Vertical Takeoff and Landing Aircraft, Vertical Takeoff and Landing Ground Effects

<div>The ground-effect problems of loss of thrust and <i>fountain-effect</i> instabilities are quantified. Experiments to control and augment ground-effect lift and stability are presented, including jet <i>momentum reflection</i> and fountain redirection using various types of internal and external underbody ventral strakes. By strategically designing the vertical takeoff and landing (VTOL) ventral surface, reflection of the impinging fountain momentum is possible so that instead of losing 10% thrust while in ground-effect, remarkably, thrust is augmented 10% or more to a considerable height above the ground, in addition to stabilizing random pitch and roll moments caused by fountain instability.</div>