Page 456 - PPL-engelsk 2025

Principles of flight

The red arrows show the separation point, where the air can no longer follow the

curvature of the profile because the angle of attack becomes too high.

As the angle of attack increases, the separation point moves forward along the

wing, and eventually, the wing stalls, meaning it loses its lift.

5.3.6.3 Lift, speed, area

Doubling the wing area doubles the lift.

Doubling the speed quadruples the lift.

The same applies to drag.

The wing encounters twice as many
molecules moving at twice the speed.

If the angle of attack is not reduced, it will result in an increase in climb rate.

5.3.6.4 The critical angle of attack

As the angle of attack increases, lift also increases. If you, for example, double the

angle of attack, the lift will also double (assuming speed remains unchanged).

However, this only applies to angles of attack under about 12 degrees. See the

figure on the next page.

Many wing profiles generate lift at negative angles of attack. Lift increases almost
proportionally with an increase in angle of attack, up until the maximum lift is

reached.

Further increases in the angle of attack cause the wing to stall.

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 456