ACV aerodynamic aerodynamics air air-cushion air-cushion-vehicle air-pressure amphibious craft cushion drive engines fans flexible flexible-skirt flight friction high-air-pressure hovercraft hull hybrid-vessel impeller inflated inflated-skirt low-frictional-force MTV multi-terrain-vehicle multiple-terrain on-board pilot propel propellers rise sightseeing skirt skirted specialised-transport speed stationary surface surfaces thrust tourism tourists transport transporting travel travelling vehicle