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Aircraft Power Plants > Exam 1 Revision > Flashcards

Exam 1 Revision Flashcards

0
Q

Describe the properties and effects of a ‘Lean’ Air:Fuel ratio.

A
  • Excess of air over fuel (by weight) - Decreased combustion rate (flame speed) - Increase in combustion temperature - Decrease in power with increasing lean mixture settings
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1
Q

What is the ‘best power’ Air:Fuel ratio? Describe it.

A

Approx 12:1 - Highest combustion energy produced - Slower combustion rate than full rich - Higher combustion temperature than full rich. Source: APP 5 - Slide 17

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2
Q

Describe the properties and effects of a ‘Rich’ Air:Fuel ration.

A
  • Excess of fuel over air (by weight) - Increased combustion rate (flame speed) - Decrease in combustion temperature - Decrease in power with increasing rich mixture settings
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3
Q

Carburettors Advantages? Disadvantages?

A

Advantages: - Reliable and relatively simple Disadvantages: - Affected by gravity (float type) - Susceptible to icing - Susceptible to vapour locks - Non precise fuel metering to each cylinder

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5
Q

What is the equation for Specific Fuel Consumption (SFC)?

A

SFC= Fuel Flow / Power = FF / BHP

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6
Q

What is the chemically correct mixture called and what is it’s ratio of Air:Fuel? What makes it chemically correct?

A

Ideal or Stoichiometric mixture – 15:1 - All oxygen is consumed and all fuel is burnt - Peak EGT - Minimum SFC

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7
Q

What type of fuel injection is used in the CT4B?

A

Continuous Flow

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8
Q

What is the purpose of a Carburettor?

A
  • Mix the fuel and air in the correct ratio - Provide a means of controlling engine power - Provide a means of engine shutdown via the mixture control
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9
Q

What are the benefits of impulse coupling?

A
  • Induced voltage increase at START - Retarded ignition to prevent ‘kick back’ - Advanced Ignition after start
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10
Q

What is the purpose of impulse coupling?

A

To be able to rotate the magnet inside the magneto at a sufficient rate to enable a spark to be generated.

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11
Q

What are the benefits of having two spark plugs per cylinder?

A
  • Increased Combustion Efficiency - Redundancy (Safety)
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12
Q

What are the main components of the aircraft ignition system?

A
  • Magnetos - Ignition Harness - Ignition Switch - Spark Plugs
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13
Q

What are some limitations of the OTTO cycle?

A
  • Valve operating speed: limited by mechanical stresses at high speed - Reduced volumetric efficiency - Reduced effective cylinder pressure and therefore power - Ineffective crank angle
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14
Q

What is the maximum Manifold Absolute Pressure (MAP) for a normally aspirated engine like the CT4B has?

A

The ambient static pressure (29.92 inHg when ISA)

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15
Q

Define the compression ratio.

A

Compression Ratio = (Swept Volume + Clearance Volume) / Clearance Volume

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16
Q

What is the gear ration between the camshaft and the crankshaft?

A

2:1

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17
Q

Why must CHT be above 115 degrees before useful power is applied?

A

To allow for metal expansion in the cylinder so that the cylinder walls are parallel

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18
Q

What are some typical fuel contaminants?

A

Water - Ice - Bacterial Growth Foreign matter and system residues Other fuels

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19
Q

Fuel injection Advantages? Disadvantages?

A

Advantages: - Not affected by fuel icing - more uniform delivery of fuel:air ratio mixture to each cylinder - improved control of fuel:air ratios - instant response during acceleration - increased engine efficiency Disadvantages -vapour locking problems with hot engine - more susceptible to fuel contamination problems - surplus fuel normally requires re-routing back to tank - more complex and expensive to maintain

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20
Q

What type of oil is used in CT4B engines?

A

SAE 50 Ashless dispersant Example: AEROSHELL W100

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21
Q

List the 7 functions of oil in a piston engine.

A
  1. Lubrication 2. Cooling 3. Cleaning 4. Protection 5. Sealing 6. Cushioning 7. Propeller control
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22
Q

Define: Flashpoint

A

Temperature of the fuel at which sufficient vapour is released that will ignite in the presence of a spark or flame.

