Behavioral Animation - Computer Animation: Algorithms and Techniques - page 349

Roll

Pitch

Ya w

FIGURE 11.8
Roll, pitch, and yaw of local coordinate system.

Lift

Thrust Drag

Gravity

FIGURE 11.9
Forces of flight.

lift

drag

relative
wind

angle of attack

FIGURE 11.10
Lift produced by an airfoil.

forward and is produced by an airplane's engine or the flapping of a bird's wings. Drag is the force
induced by an object traveling through a medium such as air (i.e., wind resistance) and works in
the direction directly against that in which the object is traveling relative to the air. Gravity is the force
that attracts all objects to the earth and is modeled by a constant downward acceleration. Lift is the
upward force created by the wing diverting air downward. During flight, the airfoil's shape and ori-
entation is such that air traveling over it is bent. A reaction to the change of momentum of the air
is the lift ( Figure 11.10 ) . At higher angles of attack the downward velocity of the diverted air is greater.
For straight and level flight, lift cancels gravity and thrust equals drag.