Aero Chapter 03, High AOA/Stall/Spin
T-45 Aerodynamics Student Workbook
HIGH-LIFT DEVICES
Any device that increases the CLor area of the wing is a high-lift device. The desired result is to reduce
the takeoff and landing speeds.
Increases in CL are achieved by increasing the camber of the airfoil, or by controlling the boundary layer’s
kinetic energy. The main contributors to increasing CL generally are flaps (Figure 51) and slats
(Figure 52).
CL
AOA in Degrees
Figure 51: EFFECT OF FLAPS
Figure 52: SLATS
Boundary layer control, whether from the engine’s bleed air or from slots in the high-lift devices, adds
kinetic energy to the boundary layer, increasing the CL and permitting the aircraft to fly slower.
The T-45 has double-slotted flaps and slotted slats that increase CL. The flaps increase the camber of the
wing while the double slots add energy to the air over the flaps. When extended, the T-45’s slats increase
the thickness and radius of the leading edge and open a slot for high-pressure air to energize the lower
pressure boundary layer over the top of the wing. The flaps’ downward transit opens the double slots
allowing high-pressure air from the underside of the wing to pass through the slots and energize the
boundary layer of the flap.
STABILATOR
The stabilator is a moveable control surface that replaces the horizontal stabilizer and elevators. The
T-45’s stabilator has 10 degrees of anhedral (negative dihedral) which makes it more effective over the
aircraft’s speed range.
VORTEX GENERATORS
The T-45 wing has vortex generators on the upper
surface. They were added, primarily, to correct
performance problems in the transonic flight
regime. At some airspeeds, wing downwash was
found to be interfering with the stabilator. The
addition of vortex generators greatly reduced the
problem. A beneficial by-product, due to
reenergizing the wing boundary layer, is that slow
speed performance was also improved. Boundary
layer separation was retarded. The result is a
reduction in the aircraft’s slow speed stall onset and
a lowering of the minimum slow-flight airspeed.
Figure 53: VORTEX GENERATORS
The vortex generators are shown in Figure 53.
(7-99) Original
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