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23
Q

Define: Vapour Lock

A

When air is released from the fuel as it vaporises before it reaches the cylinder.

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24
Q

Define: Volatility What conditions will influence the volatility of a fuel?

A

Measurement of the tendency of a fuel to change from a liquid state to a vapour state. Pressure and Temperature

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25
Q

Define: Octane rating or number What is it also referred to as?

A

Measurement of the resistance of a fuel to detonation. Also known as the fuels ‘Anti-Knock Value’

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26
Q

What would the octane rating be for a fuel comprised of 92% Iso-Octane and 8% Heptane?

A

92

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27
Q

Define: Specific Gravity What is the specific gravity of AVGAS?

A

Fuel density in relation to water. Specific Gravity of AVGAS = 0.71

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28
Q

Define: Calorific Value

A

Measurement of the heat content of a fuel

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29
Q

What is the primary and secondary AVGAS for the CT4B and what colour are they?

A

AVGAS 100LL (low lead) - Blue AVGAS 100/130 - Green

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30
Q

What additive is used to give an AVGAS fuel an octane rating over 100?

A

Tetra Ethyl Lead (TEL)

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31
Q

How is the modified OTTO cycle modified?

A

Inlet Valve lead and lag Exhaust Valve lead and lag Valve overlap

32
Q

How thermally efficient is a typical piston engine?

A

30%

33
Q

What is the 4 stroke cycle (list the 4 strokes)?

A
  1. Intake (Induction) 2. Compression 3. Power 4. Exhaust
34
Q

List the functional components of an aircraft piston engine.

A

Cylinder Piston Connecting rod and crankshaft Camshaft Inlet valve Exhaust valve; and Spark plugs

35
Q

Define: Detonation

A

Instantaneous and explosive burning of the air:fuel mixture in the cylinder

36
Q

List the 4 effects of detonation.

A
  1. Mechanical stress 2. Piston failure (cracking / burning etc) 3. Cylinder failure (head, base studs) 4. Valve failure (burning / warping etc)
37
Q

What are the 4 symptoms of Detonation?

A
  1. Power loss 2. Engine instability 3. Rising CHT 4. Fluctuating MAP
38
Q

What are the 7 causes of detonation?

A
  1. High CHT 2. High cylinder head pressure 3. Fuel octane rating (too low) 4. High induction/carburettor temperature 5. Lean Air:Fuel ratio 6. High MAP / low RPM 7. Contaminated or Incorrect fuel
39
Q

Define: Pre-Ignition

A

Premature ignition of the Air:Fuel mixture within the cylinder before the spark is timed to occur.

40
Q

What are the 5 effects of pre-ignition?

A
  1. Significantly advanced ignition 2. Power loss 3. High CHTs 4. Unstable engine operation 5. Engine mechanical damage and/or failure
41
Q

What are three causes of pre-ignition?

A
  1. Excessive CHT 2. Cylinder ‘hot spots’ 3. Incorrect spark plug heat range
42
Q

What is Afterfiring?

A

In an excessively rich mixture, unburnt fuel is in the exhaust and ignites with sufficient oxygen. Creates a popping sound sometimes heard during a glide approach.

43
Q

What are 4 combustion limitations?

A
  1. Fuel controlled (octane rating) 2. Design controlled (combustion chamber) 3. Mixture controlled (monitoring) 4. Detonation controlled
44
Q

What are the two types of oil sumps in piston engine and which one does the CT4B have?

A
  1. Dry sump oil system 2. Wet sump oil system (CT4B)
45
Q

Which oil sump is ideally better for aerobatics?

A

The dry sump system

46
Q

How is oil returned in the dry sump oil system?

A

Via a scavenge pump

47
Q

Where are the oil pressure and oil temperature ‘sensors’ located in relation to the lubrication system schematic?

A

Immediately after the oil cooler

48
Q

What are the two types of engine cooling used for piston engines and which does the CT4B use?

A
  1. Air cooling (CT4B) 2. Liquid cooling
49
Q

What are the advantages of air cooling? What are the disadvantages of air cooling?

A

Advantages 1. Constant supply of cooling medium 2. Minimal parts required 3. Simple and lightweight 4. Reliable Disadvantages 1. Slow warm up times 2. Temperature variations with power changes 3. Thermal shock

50
Q

What are the advantages and disadvantages of liquid cooling?

