Aircraft Systems 2 Flashcards
What is a key property of hydraulic fluid?
It is incompressible
What is a WOW switch?
Weight on wheels switch.
What is the process at which hydraulic systems work?
Force multiplication
What are the key common components of a hydraulic system?
Reservoir - fluid is stored in sufficient quantities.
Filters - there are several stages of filtration to prevent debris from being passed between components.
Pump - generates pressure, either engine or electrically powered.
Accumulator - A cylinder containing a floating piston.
Valves - Pressure control (pressure/thermal relief), directional control (selector valves), non return and selector valves.
Actuators - convert hydraulic power into usable mechanical power. Single and double action.
The majority of engine or motor driven hydraulic pumps are what type?
Rotary swash plate pump.
What is the purpose of a hydraulic accumulator?
Can be used from damping, absorbing sudden shocks and changes in system pressure.
Can also be used as a stored vessel of emergency hydraulic pressure.
What is a PFCU?
Powered Flying Control Unit
Enables the large aerodynamic forces on larger control surfaces to be overcome at high speeds.
What hydraulic system malfunctions can occur?
High hydraulic fluid temperature
Low hydraulic pressure
Landing gear faults.
How long must a backup hydraulic system operate for?
Indefinite period.
What system can provide a rapid emergency power source in the event of an emergency?
RAT
Ram Air Turbine
What does an actuator convert?
Fluid pressure into mechanical energy.
If landing gear presents red lights what does this mean?
The gear are travelling or unlocked.
Where is air for cabin pressurisation supplied from?
Pressurised air is normally obtained from a late compressor stage, as bleed air.
What is complement density?
Complement Density
The rate of ventilating airflow is dependent upon volume of cabin space per occupant, this is the complement density (in m3/passenger)
What is the comfort zone?
Comfort Zone
The range of ambient temperatures and humidity in which a crew can operate comfortably without rapidly becoming fatigued.
Within the cabin conditioning heat exchanges how is hot air cooled?
Cold ram air is routed through the primary and secondary heat exchanges to cool the hot air from the engine compressor.
What are the advantages and disadvantages of a Gaseous O2 system for aircraft oxygen system?
Gaseous O2
Relatively simple system, and O2 is not lost by venting when not in use, it can be used immediately after filling.
However, the cylinders are bulky and heavy. They are not suitable as a primary O2 source when space and weight are at a premium.
What are the advantages and disadvantages of a Liquid O2 system for aircraft oxygen system?
Liquid O2 System
Reduced bulk and weight compared to cylinders and will not explode when damaged.
However oxygen is lost via venting and must be stabilised, it can also become contaminated.
What is a Molecular Sieve O2 Concentrator (MSOC)?
Molecular Sieve O2 Concentrator (MSOC)
A molecular sieve is synthetic porous metal that removes nitrogen from the air under pressure. The result is oxygen enriched gas, back purging and depressurisation removed nitrogen when fully saturated (this is pressure-swing adsorption).
This system effectively removes contaminants, however a separate gas supply is required for ejection seats and may not provide enough oxygen under rapid decompression.
What is rectification?
The conversion of AC to DC.
What primary electrical sources are present on an aircraft?
Batteries
AC Generators
DC Generators
What is an EPU?
Emergency Power Unit
Small self-contained gas turbine capable of developing full power within two seconds of initiation. EPUs use mono-fuel such as hydrazine.
What is the difference between a Primary and Secondary cell?
Primary Cell - Cannot be recharged
Secondary - Always regenerating
What is a Transformer/Rectifier Unit?
TRU
Converts AC input of one voltage into DC outputs of other voltages.
What is the role of a converter?
Converter
Changes the frequency of the primary AC supply to a different secondary frequency.
What is the role of an Inverter?
Inverter
Changes the primary DC supply into a secondary AC supply
What is a key distinction between Essential/Non-essential and Vital services?
Essential and Nonessential are for inflight
Vital are needed after emergency landing or crash.
What is a CSDU?
Constant Speed Drive Unit
The CSDU maintains the drive to the generator at a constant RPM.
It is an interlink between the engine auxillary gearbox and AC generator.
What is an IDG?
Integrated Drive Generator (IDG)
IDG is a generator with an integrated CSDU which is designed and built as a single unit.
What eletrical fault conditions are there and what are the protection mechanisms?
Over-voltage
Over-current
Reverse Current
Fuses
Circuit Breakers
Reverse Current cut-outs
What three factors affect electrical output of a generator?
Speed
Magnetic Strength
Number of Coils
What is the typical voltage of a DC aircraft system?
24V
DC generators and systems are rated at 28V to maintain a positive charge state to the 24V batteries.
What voltage are AC electrical systems?
200V
400Hz
Three-phase.
What are the two types of shock absorbers available for braking?
One utilises the incompressibility of oil.
The other utilises various combinations of oil and nitrogen.
What is the role of doors and fairings in an undercarriage system?
Doors and Fairings
To improve aerodynamic efficiency.
What is the role of jacks and linkages in an undercarriage system?
