AC Fuel Systems Flashcards by Unknown Unknown

Integral Fuel Tank

Part of the wings
Baffles used to prevent fuel moving outwards
“Wet wing design”
+ saves weight

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Flexible

Rubberised fabric casing attached to AC via chord/buttons
- less capacity than integral
- can puncture easily

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Drum Fuel System

Rigid design made from metals
Found on large ac

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Purpose of fuel system

Store fuel/deliver/ensure no contamination/not excessively cold

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Fuel Booster Pumps are

Low pressure pumps
High flow rate
Three phase AC pumps
Cooled by the fuel

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How are fuel tanks pressurised

With ram air

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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

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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

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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

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Waxing

Prone in turbine fuel systems
Waxy deposits as fuel does not freeze at one temperature
Starts around -40 degrees

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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

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Large AC Fuel Systems have what pumps

Two electrically powered low pressure booster pumps
LP pumps supply fuel direct to the engine

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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

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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

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Jet Pump

In event of both LP pumps failing scavenge fuel from lowest part of tanks using Venturi effect

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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