Tailwinds and supersonic flight
In 2015, a 777-200 made the Newyork-London route in 5 hours,16 minutes where the usual journey time is ~7 hours.
The flight reached ground speeds of up to 1200 km/h (745 mph),
riding a powerful jet stream of up to 322 km/h (200 mph) tailwinds and breaking the sonic barrier ( 1224 km/h (761 mph)).
Tail and headwinds
The principle is analogous to those high school problems in relative velocity:
“A man rows a boat in a river. The velocity of the
boat is … Find the stream velocity”
If you are headed downstream i.e in the same direction as the river stream you will reach your destination faster than if you were rowing upstream.
Similarly a tailwind is one that blows along the same direction of the aircraft increasing the net speed of the aircraft ,and headwind is one that blows in the opposite direction and slows the craft down.
So, does this mean that if you are moving at v kmph and there is a headwind of -v kmph, you would just hover? Hell yeah!
Take a look at this video:
A phenomenon known as ‘wind shear’ occurs when the wind speed changes abruptly, which can cause turbulence and rapid increase/decrease in velocity of flight.
This can be really challenging during landing since if the headwind turns tailwind, there is a possibility of the aircraft overshooting the runway due to the increased velocity.
What causes this ?
The aviation industry takes advantage of trade winds and jet streams in order to cut time off the flight and save fuel.
Tradewinds are caused by the unequal heating of the atmosphere
at different latitudes and altitudes and by the effects of the Earth’s
rotation (Coriolis effect).
Trade wind pattern. Credit: Earth Wind Map
Jet streams on the other hand are this narrow current of fast moving
winds in the upper troposphere flowing west to east. And riding one can
definitely make your travel time shorter.
Jet streams in the northern hemisphere
As a result of jet streams, within North America the time needed to fly east across the continent can be decreased by about 30 minutes if an airplane can fly with the jet stream, or increased by more than that amount if it must fly west against it.
How do pilots know about this ?
Pilots receive a weather briefing actively during flight. Included in the briefing is the best combination of jetstreams and other wind patterns that the pilot can take advantage of saving time and fuel.
Many airports have runways facing in different directions in order to allow the pilots to use the runway that faces the wind during take off/landing.
Have a great day!