Ground effect is a critical aerodynamic phenomenon experienced during takeoff and landing. It occurs when an aircraft flies within one wingspan length of the ground, causing wingtip vortices to be disrupted and creating a cushion of higher pressure beneath the wings. This effect increases lift and decreases drag, influencing aircraft performance in ways pilots must understand for safe operation, especially during soft-field takeoffs and landings.
What is Ground Effect?
Ground effect happens when an aircraft flies close to the ground, typically within one wingspan, reducing wingtip vortex rotation. This leads to an area of higher pressure under the wing, which provides additional lift and reduces drag. Pilots commonly experience ground effect during takeoffs and landings, often feeling the aircraft “float” before settling or becoming airborne.
Impact on Takeoff and Landing Performance
During soft-field takeoffs, ground effect allows aircraft to become airborne before reaching the usual recommended takeoff speed, thanks to the increase in lift and reduction in drag. Similarly, on landing, ground effect can cause the airplane to float down the runway. Pilots should consider this especially under high-density altitude conditions, where ground effect can offer added performance benefits.
Demonstration of Ground Effect in Flight
A practical demonstration involves performing a soft-field takeoff in a Cessna 173, where the nose wheel is lifted as soon as possible to maintain ground effect. The aircraft accelerates while close to the ground, becoming airborne around 60 mph, earlier than the standard takeoff speed of 70 mph, then climbs out while gradually transitioning out of ground effect.
Aerodynamic Changes When Leaving Ground Effect
As the aircraft leaves ground effect, induced drag increases, and more thrust is required to maintain lift. The airplane may need a higher angle of attack to maintain the same lift coefficient. In soft-field takeoffs, pilots compensate by maintaining a nose-high attitude to stay in ground effect until reaching sufficient speed for a safe climb.
Ground Effect Knowledge Check
Understanding ground effect is essential for pilot proficiency. Questions commonly tested include how lift and induced drag change within ground effect and the aircraft’s thrust requirements upon leaving it. Knowledge of these principles supports safe takeoff and landing procedures, particularly in challenging field conditions.
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