T-45 Aerodynamics Student Workbook
Aero Chapter 01, General Aerodynamics Review
LONGITUDINAL STABILITY
Static longitudinal stability (stability in pitch)
Pitching Moment
is determined by the relationship between
the aerodynamic center (AC) and the
center of gravity (CG). With the AC aft of
Aerodynamic
the CG, static longitudinal stability is
Center
positive. If CG and AC are collocated,
static longitudinal stability is neutral, and
with the AC forward of CG, static
longitudinal stability is negative (Figure 8).
Load distribution, external stores, fuel, etc.,
Center of
may affect the location of CG. High AOA
Gravity
(stall or approaching stall) and transonic or
supersonic flight will affect the AC.
STABLE
The closer together the AC and CG are
Pitching Moment
located, the weaker the stability but the
greater the controllability. The greater the
separation between AC and CG, the
Aerodynamic
greater the stability but controllability is
Center
reduced. Maneuverability could be
substituted for controllability.
Dynamic longitudinal stability is the time to
recover from pitch displacement. Long-
period oscillations (Phugoid) are easily
Center of
controlled. Short-period or deadbeat
Gravity
oscillations may be impossible to control
and are both undesirable and dangerous.
NEUTRAL
Pilot-induced oscillations can occur when a
pilot attempts to counter an oscillation with
control inputs which are of the wrong
Pitching Moment
magnitude or rate to dampen the
oscillation.
Aerodynamic
Center
Center of
Gravity
UNSTABLE
Figure 8: LONGITUDINAL STABILITY (PITCH)
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(7-99) Original
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