11.10 Fuel Systems Flashcards
What are the four main types of turbine engine fuels
Jet A1
Jet A
Jet B
JP 5
What is the flash and freezing point of Jet A1 fuel
38 degrees C
-47 degrees C
Flash and freezing point of Jet A
38 degrees C
-40 degrees C
Flash and freezing point of Jet B fuel
- 20 degrees C
- 58 degrees C
Main requirements of turbine engine fuels
Low freezing point and flash point low enough to provide good ignition capabilities but high as possible for safe fuel handling
At a temperature of 15 degrees C what is the density of Jet A1 and Jet A fuel
0.81kg/ltr
Density of Jet B at 15 degrees C
0.78kg/ltr
What requirements are their for fuel characteristics? (3)
✈️Adequate lubrication
✈️low tendency to hold water
✈️widely available worldwide
What are the dangers of water in fuel and fuel tanks? (6)
- Encourages ice build up
- Supports corrosion
- Engine power fluctuations
- Engine flame outs
- irregular fuel level indications
- Microbial growth in tanks
What is the most common method to test for water in fuel
Syringe test - fuel passes through filter, filter changes colour if fuel contains water
What does the fuel storage system consist of
Fuel tanks
Tank drain system
Tank vent system
Where can fuel tanks be found
Wings
Centre fuselage
Horizontal stabilisers
Cargo compartments
On which aircraft does there have to be space for reserve fuel
All aircraft
What are vent surge tanks used for
Help make sure fuel tanks are properly vented
What purpose do trim tanks serve as well as storing fuel?
Used to trim the Aircraft
What is the most common type of fuel tank used on modern jet aircraft and why
Integral tanks - weight saving
How do integral tanks save weight on aircraft
Parts of the aircraft structure are used as tank walls
How are integral tanks made leak tight
Fillet seal where two plates join and cap seals to cover nuts and bolts
What type of tank has a light metal alloy outer housing and a flexible rubber bladder
Bladder type fuel tank
How is fuel movement dampened
Ribs in the wing and non sealing divider walls
Why does fuel movement need to be dampened
Fuel splashing around during attitude changes would make the aircraft unstable
What does a flap baffle check valve ensure
There is enough fuel for the fuel boost pumps by preventing fuel from flowing out of the collector box
What provides the metal contact between the access door and aircraft structure?
Knit Aluminium Gasket
What is the role of the clamp ring
Connects the access door to the wing structure and ensures mounting screw forces are equally distributed on the seals
How is a tank ventilated
Air is passed through the tank, which is then released into the atmosphere
What is used to indicate if there has been a leak or not
Spur pipe - leak monitor
What are the 2 types of drain valve
Direct and indirect drain valves
Which drain valve is installed at the lowest point of a tank
Direct drain valve
Where might you find find electrically operated drain valves
Stabiliser tanks
What are water scavenge systems used for
Remove water that is collected in tanks
Where might you find water scavenge systems installed
Big fuel tanks - large quantities of water can be expected
How is ram air used to reduce the tendency for fuel to vaporise
Air creates a small positive air pressure on top of the fuel surface
What happens to fuel caught in the vent duct
Drained back into the tanks
What is found inside the vent surge tank
NACA intake and Overpressure relief valves
Where is the NACA inlet located on the Aircraft
Lower wing surface
What are the overpressure relief valves made up of
Either carbon discs (break at certain pressure) or Spring loaded valves (open if differential pressure overcomes spring force)
What are the 2 types of refuelling
Gravity and Pressure refuelling
What is the main disadvantage of of gravity refuelling
Takes a long time
Which tanks do not have external filler ports and how are they refuelled
Centre tank and stabiliser tank
Refuelled by transferring fuel from main tanks
What are the two methods of pressure refuelling?
