Does the critical angle of attack change with aircraft weight?

No, the critical angle is determined by the wing's design and remains constant regardless of weight.

How can a pilot avoid exceeding the critical angle of attack?

By monitoring airspeed, aircraft configuration, and avoiding excessive pitch inputs, especially at low speeds.

What is the difference between angle of attack and attitude?

Angle of attack is the angle between the wing chord and airflow; attitude is the aircraft's orientation to the horizon.

Do slats and flaps have the same effect on the critical angle?

No, slats increase the critical angle, while flaps decrease it.

What does exceeding the critical angle of attack cause?

It causes the wing to stall due to loss of lift from airflow separation.

Critical Angle of Attack

Easy4 min readPrinciple of Flight (A)

Moderately Examined

The critical angle of attack is the maximum angle between the chord line of a wing and the relative airflow at which lift is produced. Exceeding this angle causes the airflow to separate from the wing's upper surface, resulting in a stall. The critical angle is a fixed property of the wing's design and does not change with weight or load factor.

In depth

Explanation

What is the Critical Angle of Attack?

The critical angle of attack (often called the stall angle) is the highest angle at which a wing can sustain smooth airflow and generate lift. Beyond this angle, the airflow detaches from the upper surface, and lift drops sharply, causing the wing to stall.

Angle of Attack vs. Attitude

Angle of attack (alpha) is the angle between the chord line of the wing and the direction of the relative airflow. This is different from the aircraft's attitude, which is the angle between the longitudinal axis and the horizon. A high nose attitude does not always mean a high angle of attack, and vice versa.

What Determines the Critical Angle?

The critical angle depends on the wing's shape and design features. Devices like slats can increase the critical angle by improving airflow at high angles, while flaps typically decrease it. The critical angle is not affected by changes in aircraft weight or centre of gravity.

Operational Importance

Pilots must avoid exceeding the critical angle to prevent stalls. Awareness of how configuration changes (like deploying slats or flaps) affect the critical angle is essential for safe flight, especially during takeoff and landing.

CL-Alpha Graph

On a graph of lift coefficient (CL) versus angle of attack, the critical angle is where CL reaches its maximum (CLmax). Beyond this point, further increases in angle of attack cause lift to decrease sharply.

The essentials

Key Points

The critical angle of attack is the maximum angle before stall occurs.

It is defined by wing design, not by aircraft weight or load.

Angle of attack is measured between the chord line and relative airflow.

Attitude and angle of attack are different concepts.

Slats increase, but flaps decrease, the critical angle of attack.

Exceeding the critical angle causes a stall due to flow separation.

Watch out

Common Exam Traps

Confusing attitude (nose-up or down) with angle of attack.

Assuming the critical angle changes with aircraft weight or load factor.

Believing flaps increase the critical angle (they decrease it).

Mixing up angle of incidence (fixed) with angle of attack (variable).

Test yourself

Example Exam Questions

Question 1Easy

What happens when the critical angle of attack is exceeded?

Question 2Medium

Which device increases the critical angle of attack?

Question 3Easy

The critical angle of attack is affected by:

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