Which of the following is NOT one of the four forces acting on an aircraft in flight?

• A. Lift
• B. Weight
• C. Drag
• D. Engine power

Answer: (D)

Understanding the four fundamental forces acting on an aircraft in flight is key. Lift is the upward force generated by the wings, weight is the downward gravitational force, drag is the air resistance that opposes forward motion, and thrust is the forward force produced mainly by the engines. Engine power, on the other hand, is not a force. It’s the rate at which the engine does work, and while it relates to how much thrust can be produced at a given speed (power equals thrust times velocity), power itself isn’t one of the forces acting on the airplane. So engine power is the correct choice as the item that is not a force acting on the aircraft.