Game Development Reference
In-Depth Information
Basic Force Diagram
As shown in Figure 10-3, four basic forces act upon an airplane. Thrust generated by the
airplane engine propels the aircraft forward. Aerodynamic drag resists the forward motion of
the aircraft and acts in the opposite direction to the velocity vector of the aircraft. When air
flows over the wing and other surfaces of the airplane, it generates lift that overcomes the
gravitational force pulling the airplane towards the earth.
Lift
Drag
Thrust
Gravity
Figure 10-3. Basic force diagram for an airplane
A comparison of Figure 10-3 to the boat force schematic in Chapter 9, Figure 9-3, shows
that the two figures are very similar. In fact, the buoyancy force that causes a boat to float is a
type of lifting force. Let's explore the forces on an airplane in more detail starting with a discussion
of aerodynamic lift.
Lift
Airplanes fly because the wing and other surfaces of the airplane generate a force called lift .
Most of the lift is generated by the wing surface, so we will focus on wing lift in this section, but
the general concepts apply to other surfaces (the tail and fuselage primarily) that can also
generate lift. Lift is generated when air flows over the wing, so the shape of the wing plays a crit-
ical part in lift generation. To start the discussion of lift, let's talk about the shape of a wing.
Airfoils
An airfoil is the cross-section of a surface, such as a wing, that is shaped to generate lift. A typical
airfoil is shown in Figure 10-4. The front edge of the airfoil is called the leading edge . The back
edge is called the trailing edge . In Figure 10-4, the airfoil is traveling from right to left. The
chord line is a straight line drawn from the leading edge to the trailing edge. Airfoils don't have
to be symmetric. The curvature of the top surface of the airfoil can be different from the curvature
on the bottom surface. The camber line is defined such that there is an equal airfoil thickness
above and below the camber line. For a symmetric airfoil, the camber would be the same as the
chord line.
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