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Part 4 Systems > Final Exam Systems > Flashcards

Final Exam Systems Flashcards

1
Q

Describe an alternator compared to a generator?

A

Alternator:
=AC current
=Requires battery to energise windings before it can generate
=Rotating electro magnet, static wires

Generator:
=Larger and heavier
=Less current per RPM
=Built in commutator
=Brushes and slip rings
=Rotating wire
=Commutator rectifies to DC
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2
Q

Describe generally how electricity works? how does current vs electrons flow?

A
  • Negative electrons around a nucleus can be dislodges and ‘flow’ creating current
  • When wire or conductor connected to positive and negative terminal a potential difference occurs, creating electron flow
  • Electrons ‘flow’ from negative to positive
  • Current said to ‘flow’ from positive to negative
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3
Q

Describe a Volt and Amp?

A

Volt: measure of electrical pressure (force needed to make electrons flow)
Amp: rate of current flow

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4
Q

What are common types of aircraft battery?

A

Lead Acid

NiCad (Nickel-Cadium)

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5
Q

What types of electrical circuits will be present on an aircraft and how many? Why?

A

AC and DC circuits

Will often have more than one for the purpose of redundancy

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6
Q

What is the normal configuration of electrical systems on a large/twin aircraft?

A
  • Separate AC circuit powered by alternators on each engine
  • Each circuit feeds a specific BUS
  • Split, Split-parallel or parallel BUS
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7
Q

What are the advantages of an AC circuit?

A
  • Lighter weight for same power output
  • Alternators produce more current per RPM
  • Can be rectified to produce DC, or provides AC
  • Can be transmitted long distances more readily
  • Circuit breaker operate better under high loads at high altitudes
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8
Q

What is DC power required for? How is it obtained?

A
  • Required for battery charging on ALL aircraft
  • Required for some equipment
  • Obtained by using full wave rectifier
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9
Q

How are the AC and DC circuits linked?

A

They are totally isolated on different busses

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10
Q

How is AC produced from DC?

A

By operating a static inverter from the DC battery

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11
Q

What is a CSD? Why is it required?

A

Constant speed drive is a hydro-mechanical drive similar to an automatic gearbox
Maintains constant output for electrical generators due to varying speed of engines

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12
Q

What RPM is typically required for alternators? What RPMs can be found on engines?

A

Gas turbine: 7000-10,000RPM
Piston: think DA40

Generator requires 400RPM (+/- 8Hz)

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13
Q

What is the principle of operation of the CSD?

A
  • Input shaft rotates 2 identical gears to drive a differential unit and Fixed displacement hydraulic pump
  • Fixed displacement pump will pressurise oil under high RPM and apply a brake to a variable displacement pump through the control cylinder
  • Also maintains pressure to governor with maintains stable pressure to control cylinder
  • Variable displacement pump drives a gear linked to differential unit and to output shaft
  • Differential unit similar to car clutch and is constantly slipping under every situation except 400RPM engine operation
  • Output shaft also drives oil pump for charge oil
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14
Q

How does the CSD oil system work? What instrumentation is provided for it?

A

It is independent of the engine oil system

Oil inlet and outlet temp
low oil pressure

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15
Q

What happens to the CSD if the Generator malfunctions?

A
  • Guarded “GEN DISC” switch activates a solenoid
  • This pulls a dog clutch and will shear inlet drive shaft
  • Cannot be reset in flight
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16
Q

What is the Boeing and Airbus terminology for CSD?

A

A: Integrated constant speed drive (ICSD)
B: Integrated Drive generators (IDG)

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17
Q

What things will a modern constant frequency AC generating system have? Electrical Rating? How is it excited?

A
  • Rotating rectifier, brushless AC generator
  • May be excited by Pilot, external or self excited
  • 115V, 400Hz, 20-60 kVA (kilovolt amperes)
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18
Q

What is the advantage of 3 phase AC supply compared to single phase?

A

Increase current available

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19
Q

What happens if you connect 3 phase AC to equipment when the 3 phases are not in sync?

A

Motors will rotate in opposite direction

Could cause burn out

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20
Q

What is the purpose of the cabin pressurisation system?

A
  • pressurisation for safe/ comfortable cabin environment
  • prevent condensation where there is heat build up
  • create safe environment in cargo areas for live animals
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21
Q

How can the air conditioning and pressurisation system be broken down? Sub-systems?

A
  • Pressurisation system
  • Air conditioning system
  • Heating system
  • Oxygen system
  • Pressure Cell
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22
Q

What is PD? how does it vary with altitude?

A
  • Pressure differential - the difference in pressure between the inside and outside of the aircraft hull.
  • System will try and maintain cabin alt of 8000ft and so any climb above 8000ft will increase PD
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23
Q

How is PD controlled? Describe system?

A
  • By maintaining cabin outflow rate lesser than the air conditioning airflow in.
  • Rate controller controls air outflow rate and when desired PD is reached it will maintain air outflow rate equal to the air inflow rate through the air conditioning system
  • Cabin vertical speed also controlled through this means
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24
Q

How does the aircraft RoC relate to the cabin RoC? How is the Cabin RoC/RoD controlled?

