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Part 3 Systems > Progress Test 1 > Flashcards

Progress Test 1 Flashcards

1
Q

What stress does pressurisation of the aircraft put on the skin and fasteners?

A

Fasteners under shear stress

Skin under tensile stress

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2
Q

How does pressurisation fatigue an aircraft?

A

The cyclic nature of the fuselage swelling under pressurisation and then returning to normal on the ground will fatigue the structure.

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3
Q

What will the eventual fatiguing of the aircraft fuselage and structure mean has to happen to the airframe?

A

Will lead to the end of its useful safe life. Before it reaches this it is likely that the service ceiling will be lowered to limit pressure differential to allow some additional airworthy years

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4
Q

What things will cause an aircraft to reach the end of its fatigue life sooner?

A

Manoeuvres outside the flight envelope
Heavy landings
Turbulent conditions

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5
Q

What are the 4 types of turbine engine fuels?

A
  • Jet A (AVTUR 40)
  • Jet A1 (AVTUR 50)
  • Jet B (AVTAG or Wide cut)
  • JP-5 (military spec)
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6
Q

What are the differences between Jet A, Jet A1, Jet B and JP-5?

A

Jet A1 - most common, low freeze point
Jet A - USA fuel, slightly warmer freeze point
Jet B - used in cold climates, has low flash and very cold freeze point
JP-5 - used mainly for aircraft carriers as it has very high flash point

All are straw or colourless

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7
Q

What are the differences between turbine and piston engine fuels?

A

Turbine engine fuel has:

  • More carbons per molecule
  • More viscous
  • Lower volatility
  • Higher boiling point
  • usually have more additives (microbes, oxidation, ice etc.)
  • have to sustain a continuous flame in the engine
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8
Q

What is required to ensure the correct type of fuel enters the aircraft?

A

Aircraft and tanker markings must be the same
Required fuel is in flight manual, tech log or fuel load sheet
Sticker beside the filler cap must state “Jet A-1” and include the colours

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9
Q

What type of markings must an aircraft and tanker with Jet A-1 have?

A

Filler cap: “Jet A-1” in white writing on a black background

Tanker: “Jet A-1” in white writing on a black background with grey decals

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10
Q

What 8 qualities should a turbine fuel have?

A
  • Pump-able (flow easily in all conditions)
  • Allow engine start in all ground conditions and satisfactory in flight relighting characteristics
  • Efficient combustion in all conditions
  • Highest possible calorific value
  • Minimal harmful effects on combustion system and and turbine blades
  • Minimal corrosive effects on fuel system and components
  • Provide adequate lubrication for moving parts of system
  • Reduce fire hazards
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11
Q

What are the different types of fuel tanks?

A

Metal tanks (rigid type)
Rubber tanks
Bladder tanks
Integral tanks (wet wing)

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12
Q

How are metal/rigid type tanks made?

A

Made from aluminium alloy with welded joints.
Covered in shock resistant rubber coating
Sometimes rubber coating has self sealing capability

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13
Q

How are bladder type fuel tanks made/ constructed?

A

Made of thin fabric, that can be ‘impregnated’ with neoprene or other fuel resistant fibres

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14
Q

What is the construction of the integral fuel tanks.

A

Use empty spaces in the wings and structure
Structure is sealed during manufacture to allow who,e space to be used to store fuel
They will include baffles to increase strength and prevent fuel surges

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15
Q

What is usually done to large transport aircraft fuel tanks? Why?

A

Pressurised to give a positive pressure to the fuel outlet and pumps. If the system is gravity fed, they will have venting system to stop any cavitation

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16
Q

What is a sump and what is its purpose in the fuel system? How does the drain work?

A

They are located at the lowest point in the tanks to allow impurities to collect in a way that samples can be collected (by a drain), inspected and completely removed.
The drain has a poppet valve that when pressed will allow flow out, and when released will seal the tank

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17
Q

What are the methods of preventing contamination in the fuel to get to the engines?

A 
Sumps
Drains
Standpipe
Filling tanks at the end of each day
Filters
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18
Q

How does AVTUR react with water compared to AVGAS?

