Which condition describes increased drag and decreased lift in the aft portion of the rotor disk due to higher induced velocity?

Which condition describes increased drag and decreased lift in the aft portion of the rotor disk due to higher induced velocity?

• A. Transverse-Flow Effect
• B. Induced Flow
• C. Backward Flow
• D. Spanwise Flow

Answer: (A)

The question is testing how airflow through the rotor disk changes with forward motion. In forward flight, the downwash from the rotor isn’t the same across the entire disk: the aft portion experiences a higher induced velocity because the rotor wake and translational flow interact, increasing the downward flow there. When induced velocity is higher in the rear half, the blades in that region see a reduced effective angle of attack and generate less lift, while the associated induced drag increases. This combination—more drag and less lift in the aft portion of the rotor disk—is described as the Transverse-Flow Effect. Other terms don’t capture this specific pattern. Induced Flow refers to the general downwash produced by the rotor, not the differential distribution across the disk. Spanwise Flow describes flow along the blade span, not across the disk, and Backward Flow isn’t a standard aerodynamic term used here.

The question is testing how airflow through the rotor disk changes with forward motion. In forward flight, the downwash from the rotor isn’t the same across the entire disk: the aft portion experiences a higher induced velocity because the rotor wake and translational flow interact, increasing the downward flow there. When induced velocity is higher in the rear half, the blades in that region see a reduced effective angle of attack and generate less lift, while the associated induced drag increases. This combination—more drag and less lift in the aft portion of the rotor disk—is described as the Transverse-Flow Effect.

Other terms don’t capture this specific pattern. Induced Flow refers to the general downwash produced by the rotor, not the differential distribution across the disk. Spanwise Flow describes flow along the blade span, not across the disk, and Backward Flow isn’t a standard aerodynamic term used here.