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Systems Final > Systems Pages 7 to 22 > Flashcards

Systems Pages 7 to 22 Flashcards

1
Q

What is the most major problem in terms of pressurising an aircraft?

A

Fatigue life.

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2
Q

How does the depressurisation cycle work?

A

With each cycle of pressurisation, the fuselage first swells, thus stretching and placing the structure’s skins under tension stress and the fasteners under shear stress, followed by the depressurisation returning the structure to normal.

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3
Q

How does the depressurisation cycle affect fatigue life?

A

Cycling action slowly fatigues the structure, leading to the eventual termination of its useful safe life.

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4
Q

What are other factors that lead to the degrading of the fatigue life of an aircraft?

A
  • Manoeuvres outside the aircraft’s operating envelope.
  • Heavy landings.
  • Turbulent weather conditions
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5
Q

What is the metal skin/covering of an aircraft fuselage attached to? Does it carry part of the load?

A

It is riveted to the longerons, bulkheads, and other structural members and carries part of the load.

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6
Q

What does the fuselage skin thickness vary with?

A
  • The load carried

- The stresses sustained at a particular location

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7
Q

What are the advantages of using a semi-monocoque fuselage?

A

The bulkheads, frames, stringers and longerons facilitate the design and construction of a streamlined fuselage and add to the strength and rigidity of the structure.

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8
Q

What is the main advantage regarding the usage of a semi-monocoque fuselage?

A

It does not depend on a few members for strength and rigidity.
This means that a semimonocoque fuselage, may withstand considerable damage and still be strong enough to hold together.

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9
Q

What are the main airframe elements of a large jet transport aircraft?

A
  • Fuselage
  • Wing
  • Empennage
  • Powerplant
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10
Q

What are the main airframe structural components of a large jet transport aircraft?

A
  • Wing spar
  • Ribs
  • Stringer & skin
  • Fuselage longeron
  • Frame & bulkhead
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11
Q

What is the main aircraft configuration regarding structure used in the modern day?

A

Conventional configuration

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12
Q

When dealing with metal structures, what are some precautions required to prevent corrosion?

A
  • Regular washing of aircraft
  • Hangaring of aircraft during long idle periods
  • Precaution against damaging of painted surfaces
  • Treating of internal structures with moisture excluding compounds and careful handling of substances which may contaminate
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13
Q

What happens if mercury comes into contact with the allows used in the construction of an aircraft?

A

There’s a dramatic and instant reaction which leads to the destruction of the structural integrity of the aircraft’s structure.

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14
Q

What are the four fuel types? Which one is the most common?

A

Turbo fuel A (Jet A) found in common use
Turbo fuel A-1 (Jet A-1), a low temperature fuel with a lower freezing point
Turbo fuel B (Jet B), approximately 30% Kerosene, 70% Gasoline, known as a wide cut fuel with low freezing and flash points and used by the military.
Turbo fuel 5 (JP-5), has a high flash point for safety reasons as it used on board aircraft carriers.

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15
Q

What are jet fuels composed of?

A

Liquid hydrocarbons that are similar to kerosene, some blended with gasoline

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16
Q

What is hydrocarbon fuel made up of?

A

A compound of hydrogen and carbon found in coal, natural gas and crude oil.

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17
Q

What is the importance of the mixture of hydrocarbons and the other elements it is made up of?

A
  • Designed to freely mix with oxygen at combustion flow rates and temperatures.
  • The blending of gasoline reduces the fuel’s tendency to become too viscous at high altitudes.
  • This is a problem which affects performance of some high altitude aircraft.
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18
Q

How are the oxides formed in jet fuel? What is the advantage to this?

A
  • Combustion in a gas turbine engine are mostly gases.
  • Another quality designed into jet fuels which keeps solid particles to a minimum, solids that would impinge on turbine nozzle vanes and turbine blades causing erosion.
19
Q

Are jet fuels colour coded? What is the typical colour of jet fuel?