Jacks and Linkages
Hydraulic jacks operate in a controlled sequence to raise or lower the undercarriage leg.
What are the two types of down lock in an undercarriage system?
Geometrically locked hinged lever
Small hydraulic bolt which locks a hinged lever when the undercarriage is lowered.
Integral with the extension jack
Mechanically locks the jack in its fully extended position, integral to the extension jack.
What are the three categories of ‘Attention Getter’?
Warnings (Primary), Cautions (Secondary), Advisories
What is the key principle between hydraulic action?
Force Multiplication
What is a key advantage of hydraulics?
It is capable of transmitting very high forces.
What risk does air in the hydraulic system present?
Unacceptable amount of uncompressibility.
What are the two types of actuator?
Double acting
Single Acting - Fluid in one side reset by spring
What is the purpose of an actuator?
Converting hydraulic pressure into mechanical force.
How long must a hydraulic backup last if supporting a primary system?
Indefinitely.
What is the most common type of hydraulic pump?
Rotary swash plate pump.
What is the function of an accumulator in a hydraulic system?
Acts as a damper and prevent sudden changes in system pressure.
What are key features of aircraft landing gear?
Cushion landing
Steering, Braking
Shock absorber facilites on uneven ground
Minimum moving parts
What are the two categories of aircraft undercarriage microswitch?
Downlock microswitch
Uplock microswitch
How would you describe aircraft brakes?
Hydraulically operated multi-disc brakes with carbon.
What are the three electrical parameters that modern aircraft work on?
200v/400Hz/Three-phase
What is the purpose of a voltage regulator?
Voltage regulators sample the output voltage and adjust the current fed into the generator’s main exciter field coils. Output is inversely proportional to the output of the generator.
What is the purpose of RCCOs?
Reverse Current Cut Out
Sense the difference in voltage between the generator and its busbar. Its contacts remain closed whilst the voltage of the generator is higher than that of the busbar, but open if this situation is reversed.
What is a Winding?
Winding
The coils of wire used to create the field and the power.
What are armatures?
Armatures
Armatures are the coils the produce the power.
The sentence: ‘Capable of transmitting very high forces, rapid and precise response to input signals’ refers to what aircraft system?
Hydraulic System
When a force is applied to one end of a column of confined liquid, in what direction is pressure transmitted?
The pressure is transmitted through the column equally in every direction.
What is a key property of hydraulic fluid?
It is incompressible.
What is the role of actuators in a hydraulic system?
Actuators convert the hydraulic power into usable mechanical power at the point required.
What types of valves are present in a hydraulic system?
Pressure Control Valves - (pressure/thermal relief) control the level of power produced.
Direction Control Valves - (selector valves) control the amount of fluid flow to related actuators.
Non-return valves - control the direction of fluid flow.
Selector-valve - controls the operation of the actuator.
What is the purpose of a reservoir in a hydraulic system?
The reservoir allows displaced fluid to be stored and performs the secondary function of colloing the fluid and allowing air to be separated out.
The reservoir can accomodate all hydraulic fluid when the system servo jacks and both retracted.
What is the most common pump design in a hydraulic system?
Rotary swash plate pump.
Positive displacement design, axial pistons are driven in/out of cylinders drawing in fldui at lowe pressure and expelling at high pressure.
What is the role of the accumulator in a hydraulic system?
The accumulator absorbs shocks and sudden changes to system pressre, it is commonly filled with nitrogen.
Why is nitrogen often used as the filling gas for a hydraulic accumulator?
The compressibility of nitrogen allows the accumulator to absorb and smooth out the pressure ripples caused by pump operation and also the sudden changes in pressure caused by operation of components such as jacks and valves.
What is the purpose of control valves in a hydraulic system?
Control valves are necessary to prevent damage to components should over-pressurisation occur. They are often wither rotary or linear action, they operate in an ON/OFF manner.
What is the purpose of Non-return valves in a hydraulic system?
Non-return valves are used where it is necessary to allow fluid to flow to a component but prevent it from returning along the same pipe.
What is the role of a powered flying control unit?
The Powered flying control unit is used to assist in controlled movement of large control surfaces to counter aerodynamic forces at high speeds.
What is a RAT?
Ram Air Turbine (RAT)
The RAT is a rapid response emergency, secondary power source, the operation of which relies upon aircraft forward speed. The unit will spin up to speed in 2-4 seconds.
What is the role of Up locks?
Up locks are mechanical locks that restrain the fully retracted undercarriage against ‘g’ forces in flight and when extended absorb landing loads.
What are the two types of Down locks in common use?
Geometrically locked hinged lever
Small hydraulic bolt, that geometrically locks a hinged lever when the undercarriage is fully lowered.
Integral with the extension jack
More simple design than the above.
What is a WOW switch?
Weight on wheels switch
Activated by deflection of the undercarriage on the ground and used to prevent operation of the retraction mechanism and to unlock operation of steering, braking and reverse thrust systems.
What is the most common method for lowering landing gear in an emergency?
Blow down system that involves pressurising the undercarriage hydraulic system with compressed nitrogen
Why is carbon added to aircraft tires?
