TOPICS
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Short theory
A wing in ground effect produces about double the amount of up- trust as a wing in free air ( compare the picture ). Because of this an WIG-craft of comparable size as an aircraft can almost transport double the weight on freight or passengers.
Longitudinal stability
The lift distribution around a wing in flight looks like this.
Green = maximum suction upper surface
Red = maximum pressure lower surface.
Flares = streamlines disturbed ( = drag ).
Wing in ground effect.
The very high pressure on the lower surface can be
clearly observed. And the much more "clean" air stream
around the wing is also evident.
The center of effort (CE) of a wing and
the center of gravity of the craft have to be in the same plane ( with
some markings ). No matter if it is an aircraft or a WIG-craft. The
pressure distribution around a wing in free flight and a wing in ground
effect are different. Because of this the CE of a wing in free flight
is at about 25 % and on a WIG-wing at about 45 %.
Now when a
WIG-craft is flaring out of ground effect, the moves forward like in an
aircraft and the nose wants to pitches up. To compensate for this, WIG-
craft use big horizontal stabilizers.
For the four main types of crafts the effect is more or less pronounced.
The tandem WIG is not affected.
The reversed delta ( Professor Lippisch designs ) wing is less affected, so the have only small horizontal stabilizers.
The square wing is more affected, so Ekranoplans and derivate use big horizontal stabilizers.