Fuel truck (bowser) or underfloor fuel supply system
At what pressure does the fuel get pumped into the the system
50 psi
Why is correct distribution of fuel important
Danger of CofG shifting behind MLG
Structural stresses
Main components of a refuelling system? (5)
- Coupling
- Manifold
- Valves
- Diffusers
- Refuelling control panel
What are the three types of refuelling modes
Manual
Automatic
Override
What happens when refuelling in manual mode
Calculate distribution
Monitor fuel quantities
Operate switches to control refuelling valves
What happens when refuelling in Automatic mode
Fuel quantity control computer takes pre-selected block fuel and works out the correct distribution
Controls refuelling valve
When is override mode used
No electrical power to refuelling valves available
What is the ‘Normal Mode’ and why is it used
Automatic mode
It is safer, reduces workload, stops refuelling when the pre-selected block fuel is reached
Where can control panels be found
Wing leading edge near refuelling couplings
On the fuselage
In the cockpit
What can be found to enable the setting of the required block fuel
Pre-selector
What are the types of adjuster are there for the pre-selectror
Rocker switch, rotary switch or thumb wheel
What are the typical indicators for refuelling
Tank quantity indicators
Total quantity indicators
Refuelling valve position indicators (on some)
Malfunction warning lights
When is electrical power usually supplied to the refuelling system
When the panel door is open
How is normal refuelling power supplied
External power or APU via the fuelling bus
What is the fuelling bus also known as
Ground handling bus
Can power for refuelling come directly from the battery
Yes.
Where is the fuel distribution calculation stored
Fuel control computer
Where are refuel couplings generally located if the aircraft only has one
Right hand wing
Why do couplings incorporate a spring loaded check valve
Prevents fuel leaks
Durning flight p which tank empties first
Centre tank
How is damage to the manifold avoided during flight
Drain valves at manifold low points in the wing tanks when fuel level is below the manifold
Where are the refuelling valves normally attached to
Front or rear spars of the wing tank or rear wall of the centre tank
Where are the valve control components located
Outside the tank
How can you open the refuelling valves if there is no electrical power
Manual override
What are diffusers made of
Perforated tube
What directs fuel downward once fuel is passed through a diffuser when refuelling
A baffle located on the top of the diffuser
What are diffusers called on some aircraft
Tank distribution manifolds
What is the purpose of a fuel feed system
Ensures proper fuel supply to engines and APU
What are 2 requirements of the fuel feed system if one pump should fail
2 boost pumps for every consumer
A bypass of the boost pumps
What is the fuel scavenge system used for
Reduce the amount of non usable fuel in fuel tanks
What is the fuel circulation system used for
Fuel is used to cool the integrated drive generator and engine oil system, then passed back to the fuel tank
What is the fuel feed system used for
Ensures the correct fuel feed sequence
How can reverse flow from the fuel feed manifold into the fuel tank occur and how can we prevent this
Could happen if one fuel pump is stronger than the other
Check valves prevent this
Which valve enables the isolation of fuel flow to an engine
Fuel shut off valve
How Many cross feed valves does a twin engine aircraft have?
1
(NOTE: Other aircraft have more)
What is the role of an air release valve
Allows air trapped in the fuel line to bleed out under pump pressure
How is fuel transfer controlled between the stabiliser tank and the centre tank
Transfer valves in the centre tank
Where are controls for the fuel feed system found
Centre overhead panel
What fail safe is there for boost pumps regarding electrical bus bars
Power from each pump in the tank comes from a separate bus bar, one boost pump per tank is still available
Where are engine fuel shut off valves located on the flight deck
Fire panel
Where are the most important indications for fuel feed systems located
Fuel management control panel
What fuel system information can be found on the ECAM page
Fuel quantity
Fuel temperature in the tanks
Fuel used since engine start
Total fuel on board
How can the fuel shut off valve be activated
Engine master switch or respective fire switch
What are the two methods of pressure controlled fuel feed
High pressure pumps
Sequence valves
What fuel tank is used when the aircraft is taxiing
Centre tank
What tanks are used on take off
Respective main tanks
What tanks are used first during cruise
Centre tanks and stabiliser tank
When is fuel transfer permitted during flight
Reserve tanks to main tanks in equal amounts, simultaneously
To and from trim tanks
What is another method of fuel scavenging
Electrically driven scavenge pump
How is the issue of adding hot fuel back into tanks resolved
Cold fuel is added to the hot fuel to create warm fuel
How does the boost pump force the fuel from the inlet to the pump outlet
Ac motor drives impeller (centrifugal force)
What are the two methods of defuelling an aircraft
Pressure defuelling
Suction defuelling
What is pressure defuelling and at what pressure is this carried out
Defuelling using tank boost pumps, 25-50psi output pressure
What is the defuel transfer valve
Motor driven pump which interconnects the fuel feed manifold and refuelling manifold
What is suction defuelling
Use suction from fuel truck to defuel aircraft
What is the minimum required suction required for defuelling
10-15psi
What components do you use during fuel transfer? (5)
- fuel boost pump
- fuel feed manifold
- defueling or defuel transfer valve
- refuelling manifold
- refuelling valves
When may you want to transfer fuel? (2)
- To balance the aircraft after incorrect refuelling
- to empty the tank for maintenance purposes
What are trim tank systems used to increase on the aircraft?
