# Ground Effect

> Changes in aerodynamic characteristics when flying close to the ground.

- **Subject:** 081 — Principles of Flight
- **Section:** 081-01 — Subsonic Aerodynamics
- **Topic code:** 081-01-06
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/principles-of-flight/subsonic-aerodynamics/ground-effect/

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## Mechanism
When within approximately **one wingspan** height of the surface:
*   The ground interferes with the formation of wing tip vortices.
*   The vortices are weaker.
*   Downwash is reduced.
*   The effective Angle of Attack increases.

## Effects
1.  **Reduced Induced Drag**: The clearer lift vector (less backward tilt) means less induced drag.
2.  **Increased Lift**: For a fixed angle of attack, lift increases ($C_L$ increases).
3.  **Pitch Change**: Downwash change alters the airflow over the tailplane, typically causing a nose-down moment (reduction in downwash on tail).
4.  **Local Static Pressure**: Increases below the wing (cushion effect).

## Consequences for Flight
*   **Landing**: The aircraft tends to "float". If speed is not reduced, the aircraft will glide further than expected.
*   **Take-off**: The aircraft may become airborne before reaching the safe climb speed ($V_2$). If it climbs out of ground effect too early, induced drag will suddenly increase, potentially causing it to sink back down.

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