Headwind
Air movements or winds that are directed against the direction of movement of an object are referred to as headwinds . An apparent headwind arises as a headwind even when the air is still due to the movement of the object itself. In a figurative sense, headwind also means efforts with different goals that are directed against one's own will.
meaning
Headwind is rather disadvantageous for means of transport because it reduces the speed of travel due to air resistance . Sailing ships also use the countercurrent of the air for propulsion.
There is a special situation with aircraft. In flight headwind is a hindrance, since it the actual ground speed (Engl. Groundspeed , GS ) reduces - the travel time is thus increased. Here, the modified true airspeed (Engl. True airspeed , TAS ) not.
When taking off and landing, however, a headwind is helpful: the take-off and landing roll distance is shortened; because the aircraft already has a little lift when it is stationary. This is why take-offs and landings always take place against the wind whenever airfield operations permit. From 5 knots (≈ 9 km / h) tailwind, the take-off / landing direction on the runways is usually changed.
Tailwind, on the other hand, is useful when cruising, but is a hindrance during take-offs and landings: take-off and landing taxiways are lengthened because the aircraft must take off or land at a higher ground speed .
Mathematical description
The drag force increases with the square of the relative speed through the surrounding air. A cyclist cycling at 20 km / h when there is no wind has to overcome four times the air resistance as a cyclist cycling at 10 km / h.
With increasing speed, air resistance quickly becomes higher than rolling resistance .
In modern aviation , the likely headwind and crosswind are calculated from the relative position of the flight route to the high and low pressure areas encountered en route - see Minimum Time Route and Single Heading Flight . This allows fuel consumption and drift to be taken into account.
The wind conditions are ultimately the reason why the crews do not calculate the fuel requirement according to the route, but according to the estimated flight time.
