Although ground-effect machines (GEM) might be described as VTOL aircraft that never quite made it, they are believed to have sufficient potential to warrant at least a chapter. As the name implies, a GEM is limited to operating in proximity to a surface—either a solid surface or over water. By so doing, however, it is able to sustain much greater loads for a given power than an aircraft that operates out of ground effect.
Various types of ground-effect machine have been proposed or studied. They include the air bearing, plenum chamber, and peripheral jet illustrated schematically in Fig. 12-1. Here, only the peripheral jet machine is considered, for it appears to be the most promising configuration. The airbearing type requires a smooth prepared “ road bed,” whereas the plenum chamber type requires more power than the peripheral jet configuration.