Game Development Reference
In-Depth Information
Figure 17-3. Hovercraft configurations
This approach proved impractical because hover heights were very limited and made
the clearance between the hard structure of the craft and the ground (or water) too small
to overcome all but the smallest obstacles. The solution to this problem was to fit a
flexible skirt around the craft to contain the air cushion in what's called the plenum
chamber (see Figure 17-3 ). This approach extended the clearance between the ground
and the hard structure of the craft significantly even though the gap between the bottom
of the skirt and the ground was very small. This is the basic configuration of most
hovercraft in operation today, although there are all sorts of skirt designs. Some of these
skirts are simple curtains, while others are sophisticated pressurized bag and finger
arrangements. The end result is that hovercraft fitted with skirts can clear relatively large
obstacles without damage to their hard structure, and the skirt simply distorts and
conforms to the terrain over which the craft operates.
The actual calculation of the aerostatic lift force is fairly complicated because the pres‐
sure distribution within the air cushion is nonuniform and because you must also take
into account the performance of the lift fan system. There are theories available to treat
both the annular jet and plenum chamber configurations, but they are beyond the scope
of this topic. Besides, for a game simulation, what's important is that you realize that the
lift force must equal the weight of the craft in order for it to maintain equilibrium in
hovering flight.
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