PHAK Ch. 5 · study note

Angle of attack, stall & load factor

Chapter 5 moves from “what is lift?” to how the wing is operated: angle of attack, stalls, and how banked turns and pull-ups raise load factor and stall speed. Interactive practice: AOA & Load Factor Lab.

Angle of attack

Angle of attack (AOA) is the angle between the wing’s chord line and the relative wind. It is not pitch attitude relative to the horizon.

Stall = critical AOA

As AOA increases, lift coefficient rises—until the airflow can no longer stay attached over the upper surface. That AOA is the critical angle of attack. Beyond it: separation, large loss of lift, a stall.

PHAK emphasis (knowledge-test and safety critical):

An airplane can stall at any airspeed.
For a given configuration, the wing stalls at the same critical AOA.
Critical AOA does not change just because you bank or change weight—what changes is the speed needed to support the airplane at that AOA under the current load factor.
Airspeed alone is not a complete stall-avoidance parameter (published 1 G stall speeds assume unaccelerated flight).

CL versus AOA curve with critical AOA at the peak, myth that stalls only happen at low airspeed — **Figure 2.** Stall is an AOA event. High speed + high load factor can reach critical AOA just as low speed + 1 G can.

Spins (short)

An uncoordinated stall can develop into a spin: both wings stalled, one more deeply, with autorotation. Recovery knowledge matters even though spin training is not required for the private pilot certificate.

Load factor

Load factor \(n\) is the ratio of the aerodynamic load on the airplane to its weight (often spoken in “Gs”). In straight-and-level unaccelerated flight, \(n = 1\). In a coordinated level turn, lift must both support weight and provide the horizontal force that turns the airplane path:

n = 1 / cos(φ) (φ = bank angle)

Banked airplane with lift and weight vectors; table of load factor versus bank angle — **Figure 3.** Load factor rises slowly at first, then steeply past about 45–50° of bank. A 60° level turn is 2 G.

Stall speed and load factor

To fly at the same critical AOA under a higher load factor, you need more dynamic pressure—so indicated stall speed rises:

V_s = V_s1 × √n

\(V_{s1}\) is the 1 G stall speed in that configuration. At 60° bank (\(n = 2\)): stall speed ≈ \(1.414 × V_{s1}\).

Formula stall speed equals one-G stall times square root of load factor with sixty degree bank example — **Figure 4.** Steep turns and abrupt pull-ups raise the speed at which you can stall—critical AOA is unchanged.

Maneuvering speed (awareness)

Design limit load factors and maneuvering speed (V_A) protect the structure when you make full control inputs. Below V_A, the wing should stall before limit load is exceeded (in the design model). Above V_A, abrupt full deflection can overstress before stall. Weight changes V_A (higher weight → higher V_A in the usual published family of speeds—check your AFM).

Configuration notes

Flaps change camber and the lift/drag curves; published stall speeds and critical AOA depend on configuration.
Ice, frost, damage can reduce max CL and make stalls nastier at lower AOA—keep wings clean.
AOA indicators (if installed) display proximity to critical AOA and help when airspeed is a poor cue.

Practice

Open AOA & Load Factor Lab →

Primary sources

FAA PHAK FAA-H-8083-25C Ch. 5 — stalls, AOA, load factors, turns
MIT OCW 16.687 — AOA definition, stall at any speed, critical AOA

Figures are original educational SVGs, not FAA handbook scans.

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