LESSON 02
Angle of attack & stalls
Angle of attack is the angle between the wing’s chord line and the relative wind. A stall occurs when the wing exceeds its critical angle of attack, causing extensive airflow separation and reduced lift.
Your learning goals
- Define AOA using the chord line and relative wind.
- Explain what changes beyond critical AOA.
- Connect excessive AOA, recovery, and the risk of a spin.
01 / THE ANGLE THAT MATTERS
Meet angle of attack.
Angle of attack (AOA) is the angle between an airfoil’s chord line and the relative wind. The chord line is an imaginary straight line connecting the leading edge to the trailing edge.
Relative wind is the airflow the wing experiences as it moves through the air. Its direction is parallel to and opposite the airfoil’s flight path through the air. If the flight path points forward and upward, for example, the relative-wind direction points backward and downward.
AOA is measured relative to airflow—not the horizon. A nose-high attitude does not automatically mean a high AOA, and an airplane can stall with its nose below the horizon.
FAA · Stall and Spin Awareness, §100(a) · FAA · Relative wind
02 / THE LIMIT
More angle. More lift. Until…
Increasing AOA generally increases lift coefficient up to a maximum. The angle at that peak is the critical angle of attack. Beyond it, extensive airflow separation causes lift coefficient to fall: the wing is stalled. Lift decreases; it does not disappear.
In the model below, the peak is at 18°. This is an illustrative choice, not a universal stall angle. Airfoil shape, configuration, and conditions—including contamination—can change the actual critical AOA.
NASA · Inclination effects on lift · NASA · Icing and handling effects
03 / WHAT CHANGED?
The air stops following the surface.
At high AOA, a large region of airflow separates from the upper surface. The pressure pattern changes, lift coefficient decreases, and drag increases. In the model, smooth paths give way to a detached flow region with swirling, unsteady motion.
Explore deeper · The boundary layer and adverse pressure gradient
The boundary layer is the thin region next to the wing where viscosity slows the airflow. It may be laminar or turbulent. Turbulent flow can remain attached, so turbulence by itself is not the definition of a stall.
Over part of the upper surface, air moves toward increasing pressure—an adverse pressure gradient. The slower air near the surface can lose enough forward momentum that local flow reverses and separates. Increasing AOA can strengthen this challenge and enlarge the separated region.
Some separation can occur before the lift peak. A stall is associated with enough separation to cause the lift coefficient to decrease beyond its maximum. The precise location and progression depend on the airfoil and conditions.
Explore deeper · Why airspeed alone does not define a stall
L = ½ρV²SCL . Lift depends on air density (ρ), true airspeed (V), wing area (S), and lift coefficient (CL). In level flight, slowing down generally requires a higher CL to maintain the required lift. Increasing AOA provides that increase only up to the maximum.
Higher weight or greater positive load factor increases required lift and can raise stall speed. The fundamental trigger is still exceeding critical AOA. A stall can occur at any airspeed or attitude if that angle is exceeded.
The graph uses CL to isolate the AOA relationship. Actual lift also depends on the other quantities; the plotted values are illustrative.
Reducing AOA is essential.
Recovering from a stall requires reducing AOA below the critical angle. Adding power alone does not remove an excessive AOA. In an aircraft, use its approved recovery procedure and the instruction provided by your flight instructor.
LOOKING AHEAD
A stall can develop into a spin.
A stall combined with yaw can develop into a spin. A stall does not automatically cause a spin; uncoordinated flight can set up the uneven wing behavior and rotation.
Spins can be deadly, especially at low altitude where there may not be enough height to recover before impact. Preventing the stall and keeping the airplane coordinated are essential. For further reading, see FAA Stall and Spin Awareness Training, §§107–111. Discuss spin prevention and aircraft-specific limitations with your flight instructor.
AIRFLOW LAB
Find the critical angle.
Lift coefficient vs. angle of attack
CL 0.72At constant airspeed, density, and wing area, lift follows this same trend.
Airflow around the airfoil
Air follows the upper surface. Raising AOA increases lift coefficient in this range.
Illustrative airfoil and flow—not measured airfoil data. Airspeed, density, and geometry stay fixed. Real stall onset and the post-stall curve vary; some stalls are more gradual.
Try crossing the limit.
Increase AOA from 6° toward 18°, then continue to 22°. Watch the curve peak as airflow separates. Bring AOA back below the critical angle to see attached flow return in this simplified model.
CHECK YOUR UNDERSTANDING
Explain it in your own words.
Think through each question before revealing the answer.
Is nose-high attitude the same as high angle of attack?
No. AOA is measured between the chord line and relative wind, not the horizon.
Does a stalled wing stop producing lift?
No. Beyond the critical AOA, extensive separation reduces lift coefficient; lift does not simply disappear.
Is 18° the critical AOA for every airplane?
No. It is the illustrative value in this model. Airfoil, configuration, and conditions matter.
SUMMARY
Stall review
AOA connects the wing to the airflow. Beyond the critical angle, extensive separation reduces lift coefficient. Reducing AOA is essential to recovery; a stall combined with yaw can develop into a spin.
PRACTICE
Flashcards and knowledge check
Review six flashcards, then answer five questions.
Enable JavaScript for flashcards and the knowledge check. The lesson and scenario remain available without it.
Sources & lesson notes
Lesson sources
- FAA — AC 61-67C, Stall and Spin Awareness Training AOA, stall recognition, recovery, and the connection to spins; §§100, 105, 107–109.
- FAA — Aviation Maintenance Technician Handbook General Relative wind and its relationship to an aircraft’s flight path.
- FAA — Maneuvering Flight The danger of fatal stall and spin accidents at low altitude.
- NASA Glenn — Inclination effects on lift Lift curve, separation, and variation in the stall point.
- NASA Glenn — Lift equation How lift coefficient relates to lift force.
- NASA — In-flight icing: handling effects Why contamination can reduce critical AOA.