Which factor primarily affects lift?

The shape of the wing and the angle of attack are fundamental factors that primarily affect lift. The design of the wing, or airfoil, influences how air flows over and under the wing, generating differences in air pressure that result in lift. When a wing is shaped properly, it can create a lower pressure area on top and higher pressure below, allowing the aircraft to rise.

The angle of attack, which is the angle between the wing's chord line and the oncoming air, is crucial as well. Increasing the angle of attack usually increases lift up to a certain point; however, if the angle becomes too steep, it can lead to a stall, where lift dramatically decreases.

In contrast, the weight of the aircraft materials affects the total weight but is not a direct factor in how lift is generated. The speed of the aircraft engine relates more to thrust than to lift directly, although engine power can influence airspeed, which indirectly affects lift. Finally, runway length is primarily a concern for the takeoff distance required, not for the generation of lift itself.