What forces act on an aircraft in flight?

In flight, an aircraft experiences four fundamental forces: lift, drag, weight, and thrust.

Lift is the force that acts perpendicular to the relative wind and is generated primarily by the wings as they interact with the airflow. This force enables the aircraft to rise off the ground and remain airborne.

Weight is the downward force caused by gravity, pulling the aircraft towards the Earth. It is essential to consider weight because it directly affects the aircraft's capability to gain altitude and maintain flight.

Thrust is the forward force produced by the aircraft's engines. It propels the aircraft forward, allowing it to generate the necessary lift by ensuring that airflow over the wings is adequate.

Drag is the aerodynamic resistance the aircraft encounters as it moves through the air. It opposes thrust and affects the aircraft's speed and fuel efficiency. While drag is a significant aerodynamic force, it complements the other three forces and is part of understanding flight dynamics.

When considering all four forces together – lift, weight, thrust, and drag – one gets a complete picture of the forces acting on an aircraft in flight, making option D the most comprehensive and accurate choice.