Which factor primarily affects the drag experienced by a helicopter?

The primary factor affecting the drag experienced by a helicopter is the shape and speed of the rotor blades. This is because the design of the rotor blades influences their aerodynamic efficiency.

Rotor blades are designed to generate lift while minimizing drag, and their shape—specifically their airfoil design—determines how air flows over and under them. A well-designed blade can achieve a balance that allows for effective lift generation while reducing drag. Additionally, the speed at which these blades rotate also plays a crucial role; as rotor speed increases, drag tends to increase due to friction and compressibility effects in the airflow around the blades.

While the weight of the helicopter, the angle of incidence, and the altitude do have their own impacts on performance, they contribute less directly to the drag compared to the physical characteristics and dynamics of the rotor blades themselves. Therefore, understanding the aerodynamics of rotor blade design and operation is key to recognizing how drag is influenced during flight.