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Module 15 > M15.11 > Flashcards

M15.11 Flashcards

1
Q

What is a rich blow out

A

If the quantity of fuel becomes excessive the limiting temperature of the turbine blades can be exceeded, or a compressor stall could occur

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2
Q

Gas turbine engine fuel control systems are generally divided into three categories:

A
  • Hydromechanical
  • Hydromechanical/electronic
  • Full Authority Digital Engine (or Electronics) Control (FADEC)
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3
Q

The hydromechanical/electronic fuel control is a hybrid of the two types of fuel control but can function solely as a hydromechanical control. In the dual mode, inputs and outputs are electronic, and fuel flow is set by

A

Servo motors

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4
Q

The FADEC-type control gives the electronic controller (computer) what type of control

A

Full control

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5
Q

What 2 sections do fuel controls have

A

Computing and metering

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6
Q

Does a hydro mechanical fuel system have any electronic interface in computing or metering fuel flow

A

A pure hydromechanical fuel control system has no electronic interface assisting in computing or metering the fuel flow. It is generally driven by the gas generator gear train of the engine to sense engine speed

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7
Q

What parameters do hydro mechanical fuel systems sense

A

compressor discharge pressure, burner pressure, exhaust temperature, and inlet air temperature and pressure

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8
Q

How is fuel metering achieved through a hydro mechanical fuel system

A

When the computing section determines the correct amount of fuel flow, the metering section through cams and servo valves delivers the appropriate quantity of fuel to the engine fuel system.

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9
Q

Is a hydro mechanical fuel delivery system as accurate as electric

A

No

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10
Q

Why is the fuel control unit sometimes mounted on the fuel pump

A

The fuel control unit is sometimes mounted on the vane fuel pump assembly. It provides the power lever connection and the fuel shut-off function. The unit provides mechanical overspeed protection for the gas generator spool during normal (automatic mode) engine operation.

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11
Q

What type of filter is fuel supplied through

A

A 200 micron inlet screen

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12
Q

Is the fuel manual mode solenoid valve energised or de energised in the automatic mode

A

The manual mode solenoid valve is energised in the automatic mode.

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13
Q

Fuel sub systems

A
  • Distribution
  • Control
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14
Q

LP fuel pump pressure

A

175psi

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15
Q

HO fuel pump max pressure

A

900psi at max power

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16
Q

Overpressure relief valve pressure

A

1250psi

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17
Q

Types of HP fuel pump

A
  • Gear type
  • Piston type
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18
Q

Most common type of fuel pump in turbofans

A

Gear type

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19
Q

Heat exchangers that can be found in the engine fuel system

A
  • Engine oil cooler
  • Servo fuel heater
  • IDG oil cooler
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20
Q

What prevents fuel leaks in the hot environment of the HPC and combustion case

A

Fuel lines protected by shrouds

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21
Q

Methods to protect the connections of fluid lines against leaks

A
  • Shrouded connections
  • Double sealed connections
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22
Q

Disadvantage of ding,e flow nozzles

A

Only has good atomisation at a small fuel flow range

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23
Q

How do we overcome the disadvantages of single flow nozzles

A
  • Having a primary and secondary set
  • Primary for start and idle
  • Secondary for max
24
Q

How are primary and secondary fuel nozzle usually supplied

A

Independent fuel manifolds

25
Q

What do we use in modern engines in regards to fuel nozzles

A

Duplex fuel nozzles

26
Q

What prevents residual fuel and carbon build up on duplex fuel nozzles

A
  • Combustion airflow
  • Shut off valves
27
Q

Can the air spray nozzle be a duplex type

A

Never

28
Q

Why is the air spray nozzle always simplex

A

It can provide suffice t fuel at all speeds

29
Q

Operating conditions important fuel metering

A
  • Steady state
  • Transient
30
Q

Fuel metering demand limits

A
  • Over temp
  • Over speed
  • Compressor stall
  • Flame out
31
Q

N2 speed for most engine idle

A

50-65%

32
Q

How does the FCU switch minimum idle to approach idle

A

Air config via air-ground logic or other config switches

33
Q

What is the N2 command signal

A

Signal from thrust lever to the FCU

34
Q

Types of FCU

A
  • Speed governed
  • Constant thrust FCU
35
Q

What signals do hydro mechanical FCUs have

A

Hydraulic, mechanical and pneumatic

36
Q

FCU major sections

A
  • Metering
  • Power control
  • Engine protection
37
Q

Where is the PMC (Power Management Computer) usually located

A

On the fan stator case of the engine

38
Q

PMC function

A

Calculates required N1 based on throttle lever input

39
Q

Where does the PMC send the control signal

A

Torque motor on the FCU if the required is different to the actual

40
Q

FADEC

A

Full Authority Digital Engine Control

41
Q

What is FADEC

A

Digital computer that has full authority over engine control functions

42
Q

First and second main component of FADEC

A

1 - Digital computer

2 - FMU

43
Q

Engines with FADEC do not have what component installed

A

Hydromechanical FCU

44
Q

Typical FADEC systems have what components

A

ECU
FMU
Electrical sensor
Control of other engine sub systems

45
Q

How many ECU computers are there

A

2 which are A and B

46
Q

How many sensors are at the T12 sensor

A

2 one for A and B ECU

47
Q

What concerns pressure signals to electric signals

A

Pressure transducers

48
Q

Power management calculates the thrust command based on what

A
  • Thrust lever angle
  • Ambient air temp
  • Pressure such as T12 and Ps12
49
Q

What does the FMU servo valve control

A
  • VSV
  • VBV
  • HP and LP turbine clearance control valves
50
Q

EIU

A

Engine Interface Unit

51
Q

How many EIUs are there

A

One for each engine

52
Q

What supplies the ECU with power

A

PMA

53
Q

Advantage of EIU in a FADEC system

A
  • Saves weight
  • Reduces risk of wiring faults
54
Q

What is the only signal FADEC needs to operate

A

Trust Lever Angle

55
Q

Can FADEC operate with out signals from the aircraft

A

Yes it only uses the additional signals to improve accuracy

Module 15 (20 decks)

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