What is the primary function of a propeller on an aircraft?

The primary function of a propeller on an aircraft is to generate thrust. When a propeller spins, it creates a difference in air pressure between its front and rear, which propels the aircraft forward. This thrust is essential for overcoming drag and enabling the aircraft to accelerate during takeoff and maintain speed during flight.

In contrast, the generation of lift is primarily the role of the wings, which create aerodynamic lift as air flows over and under them. Control of altitude is managed through various flight control systems and surfaces, not directly by the propeller. Roll control, which involves rotating the aircraft around its longitudinal axis, is primarily handled by ailerons and other flight control surfaces. Therefore, it's clear that the propeller's main role is in generating thrust, making it a crucial component for the forward movement of the aircraft.