIGURES

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TABLE OF FIGURES

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TABLE OF FIGURES

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