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

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

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

Answer: (A)

In ground effect, the rotor’s downwash is hindered by the nearby surface, so the induced flow through the rotor disk is reduced. With less downward airspeed through the disk, the inflow angle that the blade “sees” becomes smaller. If the blade pitch (the commanded angle) stays the same, a smaller inflow angle translates to a larger angle of attack relative to the oncoming air. So induced flow velocities decrease and the angle of attack increases in ground effect.

In ground effect, the rotor’s downwash is hindered by the nearby surface, so the induced flow through the rotor disk is reduced. With less downward airspeed through the disk, the inflow angle that the blade “sees” becomes smaller. If the blade pitch (the commanded angle) stays the same, a smaller inflow angle translates to a larger angle of attack relative to the oncoming air. So induced flow velocities decrease and the angle of attack increases in ground effect.