Game Development Reference
In-Depth Information
Lift
c.g.
mg
Figure 10-27.
Lift from the wing generates a moment about the c.g. of the airplane.
Figure 10-28.
A counterbalancing moment is generated by the horizontal stabilizer.
If the distance between the wing lift force,
F
Lw
, and the c.g. is equal to
d
w
, and the distance
from the horizontal stabilizer lift force,
F
Lt
, and the c.g. is equal to
d
t
, then the condition for
zero moment about the center of gravity is when the magnitudes of the two moments are equal.
M
==
0
F d
−
F
d
(10.39)
cg
Lt
t
Lw
w
An airplane is said to be
trimmed
if there is no moment about its center of gravity. The
angle of attack at which trim occurs is called the
trim angle of attack
.
In Figures 10-27 and 10-28, the center of gravity of the airplane is behind the center of
pressure of the wing. For many airplanes, large jetliners for instance, the center of gravity will
be in front of the center of pressure of the wing. In this case, as shown in Figure 10-29, the
moment caused by the wing lift will pitch the nose of the airplane downwards. To counteract
this moment, the tail must produce negative lift. This can be accomplished by either orienting
the horizontal stabilizer at a negative angle of attack or by using an upside-down cambered
airfoil for the horizontal stabilizer.
Lift
c.g.
Lift
mg
Figure 10-29.
To create the proper counterbalancing moment, sometimes the horizontal stabilizer
lift must be negative.
