The stall and the angle-of-attack limit

A stall is a flow-separation condition

A wing can stall at many speeds and attitudes when its critical angle of attack is exceeded.

What is lost at the peak

Increasing α initially increases CL. Near the maximum, separation becomes extensive enough that further α no longer gives the required increase and lift can decrease while drag rises. Buffet, warning and roll-off characteristics depend on design.

Critical α is not a universal number. Configuration, contamination, Mach, Reynolds number and three-dimensional effects influence the onset and warning characteristics.

Recovery must reduce α

Reducing α is the essential aerodynamic action for recovering from a stall. Thrust, attitude, roll and configuration actions follow the approved aircraft recovery procedure and circumstances.

Adding power alone does not guarantee recovery if the wing stays beyond its critical α. A nose-down input and the resulting height loss can be necessary to regain attached-flow control.

Identify the missing response in a failed recovery

Suppose a pilot adds thrust after the stall warning and subsequent loss of lift, but continues to increase the aft control input to prevent any height loss. The added energy does not guarantee that the separated wing returns below critical α. In some conditions the extra pitch demand can sustain or worsen the stalled state even while engine indications rise.

The aerodynamic objective is to reduce α sufficiently to regain effective attached-flow lift and control. That may require accepting a temporary loss of height. The aircraft procedure specifies the coordination of pitch, thrust, roll and configuration, including any type-specific limitations or effects of engine position and control law.

Move α past the supplied peak in the laboratory, then try to satisfy a high CL demand by adding more α. The available coefficient falls instead of rising. Bring α back onto the attached branch and find the required intersection if one exists. This visual test explains the need for α reduction without claiming a universal recovery attitude or altitude loss.

Calculate the speed at a stated load

Stall speed is a consequence of required load, density, area and maximum lift coefficient.

Square-root relationships

Vs = √(2nW/(ρSCLmax)). At fixed configuration and density, Vs varies with √weight and √load factor. A 44% weight increase gives a 20% speed increase.

For EAS under an unchanged CLmax, density is absorbed in the speed definition. TAS at the stall increases as density decreases. The displayed laboratory is a simplified EAS proxy unless TAS is explicitly shown.

Margins change during manoeuvres

A coordinated level turn needs increased lift. At 60° bank, n = 2 and stall speed is √2 times the 1 g value. The critical α need not rise to produce this increase in stall speed.

The formula assumes a quasi-steady condition and a stated CLmax. Gusts, rapid control inputs, ice and compressibility can invalidate a simple comparison with one published speed.

Use the speed ratio to infer the load limit

An aeroplane has a 1 g stall EAS of 80 kt in a stated configuration. At 100 kt, the ideal maximum load before reaching the same CLmax is (100/80)² = 1.5625 g. If the pilot demands 2 g at that speed, the coefficient requirement exceeds the supplied capability, even though 100 kt is above the published 1 g stall speed.

At 120 kt the same model gives 2.25 g. That is an aerodynamic bound, not permission to command 2.25 g: structural, thrust, handling and operational restrictions still apply. The lower of the applicable limits determines what can be sustained or commanded safely in the actual aircraft.

Use the inverse relationship to find the speed required for a specified n, then return to the original speed and lower weight. State why the maximum coefficient is unchanged in this comparison while the required coefficient changes. Avoid describing the result as an increase in the wing’s critical α; the speed change is created by the force requirement.

Can you explain and apply the mechanism?

Four original questions. Work from the stated facts, then compare your reasoning with the explanation.