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M14 > M14.1 > Flashcards

M14.1 Flashcards

1
Q

A/C engine supplies:

A

hydraulic, electric, pneumatic

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2
Q

2 types of engines:

A

Piston type & Gas turbine

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3
Q

Piston type

A

Advantages:
-simple in design
-more fuel efficient

Disadvantages:
-performance decrease at higher altitude -can’t be on large A/C (weight to power ratio)

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4
Q

Gas Turbines

A

Advantages:
-operate at high altitudes & speed
-easily provide thrust, torque, & bleed air -powers either a single fan or a set of a counter-rotating fans via a gearbox

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5
Q

Different types of Gas Turbines

A
  • Turbofan engine
  • Turbojet engine
  • Turboprop engine
  • APU
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6
Q

Turbofan engine

A

-used on modern aircraft
-high A/C speed is possible w/ good engine efficiency @ high altitude
-developed from turbojet
-usually twin or triple spool engine
-fan is always driven by a turbine via drive shaft
-do not have reduction gear to reduce fan speed

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7
Q

Turbofan engine

A

-converts large part of gas energy into torque to drive the fan and compressor engine -remaining hot gas from core engine is directly converted into thrust
*Total thrust = core engine + fan

-fan accelerates high airflow, low outlet
velocity

-core engine accelerates small quantity of air, high outlet velocity

-fan can produce 80% of total thrust ;
primarily dependent on bypass ratio

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8
Q

Turbojet engine

A

-first type of gas turbine used on A/C

-give VERY high A/C speed

-VERY LOUD because of extremely high
exhaust gas velocities

-need too much fuel

-all gas energy is converted into thrust

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9
Q

Turboprop engine

A

-specially design to produce shaft horsepower only which is to drive a propeller

-installed on small commuter A/C

-achievable A/C speed & fuel efficiency

-produce their thrust by a small acceleration of a large quantity of air with propeller

-driven directly on compressor shaft or by a turbine and a long center drive shaft.

-all gas energy into torque

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10
Q
  • always required to reduce
    the high gas turbine engine rotation to speeds that can be managed by the propeller
A

Reduction gear

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11
Q

Auxiliary Power Unit:

A

-small gas turbine engine

-supply A/C w/ electric & pneumatic power if the engine is not available

-A/C is independent of airport equipment

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12
Q

– propelling force, which is generated in the opposite direction to the flow of mass through the jet nozzle.

A

Jet Propulsion

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13
Q
  • engine which uses jet propulsion.
A

Reaction Engine

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14
Q

this engine uses Newton’s 3rd law of motion (for every force which acts on a body there is an opposite & equal reaction)

A

Reaction Engine

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15
Q

F=MxA

A
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16
Q

To accelerate air, air pressure must increase:

2 ways of doing it:

A
  • mechanically w/ compressor
  • thermally by increasing volume of air when a fuel/air mixture is burned/heated
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17
Q

Base for all gas turbine engine:

A
  • Hans Van Ohain, 1937
  • Frank Whittle, 1941
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18
Q

centrifugal flow compressor driven by radial turbine

A

Hans Van Ohain, 1937

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19
Q

centrifugal flow compressor driven by axial turbine; these engines were only possible after the development of materials heat-resistant enough for continuous combustion

A

Frank Whittle, 1941

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20
Q

– generated by the acceleration of ambient air which is forced through the engine.

A

Thrust Force

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21
Q

2 parameters of THRUST:

A
  1. mass of ambient air which is accelerated
  2. quantity of acceleration itself
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22
Q

series of changes of state of a working medium which occur periodically

A

Cyclic Process

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23
Q

– technical processes usually used for converting heat into mechanical work (combustion engines) or for heating & cooling by performing work.

A

Brayton Cycle

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24
Q

– line of equal pressure

A

Isobars

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25
Q

– lines of equal entropy

A

Isentropes

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26
Q

– change of state of gases which there is no change in entropy. Energy content is constant.

A

Isentropic

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27
Q

– a system is transferred from one state to another w/o exchanging thermal energy w/ its environment.

A

Adiabatic

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28
Q

quantity of airflow to the engine can be changed by

A

Control Valve

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29
Q

Control Valve – quantity of airflow to the engine can be changed by:

A
  • Nozzle w/ small diameter high outlet velocity; high thrust
  • Nozzle w/ medium diameter medium outlet velocity; medium thrust
  • Nozzle w/ large diameter low outlet velocity; low thrust
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30
Q

– thrust of the jet nozzle does not change.

A

Deflector Plate

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31
Q
  • Thrust is generated by acceleration of airflow and not by pushing against an object
A

Deflector Plate

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32
Q

4 main environmental parameters that cause changes in thrust of a jet engine:

A
  1. Ambient air pressure
  2. Air temperature – changes density
  3. Operating altitude
  4. Airspeed- speed increases; thrust
    decreases. Net effect on thrust is a combo of thrust decrease from acceleration effect & thrust increase from the ram effect.