A

It is more hydroscopic, droplets suspend in the fuel and it is more common.
Turbine engines are more equipped to deal with water in the system.

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19
Q

What are the different types of fuel quantity indicators? Briefly explain each

A
  • Sight glass (tube in the cockpit that fills to the same level as the tank, calibrated to gallons
  • Float type (float is directly connected to indicating needle)
  • Electric type (fuel level float moves a variable resistance dc thing to drive a radiometer indicator)
  • Electronic type (the capacitance between two or more sensors in the tank varies. Bridge circuit measures the dielectric constant and additional probe accounts for temp/density)
  • Magnetic or drip type dipstick (rod in bottom of wing with quantity indicators, will have float to determine fluid level within)
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20
Q

What is the purpose of fuel cross feed systems? What could cause this?

A
  • correct fuel imbalances
  • engines drawing from only one tank, uneven fuel burn (due to engine age etc.), simulated engine out training, heaters/APU using fuel from only one side,
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21
Q

How can mechanical advantage of a hydraulic system be created? Describe pascals law to answer this

A

Pascal’s law: Pressure = Force/Area, so if force one is acted over a large area, the pressure generated will spearhead equally and exert at the same amount across the entire liquid, so if the second piston has a larger area, the force it will produce will be greater

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22
Q

What type of seals are comparable with vegetable based hydraulic oil?

A

Natural rubber seals, on older aircraft with less demand

Coloured Blue fluid

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23
Q

What seals are comparable with mineral based hydraulic oils?

A

Neoprene rubber seals (synthetic)

Coloured red fluid

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24
Q

What seals are compatible with synthetic hydraulic oils?

A

Ethylene propylene seals (synthetic)

Light purple colour fluid

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25
Q

Describe the open circuit hydraulic system

A

Fluid from reservoir passes pump or hand pump and flows through selector valves in series, and if no action is needed will simply pass through the selectors, through a filter and back into the reservoir. If it is needed, only one function can operate at a time. The selector valve will direct pressure to the required side of the actuator.

The system also has a pressure relief valve to bypass the selector valves if pressure is too great.

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26
Q

Describe the principal of operation of the pressurised (closed circuit) hydraulic system?

A

Pump (hand or engine driven) directs fluid to the unloading valve, which will direct pressure to the selector valves, up to a predetermined level, when it will just discharge back into the reservoir through the filter. The unloading valve will hold pressure in the selectors with help from the accumulator until the system demands a function, when the unloading valve will deliver more pressure for the selectors.

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27
Q

In what situation might a closed circuit/ pressurised system not require an unloading valve?

A

When a variable delivery/constant pressure pump (that is designed to maintain pressure is installed instead of a constant delivery pump) is installed in the system

28
Q

What happens to the system pressure when a hydraulic function is required of the system?

A

The pressure will drop;

  • causing the unloading valve to deliver more pressure until it builds up again, or if this fails
  • the accumulator will soften out any large spikes/dips in pressure
29
Q

What are the types of engine driven hydraulic pumps? Briefly describe each one

A

Vane type: offset axle, with spins loaded arms will cause the chambers to construct, increasing pressure. It can move large volumes, at low pressure.

Gear type: counter rotating gears will force fluid through a smaller space. They can handle medium volumes up to about 1500psi

Piston type: have several pistons rotating on an axle. The pistons are at an angle to the axle so the inlet will be on the top side of the unit, and as it rotates the chamber gets smaller and pressure increase on the lower side. Can deliver 3500psi, but at relatively low volumes, multiple may be required.

30
Q

What are the non engine drive hydraulic pumps? Describe them

A

Hand pump: hand actuated will provide pressure created by the pilots in an emergency or during ground tests

RAT: spring loaded propeller will move into airflow and will be driven by the airflow to provide hydraulic pressure

Electrically driven: will act as auxiliary pumps for on the ground and to supplement engine driven in flight

31
Q

How can hydraulic pumps be classified by how they move the fluid through them? Define each? Examples?

A

Positive displacement:
Provides a continuous flow, and has good internal seals so there is no slippage of the fluid. Most are of this type, and will cause a pressure relief valve to actuate in an over pressure/blockage.

