Which term describes a configuration with minimum drag?

• A. Cruise configuration
• B. Clean configuration
• C. Landing configuration
• D. Takeoff configuration

Answer: (B)

Minimum drag occurs when the airplane is in clean configuration: all lifting surfaces and external items streamlined, with landing gear retracted and flaps up. In this state there are no protruding components to create parasite drag, so the air flows smoothly across the airframe and drag is minimized for a given speed. Lowering flaps or extending the landing gear increases drag (and often changes lift) because those devices disrupt the smooth airflow and add form and surface drag. Takeoff and landing configurations intentionally increase drag to gain lift at lower speeds, while clean (cruise) configuration is used to maximize efficiency. That’s why clean configuration best describes minimum drag.