A
  • No

- Straw

20
Q

What are metal tanks known as?

A

Rigid type, rubber tanks, bladder type and integral tanks.

21
Q

What are rigid type tanks made out of?

A

Aluminium alloy with welded joints, sometimes they can be covered with a shock resistance rubber coating which often has self sealing capabilities.

22
Q

What are bladder type tanks made out of?

A

Thin fabric, impregnated with neoprene or some similar material that is impervious to fuel.

23
Q

What are integral tanks? What material is included in integral tanks?

A
  • Integral tanks make best use of the empty spaces within the aircraft wings.
  • The structure is sealed during construction, enabling the complete structure to become the fuel cell.
  • Included in these tanks are baffles, which increase strength and reduce fuel surging during attitude changes.
24
Q

Are fuel tanks pressurised?

A

Yes, to provide a positive head of fuel to the system pumps.

25
Q

Tanks relying on gravity are required to have _____?

A

A venting system to ensure the tanks don’t suffer from cavitation.

26
Q

Is it true that the location, size, shape and construction of fuel tanks do not vary with the type and intended use of the aircraft?

A

No, it is true that they vary.

27
Q

What are sumps and drains used for?

A
  • Sump is known as a sediment trap.
  • A drain point at the lowest point of each fuel tank allows all impurities to accumulate in such a way as to allow samples to be collected, inspected and totally drained off from this point.
28
Q

How does a drain collect impurities? (i.e. its principle of operation)

A

The drain valve has a sealing poppet, which when depressed, its contents are allowed to flow out and when released, it completely seals again.

29
Q

Describe how to prevent water impurities from getting into the fuel tank

A

To prevent the introduction of water through condensation, it is normal to fill tanks at the end of each day.

30
Q

What is the purpose and function of a standpipe?

A
  • A stand pipe prevents fuel contamination as it prevents the last of the fuel and possibly some contaminants entering the system.
  • The reason for such precaution is that AVTUR is more hydroscopic than AVGAS.
  • Hydroscopic means that the tendency to absorb moisture from the atmosphere.
31
Q

What is the purpose of a cross-feed system?

A

Cross-feed systems are required to correct imbalance of fuel between wings as a result of engines burning unequally due to differing TBO ages, heaters using fuel from one side only or single engine operations during training exercises.

32
Q

Describe the function and purpose of a tank water drain?

A
  • Most engines can tolerate dissolved water in the fuel.
  • Free water (large slugs) can cause engine damage and failure.
  • Free water will freeze and could block filters and impede flow.
  • Can also facilitate corrosion and microbial growth.
  • Water is denser than fuel, so it is collected at the bottom of tanks and must be drained off.
33
Q

Explain the principle of operation of an electronic capacitance type gauge?

A
  • A capacitor is a device that stores electricity.
  • The amount it can store depends on three factors:
  • The area of its plates
  • The distance between the plates
  • The dielectric constant of the material separating the plates.
  • A fuel tank unit contains two concentric plates that are a fixed distance apart. Therefore, the capacitance of a unit can change if the dielectric constant of the material separating the plates varies.
  • The material between the plates is either fuel (if the tank is full), air (if the tank is empty), or some ratio of fuel and air depending on how much fuel remains in the tank
  • The bridge circuit that measures the capacitance of the tank units uses a reference capacitor for comparison.
  • When voltage is induced into the bridge, the capacitive reactance of the tank probes and the reference capacitor can be equal or different.
  • The magnitude of the difference is translated into an indication of the fuel quantity in the tank calibrated in pounds
  • A compensator unit (mounted low in the tank so it is always covered with fuel) is wired into the bridge circuit. It modifies current flow to reflect temperature variations of the fuel, which affect fuel density and thus the capacitance of the tank units.
  • Additionally, the dielectric constant of different turbine-engine fuels approved for a particular aircraft may also vary. Calibration is required to overcome this.
  • System is calibrated to indicate fuel mass
34
Q

