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ATPL AGK > Powerplants > Flashcards

Powerplants Flashcards

1
Q

What is Boyles law

A

If mass if constancy

P1V1=P2V2

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2
Q

What is Charles law

A

If pressure constant

V1/T1=V2/T2

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3
Q

What is the general gas equation

A

P1V1/T1=P2V2/T2

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4
Q

What is the equation of continuity

A

AVp

Constant mass flow

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5
Q

What is Bernoulli’s equation

A

Static pressure + dynamic = constant

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6
Q

What is convection

A

Hot air / fluid rises

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7
Q

What is conduction

A

Heat energy passes directly molecule to molecule

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8
Q

What is radiation

A

Heat transfer with electromagnetic waves

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9
Q

What is Newton’s first law

A

Body will continue unless acted upon by external force

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10
Q

What is Newton’s second law

A

Rate of change of momentum proportional to force applied

F=ma

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11
Q

What is Newton’s third law

A

Every action

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12
Q

Momentum formula

A

Mass x velocity

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13
Q

Thrust formula

A

Mass x acceleration

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14
Q

Work done formula

A

Force x distance

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15
Q

Power is…

A

Rate of doing work

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16
Q

Torque is..

A

Twisting force or moment

Depends on:
Force applied
Length of lever arm
Included angle

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17
Q

What is efficiency

A

Measure of output compared to input

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18
Q

4 stages of the 4 stroke cycle “Otto cycle”

A 
Suck = induction 
Squeeze = compression 
Bang = combustion 
Blow = exhaust
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19
Q

Advantages / disadvantages of inverted 4 stroke in line engine

A

Oil could collect at top of piston (hydraulicing)

Cylinders at front more cooled

Better forward view

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20
Q

Advantages and disadvantages of radial engines

A

All cylinders cooled evenly

Bottom cylinders still have oil collected

Large frontal area = lots of drag

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21
Q

Advantages / disadvantages of horizontally opposed engines

A

Slight temperature differential

Better view over top of engine

Short crank shaft = less “whip”

No hydraulicing

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22
Q

What is the crankshaft made it of

A

Hardened steel

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23
Q

What does the crankshaft do

A

Convert linear motion into rotational

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24
Q

What is a crankcase made out of

A

Iron

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25
Q

How is oil transferred from the main journals to the big end journals

A

Via internal oilways

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26
Q

What is the stroke distance

A

Distance from top to bottom of stroke (top dead centre to bottom dead centre)

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27
Q

What is throw distance

A

Distance between centre of crankshaft to top / bottom of stroke

2 x throws = 1 stroke

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28
Q

What are connecting rods

A

Connects pistons to crankshaft

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29
Q

What is a gudgeon pin

A

In piston head

Allows a bit of movement

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30
Q

What do piston rings do

A

Allow a air tight seal

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31
Q

What are the inlet / outlet valves called

A

Popper valves

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32
Q

How do the poppet valves open

A

Cam shaft pushes up on the rocker arm (which piviots round the rocker shaft) opening and closing poppet valves

Rotates at half the speed of crankshaft

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33
Q

What is the exhaust poppet filled with

A

Sodium to absorb the heat

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34
Q

What is the swept volume

A

Area at top of piston x Stoke

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35
Q

What is compression ratio

A

Swept volume + clearance volume (total volume) / clearance volume

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36
Q

What is the firing order of a 4 cylinder engine

A

1,3,4,2

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37
Q

What is break horse power

A

Torque x RPM

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38
Q

What is indicated horse power

A

PLANE / 33000

= theoretical before friction

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39
Q

What does PLANE stand for

A 
P = indicates mean effective pressure 
L = length of stroke 
A = area of piston crown 
N = number of power stokes per min
E = number of cylinders
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40
Q

What does BHP equal

A

IHP - FHP

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41
Q

What factors affect power output

A

Density : pressure / temp / humidity

Mixture ratio : higher alt = before richer

Exhaust back pressure = static pressure down = pressure acting on open exhaust pipe reduces

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42
Q

What is thermal efficiency

A

Work out (BHP) / work (energy) container in fuel

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43
Q

How much of the fuel energy gets used in a piston

A

30% gets used usefully

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44
Q

Mechanical efficiency is…

A

Ratio of BHP to IHP

% power in engine available to turn propeller

80-85% typically

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45
Q

What is Volumetric efficiency

A

Ratio of volume of mixture into cylinder on induction stoke compared to swept volume of cylinder

