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Systems Part 4 > Final Exam 1 > Flashcards

Final Exam 1 Flashcards

1
Q

How is the electrical system of an aircraft configured?

A

A separate AC circuit powered by the alternator fitted to each engine and each circuit feeds a specific bus.

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2
Q

What type of aircraft utilises DC? Why do they utilise DC?

A
  • Light twin and single-engine aircraft.
  • Those aircraft have a lower demand for electrical power and;
  • Easily stored/supplied by the battery.
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3
Q

What are the advantages of using AC compared to DC? (8)

A

More common in use because:

  • Generators, specifically alternators, are lighter than DC generators of similar capacity.
  • Larger aircraft require a higher demand for electrical power.
  • Size of the aircraft means lots of wiring.
  • High voltage/low current AC wiring has a smaller diameter, thus lighter than low voltage/high current DC wiring.
  • Alternators produce more current per RPM
  • Can be rectified to produce DC, or provides AC
  • Can be transmitted to long distances more readily
  • Circuit breaker operate better under high loads at high altitudes
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4
Q

Describe an alternator compared to a generator? (9)

A

Alternator:

  • AC current
  • Requires battery to energise windings before it can generate
  • Rotating electromagnet, 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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5
Q

What is DC power used for on large aircraft?

A

Necessary for certain equpment and battery charging for some equipment on large aircraft.

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6
Q

What is an electrical bus?

What is its prime purpose?

A
  • A system whereby a power supply is routed to a common bar, off which several components or services can be powered.
  • This breaks the electrical system into channels and the prime purpose of that is so that systems can be prioritised for the use of essential services in the event of a supply breakdown.
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7
Q

What is the different type of bus systems?

A
  • Parallel type.
  • Split bus type.
  • Split-parallel type.
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8
Q

How is DC provided when using AC power?

How are DC and AC circuits linked?

A
  • Rectified using a full-wave rectifier.

- DC circuits will have their own bus system, isolating them from AC.

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9
Q

How can you convert AC from DC?

A

In an emergency, it can be done by using an inverter, specifically, a static inverter from the DC battery.

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10
Q

What are the conditions required to operate AC generators in parallel?

A

The output voltage, phase rotation and frequency of all the generators are the same.

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11
Q

What is a CSD?

A

Is a hydromechanical drive that is similar to an automatic gearbox.

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12
Q

How does a CSD work? Why is a CSD required?

A
  • As the output of the generator is required to be at a constant frequency, its input drive speed (rotor RPM) must also be constant.
  • To convert the varying speed drive from the engine into a constant speed for the generator.
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13
Q

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

A
  • Generator requires 400RPM (+/- 8Hz)
  • Gas turbine: 7000-10,000RPM
  • Piston: think DA40
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14
Q

What maintains a constant output rotation speed with respect to the CSD?

A

Mechanical governors in the CSD… with fine adjustments from the frequency controller.

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15
Q

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

A
  • Oil system of CSD independent of the engine oil system.

- Oil inlet and outlet temperatures and low oil pressure are monitored and displayed.

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16
Q

What would happen to the CSD in the event of an electrical fault? What about an overheating or mechanical problem?

A
  • Circuit breakers protect each circuit.
  • If the generator overheats or has a mechanical problem, its rotation may need to be stopped before serious damage can occur.
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17
Q

What protection devices are there in the event of a CSD malfunction? (3)

A
  • Guarded switch provided for the pilot labelled “GEN DISC” activates a solenoid, pulling a dog clutch open.
  • This breaks the drive between the engine gearbox and the CSD.
  • Once the generator has been disconnected, it cannot be reset in flight, can only be reset on the ground my maintenance personnel.
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18
Q

What are the terms Boeing and Airbus use respectively for CSD?

A

Boeing: Integrated Drive Generator (IDG).
Airbus: Integrated Constant-Speed Drive (ICSD).

