How Do Aircraft Fuel Systems Work?

Posted on July 29, 2020 Anthony Cordle How Do Aircraft Fuel Systems Work?

While the aircraft fuel system may be complex in design and construction, it is fairly simple in its purpose, which is to deliver a steady supply of fuel to the engine during operation. This flow must be supplied in exact amounts, accommodating for power settings, attitude, altitude, or any other flight condition or combination thereof. Depending on the aircraft in question, fuel systems such as the gravity fed or fuel pump system may be implemented. In this blog, we will discuss each type of fuel system and how they function.

Types of Aircraft Fuel System

Across light aircraft types and others, the most common location in which the fuel tanks are installed is the wings. Filler caps are typically in these areas as well, allowing for the tanks to be filled with fuel with ease. Drains at the bottom permit the sampling of fuel for inspections, as well as help remove moisture from the system. Within each tank, a sensing unit is also implemented so that fuel levels may be measured and monitored by the pilot from within the cockpit.

When an aircraft features a high-wing configuration, fuel is transferred to the carburetor through a gravity fed system. If a high-wing aircraft features a fuel-injected system, however, an engine driven pump is needed to supply fuel to the engine. This is the case in low-wing light aircraft as well, as they also rely on fuel pumps for the transferring of fuel. To start the engine of such aircraft types, an electrically operated pump is utilized and may be relied on as a backup system during normal operations after starting. When aircraft are fitted with carbureted engine types, they may require a manual primer to supply additional fuel for the engine in order to start.

As many aircraft feature two or more engines that are placed within the wings, a fuel selector valve may be present that allows the pilot to select which tank will be used for fuel supply. In some aircraft, the pilot may be required to alternate between the left and right tank throughout the flight for balancing weight, while others may have a “both” option. If there is an option to feed from both sides, the pilot should still monitor the fuel of each tank as an aircraft may tend to draw more from one side as compared to the other, resulting in an imbalance of weight between the two sides.

Before fuel can enter the carburetor or fuel injector to be supplied to an aircraft engine, it must first pass through a strainer. The strainer is typically placed near the lowest point of the aircraft fuel system as contaminants that are denser than Avgas will sink to the bottom. Once fuel passes through the strainer, it may then enter into the carburetor or fuel injector so that it may be mixed with air and ignited for propulsion generation.

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