Indicated how well engine is breathing

Typically 85%

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46
Q

What is the ineffective crank angle

A

10° before and after top dead centre

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47
Q

What is valve lead

A

20° before TDC

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48
Q

What is valve lag

A

50° after BDC

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49
Q

What is specific fuel consumption

A

Ib (kg) / BHP / hour

Mass of fuel / horsepower produce / unit time

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50
Q

What is oil used for

A

Minimise friction

Cools = absorbs heat

Cleaning = removes deposits

Protection = protects from corrosion

Hydraulic operations

Seals / cushions impact loads of piston

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51
Q

What 4 types of oil are there

A

Straight mineral oil

Detergent oil

Ash less dispersant

Synthetic oil

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52
Q

What are the characteristics of straight mineral oil

A

No additives

Evaporates (oxidises) at high temperatures

Sludge can form which can block filter

Typically used for first 50 hours of engine operation

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53
Q

What is detergent oil (flushing oil)

A

High cleaning effect = blocks filters

Not approved for aero engines

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54
Q

What is ashless dispersant oil

A

No carbon forming limitation of straight oil and does not form ash deposits like detergent oil

Approved for all aero piston engines

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55
Q

What is synthetic oil

A

Very expensive = not usually used

Better than other oils

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56
Q

What are oils graded according to

A

Viscosity

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57
Q

What is multi grade oil

A

Thinner in winter

Thicker in summer

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58
Q

Advantages and disadvantages of a wet sump oil system

A

+ simple

  • can’t do aerobatics
  • oil not cooled after being in engine
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59
Q

When is a good time to check oil in a wet sump system

A

Before start

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60
Q

What is a dry sump oil system

A

Oil cooled after been in engine

Can do aerobatics as positive flow all way round

Makes shallower engine

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61
Q

When is a good time to check oil in a dry sump system

A

ASAP after shutdown

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62
Q

What is a hot well in a dry sump oil system

A

Helps promote the heating up of oil

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63
Q

What is a spur gear pump

A

Provides flow of oil

One gear driven by engine which drives a second gear

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64
Q

What is a pressure relief valve

A

If too much pressure then a sample of the pressure will push against a spring which will release the pressure

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65
Q

How does a oil cooler work

A

When cold thermovalve is open so the oil can flow round outside = not cooled

When hot = thermovalve closed = forces oil through cooling system

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66
Q

Types of oil filter

A

Cartridge type
Canister type

Ridged to increase filter area

If filter blocked = bypass valve allows oil to still flow

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67
Q

What do cowl flaps do

A

Can be moved to regulate the amount of hot air leaving the air cooling

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68
Q

What do engine baffles do

A

Attempt to evenly cool the engine

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69
Q

How to measure cylinder head temperature

A

Temp of hottest (usually rear most) cylinder

Measure by thermocouple

Voltage proportional to temp

Does not require aircraft power

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70
Q

What is liquid cooling for engine

A

Coolant mixture of water / anti freeze

If cold = bypasses coolant heat exchange

Controlled by thermostatic valve

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71
Q

What is the advantages of a liquid cooled engine

A

More consistent temperature across cylinders

Good for cabin heating / window de-misting

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72
Q

Disadvantages of liquid cooled engines

A

Weighs more

Leak = engine overheats quickly

Greater maintenance

Greater complexity

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73
Q

What is mixture ratio

A

Mass of air compared to mass of fuel

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74
Q

What is the mixture ratio to burn all fuel and all oxygen

A

15:1

Chemically correct (stoichiometric)

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75
Q

What does a fully rich mixture do

A

Helps cool inside of engine (9:1)

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76
Q

What is best power mixture

A

12:1

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77
Q

What is detonation

A

Shock wave propagating infront of shockwave = occurs after ignition

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78
Q

What is pre-ignition

A

High temps cause sharp edges (spark plugs etc) to become hot (like coal)

On subsequent compression strokes these hot points may ignite the mixture before normal ignition