No positive displacement:
Provides a continuous flow but does not have a positive internal seal so in a blockage the fluid will slip within the pump and flow will reduce to 0. Impellers and centrifugal pumps are examples of this.

32
Q

What are the different types of valves in the hydraulic system? Describe each one

A

Check valve/ non return valve: a one way valve, usually a spring with a ball, with the sprink opposing the normal fluid flow, so if a leak upstream occurs, the ball will prevent any fluid from returning

Relief valve: a valve that will release pressure in the instance of an over pressure beyond a certain predetermined level, potentially caused by an increase in temp while the system is static.

Selector valve: will initiate the movement of actuators by providing an appropriate flow path for the pressurised fluid. Can be rotating plug, poppet type, or an open centre rotating plug.

Bypass valve: allow fluid to bypass certain components if it is not required or the pressure becomes too great.

Sequencing valve: if certain things need to be sequenced, eg gear doors then gear etc.

Shuttle Valve: will allow pressure from other system to enter if original pressure drops below a certain calibrated threshold

Pressure control valves: reduces pressure down to required pressure, through a differential in the are on different sides of the unit

33
Q

What is a hydraulic fuse? How does it work?

A

A form of shutoff valve to stop the complete loss of fluid should a leak occur downstream. In normal operation the hydraulic pressure will oppose a spring to hold a piston open, however if pressure is lost on one side the spring will overcome it and any remaining pressure will force the piston shut, preventing any more flow.

34
Q

What is the purpose of filters in the hydraulic system? What tolerances can they perform to?

A

Designed to clean solid particulates out of the fluid, all greater than 25microns, and most greater than 10 microns. They have built in bypass valves if they become clogged

Can remove particles between 15-1.5 microns (slides)

35
Q

What is the purpose of a hydraulic actuator? What are it’s components

A

To convert the pressure of the hydraulic fluid into useful fo4ce to do work.

Contains:
Polished cylinder
Piston connected to the desired component

36
Q

What are some purposes of the hydraulic reservoir?

A
  • Provide system fluid and cover for any leaks
  • Allow bubbles to be purged
  • Seperate foreign matter from the fluid (standpipe)
  • Overflow basin
  • Includes baffles
37
Q

What is the purpose of a standpipe?

A

To create a small amount of unusable fluid in the system for debris to collect without risk of being drawn through the system causing damage, and to ensure that there will be some fluid should the emergency system require it.

38
Q

Describe the emergency hydraulic fluid system?

A

An emergency pump will draw fluid from the bottom the reservoir (not the standpipe) and deliver it the components. It will also operate if the engine driven pump stops working and the alternating current motor driven pump (ACMP) will still provide the system enough pressure to perform emergency operations

39
Q

How can hydraulic fluid levels be determined? Describe?

A

Sight glass: provides a visual indication on the ground

Reservoir quantity indicator: will give direct or electrical indication to be transmitted to the cockpit

40
Q

What are the advantages of Pneumatics over hydraulics?

A

Endless supply of air
Components are simple and lightweight
Compressed air is lightweight and no return system is needed
Relatively free from temperature problems
No fire hazard and good design will minimise explosion hazard
Proper filters will reduce contamination

41
Q

What are the disadvantages of pneumatics compared to hydraulics?

A

Air needs to be significantly compressed before it will actuate a heavy device
Compress ability of air will lead to lag in response
Not good for precise control operations
Difficult to provide air tight seals
Difficult to find leaks

42
Q

Describe the low pressure pneumatic system

A

Provides low air pressure for gyro instruments etc.

43
Q

Describe the medium press pneumatic system?

A

Operates at 10p-150psi.

Used for engine start, anti icing and deciding, air conditioning, cabin pressurisation.

44
Q

Describe a high pressure pneumatic system?

A

Operates at 3000psi, full system pressure
Provides back up operation of the hydraulic landing gear and brakes
Pressure is normally stored in large metal bottles and is therefore limited to what is onboard at the start of flight.

45
Q

Describe how pneumatic pressure can actuate a hydraulic system asa back up?

