Hovercraft Design and Construction
How it works
When the hovercraft is parallel to the surface the flexible keel distributes all lift air evenly between both sides of the air cushion, so that air pressure is the same in both chambers (P2 = P3). But when the hovercraft is inclined to the surface the flexible keel directs most of the lift air to the fallen side and since there is practically no possible escape of the air under this fallen side the air pressure in this chamber is the same as the maximum system pressure (P1). At the same time the flexible keel has closed almost all air passage to the other, risen side, which for the very fact of being risen is open to the outer, atmospheric pressure. Since there is practically no air flow to that risen side the air pressure in this chamber is almost equal to the atmospheric pressure (P3). This way a very impressive pressure differential effect is obtained between both chambers of the air cushion.
The result is a very impressive pressure differential effect between both chambers of the air cushion, thus creating a very high righting moment and at the same time limiting the escape of air under the risen side and therefore limiting the total power required for lift.