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79
Q

What is normal heptane

A

Easily detonated and has a zero reference number

Fuel

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80
Q

What is iso octane

A

Fuel

Does not readily detonate and has a reference number of 100

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81
Q

What does a octane rating of 80 mean

A

20% heptane 80% octane

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82
Q

What is a higher octane number

A

Greater resistance to detonation

“Anti knock” number

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83
Q

What is tetra ethyl lead like when used in fuel

A

Reduces combustion temperature but corrosive to valves and spark plugs

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84
Q

What is ethylene di-bromide like when added to fuels

A

Not corrosive

But cumulative position

Affects mental capacity

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85
Q

Can you use a higher grade fuel

A

Yes but not a lower

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86
Q

What is fuel ice

A

Cooking effect on water droplets from the evaporation of fuel

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87
Q

What is throttle ice

A

Freeing of water vapour in the air at or near the throttle

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88
Q

What is impact ice

A

Supercooled water droplets in atmosphere coming into contact with intake

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89
Q

What is carb heat

A

Hot unfiltered air into carburettor

Makes mixture richer

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90
Q

How many volts is required to jump a 1mm gap at sea level pressure

A

3000v

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91
Q

How many volts is required to jump a 1mm gap in a aircraft ignition system

A

20,000v

92
Q

What is a magneto

A

A generator
A transformer
A distributing system

93
Q

In a magneto what does a condenser do

A

Reduces arcing at the contact breaker and assists the rapid collapse of the magnetic field

94
Q

How to switch off the magnetos

A

Ignition switch grounds (earths) the PRIMARY CIRCUIT

95
Q

What is a auxiliary starting system for

A

At low rpm during starter motor engagement the magneto will not produce a high enough voltage

96
Q

Why is started ignition delayed

A

Engine rotating slowly

To prevent kick back

Spark is delayed so it still achieves peak pressure 10° after top dead centre

97
Q

What is impulse coupling

A

Fitted between engine and magneto

Provides retarded fat spark for starting

Engine shaft winds up a spring

Spring overcomes cams = drives hub and magneto generator at high speed

98
Q

What is a HT booster coil

A

For starting bigger piston engines

Uses a battery red into a trembler circuit

Created pulsed DC

99
Q

How quickly does avgas burn

A

60-80 feet per second

100
Q

How quickly does avtur (diesel) burn

A

2-3 feet per second

101
Q

What is the approx compression ratio of a diesel

A

22:1

102
Q

What is the approx thermal efficiency or a diesel

A

45%

103
Q

What is a glow plug for in a diesel

A

To heat combustion chamber to improve fuel vaporisation when started from cold

104
Q

What is the induction stroke of a Diesel engine

A

Only air drawn into cylinder

105
Q

What is the compression stroke of a Diesel engine

A

Air compressed and fuel is injected into cylinder where is ignites under pressure

106
Q

What is the power stroke of a Diesel engine

A

Power output is controlled by the amount of fuel injected into cylinder

107
Q

What is the exhaust stroke of a Diesel engine

A

As per petrol

108
Q

What is the most common fuel injection system for modern diesels

A

Common rail systems

109
Q

What is the benefits of fuel injection

A

Accurate metering of fuel

Fuel is delivered direct to each cylinder

Only air travels through inlet

No Venturi in inlet = no icing

110
Q

What is a electric diesel fuel pump for

A

Vapour suppression when operating at high ambient temperatures

Back up in the event of a failure of the engine driven pump

Engine priming during start

Excess fuel is returned to inlet side of fuel pump

Min fuel return occurs at full throttle

111
Q

What is the engine control unit (ECU)

A

Controls injection parameters

Receives inputs from;
Throttle position 
Mixture lever 
Engine rpm 
Temperature
112
Q

What is a common rail injection system

A

Generation of the injection pressure is separate from the injection itself

High on easier pump generates in an accumulator a pressure of upto 1600 bar
Independent of engine speed

These high pressures improve vaporisation of fuel

113
Q

How are Diesel engines cooled

A

Liquid cooling

Mixture of water and anti freeze

114
Q

How does supercharging work

A

compressor rises temperature and pressure

Manifold absolute pressure (MAP) 
= increases
= more mass of air in engine 
=More fuel can be burned
= more power
115
Q

What is a altitude boosted system

A

A supercharged designed to maintain sea level MAP with increasing altitude

116
Q

What is a ground boosted system

A

Designed to increase MAP above sea level standard conditions

117
Q

What is a waste gate

A

Let’s exhaust gasses escape without going across compressor turbine = controlling amount of pressure

