Chapter 3- Fuel System Components and Operation Flashcards
Fuel Storage
Stored in tanks which can be an integral (parts of the aircraft structure) constructed from metal(RIGID) or flexible fabric membrane(BAG TANKS).
Where are fuel tanks situated?
Transport Aircraft-Wings
Combat Aircraft- both wings and centre fuselage
Helicopter Fuel Fuselage storage
Beneath the cabin floor
(Eg:Lynx fuel storage system)
Forward tank and the two collector tanks are installed
Below cabin floor
-Forward tank is on aircraft centreline forward of the collector tanks
The left and right main tanks are installed
Above the cabin floor
How to extend the range of the aircraft
One or two auxiliary tanks can be installed in the aircraft cabin.
Baffles
Reduce the effects of fuel surge when aircraft manoeurve.
What the need to maximise the amount of fuel carried in flight has led to?
Much ingenuity in tank location.
In Various aircraft types this have been used as tanks
-Tail fins
-Flaps
-Outer walls of air intakes
Rigid Fuel Tanks
Fitted internally where space permits or as external drop tanks
Metal fuel tanks constructed from
-Aluminium alloy
-Stainless steel
And made in shape and sizes to fit the space available in each particular airframe.
Rigid fuel tanks is a light structure which
Is strengthen by internal stiffeners and baffles.
Integral Fuel Tanks
Formed by aircraft structure
In INTEGRAL FUEL TANKS
Considerable care must be taken during construction to ensure what
-That all joints and inspection hatches in the structure are adequately sealed
-tank walls treated to prevent corrosion
Flexible Fuel Tanks (Bag Tanks)
Attached to the compartment walls by a type of press stud fitting
*Resilient and so can withstand a considerable amount of distortion or shock loading
Self-Sealing coverings
To reduce the magnitude of a fuel leak
Explain Self-Sealing Coverings
Its usually made from layers of cellular rubber with an overall protective cover. This type of rubber is easily affected when in contact with fuel. The cellullar rubber swells on contact with fuel forcing its way into the punctures to block the hole and reduce or stop the leak.
Collector tank
Feeds the engine directly but an uninterrupted supply of fuel is ensured to each engine.
Always gonna be filled with fuel.
Fuel Tank Pressurisation and Venting System
As fuel level in a tank reduces, the space above the fuel must be replaced with air,otherwise the vacuum will be created slowing the flow of fuel and possibly causing tank damage.
Fuel Tank Pressurisation and Venting System
As fuel level in a tank reduces, the space above the fuel must be replaced with air,otherwise the vacuum will be created slowing the flow of fuel and possibly causing tank damage.
Effects of altitude on fuel tank pressurisation and venting system
As altitude increases atmospheric air pressure decreases and the boiling point of all liquids, including fuel also decreases.
Excessive fuel vapours would be produced increasing the risk of fire in fuel tanks and the loss of fuel due to
Evaporation
Aircraft that encounter high altitude will need their fuel tanks at a pressure higher than the?
Surrounding atmospheric pressure
What is the purpose of tank pressurisation and vent system?
To maintain the pressure of air above the fuel at an appropriate level
Unpressurised Tanks (vented tanks)
Allows inward venting of air when fuel level is lowering and outward venting of air when the fuel level rises in the tank
Air/No Fuel Valve
Fitted at the top of the tank which allows air in and out of the tank during normal flight
But prevent loss of fuel during inverted flight of climb.
During inverted flight the weighted ball is affected by what?
Gravity and pushes the plastic float into a position to seal the tank and stop fuel escaping.
During a climb the aircraft would be in a nose up altitude and fuel will do what?
Rush to the rear of the tank and rise into the vent lines, escaping to atmosphere.
Pressuried tanks
Air above the fuel is at a pressure greater than local atmospheric air pressure.
Advantages of pressurising fuel tanks.
a.Transfer
b. Prevents Excessive Fuel Vapour
c. Reduces Fire Risk
d. Maintains the shape of flexibe tanks
Disadvantages of pressurised system.
-added weight
-routing complexity of additional components and pipework
Pressurised Tank Components
(Ram air/Bleed air from the engine compressor)
a.Non-Return Valve (NRV)
b.Pressure Reducing Valve (PRV)
c. Outward Relief Valve d.Inward Relief Valve
e. Fuel/No air Valve
f. Vent Valve
g. Pressure Switch
PRV
The valve closes when this pressure is reached but will reopen if it falls
Outward relief valve
Prevent damage from excessively high pressures inside the tanks in comparison to atmosphere
Inward relief valve
Prevent cavitation of pressurised tanks.
What can result in cavitation?
Rapidly increasing in atmospheric pressure and a continued rise in atmospheric pressure .
What prevents cavitation?
The spring loaded inward relief valve is forced open by atmospheric pressure if it becomes higher than tank pressure this allows air into the tank to prevent cavitation.
Fuel/No air Valve
Only fitted if pressurised tank transferred its fuel to an unpressurised tank.
Vent valve (depressurised valve)
-Depressurise the tanks
-Necessary before and during refuelling.
Pressure switch
Provides the electrical signal to the cockpit warning indicator of low tank pressure
Inert Gas Pressurisation
To reduce fire or explosion hazards
Purpose of basic Airframe fuel supply system
Supply a sufficient and uninterrupted flow of fuel to each engine under all operating conditions.
Booster pump
Positioned in a sump to ensure a positive supply regardless of the attitude of the aircraft.
Impeller type pump (the booster pump)
Allows it to continue rotating unaffected when there is no demand (ZERO FLOW)
Creates flow
How is the pump cooled
By the fuel surrounding it
What protects the pump from the ingress of FOD.
The intake of the pump incorporates a coarse filter.
Non return valve
Permit fluid to flow in one direction only.
How to ensure correct fitment of NRV
May be marked with arrow to indicate the flow and have different end fittings to prevent it being installed the wrong way.
Low pressure (LP) fuel filter
Will remove any Foreign particles from the fuel before reaching the engine fuel control unit.
Mechanical bulit into the bypass may indicate what?
The onset of filter blockages and give a warning of impending blockage.
Two Fuel system
a. Airframe fuel system
b.Engine fuel system
LP Fuel Cock
Separates the airframe fuel system to the engine fuel system.
Purpose of LP Fuel Cock
Allow full flow or no flow at all to the engine.
( can be either Mechanical or electrical in operation)
What will cause the closed for maintenace activities
Engine change
LP Fuel Cock may be used
To shut down engine in the event of an emergency.
Fuel cooled oil cooler (FCOC)
Heat exchanger where hot oil is cooled as it flows around a series of small pipes carrying cool fuel.
The temperature increase in fuel will also prevent any water it may hold from turning to ice which could block the supply line.
Whats the purpose of recirculation system
To maintain a sufficient flow of cool fuel through FCOCs