A

Both start at departure airfield altitude
Cabin altitude increases at a lesser rate than the aircraft itself

Controlled by:

  • Crew settings control outflow valve position (via rate controller)
  • Cabin vertical speed in 1000’s of fpm
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25
Q

What capabilities/ components must the air con system have?

A
  • Pressure cell to withstand PD
  • Ability to rapidly respond to ambient temp changes
  • Supply capable of sufficiently pressurising aircraft
  • Sufficient supply for air conditioning
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26
Q

How will cabin temp be obtained?

A

Heating system or air con system where crew sets temp.

System will automatically maintain temp by engaging and disengaging different systems.

27
Q

What are the requirements of a cabin air con system?

A
  • Provide minimum stratification (hot/cold layers)
  • Heating and cooling cockpit and cabin
  • Humidity control (prevent condensation on windows)
  • Keep wall and floor panels at comfortable temp
28
Q

describe the process through which conditioned air reaches the cabin? Where does it come from?

A
  • Compressor bleed air cooled by primary heat exchanger to 300˚F
  • Secondary heat exchanger cools air further to allow for efficient use of refrigerator unit
  • Refrigeration unit provides cabin air at appropriate temperature
29
Q

How is cabin air distributed? How do redundant/ duplicated systems integrate into the system

A
  • Through vents in the cockpit and cabin
  • May have duplicated systems, with one engine feeding one half of the cabin
  • System 1: cockpit, avionics bay, half of cabin
  • System 2: half of cabin, cargo bay

Redundant ram air system can be used if both air con systems fail

30
Q

Why might the crew opt to shut down one air con system? What conditions?
How are loads further reduced on the system?

A

When high power settings are required:

  • High altitude runway
  • heavy icing conditions
  • Heavy load

Loads further reduced by recirculating 50% of of air

31
Q

Describe a simple vs modern environmental control panel?

A

Simple: ‘Off’ - ‘Normal’ - ‘Ram’

Modern: zone controls with temp adjusting.

  • Provision for duplicated systems
  • Pressurisation controls and instrumentation
  • Cabin pressure controller
  • Rate selector
  • LDG altitude selector
  • BARO pressure selector
  • Emergency controls and warning lights
  • APU selection to operate if available
32
Q

What safety features are present in the environmental control system?

A
  • Pressure control valve (outflow valve in normal ops)
  • Pressure relief valve
  • Negative pressure relief valve
  • Emergency depressurisation valve operated by WoW or cockpit
  • Emergency cabin altitude control in cockpit
33
Q

What components make up the temperature control system?

A
  • cabin temp controller
  • temp selector knob
  • 2 position temp control switch
  • bypass valve
  • control network
34
Q

How does the temp control switch work? What happens when it is set to different positions?

A

Auto: bypass valve will seek valve position to maintain duct temp the same as that on the temp selector. Electrically positions valve
Manual: temp controller will directly control bypass valve position. Temp maintained by adjusting temp knob as cabin conditions change

35
Q

How does the primary heat exchanger work? Where can heated air come from? What controls how much air is cooled?

A
  • Engine bleed or supercharger air is ducted through veins in the core
  • Core is cooled by ram air
  • Amount of air to be cooled is controlled by primary heat exchanger bypass valve
36
Q

Describe the vapour cycle air conditioning system?

A
  • Heat can be added or removed to refrigerant without changing its temp
  • Heat absorbed from atmosphere by refrigerant as latent heat and changes its state from liquid to gas
  • Heat is removed to external air and refrigerant returns to liquid state.
37
Q

What refrigerant is most commonly used in vapour cycle systems? Why? What are its properties?

A

Dichlorodifluromethane (Refrigerant-12 or R-12)

Stable at high and low temps
Non reactive with system materials
Won't attack rubber hoses and seals
Colourless
Odourless
38
Q

How much oxygen must a transport aircraft carry?

A

Enough for it to descend from cruise to 14,000ft in less than 4 minutes without exhausting the supply

39
Q

What are the advantages of Chemical Oxygen compared to gaseous Oxygen systems?

A

Chemical system is:

  • More efficient space wise
  • Requires less equipment
  • Requires less maintenance
40
Q

What are the disadvantages of chemical O2 compares to gaseous O2 systems?

A
  • Fire hazard
  • Not tamper-proof
  • Can’t be turned off
41
Q

What 2 types of systems may a passenger O2 supply system be?

Describe how oxygen flow is actuated?

A
  • Drop out: where masks are presented if pressurisation fails
  • Plug in: Oxygen masks plugged in to supply sockets next to each passenger

In both systems oxygen flow will be automatically supplied from a manifold, or overridden manually by the crew

42
Q

What maintenance is required for a solid state oxygen system?

A

Only requires integrity inspection

43
Q

What types of fire detection systems could be present on an aircraft (not engines)?
Which is more common?

A

Spot Type

More common: Continuous loop (live wire)

44
Q

Generally, what is a continuous loop type fire detection system? What condition does it sense? What benefits does it provide?