118
Q

Difference between supercharger and turbocharger

A

Supercharger is connected directly to crankshaft

119
Q

What is a supercharger

A

Connected directly to crankshaft

As alt increases power increases (to an extent) exhaust back pressure reduces

120
Q

To increase power what order should things be done to mixture rpm and MAP

A

1 richen mixture
2 increase rpm
3 increase MAP

121
Q

To decrease power what order should things be done to mixture rpm and MAP

A

1 decrease MAP
2 decrease rpm
3 adjust mixture

122
Q

What is rated power

A

Specified manifold absolute pressure (MAP) and rpm that is permissible for safe continuous operations

123
Q

How can you measure rpm

A

Gauge;
Mechanically driven by a flexible drive shaft from the engine turning a magnet inside a drag cup

Tacho-generator, 3 phase generator driven by engine = synchronous motor turning at same speed as generator - motor turns magnet in drag cup

124
Q

Manifold absolute pressure

A

Power developed - mass of fuel burned determined by mass of air it mixes with

Measures between throttle valve and inlet valve

2 capsules, one sealed
The other open to manifold pressure

Normally aspirated engines at sea Level (max power)
Pressure slightly less than ambient due to induction system losses

125
Q

What is a oil pressure gauge

A

Bourbon tube

126
Q

How is oil temperature measured

A

Wheatstone bridge

127
Q

How is cylinder temperature measured

A

Thermal couple

128
Q

How is exhaust gas temp measured

A

Thermocouple

Used to make adjustments to mixture ratio

Mixture adjustment carried out less than 75% power

129
Q

How is fuel flow / pressure measured

A

Pressure drop across a fixed orifice is directly proportional to flow through it

Bourbon tube

130
Q

What is blade angle

A

Angle between plane of rotation and chord line

Measured 70/75% of the distance from hub to tip

131
Q

What is flight fine pitch

A

The finest pitch available in flight

132
Q

What is the alpha blade pitch range

A

Range of blade angles within which Constant speed is maintained

133
Q

What is the beta range for blade pitch angle

A

Range of blade angles which are scheduled (selected manually)

134
Q

What is propeller efficiency

A

Typically 80%

Power output = product of thrust and TAS

power input = product of torque and RPM

135
Q

Where is a fixed pitch prop most efficient

A

Cruise

136
Q

What is ATM (propellers)

A

Aerodynamic turning moment

Increases blade angle

137
Q

What is CTM (propellers)

A

Centrifugal turning moment

Decreases blade angle

138
Q

What is a reduction gear box

A

Reduces prop speed compared to High speed engine

139
Q

What is positive torque

A

Engine driving the propeller

140
Q

What is negative torque

A

Propeller is driving the engine

141
Q

what is pitch control unit

A

Uses operating pins (or links) to swivel blades in the hub

142
Q

What is a single acting pitch control unit

A

In a twin = if oil pressure drops = feathers naturally

In a single = oil pressure drops = fine blade pitch to try restart

A spring (assisted by compressed nitrogen) acts on the piston to increase blade angle

Engine oil fed to the other side of piston to reduce blade angle

143
Q

How is aerodynamic turning motion (ATM) and centrifugal turning motion (CTM) balanced

A

Use of counterweights on blade roots (reduces CTM)

144
Q

What is a centrifugal larch

A

Holds blade at ground fine position on shut down

Only works when blade already in ground fine position so it won’t work in flight

145
Q

What is a constant speed unit

A

Controls how much oil that is allowed into pitch control unit

146
Q

What are governor fly weights for

A

Maintains blade angle for constant rpm

If prop over speeds slightly = governor flyweights = reduces oil supply to PCU
= coarser

147
Q

How to unfeather a single acting prop

A

Uses a accumulator to provide oil pressure to unfeather prop

148
Q

What is a double acting PCU

A

Uses oil on both sides instead of spring on one side

Greater control of blade angle

To unfeather = uses 3 phase motor to drive pump

149
Q

What is a mechanical pitch lock

A

Loss of hydraulic pressure = lock blade angle

150
Q

When does a automatic feathering system work

A

Only at high throttle (take off)

