Page 451 - PPL-engelsk 2025

Principles of flight

The angle of attack has increased.

Note that the lift is now directed forward. This force acts perpendicular to the

relative wind.

The drag is seen to act opposite to the direction of motion.

5.3.5 Airflow around wing profiles

Here, you can see the airflow

around a wing profile.

There is almost no vortex drag.

5.3.5.1 Downwash

You can observe a downward deflection of the airflow. One consequence of the

increased speed of the air over the top of the wing is that the air continues

downward after it passes the trailing edge of the wing. This is called Downwash.

It costs something to change the direction of an airflow! In return, we get lift, but
changing the airflow's direction results in drag.

In our case, thrust equals lift.

5.3.5.2 Wing shape

The profile is asymmetric. Due to the curvature on the upper surface, the air

moves faster there. This creates a low-pressure area and, as seen, a downward

airflow behind the profile.

Two-thirds of the lift is generated by the low-pressure area above the wing.

The remaining third of the lift comes from the lower surface, due to the angle of

attack.

The figure on the next page shows what happens to the airflow when it passes a
wing.

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 451