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19
Q

What is the purpose of the cabin air conditioning and pressurisation systems? What does it specifically cover? (i.e. different spaces) (4)

A
  • Provide conditioned air for heating and cooling the cockpit and cabin.
  • Also provides pressurisation to maintain a safe, comfortable cabin environment.
  • Some aircraft equipment and equipment compartments require conditioning to prevent condensation, which follows heat build-up, leading to damage such as avionics components.
  • Baggage/cargo compartments are typically air-conditioned and pressurised due to animals carried in those areas.
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20
Q

How can the cabin air conditioning and pressurisation systems be broken down to?
What are the different subsystems of the cabin air conditioning and pressurisation systems? (6)

A
  • Into subsystems which are:
  • Pressurisation system.
  • Air-conditioned system.
  • Oxygen system.
  • Pressure cell.
  • All of which are essential to the safe control of the aircraft onboard environment.
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21
Q

What do the subsystems of the cabin air conditioning and pressurisation systems provide? (2)

A

Supply inhabited areas of the aircraft with:

  • Temperature control.
  • Safe level of atmospheric pressure, ensuring a safe level of oxygen at altitude.
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22
Q

What is pressure differential? Why does this differential exist?

A
  • Difference between the pressures inside the pressure hull and the ambient pressure outside at the altitude at which the aircraft is flying.
  • Exists because the system maintains the cabin altitude at 8000ft regardless of the aircraft altitude, so the PD will be increasing as the aircraft climbs beyond 8000ft.
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23
Q

How can pressure differential be controlled? (3)

A
  • Controlling the outflow of air from the fuselage.
  • As air conditioning air flows in, the exit rate is maintained at a lesser rate by a rate controller, allowing the PD to build up to a set amount determined by aircraft altitude and pilot settings.
  • When the desired PD is achieved, outflow is allowed to increase to a rate that will maintain the PD at the required level.
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24
Q

How is vertical speed within the fuselage controlled?

A

Controlled by the rate controller to ensure that the cabin climbs at a rate that is comfortable to pax.

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25
Q

How does the aircraft RoC relate to the cabin RoC? How is the Cabin RoC/RoD controlled? (3)

A
  • Aircraft starts its flight at airfield elevation, as the aircraft climbs, ambient pressure decreases. Higher the altitude, lower the pressure, so the altitude in the cabin also climbs but at a lower rate than the aircraft itself.
  • This is cabin altitude, controlled on climb and descent by cabin vertical speed in 1000’s fpm.
  • So the outflow valve, controlled by the crew settings, controls cabin altitude and cabin vertical speed to maintain a safe cabin PSID.
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26
Q

What is the function of an air-conditioning system?

How is it achieved?

A
  • Maintain a comfortable air temperature within the aircraft fuselage.
  • Achieved through the use of a heating system and an automatic control system where the crew can select a temperature that the system will automatically maintain.
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27
Q

What does an air-conditioning system require? (3)

A
  1. ) Pressure cell to withstand PSID.
  2. ) Ability to respond to rapid changes in ambient temperature and pressure.
  3. ) Air supply capable of providing sufficient air for cabin pressurisation and air-conditioning.
28
Q

How does the cabin air conditioning and pressurisation system work? (4) Include components.

A
  • Three components, two are primary and secondary heat exchangers, last is a refrigeration unit.
  • Primary heat exchanger cools the compressed air being bled directly from the engine compressor to roughly 300ºF.
  • Secondary heat exchanger is used to cool the system air further so that the refrigeration unit can operate efficiently.
  • Refrigeration unit provides the system with air temperature appropriate for the provision of the necessary cabin comfort expected of the air-conditioning systems.
29
Q

How is cabin air distributed?

A

Ducts and diffusers.

30
Q

With respect to cabin air distribution, describe what a duplicate environmental system is and how it works?

A
  • One may feed from each engine.
  • In such cases, each system may feed to different areas of the aircraft, such as cockpit, avionics bay and one side of the cabin being fed by one, while the other feeds the rest of the cabin.
31
Q

Why might the crew shut down one air-conditioning system? i.e. what conditions?

A
  • Due to the duplicated system, the setup allows the crew to shut down one system and still operate satisfactorily on the remaining system.
  • This could be required in high power operating conditions such as high altitude runway operations, heavy icing conditions or max payload.
32
Q

How are loads reduced on the system? What is included in most air conditioning systems and why are they included?

