What is ground effect and how does it affect aircraft performance?

Ground effect occurs when aircraft fly within approximately one wingspan of the ground, where the surface restricts downwash and reduces induced drag. The reduction can be 40-50% when very close to the ground. Effects include: increased lift at same AOA, reduced induced drag, changed pitching moment, and potential cushioning during landing. Wing-in-ground (WIG) vehicles exploit this for efficiency. Pilots must understand that leaving ground effect requires more power/higher AOA, and entering it during landing can cause floating. Ground effect is modeled using image vortex systems.