Fuel Systems Flashcards
Distinguish between gravity-fed and pump-fed fuel systems.
Gravity fed
Head of fuel is maintained between the tank and engine, pressure must be given 150% of maximum flow rate required. Priming system is required. Attitude changes affect fuel flow and is prone to vapour lock
Pump feed
On light aircraft, electrically driven and one or two pumps are installed, engine driven and electric which has a switch.
For a typical fuel system, explain the function, and where appropriate, the correct handling of the following: fuel strainers and filters;
Each tank will have its own filter at the outlet, each tank will have a drain at its lowest outlet.
Prior to fuel entering the carburettor, there’s likely to be another strainer (some aircraft have a gascolator)
For a typical fuel system, explain the function, and where appropriate, the correct handling of the following: engine driven fuel pump
A pump thats driven off by the engine and is continuous and cannot be turned off.
For a typical fuel system, explain the function, and where appropriate, the correct handling of the following: boost auxiliary pumps
Electrically driven, and can sometimes purge fuel lines of vapour locks. May prime the cylinders but supplies fuel if engine driven pump fails. On for critical stages of flight.
For a typical fuel system, explain the function, and where appropriate, the correct handling of the following: engine primer
The function is because the engine turns too slowly during start for the main jets to supply fuel and In cold weather vapourisation is poor.
Priming system ensures a positive supply of fuel to each cylinder during start, The primer is a small pump that injects fuel directly into the cylinders (usually only 3 out of 4 cylinders)
Priming fuel bypasses the carburetor and gives a richer than normal supply directly into the cylinder head
•Hand pump or electrical solenoid activated
•Locked after start to prevent over-rich mixtures at low power settings
For a fuel system, explain the function, and where appropriate, the correct handling of the following: filler caps and drains
Caps should be easily accessible and locked on during flight. Have a drain that discharges spillage overboard and clear of the aircraft structure.
For a fuel system, explain the function, and where appropriate, the correct handling of the following: expansion spaces
Should have an expansion space above the maximum level to which they can be filled at the cap. Allows fuel to expand should it become heated through atmospheric temperature.
For a fuel system, explain the function, and where appropriate, the correct handling of the following: tank vents
Tanks vented to atmosphere to provide for both the release of air pressure caused by fuel expansion and to enable air to replace fuel as its being used from the tank.
For a fuel system, explain the function, and where appropriate, the correct handling of the following: baffles
Fitted inside aircraft to increase strength, reduce sloshing.
For a fuel system, explain the function, and where appropriate, the correct handling of the following: sumps and drain.
Sump and drain located at the lowest point of each fuel tank allow heavy impurities to accumulate which can be collected, inspected and drained.
Outlet from each tank to fuel supply line is place above the sump as a standpipe with screen fitted to it preventing impurities from entering fuel system.
For a fuel system, explain the function, and where appropriate, the correct handling of the following: fuel quantity detectors;
Mechanical float with arm that measures amount of fuel with a change of resistance anda circuit is then sent to the fuel quantity detector. Transmitted electrically to the cockpit to give an indication of fuel quantity.
Fuel flow meters used on modern aircraft and if there is non a fuel pressure gauge is used instead.
For a fuel system, explain the function, and where appropriate, the correct handling of the following: fuel strainers and filters
Fuel required by the engine is fed through a system of lines, from tank to carburettor or injection pump.
Lines and other system components are bonded together to avoid static build up.
On its way through the system the fuel is strained usually at three points - first to remove contaminants, 2nd at lowest point where another drain is used to check and clear contaminants. 3rd located at carburettor or FCU.
For a fuel system, explain the function, and where appropriate, the correct handling of the following: tank selector valves, cross feed valves
Fitted to enable tank changing or cross feeding. Also provides a shutoff valve where fuel stops flowing (takes 2-3 minutes)
Cross feed - if you have 2 or more fuel tanks and 2 engines its sensible to able to draw fuel from the left tank for the right engine and vice versa. Any engine can be fed from any tank.
Describe:
a) the general rules for refuelling; (10
Check fuel type and grade •Park brake off •No one in the aircraft •Engine/ignition off •No smoking •Bonding/Earthing •Electrical storms •Hold the nozzle •Contamination - no phones
Describe correct use of fuel tank dipsticks
Partially filled tanks can be misleading and don’t borrow a dipsticks from other aircraft as each dipstick is unique to the plane.
Describe the correct use of a Magna-stick
When rod/stick is released let if fall slowly until resistance is felt as the rod magnet becomes attracted to the float magnet.
Read the tank contents from the bottom of the stick.
Describe the correct procedures to be used for carrying out fuel quality checks.
Use a clean glass container and drain a small quantity of fuel from each tank checking if there are any contaminants such as water present.
Describe the indications of water in a fuel sample.
Small globules at the bottom of the container.
Describe the symptoms of a blocked fuel tank vent in a gravity feed fuel system.
Describe the importance of correct management of fuel selection. (6)
Correct grade and free from impurities
•Sufficient for flight & reserves
•Ensure tank caps are secure
•Use good time management
•Do not change tanks unnecessarily prior to T/O or at low altitude
•Fuel available prior to changing tanks and electric pump on
Detail the actions recommended in the case of loss of power through faulty fuel selection.
Change fuel tanks or land ASAP
Describe the typical methods of cross-feeding fuel.
Twin engine fuel system will have the ability to cross feed fuel from the tanks on one side of the aircraft to the opposite. This is to enable the fuel that would normally be used by a failed engine to be consumed by the live engine when required.
This is done by cross feed valves to be incorporated in the fuel tank selection valve system.
Explain the differences between aviation gasoline (AVGAS) and motor gasoline (MOGAS).
A gas is more leaded than Mona’s giving it a higher octane or performance rating to delay the onset of detonation. Less volatile so vapour lock is reduced and has higher quality control standards.
Explain fuel octane ratings and performance numbers.
Anti detonation properties designated by octane rating or performance number
•Originally rated at a max octane of 100.
•Advances in technology meant that more efficiencies could be gained
•By adding chemicals, the octane rating can be artificially improved
If improvement exceeds 100, then a performance number is used
•Many fuels have a dual performance number, eg: 100/130
•This represents the power available (before detonation) with a weak/lean mixture (100) and the second number (130) represents the power available at a rich mixture
