In a turbofan engine, most thrust is produced by which combination?

• A. Thrust from both the core exhaust and the fan exhaust
• B. Thrust from the core exhaust alone
• C. Thrust from the fan exhaust alone
• D. Thrust from bypass air only

Answer: (A)

Two air streams are responsible for thrust in a turbofan: the bypass air accelerated by the fan and the core exhaust from the combustor. The engine creates thrust by changing the momentum of both streams as they exit the nozzle. The bypass stream provides a large mass flow at a moderate velocity, contributing a substantial portion of thrust, while the core exhaust, though smaller in mass, exits at a much higher velocity and adds a strong thrust component as well. The total thrust is the sum of both contributions, so the best description is thrust from both the core exhaust and the fan exhaust. Focusing on only one stream wouldn’t account for the full thrust the engine produces, since the momentum change of both streams combines to produce the overall thrust.