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

In the context of aerodynamics, there are four primary forces that act upon an aircraft during flight: lift, drag, weight (gravity), and thrust. Lift is created by the wings as air flows over and under them, enabling the aircraft to rise. Thrust is generated by the engines, providing the necessary power to propel the aircraft forward. Drag acts as a resistance force opposing the aircraft's motion through the air, caused by friction and the shape of the aircraft.

Torque, on the other hand, is not classified as one of the four main forces in flight. Instead, it refers to the rotational force that can affect an aircraft's movement, mainly around its longitudinal axis. While torque can influence flight characteristics, especially in terms of controlling an aircraft, it is not a fundamental aerodynamic force like lift, drag, or thrust. This distinction highlights why torque is the correct answer to the question as it does not belong to the set of primary forces impacting an aircraft during flight.