Cap 13 Fuel System Flashcards
Fuel tank construction
~integral tank»interior structure of the wing
~flexaxible tank»rubberished fabric material and are attached to the structure using chords or buttons.
~drum tank»rigid tank made from aluminium
Tank construction
~rigid»alluminium ,no part of structure
~felxibile»rubber,disadvantages can trap water and fuel
~integral»_space;uses inside the wings
Cs25 require 2% expansion space
Fuel tank inerting
~nitrogen is introduced into the fuel tanks
~nitrogen displaces the air
~reduce the tisk of fuel explosion
FAA»mandated all a/c must have a feul inerting
Easa»_space;is scoisidering
Calorific value of the fuel can give how much energy contains
Avgas100LL»died blue,specific gravity 0.72,realtivie low lead lead
avgas100»died green,specific gravity 0.72,high lead content, same octane as avgas100ll
JetA»sg0.8,,freezing/waxing poiny -40
JetA1» sg0.8,freezing point -47
Both Higher flash point and fire point
Wide cut fuel JET B
Low freezing point -60
Lower flash point makes it danger
Turbine fuel may have additives to reduce icing or fungal growth
Fuel colour. Decal
~avgas100»green»_space;. Green/red
~avgas100ll»blue». Blue /red
~JETA»_space;colourless or straw». Black/balck jeta
~JETA1» colourless or straw». Grey/back jeta1
~jetB»_space;colourless or straw». Yellow/black jetB
A collector box with one way flop tubes or check valves ensures a constant supply of fuel even when the a/c is manoeuvring
Drain valve s at the bottom of the tank allow water to be drained
The engines does not draw fuel from the lowest point in the tank
Ensures sludge,water or other contamination does not get pecked up
~high mounted wings»gravity fed,after the fuel filter the fuel passes to he enigne driven pump
~low wings»_space;eleictrically powered booster pump draws fuel through a filter and supplies at a constant pressure
Vapour lock
Bubbles of vapour can interfere with fuel flow
Is a most typically a problem of gravity fed fuel systems
Fuel Gauges
~gallons
~us gallons
~litres
Pressurised fuel tanks
Some a/c may be pressureides fuel tanks,using ram air or pump,this helps force down the fuel into the eniges.
Vent excess relief the pressure
Fuel tank coponents
~LP boost pump
~operated on 115 V AC
~each pump has supply from different generators
~output is about 20-25psi
~centre tank pumps operate at higher pressure to drain first
~pumps located at the lower part of the tank
Flapper valves preevetn fuel lfowing outboard
~a non return valve ensure no flow back if the pumps fails
By pass valve
The bypass valve sits immediately downstream of the LP pump
~if the LP fails while the engine is running the suction from the enigines own high pressure (HP) pump will draw fuel
Jet pump
~used to scavenge fuel from the lowest part of the fuel tanks using Venturi effect
~the main motive flow generated by the LP pumps is used to draw in fuel from other locations in the tank
Fuel tanks are pressurised to prevent vapour lock and reduce vaporisation of the fuel
~allows air to replace fuel
~vent surge tanks at the wings tips collect overflow and drain back to the main tanks or if the re is too much ,dump it overboard
Naca duct
Posictve pressure aroun 5psi
~airlfow moves into vent and expads .as it does so the pressure drops and sucks air into the vent
~different NACA sizes deponding on the wing type
Fuel shut off valves
~one is know as the wing spar valve»located at the entrance to he engine bay
~other one is the main engine fuel shut off valve»sue for routine engine shut down
Fuel heating
~required to prevent waxing
~heated by fuel cooled oil cooler (FCOC) or fuel oil heat exchanger (FOHE)
Crew have no control over this system
~some a/c use heat excess from hydrraulisc system to haet the fuel
Fuel gauge content
~resistive»electrical resistor operated by dc power,a float on the end is connected to a variable resistor
~capacitance»different in dielectric between fuel and air is able to say the level of fuel and then knowing the specific gravity it can calculate the mass of fuel
Manual fuel checking gaugung
~drip stick»comprises of an hollow tube with a small hole near the top,fuel starts to drip out when is lowered and then the operator can see the fuel content from a graduated scale on the stick
~magnetic system»float with a magnet,unlock stick and allow it to float,read from the graduated scale (no fill leak in case if it breaks)
Fuel jettison
Must able to jettison fuel within 15 min to reduce the weight from MTOW to MLW
Fuel is pumped out using the LP booster pumps
A limit switch limits the amount that can be dumped and prevents the entire fuel content being dumped
Climb to 10000ft
Cruise for 45min
Must not be done below evaporation altitude,in rain and over built up area
Refuelling
Positive pressure 50 psi max to refuel
Neagtive pressure -5psi. To de fuel