The addition of carbon into the rubber mix allows static charges, built up during flight to be discharged automatically upon landing.
What is the purpose of creep marks on aircraft tires?
Creep marks
If tubed tires creep, the valve stem of the inner tube is stretched and can fracture. Creep marks are painted on the tires so the degree of creep can be measured.
What is the purpose of fusible plugs in aircraft wheels?
Fusible plugs
These melt at a preset temperature to allow the aircraft tyre to deflate at a steady controlled rate rather than exploding under the high temperatures of braking.
What are the advantages of disc brakes over drum brakes for aircraft braking systems?
Multi disc brake assemblies allow for greater surface area of contact between the brake material and the rotating surfaces and larger capacity heat sinks to absorb the heat generated during braking.
What is the basic structure of a multi disc brake assembly?
Multiple stacks of carbon composite discs.
Four or more rotors keyed to the inside of each main wheel.
Five or more statos assembled on to splines of each main undercarriage wheel assembly
What is aquaplaning?
Aquaplaning by the tires of an aircraft occurs when a layer of water builds between the wheels runway surface, leading to a loss of traction that prevents the aircraft from responding to control inputs.
What is an aircraft anti-skid system?
The anti-skid system aims to reduced the chance of skidding by varying the frequency and amplitude allowing braking forces to be maintained just below skidding conditions. The brakes are held off until touch down and wheel spin up has occured.
What are the main causes of hypoxia?
Hypoxia
Caused by:
Ascent to altitude
Failure of equipment to provide adequate pressure
Decompression of cabin at altitude
Toxic fumes.
How do the symptoms of hypoxia vary with altitude?
Up to 10,000ft - little impairment on performance.
10-15,000ft - Ability to perform skilled tasks progressively impaired.
15-20,000ft - Marked impairment in even simple tasks, clumsiness and euphoria or violence may arise.
20,000 ft+ - Severe symptoms, unconsciousness soon occurs.
What are the causes and symptoms of hyperventilation?
Hyperventilation is caused by:
Anxiety, apprehension or fear. Rise in body temperature. Hypoxia
and can cause symptoms including:
Tingling in hands, feet and lips. Dizziness and faintness. Spasms, impaired performance and unconsciousness.
What are the common effects of decompression sickness?
Bends - can lead to agonising pain in joints.
Chokes
Collapse
Neurological symptoms
What is barotrauma?
Barotrauma is pressure injury often caused by the imbalance of pressure on the eardrum when gases in the middle ear and sinuses fail to balance.
Symptoms can include pain in ears, teeth and/or sinuses. Ruptured ear drum and deafness.
What is the comfort zone when referring to cabin conditioning?
Comfort zone
The range of ambient temperatures and humidity in which crew can operate comfortably without becoming fatigued.
What is the typical combat aircraft airflow?
Combat aircraft airflow
5kg/min
In normal flight conditions 80% of the air is circulated around the crew, whilst the remainder is used for demisting and ventilation.
What standard must oxygen system oxygen be?
High standard 99.5% O2
Low water and carbon monoxide content.
What are the advantages of a liquid O2 system?
Liquid O2 system
Reduced bulk and weight compared to cylinders.
However supply can be lost through evaporation and it must be stabilised before use.
How long must continuous flow emergency oxygen last on an ejection seat?
At least 10 minutes.
What is the role of an inverter?
Inverters change the primary DC supply to a secondary AC supply. They can be either rotary or solid state.
What types of power units are there?
Ground Power Units
Auxillary Power Units
Airborne Auxillary Power Units
Emergency Power Units
What is the role of busbars in an aircraft power system?
Busbars
Provide a point from which supplies can be taken to the consumer unit. The output from the generators is coupled to the conductors (busbars). They are insulated from the main structure and coated with protective covering.
Aircraft electrical consumer services are split into three categories, what are they?
Non-essential (not essential for flight)
Essential (for safe flight and in flight emergencies)
Vital (for crash landings)
‘The voltage regulators operate in an inverse relationship to changes in system voltage’. Explain what is meant by this statement.
If system voltage drops because of an increase in the load, the generator exciter current is automatically increased. Therefore, the generator output increases until the balance is restored.
What method is used to ensure that a system utilising multiple generators achieves equal output?
The generators have their respective voltage regulators interconnected so that the output of each generator is adjusted to balance with those of others.
What is a CSDU and what is its role?
Constant Speed Drive Unit
The CSDU is an intermediary from the engine auxillary gearbox drive shaft to the AC generator. The CSDU maintains the drive to the generator at a constant RPM.
What system controls the Central Warning System?
A Master Control Unit (MCU) controls the Central Warning System.
What will pushing the Master Caution button do?
Momentarily pushing the Master Caution button will stop the attention getter flashing, and cancel audio tones and voice messages.
If there is more than one malfunction, subsequent Warnings and Cautions will again trigger the attention-getter, which must be pushed to cancel each one.
What colour are primary warnings captions?
Red
What colour are secondary warning captions?
Yellow
What colour are advisory warning captions?
Green