A
  • Common for a system to recycle 50% of the cabin air back through the air conditioning cycle.
  • This reduces the load on the air delivery system, especially when the air is drawn from the engine compressors.
  • Alternate ram-air provision which allows for fresh air to be provided should both engine driven systems fail.
33
Q

What are the three positions that control the environmental system?
What type of controls do modern aircraft have with respect to the environmental system?

A
  • Three position switch with just OFF - NORMAL - RAM selections available.
  • Most modern aircraft have a control panel which temperatures can be set and indicated with separate temperatures achieved in the cockpit and cabin.
34
Q

What provision will there be for on the panel of the environmental system?

A

Provision for duplicated systems and includes pressurisation controls and instrumentation.

35
Q

What are the different types of instrumentation used in the environmental system? (7)

A
  • Cabin pressure controller
  • Barometric pressure selector.
  • Rate selector.
  • Landing altitude selector.
  • Warning lights.
  • Emergency controls.
  • APU if it has the ability to operate the system.
36
Q

What are the different safety features of the environmental system? Describe each one and how they’re operated (i.e. manually etc..)

A
  1. ) (Positive) pressure relief valve. Ensures that the pressure does not build up beyond the max operating pressure and operates automatically.
  2. ) Negative pressure relief valve. Ensures that the pressure outside the cabin never exceeds pressure inside, also operates automatically.
  3. ) Emergency depressurisation valve. Operated by the WOW switch. Can be activated from the cockpit control panel, where there is an emergency cabin altitude control.
37
Q

What does the temperature control system consist of? (5)

A
  • Cabin temperature controller.
  • Temperature selector.
  • Two-position temperature control switch.
  • Modulating bypass valve.
  • Control network.
38
Q

Describe how the temperature control switch operates? (4)

Include what happens when it’s in the ‘auto’ and ‘man’ position.

A
  • When it’s in the “auto” position, bypass valve seeks a valve gate position, resulting in duct temperature corresponding to the temperature controller setting.
  • This is achieved through the control network, which sends signals from the sensing element to the cabin temperature controller, which then electrically positions the valve in relation to the settings of the temperature control knob.
  • With the temperature control switch in the “man” position, the controller will control the bypass valve directly, with no reference to the duct temperature.
  • In this mode of operation, desired temperatures are maintained by monitoring the air temperature knob as varying conditions alter cabin temperature.
39
Q

How does the primary heat exchanger work?

How is the amount of air controlled in the primary heat exchanger?

A
  • Reduces the temperature of the bleed air or the supercharger discharge air by routing it through the veins in the core of the heat exchanger.
  • Amount of air to be cooled in the primary heat exchanger is controlled by the primary heat exchanger bypass valve.
40
Q

Describe the vapour cycle air conditioning system process? (3)

A
  • Refrigerant changes state from a liquid into a vapour, absorbing heat from the cabin.
  • Heat is taken outside of the aircraft and is given off to the outside air as the refrigerant returns to a liquid state.
  • This cycle is continuous.
41
Q

What refrigerant is used in most aircraft air conditioning systems? What makes this refrigerant the most desirable?

A
  • Dichlorodifluoromethane (Freon 12 or Refrigerant 12).
  • It’s a stable compound at both high and low temperatures.
  • Does not react with any of the material in an air-conditioning system.
  • Will not attack the rubber of seals and hoses, is colourless, and practically odourless.
42
Q

What are the other names of Freon 12?

A
  • Ucon-12.
  • Isotron-12.
  • Genetron-12.
43
Q

How much oxygen is usually carried by most transport aircraft?

A

Enough so that the aircraft can descend from cruise altitude to 14,000ft in less than four minutes without exhausting the oxygen supply.

44
Q

What are the advantages and disadvantages of the chemical system vs the gaseous oxygen system?

A 
Advantages:
1.) Lightweight.
2.) Less equipment.
3.) Less maintenance.
Disadvantages:
1.) Dangerous and must be handled properly.
2.) Causes flammable materials to burn violently or even explode.
3.) Not tamperproof.
4.) Fire hazard is greater.
5.) Won't turn off.
45
Q

What are the two types of pax O2 supply system?

