Which factor does NOT influence the strength of rotor downwash?

The strength of rotor downwash is primarily influenced by the rotor's performance and the operating conditions of the helicopter. Each factor plays a role in determining how air moves around the helicopter and is affected by its design and environment.

The configuration of the wings (or rotor blades, in the case of helicopters) does not directly influence rotor downwash in the same way that other factors do. Wings and rotor blades are designed to generate lift, but their configuration is typically fixed for the helicopter's operation. Instead, factors like forward speed, air density, and the weight of the helicopter significantly affect the airflow and downwash characteristics.

For instance, increased forward speed generally enhances downwash due to the forward movement of the rotor system. Similarly, changes in air density can alter lift characteristics, thereby affecting downwash. The total weight of the helicopter impacts how much lift is required, which in turn affects the downwash produced.

In contrast, while wing configuration can influence overall aerodynamic performance and efficiency, it does not significantly alter the fundamental behavior of downwash produced by the rotor system at any given moment. Hence, it is the factor that does not influence rotor downwash strength.