What is Total drag?

• A. The sum of lift and weight
• B. The sum of induced, profile, and parasite drag
• C. Drag due to air viscosity only
• D. The product of velocity and drag coefficient

Answer: (B)

Total drag is the sum of all resistive forces the air exerts on the rotorcraft as it moves. In a rotor system, you have three main contributors. First, induced drag arises from the rotor generating lift and the energy lost in creating downwash and tip vortices. Second, profile drag comes from the rotor blades themselves as they move through air, including skin friction and form drag on the blade sections. Third, parasite drag comes from parts that do not generate lift—fuselage surfaces, tail rotor hardware, landing gear, and other attachments—that add drag that increases with speed. Put together, these components give the total aerodynamic drag at a given speed and configuration.

It isn’t the sum of lift and weight, which are separate forces. Drag due to air viscosity alone omits a significant portion of the drag from lift generation and non-lifting structures. And drag isn’t simply velocity times a coefficient—the standard relation involves dynamic pressure, reference area, and a drag coefficient: D = 0.5 ρ V^2 Cd A.