How is oxygen supplied from these two systems?

A
  • A series of plug-in supply sockets fitted to the cabin walls adjacent to the pax seats to which oxygen masks can be connected.
  • The “drop-out” mask arrangement where individual masks are presented automatically to each pax if pressurisation fails.
  • Supplied automatically through a manifold. Any automatic control in the system can be over-riden manually by a member of the crew.
46
Q

What is the most space-saving oxygen system?

What kind of maintenance does it require?

A
  • Solid state oxygen generator system.
  • Less equipment and maintenance is required, maintenance only required for solid state oxygen system
  • Integrity inspection is the only requirement until actual use is implemented.
47
Q

What are the detection systems in use on aircraft?

Which one is more common?

A
  • Spot type and continuous loop detector (also known as live wire detection system).
  • Continuous loop more common.
48
Q

What is a continuous loop detector?

What does it provide?

A
  • Overheat systems, heat sensitive units that complete electrical circuits at a certain temperature, activating the warning system.
  • Provide more complete coverage of a fire hazard than any spot-type temperature detector system.
49
Q

What are the two types of continuous loop systems?

Describe them briefly (slides)

A
  • Kidde and Fenwal system.
50
Q

How does the power plant fire extinguishing system work (engine nacelle)?
Include how fire extinguishing bottles can be cross fed and how fires can be extinguished?
What pressures they are held at?
(6)

A
  • Includes a cockpit control switch, fire extinguishing agent containers, and an agent distribution system.
  • An engine can be protected with one bottle only, or a cross-feed system with two or more bottles.
  • Bottle is pressurised in the range of 500 to 600 PSI - gauge with the agent. Gauge indicates the correct charge.
  • To discharge the bottle from the cockpit, an electrical current is applied to the contactor which detonates an explosive cartridge.
  • This shatters a disk in the bottle outlet. From there, the agent flows to the engine.
  • A number one engine fire can be extinguished with a number one fire bottle and also number two bottle. The same is true for number two engine through the distribution system.
51
Q

What extinguishing systems are used for the cabin and cargo compartment?

A
  • Cabin and cockpit systems utilise hand-held fire extinguishers.
  • Cargo area utilises fixed remote controlled system designed to extinguish fires in two steps.
52
Q

How does the cargo compartment fire extinguishing system work? (3)

A
  1. ) An initial amount of agent is sprayed into the compartment.
  2. ) More agent is slowly added in order to maintain the amount of agent in the compartment for 30 minutes or more, depending on the size of the compartment.
  3. ) Container discharges into a line, spraying the agent out into the compartment when the extinguisher switch is actuated.
53
Q

Describe what an automatically fired fire extinguishing system is and where they usually found?

A
  • In these cases, the fire bottle is fitted with a eutectic head, known as a ‘squib’, which melts at about 70ºC to 75ºC, allowing the extinguishing agent to exit the bottle.
  • Found in toilet installations.
54
Q

What are the different types of extinguishing agents?

Include how they work and what type of fires they are used for?

A
  1. ) Water: Cools the fire and excludes oxygen. Is used for non-electrical fires such as smouldering fabric cigarettes.
  2. ) CO2: Displaces the oxygen in the atmosphere. Used for electrical fires.
  3. ) Dry chemical: Smothers the fire, so excluding the oxygen. Used to extinguish any type of fire.
  4. ) Halogenated carbons: Chemically interferes with combustion.
55
Q

Why are halogenated carbons the best fire extinguishing agent? (5)

A
  • The development of halogenated hydrocarbons (freons) as fire extinguishing agents with LOW TOXICITY for airborne fire extinguishing protection systems logically directed attention to its use in hand type fire extinguishers.
  • Its low concentration is very effective.
  • It may be used in occupied personnel compartments.
  • It is effective on all 3 fire types, and;
  • No residue remaining after its use.
56
Q

What is the purpose of a smoke detection system?

Why are they used?

