Aero Chapter 03, High AOA/Stall/Spin
T-45 Aerodynamics Student Workbook
TIP STALL EFFECTS
While tip stall is defined as
the stall of the outer portion
of the wing (Figure 47), a
wing does not necessarily
stall everywhere along its
length at the same AOA.
Unstable
Tip stall may cause a loss of
ailerons and reduced control
near stall.
Region of Stall
Tip stall often comes with
Center of Pressure
swept wing design and is
Center of Gravity
undesirable since there
Aerodynamic Center
would be little stall warning,
a serious reduction in lateral
control effectiveness and the
Figure 47: TIP STALL
forward shift of the center of
pressure would contribute to
pitchup. Since impending root stall is primarily signaled by turbulence from the root impacting the
stabilator, the pilot would receive little natural warning if the tips stalled well before the root.
Tip stall causes the center of pressure (CP) on each wing to move in and forward (Figure 47). The
aerodynamic center (AC) consequently moves forward relative to the CG. Should the AC move forward of
the CG, the aircraft could pitch up uncontrollably if the stabilator cannot counter the pitchup. The T-45
does not have sufficient stabilator effectiveness to raise the nose high enough to achieve a total loss of
longitudinal stability at slow speed.
ROOT VERSUS TIP STALL
The aeronautical engineer and flight conditions determine the relationship between the onset of root stall
and tip stall. Ideally the pilot wants control of the aircraft all the way to stall. The aircraft is consequently
more controllable, predictable, and less violent at stall.
The tip is more prone to stall than the root due to the lower camber and shorter chord length at the tip
(Figure 47). The energy level of the boundary layer is also lower at the tip, aggravated by spanwise flow
and leading edge vortexing.
AIRFLOW
Leading Edge
STALL STRIPS
of Main Wing
Stall strips are sharply
angled devices installed on
the wing and slat leading
Slat Leading Edge
Stall Strip
edges near the fuselage.
Stall Strip
The strips on the leading
WUSS Stall Strip
Slat
edge of the wing cause the
root to stall at a lower AOA
by inducing premature
Wing Leading Edge
Slat Leading Edge
boundary layer separation
WING
SS
at high angles of attack in
the landing configuration.
The slat leading edge stall
strips contribute to root stall
Slat Leading Edge
WUSS Stall Strip
at high speed (Figure 48).
Stall Strip
Figure 48: STALL STRIPS
(7-99) Original
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