Angle of Attack

Because of an airfoil’s shape, it will generate (make) lift as it moves through the air. To generate even more lift, we can change the wing’s angle of attack. Angle of attack is the angle at which the leading edge of the wing meets the oncoming air. By tilting the leading edge up (or increasing the angle of attack), it will change the speed of the airflow. The air flowing over the top of the now upward-tilted wing will flow at an even greater speed than the air moving under the wing. This increases the difference between the air pressure underneath the wing and the air pressure over the wing. This increased difference generates even more lift. As an airplane speeds along the runway during takeoff, the airfoil-shaped wings are generating some lift. Farther along the runway, the pilot pulls the nose of the airplane up. This increases each wing’s angle of attack and causes even more lift to be generated. The airplane rises even more as it lifts off the ground and heads skyward.

However, there can be too much of a good thing! The airfoil’s ability to create lift depends upon the airflow around the wings being smooth. Think of a stream flowing gently around a smoothly rounded rock. The stream changes direction to go around and over the rock, but the flow remains smooth. If the rock were not smoothly rounded, but jagged with a rough surface, the flow would be different. The flow would be rough and choppy. The water might even appear to become jumbled up as it flows by. The same thing happens with the airflow around a wing. If the angle of attack becomes too great, the air stops flowing smoothly around the wing. If this happens, lift stops being generated. We call smooth airflow laminar flow. Choppy and jumbled airflow is called turbulent flow. When the airflow becomes too turbulent the airplane will stall. That means it stops generating lift. When that happens its weight force becomes too strong to keep the airplane up.

So we see how the airfoil shape can generate lift, but if the wing is tilted at an even greater angle of attack, then even more lift will be generated.As long as the airflow around the wing remains smooth (laminar airflow), lift will continue to be generated. If the air flowing around the wings becomes jumbled (turbulent airflow) then the wings will stop making lift.