A
  • Monitors the cargo and baggage compartments for the presence of smoke, which is indicative of a fire condition
  • They are used where the type of fire anticipated is expected to generate a substantial amount of smoke before temperature changes are sufficient to actuate a heat detection system.
57
Q

What are the three types of smoke detection instruments?

A
  • Type 1: Measurement of CO gas (CO detectors).
  • Type 2: Measurement of light transmissibility in air (photoelectric devices).
  • Type 3: Visual detection of the presence of smoke by directly viewing air samples (visual devices).
58
Q

What is the principle of operation of the thermal switch loop?
Include test switch, short circuit and dimming relay and what they provide/indicate?
(6)

A
  • 28V DC applied to both paths of the thermal switch loop.
  • If an overheat to alarm temperature or a fire occurs which closes any of the switches, a path to ground is completed through the closed switch.
  • With this loop arrangement, one open circuit can occur and the system will still provide protection at all fire surveillance points.
  • Test switch tests the entire loop and will show the operator whether an open circuit is present in the power input lead of the loop.
  • Short circuit in the loop will cause a false fire warning indication.
  • Dimming relay provides low voltage to the light for night operation.
59
Q

Describe the principle of operation of the continuous loop system?

A
  • 28V DC supplied to the hot lead through an alarm relay coil.
  • When cool, the insulation material does not allow current to flow between ground and the hot lead.
  • When a fire occurs, the insulator material heats and loses resistance sufficiently to complete a path to ground.
  • The relay coil is energized by this current flow and the alarm light is illuminated in the cockpit.
60
Q

What is the effectiveness of a primary flight control dependent on?
What happens to the flight controls at low and high speeds?

A
  • Aerodynamic force generated by control deflection and the moment arm of the CoG.
  • Low speeds: Control effectiveness is less for a given deflection at high speed.
  • High speeds: Effectiveness of the control may be so great that with the necessary flexibility inherent in the structure, resultant force may twist the wing about its torsional axis.
61
Q

How is torsional twisting removed with regards to primary flight controls?

A

Provides system redundancy, primary flight controls are split, with swept wings having multiple surfaces.

62
Q

How do split primary flight controls work?

What are the different type of split primary flight controls?

A
  • Split controls are operated in tandem at low speeds, but a lockout system is utilised to provide for the split operation at high speeds.
  • Lock out system is actuated automatically on receipt of a speed signal from the ADC, allowing in the case of ailerons, only the inboard sections to be used over a specified speed.
  • Controls known as Flaperons and Elevons may be employed.
63
Q

What are the problems associated with a power-boosted control system?
How is this problem mitigated?

A
  • During transonic flight, shockwaves form on the control surfaces and cause control surface buffeting, this force is fed back into the control system.
  • To prevent these forces reaching the pilot, aircraft flying these speeds use a power-operated irreversible control system.
  • The flight controls in the cockpit actuate control valves positioned near the cockpit control.
  • This directs the hydraulic fluid to control surface actuators known as Power Control Units (PCU’s).
64
Q

How can the pilot experience a feeling of the control surfaces?

A
  • Artificial feel is built into the system that will make the control stick force proportional to the flight loads on the control surfaces.
  • Known as ‘q’ feel.
65
Q

Describe the possible options a pilot has should all hydraulic systems fail? (3)

A
  • Some aircraft have a manual disconnect or manual reversion system, allowing the flight crew to fly the aircraft manually.
  • Modern back up systems are electrically powered.
  • In extreme cases, aircraft in stable flight have been controlled by fuel transfer to roll the aircraft and engine power imbalance to turn the aircraft.
66
Q

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

A
  • Position transducers convert the flight crew command inputs to analogue electrical signals.
  • These signals are converted into digital formal and sent to the primary flight computers.
  • This allows for the pilots input to be analysed.
  • If it is outside the aircraft’s operating envelope, it can be modified, thus operating the appropriate control within the aircraft’s correct envelope.
67
Q

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

A

Such a system can be operated via the IFS system, providing auto-flight control and feed flight control position data to the FDR.

Systems Part 4 (6 decks)

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