Systems Pages 7 to 22

Question 1

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

Answer 1

Fatigue life.

Question 2

How does the depressurisation cycle work?

Answer 2

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.

Question 3

How does the depressurisation cycle affect fatigue life?

Answer 3

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

Question 4

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

Answer 4

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

Question 5

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

Answer 5

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

Question 6

What does the fuselage skin thickness vary with?

Answer 6

• The load carried

- The stresses sustained at a particular location

Question 7

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

Answer 7

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.

Question 8

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

Answer 8

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.

Question 9

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

Answer 9

• Fuselage
• Wing
• Empennage
• Powerplant

Question 10

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

Answer 10

• Wing spar
• Ribs
• Stringer & skin
• Fuselage longeron
• Frame & bulkhead

Question 11

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

Answer 11

Conventional configuration

Question 12

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

Answer 12

• 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

Question 13

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

Answer 13

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

Question 14

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

Answer 14

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.

Question 15

What are jet fuels composed of?

Answer 15

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

Question 16

What is hydrocarbon fuel made up of?

Answer 16

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

Question 17

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

Answer 17

• 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.

Question 18

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

Answer 18

• 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.

Question 19

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

Answer 19

• No

- Straw

Question 20

What are metal tanks known as?

Answer 20

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

Question 21

What are rigid type tanks made out of?

Answer 21

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

Question 22

What are bladder type tanks made out of?

Answer 22

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

Question 23

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

Answer 23

• 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.

Question 24

Are fuel tanks pressurised?

Answer 24

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

Question 25

Tanks relying on gravity are required to have _____?

Answer 25

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

Question 26

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?

Answer 26

No, it is true that they vary.

Question 27

What are sumps and drains used for?

Answer 27

- 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.

Question 28

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

Answer 28

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

Question 29

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

Answer 29

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

Question 30

What is the purpose and function of a standpipe?

Answer 30

- 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.

Question 31

What is the purpose of a cross-feed system?

Answer 31

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.

Question 32

Describe the function and purpose of a tank water drain?

Answer 32

- 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.

Question 33

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

Answer 33

- 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

Question 34

Describe the function of a typical boost (auxiliary) pump

Answer 34

- 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

Question 35

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

Answer 35

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

Question 36

Describe the function of fuel jettison systems

Answer 36

- 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.

Question 37

Describe the function of a fuel jettison valve

Answer 37

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.

Question 38

When are fuel boost pumps usually used?

Answer 38

- 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.

Question 39

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

Answer 39

- 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.

Question 40

How many boost pumps do aircraft use per fuel tank?

Answer 40

- Most aircraft use two or more boost pumps per fuel tank.

Question 41

What is vapour lock and how does it occur?

Answer 41

- 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.

Question 42

What causes vapour lock?

Answer 42

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

Question 43

What are the effects of vapour lock?

Answer 43

Engine will experience fuel starvation.

Question 44

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

Answer 44

- 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