Airframe Fuel Systems Flashcards
What are the two categories of aviation fuels?
Aviation Gasoline (AVGAS)
Aviation Turbine Fuel (AVTUR)
Which fuel is used for piston engine aircraft?
AVGAS
Which fuel is used for Gas turbine aircraft?
AVTUR
Whats calorific value?
Amount of heat released when a unit mass of fuel is burned and measured in heat units (KJ)
The higher the calorific value, the more efficient the fuel
Whats volatility?
The tendency of a substance to evaporate at normal temperatures.
What kind of volatility is needed in aircraft fuel?
Volatile enough to start the engine but not so volatile that fuel is lost from tanks due to vaporisation
Whats specific gravity?
Used to define weight or density of a liquid compared to an equal quantity of water
Water has a S.G. of 1.0
Four types of approves fuels?
AVTUR
AVTAG
AVCAT
AVGAS
Whats AVTAG?
A wide-cut fuel (blend of gasoline and kerosene)
Whats AVCAT?
Kerosene type fuel similar to AVTUR but with a higher flashpoint, used by Royal Navy on ships
Whats the fuel anti-icing additive called?
Fuel system Ice Inhibitor (FSII)
Two aircraft systems that contain fuel?
Airframe Fuel System (Storage)
Engine Fuel System (for ignition)
Design objectives of fuel systems?
- Facilitate rapid and safe fuel replenishment
- flexibility to provide different ranges & endurance for operational requirements
- auto or semi-auto control & management of fuel system
- Tolerance to aircraft manoeuvre or damage
- secondary uses for fuel
Where is fuel usually stored on aircraft?
Wings & centre fuselage
Where are fuel tanks usually on helicopters?
Beneath cabin floor or to increase range tanks can be installed in aircraft cabin
Types of fuel tanks?
Rigid
Integral
Flexible
Whats the point of a press stud fitting on a bag tank?
To attach the bag to the aircraft structure and allow the weight of the bag tank to be carried by the structure of the aircraft
How do self sealing coverings work on a bag tank?
When punctured the fuel leaks out and instantly causes a swelling reaction either the rubber which causes swelling and blocks the hole
Why do we need a collector tank?
So theres a constant flow of fuel to the engine, regardless of aircraft manoeuvres, collector tank always full
Why do high altitude aircraft need high pressure fuel tanks?
Increased altitude decreases boiling temperature of liquids causing an increase in fuel vapours and risk of fire etc.
Whats the purpose of tank pressurisation?
To maintain the pressure of the air above the fuel at an appropriate level
How does an air/no fuel valve work?
In inverted flight, gravity pushes the float and ball into place to prevent fuel loss
In nose up attitude, the float rises with the fuel and prevents fuel loss
Advantages of pressurising a fuel tank?
Transferring fuel between tanks using air pressure
Prevents excessive fuel vapour by increasing boiling point of fuel
Less of a fire risk
Maintains shape of flexible tanks
Disadvantages of pressurising a fuel system?
Added weight
Routing complexity
Whats a pressure reducing valve?
Senses changes in atmospheric pressure and opens/closes to allow air from engine into pressurised tanks to moderate system pressure
Whats an outward relief valve?
Spring loaded valve that opens if tank pressure reaches highest system limit to prevent damage
Whats an inward relief valve?
Spring loaded valve forced open by atmospheric pressure when it becomes higher than tank pressure to prevent cavitation
Whats a vent valve?
To depressurise tanks (during and before refuelling)
Whats a Pressure switch for?
Provides electrical signal to cockpit warning indicator of low tank pressure Prevents excessive
Whats APU stand for?
Auxiliary power units
Whats used to ensure a positive supply of fuel to the engine regardless of aircraft attitude?
Booster pumps (positioned in a sump)
What must be carried out after disturbing any NRV in fuel system?
A mandatory flow check
What an LP Fuel Cock for?
Separates the airframe fuel system from the engine fuel system (full flow or no flow)
Why should you only shut down an engine using an LP Fuel cock in emergencys?
It can damage the engine components and pipe
Whats a Fuel cooled oil cooler (FCOC)?
Hot oil is cooled as it flows around a series of small pipes carrying cool fuel.
The temperature increase of fuel will prevent any icing.
