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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 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 derivades
use big horizontal stabilizers.
Longitudinal
stability
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
margings ). 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 CE moves
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,
because he flares always in ground effect.
Inherent
on the wing geometry the reversed delta wing is less
affected, so the have only small horizontal stabilizers.
The square wing is more affected, so Ekranoplans and
derivades use big horizontal stabilizers.
For
more information on this issue go to the
WIG-page |
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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
).
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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.
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