The role of an aircraft fuel system is to store fuel and supply it to the engines and auxiliary power unit. Aviation fuel is converted into heat energy and subsequently kinetic energy in the engine to power an aircraft. All engine-powered aircraft must have a fuel system onboard, the basic requirement of which is to provide a continuous flow of uncontaminated fuel to the engines at a pressure and flow rate to sustain operation at any attitude. The aircraft fuel system is not a single system, but rather a collection of various subsystems. The exact configuration varies from aircraft to aircraft, but the basic principles remain the same.
The first part of any fuel system is the fuel storage. There are three basic types of aircraft fuel tanks: rigid removal tanks, bladder tanks, and integral fuel tanks. The vast majority of modern aircraft use integral fuel tanks as their main fuel storage system. Fuel tanks of this type are either part of the structure of the aircraft wings or fuselage. There are two methods of refueling an aircraft: overwing and pressure refueling. In overwing refueling, the aircraft is fueled similarly to the way a car is. The disadvantage of this method is the time it takes. Accessing the tanks requires step ladders, platforms, etc., and the actual fueling process is also slower. Pressure refueling refers to a system wherein pressurized fuel is supplied to an aircraft from a bowser, tanker, or refueling vehicle. This system is preferred because it is faster while also lowering the risk of spillage, fuel contamination, and fire.
As fuel is pumped into or out of the tanks, air must be allowed in and out. Failing to do so could cause the tank to rupture or a vacuum to occur when the engines are running, thereby starving them of fuel. The process of allowing air in or out of the engine is known as venting. The purposes of venting are to use ambient air to balance the air pressure within the fuel tanks with ambient air, allow for thermal expansion of the fuel/air mixture in the tank, and protect the tank from excessive internal pressure.
Finally, the most important function of the fuel system is to provide fuel to the engines. This is done by the engine fuel feed. Although engines intake fuel using their own pumps, booster pumps are necessary to ensure a positive flow. Positive flow is required to ensure the flow rate is at an adequate level and to prevent cavitation in fuel lines and components. Most aircraft also have a separate pump for the auxiliary power unit, which receives fuel from the main fuel tank. Despite this, through the use of fuel pump switches, any tank can be used to supply the APU. the aircraft fuel system is unquestionably among the most important aspects of any aircraft. As such, when buying components for these systems, ensure you are getting them from a trusted and reliable source.
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