Aerodynamic Principles

Out-of-Control Flight

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)

With respect to any given axis, the moment of inertia is a measure of the resistance of a body to angular

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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