Game Development Reference
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Figure 9-2. Simple hovercraft model
We're assuming this hovercraft operates over smooth land and is fitted with a single
airscrew propeller, located toward the aft end of the craft, that provides forward thrust.
For controllability, the craft is fitted with two bow thrusters, one to port and the other
to starboard. These bow thrusters are used to steer the hovercraft.
We use a simplified drag model where the only drag component is due to aerodynamic
drag on the entire craft with a constant projected area. This model is similar to the one
used in Chapter 8 for particle drag. A more rigorous model would consider the actual
projected area of the craft as a function of the direction of relative velocity, as in the
flight simulator example discussed in Chapter 15 , as well as the frictional drag between
the bottom of the craft's skirt and the ground. We also assume that the center of drag—
the point through which we can assume the drag force vector is applied—is located some
distance aft of the center of gravity so as to give a little directional stability (that is, to
counteract rotation). This serves the same function as the vertical tail fins on aircraft.
Again, a more rigorous model would include the effects of rotation on aerodynamic
drag, but we ignore that here.
In code, the first thing you need to do to represent this vehicle is define a rigid-body
class that contains all of the information you'll need to track it and calculate the forces
 
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