Fuel System

The function of the fuel system is to provide a means of storing fuel in the air­plane and transferring this fuel to the air­plane engine. Fuel systems are classified ac­cording to the method used to furnish fuel to the engine from the fuel tanks. The two classifications are the "gravity feed" and the "fuel pump system."

The gravity feed system utilizes the force of gravity to transfer the fuel from the tanks to the engine. This system can be used on high-wing airplanes if the fuel tanks are installed in the wings. This places the fuel tanks above the carburetor and the fuel is gravity fed through the system and into the carburetor.

If the design of the airplane is such that gravity cannot be used to transfer fuel, fuel pumps are installed. This is true on low-wing airplanes where the fuel tanks in the wings are located below the carburetor.

Two fuel pump systems are used on most airplanes. The main pump system is engine driven and an auxiliary electric driven pump is provided for use in the event the en­gine pump fails. The auxiliary pump, com­monly known as the "boost pump," provides added reliability to the fuel system, and is also used as an aid in engine starting.

1. What is the fuel system designed for?

2. How are fuel systems classified?

3. Where is fuel stored on the aircraft?

4. How is fuel delivered to the engine(s)?

5. Why is it necessary to filter the fuel?

A voltage regulator controls the rate of charge to the battery by stabilizing the electrical output which is usually slightly higher than the battery voltage.

An inverter is installed on airplanes to change direct current to alternating current.

The electric auxiliary pump is controlled by a switch in the cockpit.

Most airplanes are designed to use space in the wings to mount fuel tanks. All tanks have filler openings which are covered by a cap. This system also includes lines connecting to the engine, fuel gauges indicating the pressure in the fuel lines, strainers, and vents which permit air to replace the fuel.

Fuel overflow vents are provided to discharge fuel in the event the fuel expands because of high temperatures. Drain plugs or valves (sumps) are located at the bottom of the tanks from which water and other sediment can be drained from the tanks.

Fuel lines pass through a selector assembly located in the cockpit which provides a means for the pilot to turn the fuel "off," "on," or to select a particular tank from which to draw fuel. The fuel selector assembly may be a simple on/off valve, or a more complex arrangement which permits the pilot to select individual tanks or use all tanks at the same time.

Many airplanes are equipped with fuel strainers, called sumps, located at the low point in the fuel lines between the fuel selector and the carburetor. The sumps filter the fuel and trap water and sediment in a container which can be drained to remove foreign matter from the fuel.