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