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Principles of flight

5.3.2 Drag

When an aircraft moves through the air, it is affected by different forms of drag:

- Profile drag

- Form drag
- Friction drag / surface drag

- Induced drag

- Interference drag

All forms of drag are important for the aircraft's performance, and we will cover
them all in this section.

5.3.2.1 Profile drag

Profile drag can be divided into 2 parts:

- Form drag

- Friction drag / surface drag

A significant part of drag is caused by vortex drag / turbulent air.

5.3.2.2 Form drag

Form drag, as the name suggests, is related to the shape of the object. Form drag
is important because aircraft and wings are designed based on how much form

drag is desired.

Here are two objects with

different form drag.

On the left, an object with high form drag and, as a result, a large vortex drag.

On the right, an object with low form drag and, consequently, a small vortex

drag. As you can see, this resembles a wing.

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 448