151
Q

What does a pitch stop do

A

Prevents blades becoming to fine in the air

152
Q

What are the 3 conditions in a condition leaver

A

Run
Stop
Feather

153
Q

What is synchronising of propellers

A

Synchronise to same engine rpm

More comfort
Reduce airframe fatigue

Reference to a master rpm

154
Q

What is synchrophasing propellers

A

Blades interlinked instead of exact same phase

Increases comfort
Reduces cabin fatigue

155
Q

What is negative torque signal

A

Prevent propeller driving engine when low power setting and sufficient airspeed

156
Q

Which of Newton’s laws related to gas turbine engines

A

3rd law

Every action

Solely reaction of mass of air exiting the engine

No ‘pushing effect’

157
Q

What cycle refers to gas turbine engines

A

Brayton cycle

158
Q

Where is the highest pressure in a gas turbine engine

A

Entry to combustion zone

159
Q

What is the compression in a gas turbine engine

A

Air pressure increases

Entire unit contained in a convergent duct to maintain constant axial velocity whilst pressure increases

160
Q

What is a diffuser in a gas turbine engine

A

Divergent duct between compressor and combustion section

Highest pressure occurs here

161
Q

What is the combustion section of a gas turbine engine

A

Continuous combustion

Theoretically constant pressure

Highest gas temp occurs here

162
Q

What is the exit of a gas turbine engine like

A

Convergent duct

Gas velocity increases as it exits the combustion chamber and enters nozzle guide vanes

163
Q

What does net thrust equal

A

Net thrust = mass (Vj-Va)

Vj= jet velocity 
Va = aircraft velocity
164
Q

When is max thrust for a aircraft

A

When static

165
Q

What happens to thrust above tropopause

A

Decreases more rapidly

166
Q

How does bleed air affect thrust

A

Reduces mass flow

Which reduces thrust

167
Q

What does intake heating do to thrust

A

Reduces air density
Which reduces mass of air
Which reduces thrust

168
Q

What is flat rated thrust

A

Cooler / denser air means full power is produced before throttle reaches max detent

= rpm limited

169
Q

What is specific fuel consumption

A

Mass of fuel / unit of thrust / time

170
Q

What is propulsive efficiency

A

Efficiency with which kinetic energy is translated into propulsive force

At low speeds the high velocity exhaust wastes more energy than the propeller

Prop more efficient at low speeds

Some engines have efficiently of 80/90%

171
Q

Characteristics of single spool axial flow turbojet

A

Only efficient at high speed
Small frontal area
Inefficient and noisy

172
Q

Most common type of reduction gear box

A

Sun and planet gear train

173
Q

Purposes of gas turbine air inlet

A

Provide supply of turbulence free air, evenly distributed to the face of the compression

Present air at Mach 0.5
Maximise ram effect

174
Q

What happens to pressure velocity and temperature at the gas turbine air inlet

A

Pressure increases
Velocity decreases
Temperature increases

175
Q

Advantages of centrifugal compressor

A

Simple
Robust
Short length
Not prone to stall and surge

176
Q

Disadvantages of centrifugal compressor

A 
Broad frontal area
Low mass flow
Low pressure ratios 
Poor acceleration 
High SFC
177
Q

Axial flow compressor pressure ratio and temperature rise over one stage

A

1.1:1 to 1.2:1

25°c

178
Q

What happens to velocity pressure and temperature across a compressor rotor

A

All increase

179
Q

What happens to temperature pressure and velocity across a compressor stator

A

Velocity reduces

Temperature pressure increases

180
Q

Advantages of a axial flow compressor

A

Small frontal area
High mass flow
High pressure ratios
Low SFC

181
Q

Disadvantages of axial flow compressor

A

Expensive
Complex
Prone to stall / surge
Easily damaged

182
Q

What is a axi-cf compressor

A

Half centrifugal half axial

Makes for shorter engine

183
Q

Variable inlet guide vanes (VIGV)

A

Present incoming air at the optimum angle for subsequent rotor stages

184
Q

What is internal engine air

A

Airflow that does not contribute directly to engine thrust

Bearing chamber sealing

Compressor and turbine blade tip clearance

Internal cooling

185
Q

Where is the sensor for engine over heat (turbine over heat)

A

On some engines the thermo switch is in the cooling air outlet

186
Q

What is accessory cooling

A

Air through a nozzle from the compressor sucks in atmospheric air to cool the engine while running on the ground

187
Q

Multiple can combustion system

A

Easy servicing

Doesn’t present gas stream to all areas of turbine

188
Q

Tubo annular combustion chamber (can-annular)

