FAA Powerplant Written Practice Test

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

1. Volume based meter

2. Pressure based flow meter

3. Weight based scale

4. Visual indicators

The correct answer is: Pressure based flow meter

Fuel flow in many light aircraft with reciprocating engines is typically measured using pressure-based flow meters. These devices operate by measuring the pressure drop across an orifice or similar constriction within the fuel line, which is correlated to the flow rate of the fuel. The principle behind this method relies on Bernoulli’s equation, where the decrease in pressure is directly related to the increase in flow velocity. This method provides accurate readings of fuel flow, which is crucial for monitoring engine performance and ensuring that the engine receives the correct amount of fuel for efficient operation. Pressure-based meters can deliver real-time data to the pilot, enhancing situational awareness and safety during flight. In contrast, other measurement methods like volume-based meters may not account for variances in fuel density, especially in changing temperature conditions. Weight-based scales are less practical in an aircraft setting due to space constraints and the need for dynamic measurements. Visual indicators may offer rough estimates but lack precision and are not ideal for critical monitoring tasks associated with engine performance. Thus, pressure-based flow meters are the standard for accuracy and reliability in measuring fuel flow in light aircraft with reciprocating engines.