Whats an Air cooled fuel cooler (ACFC)?
Cooling fuel by using ram air similar to car radiator
Ejector (jet pump) purpose?
A tube with a decreased cross sectional area creates a drop in pressure to suck the cold fuel into the tube to mix with the hot fuel before returning to storage
Methods of transferring fuel between tanks
Air pressure (tank 1 to 2)
Electric transfer (tank 2 to 3)
Fuel ejectors (tank 3 to 4)
Gravity (tank 4 to 5)
Whats are the purposes of fuel management and control system?
Maintain CoG by managing transfer
Provide indications of various parameters and warnings of malfunctions
Give crew various options in movement of fuel and to counter any system malfunctions
Whats are the purposes of fuel management and control system?
Maintain CoG by managing transfer
Provide indications of various parameters and warnings of malfunctions
Give crew various options in movement of fuel and to counter any system malfunctions
Automatic control of fuel system?
System design/ layout
Electrical components
Mechanical components
Fuel flow proportioners
Empties different sized tanks at proportional speeds to maintain CoG by using larger and smaller proportioner cell
Whats a fuel dump (Jettison) for?
Aircraft max permissible take off weight is higher than landing weight so they dump fuel to drop weight
What can the fuel gauging system provide?
Total fuel system counts
Contents of individual tanks or group of tanks
Amount of fuel being used at any given time
Two types of fuel contents transmitters
Float type fuel contents transmitter
Capacitance gauging units (inner/outer conductive plates)
Why is it important to know Engine fuel flow?
To estimate range and duration of flight, higher than normal flow will indicate a problem with engine performance
Fuel flow transmitter purpose?
Measures the flow of fuel after the LP cock, senses volume flow rate and transmits to the cockpit
What causes the love fuel level warning light to turn on?
The fuel reaches a predetermined low level in the tank and energises the switch
What are 3 types of manual fuel level measurements for ground use?
Dipstick
Drip stick
Drop stick
When checking for contaminants in aviation fuel, how should the fuel appear?
Clear, bright, no detectable free water or significant visible solid matter
What should you do if a BFI is suspected of being contaminated?
All aircraft refuelled from suspect source should be placed unserviceable and inspected
(Bulk Fuel Installation)
What are the principal contamination threats for fuel?
Foreign particles
Water (suspended/free)
Microbiological organisms
Cross contamination
Whats the purpose of a water sediment check?
To check for contamination of fuel with water (microbes in fuel cannot grow without water)
What does microbes in fuel eventually create with the presence of water?
Scums and sludges (biomass)
Surface scum (biofilm)
How is a water sediment check carried out?
Sample drained from a valve at bottom of tank
Visual check for water/fuel separation (cloudy is a water/fuel emulsion)
Water detection capsules detect dissolved water (yellow detection paper, turns blue if too much water)
When must a fuel system be tested?
After being disturbed by removal or fitting of any system components
Leak checks
Fuel flow test
What is required in a fuel system check?
Leak check while system is pressurised
Fuel flow test to ensure minimum fuel flow rate is being delivered to the engine (tested by an authorised person)
Why would a leak be greater during flight?
Due to flexing of the aircraft structure
How do you repair a leaky rigid tank?
Removal for specialist repair
How are leaky flexible tanks repaired?
Repair by manufacturer (tank replacement usually inevitable)
What is the leak rate of a flexible tank affected by?
Cavity drain blockage
Tank being plugged by contact with aircraft structure
Self sealing layer activation
Fuel tank level
Aircraft attitude
Tank pressurisation
How are leaky integral tanks repaired?
Categorisation and subsequent repair is carried out in accordance with the AMM
Whats preparation draining?
Fuel system drained, pockets of duel removed by mopping with fluff free absorbent material
Whats venting?
Clearing the explosive fumes from a fuel tank using an induced warm airflow to blow the vapours out through open panels.
Whats to be considered for inspection lamps inside or near a fuel tank?
An explosion proof light needs to be used
How can personnel protect themselves from solvents and fuels?
Avoid breathing fumes given off by fuels and solvents
Protect the skin by wearing approved protective clothing and barrier cream
What PPE is needed in a Fuel tank?
Rubber overalls,
rubber boots,
rubber gloves,
special head gear,
Respirator
What conditions must be met before an operator enters a fuel tank?
