What is the primary function of the helicopter rotor system?

The primary function of the helicopter rotor system is to generate lift. The rotor blades create a pressure difference between the upper and lower surfaces as they spin, which, according to Bernoulli's principle, generates an upward force that allows the helicopter to ascend and remain airborne. The angle of attack of the rotor blades can be adjusted to control the amount of lift produced, allowing the helicopter to take off, hover, and land safely.

This lift generation is essential for the helicopter's flight capabilities and is fundamental to its operation. While lateral stability and control during flight are important, they are secondary functions that rely on the effective generation of lift by the rotor system. Additionally, drag reduction is more a byproduct of rotor design and operation rather than a primary function, and engine power control is related to the power that drives the rotor system but is not a direct function of the rotor itself. Therefore, generating lift is the core purpose of the rotor system, making it the correct answer.