An aircraft fuel system is designed to make fuel available to the engine at all times. The fuel tanks and reserve tanks are located at the wings of the aircraft and one in the belly of the aircraft inside next to the wings below the seats called center tank. vent tanks and trim tanks are also available at the vertical and horizontal stabilizer as explained in parts of an aeroplane article. tanks are vented on the outside to maintain atmospheric pressure inside the tank.
Two major fuel systems in small air craft are gravity feed system and fuel pump system.
- Gravity feed system – uses force of gravity to transfer fuel from tanks to the engine. tanks in this case are located above the carburetor and the wings are high.
- Fuel pump system – tanks may be low in low wing aircraft hence tanks can be below the carburetor. pump is controlled at the cabin and it pumps fuel to the engine.
in both this a fuel primer is used to draw fuel from the tanks & to vaporize it into the cylinders before starting the engine. a fuel primer is also used in very cold weather situations to in cold starts to provide heat to vaporize fuel in the carburetor.
When fuel leaves the tank it first passes through a strainer which removes moisture and sediments. the fuel is then passed to the carburetor which at this stage is mixed with primer and a selector valve is activated. carburetor mixed fuel with air and sends it to a piston engine in small aircraft.
Fuel jettisoning system – This is practiced in situations where landing weight is less than take off weight. the plane may be too heavy too land or maneuver in air. it is applied on aircraft so that fuel can be dumped in flight to avoid structural damage cause by landing the aircraft when it is too heavy. fuel jettisoning systems are also known as fuel dumping systems.
Types of aviation fuel
- AVGAS – this is better known as aviation gasoline. it is reciprocating engine fuel different from motor gasoline.
- Jet fuel – this is turbine engine fuel better known as kerosene. this is not normal kerosene but unleaded kerosene or naptha kerosene better known as jet A-1, jet B respectively.
over wing fueling – this is fueling done at the top of the wing. it is practiced on smaller planes, helicopters & piston engine aircraft.
under wing fueling – This is fueling done at the bottom of the wing. it is practiced with jet fuel & with large aeroplanes. it is also known as single-point refueling or pressure refueling.
it should be noted that before the fuel cap is removed the a ground wire should be attached to the aircraft to prevent static electricity that could cause catastrophe is fuel fumes are ignited.
The refueling nozzle should be bonded to the aircraft before refueling begins & should remain there through out the entire procedure of refueling. if a fuel truck is used it should be grounded before attaching the fuel nozzle.
A pilot should not solely rely on fuel gauges but he should also manually inspect the tanks before flight just in case gauges are faulty as shown in my pre-flight inspection & checks article.