*1&2 are most important factors that cause a change of mass airflow because these determine the density of air
*lower density creates lower thrust because the airflow contains less mass than a high density airflow.
*higher pressure, higher thrust
*higher temperature, lower thrust

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33
Q

36k ft up to 65k ft – air temperature is constant @ -57C / -70F

A
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34
Q
  • bypass ratio of air that passes through the fan duct & core engine.
A

Bypass ratio is 4:1 and 9 :1 Older turbofan engine bypass ratio is 1:1

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35
Q
  • open rotor engines. Advantage of using up to 20% less than high bypass engine. Has mounting difficulties, not very common on modern jet A/C. Bypass ratio of 90:1
A

Propfans

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36
Q

Different Methods of Engine Design:

A
  • Non-modular Engine Design
    &
  • Modular Engine Design
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37
Q
  • saved weight & fully functional but design was complicated & parts were difficult to access. Usually found on older type of engines and some APUs.
A

Non-modular Engine Design

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38
Q
  • used on all modern A/C. whole engine is spilt up into a set of separate major modules (preassembled &balanced). Designed to be removed and replaced easily. Very often the replacement of a module is considered a minor repair and not a shop repair.
A

Modular Engine Design

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39
Q

– must be strong as required for their individual task, light, and cheap as possible

A

Engine Materials

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40
Q

– mainly used for gearbox housing, fan stator casing, and low loaded parts of the fan module

A

Aluminum alloy

41
Q
  • used in combustion section and in high pressure turbine. Serves as heat & corrosion protection.
A

Ceramic material

42
Q

– usually used in the fan module

A

Composite material

43
Q

– very heat resistant, can be found in stator of the first stage of the high-pressure turbine.

A

Cobalt base alloy

44
Q
  • can withstand high centrifugal loads at high temperatures. Used in the high-pressure compressor, in the combustion section & for the high/low pressure turbines
A

Nickel base alloy

45
Q

-used for the N1 drive shaft, engine bearings & main structural frames on some engine

A

Corrosion resistant steel alloy

46
Q
  • strong as steel but only half as heavy. Can withstand high centrifugal loads but expensive. Mainly used in fan, the low-pressure compressor and the front stages of the high-pressure compressor
A

Titanium base alloy

47
Q

– operated above idle in parallel with hydromechanical control. Only values which are necessary for determining fuel flow to maintain the desired thrust

A

Electronic Control

48
Q

– A centralized computer with all necessary sensors which controls the engine and all its subsystems

  • ECU, Fuel metering valve, electrical sensors on the engine
    *Electricity is supplied by a control alternator. Which is powered by N2 rotor via accessory gearbox
A

FADEC (full authority digital engine control)

49
Q

– digital computer of FADEC. Located at the fan stator case of the engine. Gets demand signal from thrust lever in the cockpit. Power supply from A/C or a small permanent magnet alternator.

  • Performs full power management & optimum thrust
  • Permanently monitors the engine operation & important system components & gives fault messages to the CMC
  • Almost independent from aircraft
A

Electric control unit

50
Q

2 independent computers of ECU:

A

channel A&B

51
Q

-made by a dual set of electronic cards, 1 set each per channel.

  • Signals from each ECU are either electric/pneumatic signals.
A

channel A&B

52
Q
  • channels A&B always collect the data from the engine and aircraft and they always communicate with each other
A

Cross-channel data link

53
Q
  • 1 channel at a time has the authority to control the engine

*change in command is automatic.
*all electrical sensors on the engine have individual pick-ups that are connected to the respective ECU channel.
*there are always 2 individual transducers for each pressure line, each channel has its own pressure transducer.

A

channel in command

54
Q

– any one time only one channel works together actively with the engine.

A

Active channel

55
Q

– carries out all necessary calculations for engine control but its output signal act on a steady load.

*switch over from one channel to another is usually at the beginning of each engine start sequence.

A

Standby channel

56
Q

– calculates the thrust command based on the thrust lever angle, ambient air temp, and pressure such as T12 & Ps12. Also uses mach number for info about aircraft speed.

A

Power management

57
Q

– connector from the engine to the ECU used for engine identification. Makes sure that the ECU controls the engine to the correct maximum take-off thrust.

A

Thrust rating plug

58
Q

– correction factor for the engine efficiency.

A

Performance factor

59
Q

– compares the thrust command signal with the actual N1 signal and controls an error signal to the fuel metering valve if the command signal is different to actual N1 signal.

A

Governing section

60
Q

– receives the N2, CDP, CIT to make sure that the engine operational limits are not exceeded.

A

Limiting section

61
Q

– represents the compressor inlet temp. used in the limiting section to protect the engine against compressor surge.

