Which statement about flight force equilibrium is true?

Which statement about flight force equilibrium is true?

• A. The thrust equals drag
• B. The forces of flight are equal and opposite
• C. The wings generate lift
• D. The weight equals thrust

Answer: (D)

In steady flight, forces balance along both axes. Vertically, the lift produced by the wings must counter the aircraft’s weight so there’s no acceleration up or down. Horizontally, the thrust from the engines must counter drag so there’s no acceleration forward or backward. Lift is what counters weight, and thrust is what counters drag. The wings generating lift is true, but that lift is the force that counters weight, not thrust. Saying weight equals thrust describes a balance between vertical and horizontal forces, which isn’t how equilibrium is maintained in normal flight. So the correct way to think about flight force equilibrium is lift equals weight and thrust equals drag.

In steady flight, forces balance along both axes. Vertically, the lift produced by the wings must counter the aircraft’s weight so there’s no acceleration up or down. Horizontally, the thrust from the engines must counter drag so there’s no acceleration forward or backward. Lift is what counters weight, and thrust is what counters drag. The wings generating lift is true, but that lift is the force that counters weight, not thrust. Saying weight equals thrust describes a balance between vertical and horizontal forces, which isn’t how equilibrium is maintained in normal flight. So the correct way to think about flight force equilibrium is lift equals weight and thrust equals drag.