About Ground Effects in Aircrafts
Ground effects is an aerodynamic phenomenon that happens when aircraft are flying close to the ground. The effect is quite noticeable in many aircraft and is a fun experience for beginning pilots. Experienced pilots must be aware of how ground effects will change the flying characteristics of their aircraft and be ready to use or counteract ground effects when they occur.
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Aero Basics
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An aircraft in flight is affected by four main forces. In level steady flight, lift equals weight and thrust equals drag. Lift is caused by airflow over the wing resulting in higher air pressure on the bottom of the wing, resulting in an upward force holding the plane in the air.
Turbulence
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At the wingtip the pressure on the bottom of the wing will escape around the wingtip, generating a flow of air in an upward circular pattern around the end of the wing. As the aircraft moves forward, this circular flow of air trails behind the aircraft becoming wingtip vortices. Wingtip vortices reduce the lift generated by the wing and increase the drag. The effect of the vortices on aircraft performance is significant.
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Near the Ground
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When an aircraft is flying close to the ground, the spinning vortex of air is interrupted when it contacts the ground. When a plane is less than approximately one-half of the wingspan above the ground the vortices will be affected by the ground. This vortex interruption results in the change of aircraft performance known as ground effects.
Effects
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Interrupting the wingtip vortices has a positive effect on the flight characteristics of the wing. The drag caused by the vortices is reduced and lift is no longer lost from pressure spillage around the wing tip. When the plane flies into ground effect during descent the pilot will feel the aircraft "float" on a cushion of air as lift is increased and drag reduced.
Considerations
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A pilot must be aware of what happens to his plane when it enters ground effects. The cushioning effect from the increased lift can be used to soften the landing. The loss of drag and increased lift may cause the aircraft to float, dangerously increasing the landing distance. When she starts to feel the ground effects during landing, the pilot should reduce power and work to maintain the descent path to the desired landing spot.
Warning
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An overloaded, underpowered aircraft may be able to take off, but not have enough thrust or power to climb out of ground effects. This situation can only result in a crash. A pilot should always know the power and weight limitations of his aircraft.
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