What aerodynamic effect occurs near the ground that reduces induced drag due to lower upwash and blade tip vortices?

What aerodynamic effect occurs near the ground that reduces induced drag due to lower upwash and blade tip vortices?

• A. Ground Effect
• B. Ground Resonance
• C. Vortex Ring State
• D. Autorotation

Answer: (A)

Ground effect is the tendency for rotor efficiency to improve when the rotor is close to the surface. When the rotor disk is within a rotor diameter of the ground, the air pushed downward cannot spread out and rise as freely because the ground acts as a boundary. This suppresses the upwash and weakens the blade-tip vortices in the rotor wake, so the induced velocity through the rotor is lower. With less downward flow needing to be produced, the rotor requires less power to produce the same thrust, and induced drag decreases. As you climb away from the ground, this interference diminishes and the effect fades. Ground resonance, vortex ring state, and autorotation describe other phenomena not related to this near-ground aerodynamic interaction.

Ground effect is the tendency for rotor efficiency to improve when the rotor is close to the surface. When the rotor disk is within a rotor diameter of the ground, the air pushed downward cannot spread out and rise as freely because the ground acts as a boundary. This suppresses the upwash and weakens the blade-tip vortices in the rotor wake, so the induced velocity through the rotor is lower. With less downward flow needing to be produced, the rotor requires less power to produce the same thrust, and induced drag decreases. As you climb away from the ground, this interference diminishes and the effect fades.

Ground resonance, vortex ring state, and autorotation describe other phenomena not related to this near-ground aerodynamic interaction.