A

Advantages 1. Reduced warm up times 2. Relatively constant operating temperature 3. Reduced thermal stress and shock 4. Reduced cooling drag Disadvantages 1. Complexity of the system 2. Increased weight 3. Reduced reliability 4. Possible coolant freezing

51
Q

How does oil return in the CT4B?

A

Via gravity

52
Q

Define: Thermal Efficiency

A

% of heat energy converted to WORK

53
Q

What is a source of Vapour Lock that is caused by the fuel pump?

A

Fuel pump cavitation

54
Q

AVGAS is approximately __% by volume of dissolved air.

A

12%

55
Q

What is the viscosity index?

A

It is the measure of the relative stability of a fluids viscosity over a specified temperature range.

56
Q

A fluid with a __ viscosity index has a low relative viscosity stability.

A fluid with a __ viscosity index has a high relative viscosity stability.

A

LOW

HIGH

57
Q

What are the 5 types of lubrication oil?

A
  1. Straight mineral oil;
  2. Detergent oil;
  3. Ashless dispersant oil;
  4. Multi-Grade oils; and
  5. Synthetic oil
58
Q

What is Straight Mineral Oil used for?

A

Running in of an engine

59
Q

What are the disadvantages of Straight Mineral Oil?

A
  1. Susceptible to oxidisation
  2. Sludge formation - oil starvation
60
Q

What negative effect does the cleansing action of detergent oils have? What have they been superseded by?

A

The cleansing action often blocks oil filters. Detergent oils have by superseded by Ashless-Dispersant oils.

61
Q

What is so good about Ashless Dispersant oils?

A

They don’t oxidise and they do not form a sludge (dispersant action holds in suspension until removed by filters).

62
Q

What are the advantages of Multi-Grade oils?

A
  1. Provides good temperature flexibility;
  2. Provides a high viscosity index.
63
Q

When would a Multi-Grade oil be used?

A

In aircraft engines operating in extremes of temperature.

64
Q

Which type of oil does a Gas Turbine engine use?

A

Synthetic oil

65
Q

Can straight mineral oil and ashless dispersant oil be mixed?

A

Yes, however it is not recommended.

66
Q

What are 4 effects of contaminated fuel?

A
  1. Fuel starvation;
  2. Fuel system corrosion and/or damage;
  3. Engine stoppage; and
  4. Detonation.
67
Q

What are the two types of Piston Ring?

A

Pressure ring and scraper ring

68
Q

How is the Inlet Valve cooled?

A

By inflowing mixture of fuel and air.

69
Q

How is the exhaust valve cooled?

A

By flow of sodium within the valve system.

70
Q

What is the purpose of having dual counterwound springs for the valves (inlet and exhaust valves)?

A
  1. Reduced valve bounce; and
  2. Redundancy
71
Q

CT4B Engine: IO-360-HB

Define what this identifier means.

A

I = Fuel Injected;

O = Horizontally opposed

360 = Capacity of engine (all 6 cylinders) in inches cubed [therefore each cylinder is 60 cubic inches in volume].

H = Model identifier

B = Balanced Crankshaft

72
Q

What are the three factors that determine induced voltage in the Magneto?

A
  1. Strength of the Magnet;
  2. Number of coils on the winding; and
  3. Rate at which flux lines cut coils.
73
Q

What is the purpose of a Condenser?

A
  1. Reduces contact breaker arcing and pitting; and
  2. Provides a more rapid collapse of the primary coil magnetic field.
74
Q

What is the purpose of a Starter Motor?

A
  1. To initiate the OTTO CYCLE as an essential part of the START process; and
  2. To assist where applicable with an ‘air start’ procedure.
75
Q

What is the general description of a starter motor?

A
  1. DC supplied motor;
  2. Heavy construction;
  3. High torque;
  4. High amperage; and
  5. Specific duty cycle
76
Q

Why is Take-Off power slightly richer than the ideal mixture?

A
  1. To reduce combustion temperatures and lower cylinder temperatures (low airspeed, high MAP at takeoff); and
  2. Assists in preventing detonation.
77
Q
A

Aircraft Power Plants (1 decks)

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