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Principles of flight

5.4.4.4 Use of slots and flaps

There is a concept called “aircraft configuration”. This refers to the status of the

aircraft with regard to flaps, slats, and undercarriage.

An aircraft is “clean” when none of these are in use.

The figure here shows the

dependence of lift on the angle of
attack for a clean wing, a wing with

lowered flaps, and a wing with open
slots.

Distance A is the increase in lift that
is obtained by using flaps.

Distance B is the increase in the critical angle of attack by opening slots.

Earlier you could read that with flaps, stall occurs at a lower angle of attack.

Stall with slots occurs at a higher angle of attack.

The use of slots reduces the formation of turbulent airflow along the wing at

high angles of attack.

The figures here show the principle.

The wing at the top has a leading edge slot

and the airflow is restored.

The wing at the bottom has closed slot and is

stalled.

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Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 475