Medically examined
Remote intake breathing apparatus
Intake free end of respirator upwind of fuel tank
Correct PPE worn and lifeline attached
Correct Fire extinguishers ready for use
Second person as observer outside the tank
Time in the tank controlled to adhere to guidelines
Two methods of ground refuelling?
Open line refuelling (gravity)
Pressure refuelling
What method of ground refuel is used on smaller aircraft?
Open line refuel (low pressure)
Used on motor vehicles
Whats the purpose of pressure refuelling?
To uplift large volumes rapidly, cleanly and with minimal risk of spillage
Why is the pressure for defuelling lower than refuelling?
To avoid damage to aircraft structure, suction pressure is lower at defuel
What is a risk of open line defuel?
The walls of a flexible tank being sucked into nozzle
Three methods of ground defuel
Pressure defuel
Open line defuel
Drain defuel
Whats minimum PPE to be worn for general fuelling operations?
Safety boots
Coveralls
Gloves
Goggles or visor
What should you do in event of fuel spillage during refuelling?
Stop refuelling until cleaned up
When are liquid oxygen (LOX) systems not to be replenished?
During fuelling operations
Bonding requirements during fuelling operations
Ensure aircraft and bowser are earthed
What is needed for refuelling to take place in a hangar?
- Authorised
- Adequate ventilation
- High- volume firefighting vehicle in attendance
- suitable towing equipment incase anything goes wrong
- fuel bowser located outside
- clearly defined escape route
Classifications for Ice
Trace - not hazardous unless its been accumulating for up to a period of 1 hour
Light - built up icing that can be readily removed by ice protection equipment used periodically
Moderate - hazardous, builds up quickly, removed by constant use of ice protection equipment used
Severe - most hazardous, should not fly in these considerations, ice protection equipment may fail/malfunction
What are critical areas of an aircraft in relation to icing?
Aerofoil surfaces
Engine intakes and internal surfaces
Rotor blades and propellers
Windscreens/canopies
Pitot probes and static vents
Control surfaces
Weapons and weapon carriers
Hazards of Ice on aircraft
Increase in stall speed
Increased landing speed and distance
Hampers true instrument readings
Adverse effects on radios
Severe/ destructive vibrations
Chunks breaking off can cause damage structurally or in engine intakes
Effects of Ice formation on helicopters
Rotor blade imbalance due to uneven ice build up on the blades (more towards tip)
Shedding of Ice of one blade and not the others can cause severe vibrations
Additionally:
Ice can build up rapidly on blades in freezing fog conditions
Hovering can cause a large build up of pack ice over wet snow or slushy surfaces
Caution by ground crew due to ice shed from rotors, engine risk also
How should protective covers be used to protect aircraft from snow/ice?
And what are they called?
Approved aircraft covers
Need to be a tight perfect fit
Not to be fitted when aircraft is wet due to adhesion when it freezes
Not to be fitted over snow/ice due to adhesion when thawed and refrozen
De-icing fluid can be applied before cover to prevent this
Two types of principle of operation?
(Ice protection systems)
Aftive
Passive
How do active ice protection systems work?
Increase temperature of local areas of aircraft to above freezing
Further categorised as:
Anti-icing
De-icing
Whats passive ice protection?
Harness momentum of airstream ti separate out precipitation and divert it away
Advantage if de-icing over anti-icing?
Lighter and use less energy
Where would you need to use anti-icing instead of de-icing?
Engine air intake
How does momentum separation device work?
A dam will force the airflow to change direction, causing the water particles with a higher mass to divert away from the engine intake
Types of ice protection system
Engine air intake - active and passive systems used
Thermal hot air - leading edges heated with hot air from engine
Thermal electrical - electrically heated leading edges
Mechanical (pneumatic) - inflatable/ deflatable tubes that break the ice off
Windscreen ice protection
Overheat sensors sandwiched in the glass laminations of the screen. Heated window using thin film of gold on the glass.
Rain protection windscreen
Windscreen wipers
When must windscreen wipers be used?
Worn to limits
Damaged
Contaminated
General rules of windscreen wiper maintenance?
Rubber blades replaced when necessary
Lubricated
Check for clearance between blades and screen
Check for correct tension in wiper arms
