A drift or drift (Dutch: drijven = drift) refers to a lateral displacement (drifting) of watercraft or aircraft, i.e. a deviation from the intended course . It always includes the influence of the wind , in seafaring also the current.
The drift angle s is understood as the angle between the longitudinal axis or course angle and the direction of movement. The sign is defined opposite to the lateral velocity component:
( = Lateral speed, = longitudinal speed)
Aircraft drift is caused by cross winds and gusts.
With gliders and slow powered aircraft, the drift in strong crosswinds can be 30 ° and more. Because of the clarity of the effect, the course can be corrected with open eyes - even without navigation instruments - by "holding in front". The short-term effect of gusts can be "leveled out" with the turn indicator.
A distinction is made between ships :
- Drift through cross winds and swell
- Drift due to currents (ocean currents or tidal currents), including current displacement
Wind drift and current drift add up.
In ships, a large lateral surface counteracts the drift caused by cross winds and swell. On sailing ships , the greatest drift occurs when heading close to the wind . With a course half wind the drift is already significantly less, with a brisk wind course there is hardly any more.
Correction of the drift
In the case of larger aircraft and ships, the drift is generally calculated in advance from weather data and taken into account in advance when choosing the heading (lead angle ). This ensures that the course over ground leads approximately to the desired destination. In the case of ships, the current must also be taken into account.
The drift can be critical when landing small and large aircraft: in order to avoid damage to the landing gear , in strong crosswinds or gusts, the heading is only aligned parallel to the runway just before touchdown.
- Jeppesen Sanderson - Privat Pilot Manual 2001, ISBN 0-88487-238-6
- Walter Air: CVFR textbook , Mariensiel 2001
- Luftfahrt-Bundesamt (D) - FSM, Flight Safety Messages 2/86, Flight Operations Course , Braunschweig December 16, 1986
- Wolfgang Kühr: The private aircraft pilot , flight navigation , Verlag Friedrich Schiffmann, Bergisch Gladbach 1979, ISBN 3-921270-05-7