Aero Chapter 03, High AOA/Stall/Spin
T-45 Aerodynamics Student Workbook
AERO CHAPTER 03, HIGH AOA/STALL/SPIN
INTRODUCTION
High-speed carrier aircraft must be adapted to fly the slow approach speeds necessary to land aboard the
carrier. In designing an aircraft, performance trade-offs occur to permit operation at high and low speeds.
The capability to land an aircraft on an aircraft carrier is one of the most demanding of requirements and
often leads to the addition of high lift devices on the high-speed aircraft.
The Navy’s angle of attack system permits the pilot to fly an approach at optimum airspeed in recognition
of the aircraft's weight and configuration. The angle of attack is the angle formed between the relative
wind and the chord line of the airfoil. The Navy has long used AOA to optimize an aircraft’s approach
speed to the aircraft carrier. AOA is more sensitive than the pitot static airspeed determinations at low
speed. At high speed, the reverse is true. AOA outputs can be used to determine approximate airspeeds
for certain functions should the pitot static system ice up or fail. The pocket checklist and NATOPS
contain AOA indications for various aircraft functions.
LIFT-TO-DRAG RATIO (L/D)
L/D is the ratio of lift to drag obtained by dividing the lift by the drag or coefficient of lift by the coefficient of
drag. It is a measure of the wing’s efficiency and also is the power off glide ratio at a given AOA.
LIFT-TO-DRAG RATIO MAXIMUM—(L/D)max
(L/D)max is the greatest ratio of lift to drag. (L/D)max angle of attack is the most efficient AOA for that airfoil.
SWEPT WING
A swept wing has many aerodynamic
Stall Point
+
differences from a straight wing. The
overriding differences and the reason
that swept wings are incorporated in
aircraft designs is to delay the onset of
compressibility effects to higher
speeds and reduce the forces on the
wing caused by compressibility. The
effect of this is to reduce drag and
Stall Develops
improve maneuverability in transonic
Deep Stall
Stall Begins
flight.
The swept wing and straight wing
Straight Wing
aircraft each have their advantages
Swept Wing
and disadvantages. A primary
distinction between the wing designs is
0
+
the aerodynamic stall characteristics.
AOA
Straight wings display abrupt stall
Figure 45: SWEPT WING VS STRAIGHT WING
characteristics and minimal stall
CHARACTERISTICS
warning; whereas swept wings tend to
enter their stall regimes as the stall
develops to the maximum. On a graph of CL versus AOA, the straight wing develops CL on a more vertical
line and stalls quicker. The swept wing increases CL more gradually and stalls at a higher AOA and lower
CL over a greater AOA range (Figure 45).
(7-99) Original
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