Which term describes the forward thrust generated by the propulsion system?

• A. Lift
• B. Weight
• C. Thrust
• D. Drag

Answer: (C)

Thrust is the forward force produced by the propulsion system that moves the airplane through the air. In flight, the aircraft is acted on by four forces: lift acting upward, weight downward, thrust pushing forward, and drag opposing the forward motion. The propulsion system, such as a propeller or jet engine, accelerates air backward, and by Newton’s third law the aircraft is pushed forward. This forward push is the specific force that drives the airplane through the air, making it the correct term for the question. Lift and weight are vertical forces, while drag is the rearward resistance, so they don’t describe the forward propulsion. In steady flight, thrust is what overcomes drag, allowing a constant airspeed.