A

T25

62
Q

– represents the compressor discharge pressure. It is used to protect the engine against over boost.

A

PS3

63
Q

– receives a position feedback signal from the fuel metering valve to control the necessary fuel flow.

A

Governing/limiting

64
Q

– it only receives orders from the ECU to move the fuel metering valve

A

Fuel metering unit

65
Q

Components of fuel metering unit:

A
  • Fuel metering valve – located @ HMU
  • Bypass valve
  • HP shut off valve
  • Servo valve with a torque motor
66
Q

– reduces the fuel flow through the fuel metering valve if the electrical overspeed protection by the ECU fails.

A

Overspeed governor

67
Q

– independent of ECU. a fuel metering with these additional servo valves

  • Variable stator vanes
  • Variable bleed valves
  • High/low pressure turbine clearance
    control valves
A

Hydromechanical unit

68
Q

– transmit the data between FADEC and A/C. also control power supply from the A/C to ECU. Located @ electronic compartment.

  • It limits the number of signal wires between aircraft and engine, because 1 single data bus can transmit all digital data. Saves weight, reduces risk of wiring faults.
  • Heart of FADEC

*during engine operations the electrical power supply to the ECU is just a back-up to prevent loss of electrical power, normally, a permanent magnet alternator on the engine accessory gearbox supplies the ECU with electrical power

A

Engine interface unit

69
Q

– produces the fuel pressure for operating hydraulically powered actuators of the corresponding engine systems

A

Electro-hydraulic servo valve

70
Q

– monitors adjustments of the actuated system components, and reports their actual position to ECU

A

LVDT/RVDT

71
Q

– supply of electricity to the ignition system as well as certain processes during transition of the thrust reverser.

*temperature increase across LP compressor is always in a fixed relation to the fan speed

A

Starter valve

72
Q

What will happen to Force if the mass increases?

A

The Force will also increase

73
Q

What will happen to Force if the Acceleration decreases?

A

The Force will also decrease

74
Q

What will happen to Pressure if Velocity increases?

A

Pressure will decrease

75
Q

The higher altitude the lower the density and the pressure also decrease, causing the Thrust to decrease. What will compensate the Thrust?

A
  • In high altitude the temperature is colder and that will compensate the thrust
  • In high altitude the ram air will compensate the Thrust
76
Q

It is a pressure-volume diagram of a thermodynamic cycle of a turbojet engine.

A

Brayton Cycle

77
Q

Section which the pressure reaches the maximum value and volume flow reaches its minimum value.

A

Section 2 to 3

78
Q

This process is called isobaric heat addition, which takes place in the combustion section.

A

Process 3 to 4

79
Q

How many percent of thrust does the fan can produce and how many percent does the fuel burn in the core engine?

A

80% Fan; 20% Core Engine

80
Q

Semi-Electronic Control Systems

A

PMC; HMC/MEC

81
Q

FADEC Systems

A

ECU; HMU/FMU

82
Q

Second Main Component of the FADEC System

A

Fuel Metering Unit

83
Q

Power Supply of ECU

A

PMA

84
Q

Location of the ElU (Engine Interface Unit)

A

Avionics Compartment

85
Q

Location of the ECU ( Engine Control Unit)

A

Fan Case

86
Q

Why are there two independent computers for ECU?

A
  • For redundancy
  • For backup
87
Q

Pressure signals from the engine are what kind of signals?

A

Pneumatic Signal

88
Q

The pressures are converted into digital signals by?

A

Pressure Transducer

89
Q

It makes sure that the ECU control the engine to the correct maximum take-off thrust. It also provides the engine type identification.

A

Thrust Rating Plug

90
Q

it receives control signals from the electronic control unit to move the fuel metering valve.

A

Torque Motor

91
Q

It continuously measures the position of the fuel metering valve and transmits a feedback signal to the ECU.

A

Position Sensor

92
Q

It is necessary to keep the pressure difference across the fuel metering valve constant so that the fuel flow is proportional to the opening area of the fuel metering valve.

A

Bypass Valve

93
Q

In overspeed condition the ECU first tries to decrease the fuel via the ____. If the ECU fails at a slightly higher overspeed the _____ acts as a backup.

A

Fuel Metering Valve; Overspeed Governor

94
Q

limits the number of signal wires between the aircraft and engine, because 1 signal data bus can transmit all digital data. It also saves weight and reduces the risk of wiring faults.

A

EIU

95
Q

They are connected directly to ECU

A

PMA, ECAM/EICAS, TLA

96
Q

During the operation of the ECU, the 2 channels are operating but only 1 channel at a time has the authority to control the engine. This is called

A

Channel in command

97
Q

When does the switch-over from one channel to the other one happens?

A

At the beginning of each engine start sequence

98
Q

What is the secondary power source of the ECU in case PMA is not available?

A

Aircraft Power Supply

M14 (8 decks)

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