A

Over-heat systems that will activate warnings at a certain temperature

  • Provide a more complete coverage than spot type
  • Activate at a certain temperature
45
Q

What are the two types of continuous loop fire detection systems? Briefly describe each

A
  • Kidde: two wires inside a thermistor insulator

- Fenwal: one wire in a thermistor insulator with return circuit provided by conductive coating

46
Q

Describe how the power plant fire extinguishing system works?

A
  • Bottle contains pressurised extinguishing agent
  • To discharge the bottle from cockpit, an electrical current is applied to the contactor, which detonates explosive cartridge
  • This shatters disc in bottle outlet
  • Agent then flows into engine
  • Relief valve is fusible disc that will rupture if the bottle were to overheat
47
Q

What can be done if the engine fire bottle has been used, and the fire is still not out? What pressure are they held at?

A

Held at 500-600PSI

Can be crossfed between engines.. eg. No.2 bottle contents to No.1 engine if No.1 bottle does not extinguish fire

48
Q

What are the common extinguishing agents for turbine engines?

A

CO2

Methyl Bromide

49
Q

What systems are usually used for cabin and cockpit fire extinguishing systems?

A

hand held fire extinguishers

50
Q

How does the cargo compartment fire extinguishing system work? How long can it last?

A
  • Fixed remote controlled system
  • Container discharged into a line that is fed into the cargo compartment
  • Initial discharge sprayed into compartment
  • More agent slowly added to maintain amount of agent in compartment for up to 30min +
51
Q

Describe an automatically fired extinguishing system and where they can be found?

A

Can be in cargo compartments, but mainly in toilets

  • Fire bottle fitted with eutectic head (squib) which will melt at 70-75˚C
  • Bottle will release contents to extinguish fire
52
Q

What types of extinguishing agents are there and how do they work?

A
  • Water: Cools fire, excludes O2
  • CO2: Displaces O2
  • Dry chemical: Smothers fire, excludes O2
  • Halogenated hydrocarbons: Chemically interferes with combustion
53
Q

What types of fires can each extinguishing agent be used for?

A
  • Water: Non-electrical
  • CO2: Electrical
  • Dry chemical: Any type
  • Halogenated hydrocarbon: Pax compartments/ low toxicity
54
Q

What are the three types of smoke detection systems? Where would they normally be located?

A

Type 1: measurement of CO gas
Type2: Measurement of light transmissibility
Type 3: Visual detection by directly viewing air samples

Normally located where the anticipated type of fire will give off lots of smoke before an overheat is sensed

55
Q

What is the principle of operation of the thermal switch loop? How is it tested?

A
  • 28V DC applied to both paths of switch
  • If an overheat has closed any of the switches, a path to ground will be completed and the alarm sounded
  • If one open circuit occurs, fire protection is still provided at other surveillance points

-Test switch will show pilot if an open circuit is present in the power input lead of the loop

56
Q

What is the principle of operation of the continuous loop fire detection system? What electricity does it use?

A
  • 28V DC supplied to hot lead through alarm relay coil
  • When cool insulator material doesn’t;t allow current to flow
  • When heated, insulator loses resistance and a path to ground is completed
  • When current flows, relay coil is energised and cockpit alarm is activated
57
Q

What determines the effectiveness primary flight controls on large aircraft?

A

Aerodynamic force generated due to amount of deflection and moment arm from CoG.

58
Q

What can happen when controls are actuated on large aircraft at different speeds? What is sometimes done for some controls?

A

High speed: Controls so effective that the flexible structure may cause torsional rotation of the wing

Primary flight controls are sometimes split to removing twisting and provide redundancy

59
Q

How do the split primary flight controls work? Give an example

A
  • Operated in tandem at low speed
  • Lockout system actuated at speeds above threshold, when ADC sends speed signal
  • At high speeds, inboard sections called flaperons or elevons will be used, at low speeds outboard and inboard sections will be used together
60
Q

Describe a power boosted control system and the issues it faces?

A
  • Control stick directs hydraulic fluid to actuator

- Problems arise in transonic range due to buffeting being fed-back into the system

61
Q

How does the power operated flight control system stop mach buffet from reaching the pilot?

A
  • Uses power operated irreversible control system
  • control stick actuates control valves near cockpit
  • control valves direct hydraulic fluid to actuators called power control units (PCU)
  • Feedback is done artificially to make stick force proportional to flight loads on control surfaces
62
Q

What alternative are available if total hydraulic power is lost?

A
  • Manual reversion system
  • Modern a/c use electric backup systems
  • Extreme cases use alternate controls (thrust imbalance or fuel transferring)
63
Q

How is a pilot control input made through the fly-by-wire controls to the control surface?

A
  • Position transducers convergent crew inputs to electrical signals
  • Signals sent to actuator control electronics to be converted to digital format
  • Digital signals sent to primary flight computer for envelope analysis and modification (if required)
  • Signals sent to actuators
64
Q

What are the additional advantages of the fly-by-wire system?

A
  • System can be operated by IFS
  • Can provide auto-flight control
  • Can feed flight control position data to the Flight data recorder

Part 4 Systems (4 decks)

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