Game Development Reference
In-Depth Information
The following simple formula relates the superelevation angle of a roadway to the speed
of the car and the coefficient of friction between the tires and road:
tan φ = V t 2 /(g r) - µ s
Here, φ is the superelevation angle (as shown in Figure 17-2 ), V t is the tangential com‐
ponent of velocity of the car going around the turn, g is the acceleration due to gravity,
r is the radius of the curve, and µ s is the static coefficient of friction between the tires
and the road. If you know φ, r , and µ, then you can calculate the speed at which the car
will begin to slip out of the turn and off the road.
Vehicle dynamics is a complex field, and if you are interested in a highly realistic driving
simulation game, we recommend reading up on the subject. A good starting place is
Fundamentals of Vehicle Dynamics by Thomas Gillespie (Society of Automobile Engi‐
neers).
Hovercraft
Hovercraft, or air cushion vehicles (ACVs), have made their way into a video game or
two recently. Their appeal seems to stem from their futuristic aura, high speed, and
levitating ability, which lets them go anywhere. In real life, hovercraft have been around
since the 1950s and have been used in combat, search and rescue, cargo transport,
ferrying, and recreational roles. They come in all shapes and sizes, but they all pretty
much work the same, with the basic idea of getting the craft off the land or water to
reduce its drag. In Chapter 9 , we touched on what forces you have to model when
considering hovercraft, and now we'll talk about them in more detail.
How Hovercraft Work
The first hovercraft designs pumped air through an annular nozzle around the periphery
of the craft (see Figure 17-3 ). Large fans are used to feed the air through the nozzle under
the craft. This jet of air creates a region of relatively high pressure over the area under‐
neath the craft, which results in a net lifting force. The lifting force must equal the weight
of the craft if it is to attain hovering flight. This sort of lifting is known as aerostatic lift.
The hover height is limited by the amount of power available and the lifting fan's ability
to pump enough air through the nozzle: the higher the hover height, the greater the
power demand.