AC Fuel Systems Flashcards
Integral Fuel Tank
Part of the wings
Baffles used to prevent fuel moving outwards
“Wet wing design”
+ saves weight
Flexible
Rubberised fabric casing attached to AC via chord/buttons
- less capacity than integral
- can puncture easily
Drum Fuel System
Rigid design made from metals
Found on large ac
Purpose of fuel system
Store fuel/deliver/ensure no contamination/not excessively cold
Fuel Booster Pumps are
Low pressure pumps
High flow rate
Three phase AC pumps
Cooled by the fuel
How are fuel tanks pressurised
With ram air
Fuel tank inerting
System to mitigate risk of inflammability of air fuel mixture in empty tanks
787 use nitrogen generators which fed into tank to fill void
Piston Engine fuel types/properties/colour indication at pumps
AVGAS 100LL - Blue - 0.72
AVGAS 100 - Green - 0.72
MOGAS
Low flash point
Good lube properties
Non corrosive
Anti knock properties
Op across wide range of temps
Red background with white text
Diesel Aero engines use/types and properties
Aviation kerosene
Jet A1 - 0.85SG - Additives - flash point 47 degrees
Jet A - 0.85SG - flash point 40 degrees
Jet B - 0.77SG - lowest flash point
Waxing of fuel around -60 degrees
Waxing
Prone in turbine fuel systems
Waxy deposits as fuel does not freeze at one temperature
Starts around -40 degrees
Cross-feed valve
Open cross feed valve to switch between tanks
Switch off tank with lower fuel
Switch on tank with higher fuel
Never switch off a tank without cross feed valve being open
Large AC Fuel Systems have what pumps
Two electrically powered low pressure booster pumps
LP pumps supply fuel direct to the engine
LP Booster Pumps - power source/pressure
Operate on 115v AC off different busbars
Pump pressure 20-50psi
Fuel pumps in centre tank fed at HP to ensure used first
Bypass valve in booster pumps
Fitted downstream of LP pump to allow engines own high pressure pump to draw fuel directly from the tank if LP pump fails
Jet Pump
In event of both LP pumps failing scavenge fuel from lowest part of tanks using Venturi effect
Vent Surge
Collect fuel overflow and allow fuel to be drawn back to tank when over pressurise (has a limit will still spill over)
Spar valve
Cut off fuel before it enter engine bay in emergency event such as fire
FCOC
Used to prevent fuel waxing via heat exchanger of heating fuel and cooling the engine oil
Resistive fuel gauge system
Uses variable resistor DC POWER
Measures volume/prone to errors due to flight
- different tank size/shape hard to calculate actual volume
Used on large ac
Capacitance fuel gauge system
Low voltage cylindrical capacitor probe across tank with potential difference between them
System measure difference in dielectric of fuel and air to measure fuel level
+ failed probe will be discounted from calculation
+ second probe used to measure density
+ 99% accuracy
+ power failure will indicate low gauge reading
Fuel Flow Indicators
Used to monitor engine performance
Fitted after engine shut off valve between fuel control unit and engine
Indicate high fuel burn etc
Jettison Limit switch
Prevent dumping all fuel overboard
Is a low level float switch
Must be able to reduce to landing weight within fifteen minutes
Large transport AC refuelling principals
Point under the wing
Max refuel pressure 50 PSI/minimum 5 PSI
Why do crew monitor fuel tank temperatures
Ac must be operated with fuel tank temperatures within 5 degrees of fuel freezing point
Vent space for each fuel tank as required by CS23/25 is
2% of tanks volume
Flash point is defined as
The lowest temperature at which a volatile substance evaporates to form an ignitable mixture with air
Collector Box
Located at the bottom of fuel tank
Valve prevents flow of fuel back to main tank so there is a constant flow of fuel when manoeuvring
Not at the lowest point to prevent sludge blocking flow
Parts of ac fuel system include
Fuel density sensors
Collector tank
Fuel jettison system
Tank baffles
LP pump
FCU is
Fuel metering device that regulated fuel flow to engine via pilots demands
Filters are usually located before FCU
Flash point of JET A1
38 Degrees
Jet B flash point
-60 degrees
Drip Sticks
Visual means of determine fuel quantity in wing tank
Stick unlocked and lowered until fuel enters upper end of the stick and drop out of the lower end
Tables of capacities corrected for airplane attitude are found it ac documents
Main purpose of the DC fuel pump
Supply fuel to the APU
Drain Valve
Allows pilot to drain off any water from the fuel tanks
Also used for maintenance to drain fuel
Failure of AC fuel pumps how does the engine continue to provide fuel
HP fuel pumps in engine continue to suck in fuel
Feeder box
Two low pressure fuel pumps to provide uninterrupted desecrated supply of fuel to the engine driven pumps
X2 for continuous supply
Trim fuel system
Located in the tail of the aeroplane and allow fuel to be moved about to change the CG of the aircraft
Place further set away from CG at the tail
Vent Lines
Allow air into the fuel tank to replace the volume of fuel consumed by engine to equalise the pressure
