Overall Aircraft Fuel System

Figure 1 presents a basic schematic of the fuel pump components in the overall aircraft fuel system. The division between the airframe and engine systems is shown.

The primary function of the airframe fuel system is to provide a pressurized fuel feed to the engine fuel pump system under all operating conditions. In the event of the emergency conditions of non-operating or failed boost pumps, a bypass located either in the airframe plumbing or the boost pump allows the engine pump system to receive sufficient fuel to provide take-off and climb thrust. Other functions required of the airframe fuel pump system are as follows:

• Provides fuel transfer between various fuel tanks to maintain continuous engine feed and to adjust the center of gravity of the aircraft.

• Provides fuel jettison in flight in the event it is necessary to quickly reduce the aircraft weight.

• Assists in the defueling of the aircraft on the ground.

The primary function of the engine fuel system is to receive the fuel from the airframe fuel system, under normally pressurized conditions or emergency conditions, and provide pressurized fuel to the engine. This fuel is used for burning in the combustors and for powering actuators that control the engine's variable geometry.

Because fuel is the only consumable fluid carried by the aircraft, it represents the sole heat sink on board the aircraft. (For extreme conditions, some aircraft have carried an additional disposable heat sink fluid.) The on-board fuel and the air ingested by the engines or scoops provide all of the cooling necessary for the proper functioning of the various airframe and engine systems. The impact of this on the fuel pumps is a significant increase in the temperature of the fuel on which the pumps must operate.

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Survival Treasure

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