Aerodynamic Principles
Out-of-Control Flight
BODY AXIS SYSTEM
Those points about which the aircraft will rotate (Figure 5).
VERTICAL
AXIS
LATERAL
AXIS
LONGITUDINAL
AXIS
Pitching Moment (IY)
CENTER OF
GRAVITY
Yawing Moment
Rolling Moment
(I Z)
(IX)
Figure 5: BODY AXIS SYSTEM
MOMENT OF INERTIA
With respect to any given axis, the moment of inertia is a measure of the resistance of a body to angular
EFFECTS OF MASS DISTRIBUTION
Mass distribution defines the way in which the mass of an aircraft is distributed between the fuselage and the
wings. Because aircraft are “flattened” into the XY plane, the maximum moment of inertia is invariably
around the yaw, or Z, axis (Iz). Depending on the aircraft’s mass distribution, Ix is greater or less than Iy, as
illustrated in Figure 6. Mass distribution is usually expressed in terms of the inertia yawing moment param-
eter (IYMP):
Ix - Iy
IYMP =
Mb2
Where: Ix and Iy = Moments of inertia around the indicated axis
M = Mass of the aircraft
b = Wingspan
(9-98) Original
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