What are the four primary forces acting upon an aircraft?

The four primary forces acting upon an aircraft are Weight, Lift, Drag, and Thrust. Understanding these forces is essential in the field of aviation and unmanned aerial systems (UAS) because they play critical roles in flight dynamics and stability.

Weight is the force exerted by gravity on the aircraft, pulling it downward. It is a crucial factor because it must be balanced by lift for the aircraft to ascend or maintain altitude. Lift is created by the movement of air over the wings and is vital for keeping the aircraft airborne. It counteracts the weight of the aircraft during flight.

Thrust is the force produced by the engines to propel the aircraft forward. It must overcome drag, which is the resistance the aircraft experiences as it moves through the air. Understanding the balance and interaction between these four forces is fundamental for safe and efficient flight operations, as adjustments to any of these forces can significantly impact an aircraft's performance and control.

The incorrect options include elements like stability and altitude, which are not primary forces but rather concepts related to the performance and operation of the aircraft.