In ground effect, induced flow velocities are decreased, and as a result AOA is increased.

• A. Decreased; Increased
• B. Increased; Increased
• C. Decreased; Decreased
• D. Increased; Decreased

Answer: (A)

Ground effect changes the rotor’s induced flow because the ground dampens the downwash produced by the rotor. This interference reduces the induced velocity at the rotor disk when very close to the surface. With less downward air velocity to provide lift, the blade must operate at a higher angle of attack (more pitch) to achieve the same thrust in this restricted flow, so the angle of attack increases. In short, near the ground the induced velocity goes down, but the blade’s effective angle of attack must rise to maintain lift, which is why the correct pairing is decreased induced velocity and increased angle of attack.