How Airplane Fuel Flow Indicators and Fuel Gauges Function

With the majority of aircraft currently relying on fuel mixtures for propulsion generation, it is always crucial for safety that there is some type of fuel quantity indicating system present. With a mixture of fuel flow indicators and fuel gauges, pilots can closely monitor the amount of fuel present in the fuel tank, as well as the rates at which fuel is spent to ensure an efficient and safe flight operation. In this blog, we will provide an overview of fuel flow indicators and fuel gauges, allowing you to better understand the uses that they provide to the aircraft engine and pilot.

Depending on the aircraft and its complexity, a number of fuel gauge types may be present. Early fuel gauges and indicators were often simplistic in their operation, requiring no electrical power for their operations. While still in use today, such gauges are most often reserved for smaller aircraft that have a fuel tank located close to the cockpit. For other aircraft, a series of electric indicators and components are required for obtaining accurate readings for the pilot.

As another simplistic form of fuel gauge components, float-type sight gauge fuel quantity indicators are mechanical components that can be placed within the fuel tank. With a float placed in the fuel itself and an attachment to a rod that exits through the fuel cap, the float can move up and down as fuel levels change. As the float adjusts its positioning within the tank, the connecting rod will measure movement accordingly and provide a reading to the pilot.

For more sophisticated and modern aircraft, electrical fuel gauges often prove to be the most popular choice. With such devices, DC power is used to drive a ratiometer-type gauge which measures fuel quantity with a wiper and variable resistor. As the resistor faces changes in current flow, such values will be reflected to the indicator, allowing for a calibrated dial to display a reading. For some aircraft, fully digital systems may be present, and such devices utilize the variable resistance signal that is provided by electric gauge components. 

Beyond being aware of the remaining fuel present in a particular aircraft, it is also extremely useful to monitor the rate at which fuel is spent by the aircraft engine. With such information, operators can create and study fuel trends for discerning engine performance and for planning future flights. Depending on the aircraft engine present and the method in which fuel is combusted, a number of fuel flow indicators may be used. As fuel mass is affected by temperature and fuel types, most measurements are made based on volume.

Fuel flow indicators that are used alongside horizontally opposed reciprocating engines are often the most simplistic, and they can be programmed to make readings in pounds per hour or gallons per hour. With measurements being taken at the site of the fuel injectors, fuel is read based on pressure. As clogging and other issues can affect the pressure at which fuel is supplied to the engine, pilots should regularly cross-reference the flowmeter and EGT.

For larger reciprocating aircraft engines, fuel flow indicators may be a vane-type device that measures volume consumption. Located between the carburetor and fuel pump, all fuel must pass through the indicator before continuing its path. As such, fuel is forced against a vane and spring assembly, creating a measurement based on average weight.

With properly functioning fuel flow indicators and fuel gauge components, pilots can efficiently and safely operate aircraft. At Accelerating RFQs, we are the premier purchasing platform for fuel tank parts and aviation components, offering competitive pricing on over 2 billion items that we have listed. Explore our robust part catalogs today, and our team of industry experts are readily available 24/7x365 to assist you throughout the purchasing process.


March 15, 2022

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