Ram effect due to aircraft forward speed will cause the efficiency of the engine to

• A. remain constant
• B. decrease
• C. increase
• D. No change in efficiency

Answer: (C)

The key idea is the ram effect: as the aircraft moves forward, the air entering the engine has extra dynamic energy, which raises the stagnation pressure and density at the compressor face. That means more air mass reaches the compressor for a given engine speed, and the inlet provides a higher pressure for the same throttle setting. With more air available and a higher inlet pressure, the engine can produce more thrust for the same fuel flow, or achieve the same thrust with less fuel, improving the overall efficiency. This improvement grows with speed and is more noticeable at higher subsonic speeds, though it’s small at very low speeds. Since the ram effect boosts the engine’s ability to convert fuel into useful work, the efficiency increases, not remains constant or decreases.