11.10 - Fuel Systems Flashcards
How are fuel tanks vented?
Vented to prevent over or under pressure
Ports and valves installed at highest point of fuel tanks
Vent Surge tank and Ram air port installed at wing tips
RAM air port sees to it that a positive pressure is kept on fuel in each tank.
Why and how are fuel tanks pressurised?
To prevent structural damage to the fuel tanks by under or over pressure
Each tank has 2 pressure relief valves (One positive and one negative)
Also ports and valves at highest point of fuel tanks
Vent Surge tank & RAM air port at wingtips
List the components of the fuel supply system? (valves, pumps etc)
Fuel Supply system = fuel transport to engines and APU
- Booster pumps
- Check valves
- Fire-shut off valves
- crossfeed system consisting of crossfeed manifolds and crossfeed valves
Describe a boost pump, what is its principal of operation?
A low pressure booster pump feeds fuel from the tanks to the engine pump (supports engine pump)
The booster pump consists of:
- 3 phase alternating current engine
- Centrifugal pump
Where are the boost pumps located, and can they be removed without draining the tank?
(How many in each fuel tank?)
Booster pumps are located in every main tank in order to pump fuel from the main tank to the engines under all conditions in flight.
The booster pumps can be found in the pump house (2 booster pumps in each fuel tank)
The house can be closed manually or automatically closes when the pump is removed.
Yes, booster pumps can be removed without having to drain the tank
What is the purpose of the cross feed system?
Normally, each engine is fed by it’s own tank
However, if a problem occurs with this (or stagnation of fuel to engine pump) the crossfeed valve can be opened to allow the engine to draw fuel from another tank
How does a fuel quantity indication system work?
Measures fuel in each individual tank electrically by means of a probe (capacitor)
The capacitance of a capacitor depends on three factors:
- The area of the plates (constant)
- The distance between the plates (constant)
- The dielectric constant of the material between the plates (variable)
The dieletric constant of the material is on the ratio of fuel to air which will change the capacitance
It is then converted to weight by a computer
Explain how a dipstick works? (aircraft dipstick)
Manual means of checking fuel.
One magnet floats on the fuel and the other magnet is attached to the end of the stick.
The dipstick is pulled down to the point at which the magnets stick to each other. The fuel level is then determined in inches, pounds or Kg
(Levelling and a table may have to be converted determined with a plumb bob)
What is the purpose of a fuel dump system?
The fuel Dump system makes it possible to bring the aircraft weight below the maximum landing weight, while keeping enough fuel in reserve for the landing.
(System not on aircraft whose maximum take off weight is close to the maximum landing weight)
How is longitudinal balance achieved using fuel?
A centre of gravity control computer activates the corresponding valves & pumps and transfers fuel forward or aft in order to maintain the CG within a tolerance of MAC (Mean Aerodynamic Chord) of the target CG.
What sections does the fuel system consist of? (5)
5 subsystems:
- Fuel Ventilation & Storage system
- Fuel supply system
- Fueling and defueling system
- Fuel Quantity Indication system
- Fuel Dump System (some aircraft)
Where are the fuel tanks installed in the aircraft?
The fuel than an aircraft needs is stored in tanks located in the wings and in the fuselage (center tank)
What type of fuel tank construction is used most?
The integral system
(tank is shaped by the structure of the wing or fuselage which has been properly sealed)
What is a booster pump?
(Also what does it consist of?)
A booster pump is a low pressure pump that delivers fuel from the fuel tank to the engine pump.
It operates on 3 phase AC engine and consists of a centrifugal pump all in a pump house.
It can be changed without having to defuel tanks.
When is cross feeding used?
When the fuel supply of a main tank to its engine stagnates
Why is the water drained periodically from the fuel tanks?
Water is a breeding ground for mould which damages the sealing of the tank and causes corrosion
Water also freezes below temperatures of 0 degrees
What is the principle of the most used fuel quantity indication system?
Capacitor that has 3 parameters:
- Area of the plates (constant)
- Distance between the plates (constant)
- The dielectric constant of the material between the plates (variable)
As the dielectric constant changes (ratio of fuel to air changes), a computer converts this to a fuel reading in pounds or kg
Explain how an aircraft dipstick works?
Dipstick located in housing which can move up and down freely in fuel tank.
Magnet is at top of dipstick and also a ring shaped magnet in floating housing.
Dipstick is unlocked and pulled down to the point at which the magnets stick to each other.
A scale on the dipstick indicates the level of fuel in inches, pounds or kg.
When is a fuel dump system used?
The fuel dump system makes it possible to bring the weight of the aircraft below the maximum landing weight, while keeping enough fuel in reserve for the landing.
Used in emergency
For most aircrafts, the numbers of engines determine the number of ____ ____ present in an aircraft
Main tanks
Some types of aircraft have an auxillary tank installed in front of the centre wing tank or even in the horizontal stabiliser.
What is the general rule that applies to these auxillary tanks?
If auxillary tanks are filled with fuel, the rule generally applies that these should be emptied as quickly as possible by pumping the fuel to the main tanks.
NACA intake poets may also be referred to as
RAM air ports
What is the function of the RAM air port/NACA intake port in the fuel system?
The RAM air port/NACA intake port sees to it that there is positive pressure on the fuel in each tank.
How can a fire shut off valve that cuts-off the fuel supply line to the engine by closed?
The Fire shut off valve to the engine can be closed:
- Electrically
- Mechanically
The fire shut-off valve of the APU can be closed by two emergency controls. These are:
These are found on the flight deck and
outside on the fuselage of the aircraft
Filling the fuel tanks can be done _____ as well as ___
automatically
manually
In the case of automatic fueling, the process can be controlled by ______
Micro-processors
Defueling of a tank is done by fueling trucks and it has to be done …
Manually
Explain the difference between a bladder tank and an integral tank?
Integral tank = formed by structure - rivets + sealant
Bladder tank = bag like rubber structure inserted into aircraft. Shape not fixed
How are fuel tanks vented and why?
A vent surge tank containing two pressure relief valves prevent excess pressure and a ram air port ensure there is a positive pressure kept on the fuel. Ports and valves are also installed at the highest points of the tanks.
Fuel tanks are ventilated to prevent structural damage to the fuel tank due to over or under pressure.
List the components of the fuel supply system? (4)
- Booster pumps
- Check valves
- Fire shut-off valve
- Crossfeed system consisting of crossfeed manifolds and crossfeed valves