The efficiency of the aircraft in flight and reduce fuel consumption
How could you control the centre of gravity of the aircraft?
Transfer fuel fwd or aft
What does the fuel control computer do in regards to centre of gravity?
Controls the fuel between the trim tank to keep the centre of gravity at the “target centre of gravity”
How far forward is the target centre of gravity in relation to limits?
2%
When will the remaining fuel from the trim tank be transferred forward?
- When the aircraft is below a certain flight level or,
- when approx 75 minutes left until calculated landing
Which mode is the trim tank selector switch kept on so that CofG control systems can perform forward and aft fuel movement
Auto
What does a green forward pointing arrow indicate on the ECAM regarding trim tank indications
Normal forward transfer
What does an amber arrow indicate on the ECAM regarding trim tank indications
Fuel transfer is abnormal
When might the valve symbol be shown in amber on the ECAM
Valves are open when they have been ordered closed
What does the jettison system allow the pilot to do
Dump fuel overboard
Why might fuel need to be dumped overboard
Aircraft exceeds the maximum landing weight
What does the design of the jettison system make impossible to do
Empty all fuel tanks during flight
What is one of the major components of the jettison system
Jettison line
What is the difference between a fuel boost pump and a jettison pump
Jettison pumps have greater flow and pressure capacity which allows them to dump large amounts of fuel quickly
What is done with the jettison lines to save weight
They are shared with the refuelling manifolds
What are the jettison nozzles called and what do they do
Anti-corona outlets
They ensure that fuel remains in a non-vaporised compact flow
Where is the jettison control panel normally located
Overhead panel
How is accidental fuel jettison avoided
Panel has controls to arm the system and controls to start the jettison
Why is it impossible to move the jettison valve switches my accident
The switches are guarded
How can the jettison operation be interrupted and when can this be done
By operating the jettison switch
At any time
what unit is fuel on board (FOB) expressed in on the ECAM display
Kilograms
what unit is total fuel expressed in on the EICAS display
Metric Tons
How many fuel quantity probes are there in a tank
Number of probes depends on size and shape of the tank
How are fuel quantity probes installed in a tank
Vertically and reach the tank from the bottom of the tank to the top
What does a fuel quantity probe consist of
2 thin walled aluminium alloy tubes (installed coaxially and electrically isolated from each other, forming a capacitor)
What is the material dependant factor called with regards to fuel quantity probes
The dielectric constant
How does the fuel quantity computer calculate the fuel level
Measures the capacitance
What do fuel characteristic sensors measure [2]
- Density
- Dielectric constant
How many characteristic sensors are located in each tank and what are they
2
- compensator
- densitometer
Why are the fuel characteristic sensors located st the bottom of the fuel tank
Ensure they remain covered by fuel for as long as possible
What is the accuracy of the fuel quantity calculation
Normally greater than 99%
What is the fuel level sensing system used for
Automatic fuel system control
How does a float switch work
Contains a reed type switch which has an open circuit when fuel is low, as the fuel level rises a permanent magnet floats up which closes the switch
What are the 3 widely used examples of fuel level sensors
- Float switch
- Thermistor type sensor
- Single point sensor
What is used to measure the fuel temperature in one tank
A thermistor
