Page 490 - PPL-engelsk 2025

Principles of flight

The aircraft heel at the same angle, but as can be seen, the angle of attack on
the wing from the airflow under the right wing is somewhat greater in the low-

winged aircraft.

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5.7.5 Directional-stability - stability around the vertical axis

Directional stability, the aircraft's ability to maintain a certain direction and

return to it after a disturbance, is achieved by having the lateral center located

behind the center of gravity. This can also be achieved by giving the wings an
arrow shape.

There is a strong correlation between directional stability and lateral stability.

Roll causes a turn if not corrected. If the aircraft is not lateral stable, it cannot
be directional stable either.

The drawing on the next page shows a situation where the aircraft is turning to
the left in relation to the direction of flight. This gives much greater air resistance

on the right wing than on the left wing.

The larger the lateral area behind the center of gravity, the greater the

directional stability.

For extra positive stability, in addition to that from the side of the aircraft body,
a vertical fin and rudder of suitable size are mounted.

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 490