FAA Powerplant Written Practice Test

How is fuel flow measured on many light aircraft with reciprocating engines?

1. With a pressure based flow meter

2. With a mass flow meter

3. With a mechanical flow gauge

4. With a digital flow sensor

The correct answer is: With a pressure based flow meter

Fuel flow measurement in many light aircraft with reciprocating engines is commonly achieved using a pressure-based flow meter. These systems work by measuring the differential pressure across a calibrated orifice or venturi that is installed within the fuel line. As fuel flows through the orifice, it creates a pressure drop that is proportional to the flow rate. By calibrating the system, the resulting pressure differential can then be converted into a flow reading. Pressure-based flow meters are advantageous because they can provide accurate measurements while remaining relatively simple and lightweight, which is essential for light aircraft that require efficient designs. These instruments also tend to be more robust in the variable conditions experienced in aviation environments. Digital flow sensors, although increasingly used in modern applications, are typically found in more advanced or larger aircraft systems rather than in the traditional setups of light aircraft. Mass flow meters are more commonly used in industrial applications and are less frequently found in general aviation. Mechanical flow gauges, while available, may not provide the same level of precision as pressure-based meters.