A

A shuttle valve will actuate, normally allowing hydraulic pressure into the required actuator (brakes/gear etc), but in the event of a hydraulic failure, will allow pneumatic pressure into the system to actuate the jack.

46
Q

What is the purpose of a water separator?

A

To prevent the refrigeration effect, where the moisture in the compressed air will freeze when a function is actuated and the pressure drops

47
Q

What is used to remove moisture from the pneumatic system? What percentage does each remove?

A

Moisture separator: 98%

Desiccant: 2%

48
Q

What colour should the desiccant be if it is new and does not have any moisture contamination?

A

Blue

49
Q

What is used to set the timing between the landing gear and the wheel well doors? Why?

A

A sequence valve, to allow the doors to shot whenever the gear isn’t moving up or down to reduce drag

50
Q

What are the parts of the bogie undercarriage? (14)

A 
Pivot trunnion
Trunnion beam
Upper side brace
Lower side brace
Drag brace
Torque arms
Upper shock cylinder
Lower shock inner cylinder 
Positioner
Pivot fork and shaft
Pivot beam (H member)
Axle
Wheels
Equaliser
51
Q

What is the principal of operation of the boosted brakes?

A

It is essentially the same as the independent system, however as pilot pedal pressure is increased, some of the system hydraulic pressure is used to assist the pilot in adding more pressure.
When the pedal is released boosted pressure is released by a return line to the main system

52
Q

What is the purpose of the anti-skid brakes?

A

To stop the brakes from locking up and reducing the effectiveness of the brakes. Optimum braking is achieved on the verge of the skid, but will the wheels still turning

53
Q

What is the principal of operation of the anti skid unit?

A

A wheel speed sensor in the wheel axle will generate an AC or DC current that is proportional to the speed of the rotation of the wheel.
This signal is then sent to the control unit in the avionics bay which compares this signal to a predetermined level, that will detect if the skid is occurring or is imminent.
The control unit will then specify if more, less, or constant pressure is required, and will send a signal to the anti skid control valves, which will adjust the amount of pressure actuating the brakes, to achieve optimum braking.

54
Q

What protections are built into the anti skid system for touchdown and differences in wheel braking abilities?

A

A weight on wheels switch will not let the brakes be applied during touchdown until the squat switch is activated. There are sensors on each wheel pair and adjacent wheels that detect if there is a 25% difference between wheel rotation it will reduce pressure on the slower wheel.

55
Q

What are the common components of all basic hydraulic systems?

A 
Pump
Reservoir
Direction control valve
Check valve
Pressure relief valve
Selector valve
Actuator
Filter
56
Q

What is the purpose of the Pivot Trunion?

A

To anchor the undercarriage to the aircraft structure

57
Q

What is the purpose of the trunnion beam?

A

Allows the undercarriage to pivot as it is extended and retracted

58
Q

What is the purpose of the upper and lower side brace? What feature does this have to allow stowage?

A

Support the gear laterally, in cross wind conditions or when side loads are experienced.
Has a knuckle allowing it to break so the undercarriage can fold up and retract

59
Q

What is the purpose of the torque arms?

A

Maintain the fore-aft alignment of the undercarriage

60
Q

What is the purpose of the pivot fork and shaft?

A

Pivots the pivot beam (h member) to the bottom of the main strut

61
Q

What is the purpose of the pivot beam?

A

Runs in the fore-aft axis and has the 4 axles and wheels attached

62
Q

What is the purpose of the equaliser?

A

To prevent the angle of the pivot beam form being more than it should be. Set the angle of the pivot beam so that the wheels will spin up nicely when they contact the ground

63
Q

What is the purpose of the positioner

A

Hydraulic ram that will push the pivot beam into the position set by the equaliser

64
Q

What is the purpose of the shock strut?

A

It is an oleo strut. To dampen any shocks. Same principal of operation

65
Q

What is the purpose of the drag brace

A

Braces the gear in the fire-aft axis. There is one on the forward and and on the read side of the main strut

66
Q

What is the ratio of Kerosene to Gasoline in Jet B fuel?

A

30% Kerosene, 70% Gasoline

Part 3 Systems (3 decks)

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