Friday, July 13, 2012

Ground Effect

Ground Effect


When an aircraft is flying at an altitude that is approximately at or below the same distance as the aircraft's wingspan, there is an ground effect. The cause is the interruption of the wingtip vortices and downwash behind the wing. When you fly a plane very close to the ground the vortices are unable to form fully. The result is lower drag which increases the speed resultant force. If the airplane attitude hasn't changed the net result is increased downward force of air that pushes the airplane upward. Thats "ground effect." Low wing aircraft experience more ground effect than high wing aircraft. Runway surface construction can affect the ground effect. Cement construction causes more ground effect than grass. Encountering turbulence in the vortices because of rough surface conditions will destroy ground effect earlier in an approach to landing.

If the drag is reduced you can reduce engine power to maintain the same speed in the same aircraft attitude. Lowering power more, at the same aircraft attitude, will allow the plane to descend. As you approach touchdown the ground effect will increase and you can bleed power down to land. At this point ground effect dissipates, the angle of attack can increase until the plane stalls just as the wheels touch the runway. Over-controlling, while in ground effect, can result in dangerous ballooning.

Angle of Attack and the fine tuning of air mass forces pushed down that is slightly greater than the force of gravity (planes weight) is the secret to ground effect dissipation. No gross movements of the controls.