Describe the function of a typical boost (auxiliary) pump

A
  • The electrically driven centrifugal type boost pumps produce an output similar to an engine-driven pump i.e. 120% of the expected maximum demand from the engine
  • Fuel boost pumps are used to:
  • Provide fuel at the required pressure for starting to the carburettor or to the fuel metering unit of a fuel injection system
  • Purge the fuel lines of any vapour to reduce the possibility of a vapour lock
  • Prime the cylinders of fuel-injected engines for start up
  • Supply fuel if the engine-driven pump fails
  • Fuel jettisoning
35
Q

Describe the function of fuel cross-feed systems with regard to a multi-engine aircraft (slides version)?

A

On multi-engine aircraft, the individual engine fuel systems are interconnected.

  • Fuel can be fed from any tank to any engine.
  • With an engine failure, the inoperative engine’s fuel can be made available to the others.
  • Redistribute fuel for weight and balance requirements.
  • Tan leakage.
  • Keyword is flexibility
36
Q

Describe the function of fuel jettison systems

A
  • A fuel jettison system is required for transport category and general aviation aircraft if the maximum take-off weight exceeds the maximum landing weight
  • The jettison system must be able to jettison enough fuel within 10minutes for general aviation or 15 minutes for transport category aircraft to meet the requirements of the FAR (federal air regulations).
  • To adhere to design requirements fuel jettisoning must be stopped with a maximum fuel for 45 minutes of cruise at maximum continuous power for reciprocating engines
  • Turbine powered aircraft require enough fuel for take-off and landing and 45 minutes of cruising time
  • The fuel jettisoning system is usually divided into two separate, independent systems. One for each wing so that lateral stability can be maintained
  • Normally, if an unbalanced fuel load exists, fuel will be used from the heavy wing by supplying fuel to the engines on the opposite wings
  • Each wing contains a fixed or an extendable dump chute.
37
Q

Describe the function of a fuel jettison valve

A

The transfer manifold and boost pumps are used to jettison fuel overboard by opening the proper dump valves with a transfer boost pump(s) operating.

38
Q

When are fuel boost pumps usually used?

A
  • Boost pumps are normally used during start-up and switched on for critical phases of flight when it is important to have a backup supply of fuel pressure in the case of failure of the engine-driven pump.
  • When both the engine and boost pumps are operating the fuel pressure will aid in preventing cavitation and vapour locks.
  • Boost pumps are also fitted with bypass valves so that fuel may be drawn from the tank when they are switched off.
39
Q

What happens if low pressure is indicated with regards to a fuel boost pump?

A
  • If low pressure is indicated during flight the pilot should switch the electrical boost pump on and check fuel-tank selection.
  • Low fuel pressure can lead to fuel starvation and engine failure.
  • If the fuel pressure remains low with the boost pump selected on, a landing as soon as possible is required.
40
Q

How many boost pumps do aircraft use per fuel tank?

A
  • Most aircraft use two or more boost pumps per fuel tank.
41
Q

What is vapour lock and how does it occur?

A
  • The vaporisation of the fuel in the fuel lines of the fuel system.
  • Occurs when the vapour collects at a high point in the system plumbing and then prevents liquid fuel from flowing past that point.
42
Q

What causes vapour lock?

A

Excessive heat build-up or low-pressure conditions within the fuel system but most likely a combination of both.

43
Q

What are the effects of vapour lock?

A

Engine will experience fuel starvation.

44
Q

What should you do if you experience vapour lock during a ground start?

A
  • Boost pump on
  • Mags off
  • Full throttle
  • Mixture rich
  • Wind engine over on starter for a few seconds.
  • Check to see if fuel has started to flow from the carb
  • Drain carb and let engine sit for 10 minutes
  • Try a normal hot start

Systems Final (5 decks)

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