Ekranoplan Vs Lippisch
In sharp contrast with the design of the Lippisch reverse delta wing planform, the Ekranoplan type ground effect vessels are all square planform vessels. Changes to the fore and aft pitch of this type of ground effect crafts is damped at the trailing edge, through the air under the wing's resistance to further compression between the craft and the water surface. In the case of the Ekranoplan square planform design, this line of "compressive stability" runs across the craft in a straight line, and puts a critical stability control point into the fore and aft moment. This must be carefully controlled by the trail plane and elevator, much like flying balanced on a see-saw.
The situation in a Lippisch's reverse delta wing planform is quite different. The trailing edges of both wings extend from the rear of the craft and pass the craft's center of gravity to the front. The critical stability line is not across the craft but at a tangent to it. This makes the fore and aft pitch stability much more forgiving. This in turn reduces the pilot skill demands, and also allows stretching the overall performance envelope to include kinetic jumps. Not so with the Ekranoplan square planform.
The highest efficiency on record for a square planform, power assisted ram vessel is around 10 kg/kw. For a Lippisch reverse delta planform this figure is as high as 20 kg/kw. But more importantly from an operational point of view, the most efficient surface clearance height of square planforms are around only 10% of the wing span or less. On the contrary, a Lippisch type ground effect craft has surface clearance of up to 50% of the wing span. These performance limitations will always relegate the Ekranoplan type vessels to sheltered waters and rivers.