A

Servicing more difficult

Presents gas stream to a greater area of turbine compares to multi can

189
Q

Annular combustion chamber

A

Presents gas stream to all areas of turbine

190
Q

What % of air in the combustion section does what

A

20% in direct support of combustion

80% round outside

Of that 80%
- 20% shapes flame
-40% cooling
20% dilution

191
Q

Fuel to air ratio in primary zone of combustion chamber

A

15:1

192
Q

Fuel to air ratio overall

A

60:1

193
Q

Reverse flow vaporising nozzle

A

Helps vaporise fuel to be sprayed

194
Q

Duplex nozzle

A

Like a finger over a hose

Helps maintain high fuel pressure during low engine running

195
Q

On start how many spark and at what energy does the High energy ignition unit supply

A

60-100 parks per min

8-10 joules

196
Q

When engine on continuous ignition what energy are the sparks

A

4-6 joules

197
Q

Most common turbine blade attachment method

A

Fir tree route

198
Q

What is blade creep

A

Elongation of metal beyond its elastic limit

199
Q

What are turbine blades made out of

A

Nickel based alloys
With additional elements such as tantalum, aluminium, and chromium

Made with single crystal technology

200
Q

What is active clearance control

A

Uses bleed air around the turbine casing causing it to expand

201
Q

Purpose of the exhaust system

A

Straightens
Accelerated
And directs exhaust gasses

202
Q

What is the angle of reverse for reverse thrust

A

135/150°

203
Q

What is no rev thrust indication

A

Fully stowed and locks are fully engaged

204
Q

What is a Amber reverse thrust indication

A

Locks are disengaged (in transit)

205
Q

Green reverse thrust indication

A

Thrust reverser fully deployed

206
Q

Where are gas turbine temperature sensors located

A

Exhaust section or turbine

Ideal place would be turbine inlet

207
Q

What is a optical pyrometers

A

Non contacting device that intercepts and measures thermal radiation

208
Q

What seal is used on the main bearing housings for a gas turbine

A

Labyrinth seal

209
Q

What is the most common oil system on gas turbines

A

Full flow recirculating system

Used oil fed here

210
Q

What is a fuel cooled oil cooler (FCOC)

Aka (FOHE) fuel oil heat exchanger

A

Pump oil round fuel pipes to cool oil and heat fuel = before fuel filter to stop ice forming

Low pressure fcoc acts as fuel heater

High pressure fcoc acts as oil cooler

211
Q

Centrifugal breather

A

Spins round to separate oil and air

212
Q

Primary oil filtration

A

Provided by large capacity filter in combined scavenger line

Remove fine particles

213
Q

Secondary filtration

A

After pressure pump

Much coarser

Ensures coolers and oil jets not at risk of blockage when scavenger filter bypassed

214
Q

Fuel control unit senses

A 
Thrust lever position 
Air temp and pressure 
Engine speed 
EGT 
Compressor delivery pressure
215
Q

What does a acceleration control unit ACU do

A

Limits fuel flow to prevent over fuelling

216
Q

FADEC

A

Full authority digital engine control

Closed loop

Computed functions of:
Throttle lever angle 
TAT
altitude 
Mach number
217
Q

If both FADEC channels fail

A

Engine in safe condition

Fuel flow to min
VSV to fully open
Oil cooler to wide open
Active clearance control ACC shut off

218
Q

What is “self sustaining speed”

A

Speed at which the engine will accelerate without the aid of starter motor

219
Q

wet start

A

Faulty ignition unit

Important to let it drain

No indication of rise to EGT
Stagnation of RPM

220
Q

Hot start

A

EGT exceeds max

Causes

Low air pressure to air started

Failure to completely drain after wet start

Strong tail wind in jet pipe

Early opening of fuel valve

221
Q

Hung start

A

Rpm stagnated with high EGT

Causes

Fuel control malfunction
Premature starter disengagement
Compressor stall

222
Q

How long can take off thrust be used

A

5 mins

223
Q

How long can max contingency thrust be used for

A

2.5 mins

When baulked Landing one engine out

224
Q

How long can intermediate contingency thrust be used for

A

Used 1 engine failed

Unlimited duration

225
Q

How long can max continuous thrust be used for

A

Unlimited duration

All engines

ATPL AGK (3 decks)

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