Which statement about the forces of flight is true?

• A. The four forces are thrust, drag, lift, and weight
• B. Thrust and drag are the only forces acting on the aircraft
• C. Weight and lift are the only forces acting on the aircraft
• D. Drag equals lift in steady flight

Answer: (A)

Four forces act on an aircraft in flight: lift, weight, thrust, and drag. Lift pushes upward to support the weight of the aircraft, while weight pulls downward due to gravity. Thrust pushes forward to overcome drag, which opposes the forward motion.

In steady, level flight those forces balance: lift equals weight and thrust equals drag. This is what keeps the airplane flying smoothly without accelerating up, down, forward, or backward. So the statement that correctly lists all four forces is true.

The other ideas aren’t right because they leave out one of the essential forces or imply an equality that isn’t generally true. Thrust and drag alone can’t balance the vertical forces, and weight and lift alone ignore the forward/backward interaction. Drag and lift aren’t required to be equal in steady flight, since they act in perpendicular directions and balance with their respective partners.