Game Development Reference
In-Depth Information
The condition for pitch stability can be expressed mathematically. For pitch stability, the
derivative of pitching moment coefficient with respect to angle of attack for an airplane must
be negative. This situation corresponds to the moment curve having a negative slope.
dC
d
MCG
,
<
0
(10.40)
α
Stability and Trim
Ideally, an airplane should be stable, and it should be able to be trimmed. The condition for
pitch stability is given by equation (10.40). Whether an airplane can be trimmed can also be
determined by looking at the moment coefficient versus angle of attack curve. For trim to occur,
there must be an angle of attack at which the moment coefficient about the center of gravity is
zero. The moment coefficient when angle of attack is zero is designated as C MO . Depending on
the value of C MO and the slope of the moment coefficient curve, there are four different stability
trim outcomes, and they are summarized in Equation (10.41).
dC
d
(10.41a)
If
MCG
,
and
C
>
0
airplane is stable and trimmable.
<
0
M
0
α
dC
If
MCG
,
and
airplane is unstable and untrimmable.
(10.41b)
>
0
C
>
0
M
0
dC
d
MCG
,
(10.41c)
If
<
0
and
C
<
0
airplane is stable but untrimmable.
M
0
α
dC
d
(10.41d)
If
MCG
,
and
C
<
0
airplane is trimmable but unstable.
>
0
M
0
α
The four expressions from Equation (10.41) are shown graphically in Figure 10-31. Remember
that for stability, the moment coefficient line has to have a negative slope, and for an airplane
to trim, there must be an angle of attack where C M.CG = 0.
 
Search WWH ::




Custom Search