Define specific fuel consumption (SFC) and explain its significance for engine performance.

• A. SFC is the fuel flow per unit of thrust.
• B. SFC is the fuel flow per unit of thrust (lb/hr per lbf).
• C. SFC is the fuel capacity of the engine.
• D. SFC is the time required to burn a liter of fuel.

Answer: (B)

Specific fuel consumption shows how efficiently an engine uses fuel to produce thrust. It’s defined as the rate at which fuel is burned divided by the thrust produced, so in English units it comes out as pounds of fuel per hour per pound-force of thrust. This ratio matters because the lower the SFC, the less fuel is needed to generate a given amount of thrust, which translates to longer range and greater endurance for the same fuel load, as well as lower operating costs. SFC isn’t a fixed property; it changes with altitude, speed, throttle setting, and engine design, so engineers aim for configurations that minimize SFC during cruise. For planning, you can think of total fuel burn as the product of SFC, thrust, and time, so improvements that reduce SFC directly cut fuel use for the mission.