Race around the world

Q: Two identical aircraft leave from the same point along the equator, at the same time, flying the same speed, one heading east, one west. Which plane will arrive at its origin first? Will the rotation of the Earth affect it? What would happen if the jet stream part of the equation is eliminated? Calvin, Maidstone,  Saskatchewan, Canada

A: We've got a couple of effects to consider:  rotational effects of Earth and the jet stream. 

Earth rotation.  The eastward moving aircraft travels faster than the westward one (relative to our solar system) since the eastward plane moves with the Earth's rotation and, therefore, beats the westward plane. 

But we care about which plane gets to the origin point first relative to Earth's motion.  After all, the race judges, who are stationed at the point of origin, are moving through space exactly the same as the jets.  So, as far as the judges are concerned, both aircraft arrive at the same time.  Judges, aircraft and accompanying atmosphere all arrive at the point of origin at the same time.  They all ride the good mother ship, Earth.

Winds aloft over Earth, showing the "westerlies", prevailing in the 30 to 60 latitudes. Courtesy of the University of Illinois, drawing modified by author.

Jet-stream.  The jet stream also turns out to be an inconsequential factor because reader Calvin has the planes flying along the equator.  At the equator, the trade winds die and, consequently, have no great effect.  That region, bane of sailors, is called the "doldrums".  So, once again, the planes return to their point of origin about the same time.

It's a different story at higher or lower latitudes.  Winds at the altitude commercial aircraft fly, are typically 65 mph (105 km/h) but can reach jet-stream speeds of 140 mph (225 km/h) or more.  In both the northern (30N to 60N) and southern (30S to 60S) latitudes, the prevailing winds blow from west to east.  The eastward aircraft's enjoys tail winds while the westward plane battles head winds; the eastward plane wins —  by about 8 hours.  This calculation assumes a constant 65 mph westerly wind along the entire flight path, a Boeing 777 cruise speed of 550 mph (885 km/h) and a distance around Earth of 17,600 miles at 45 degrees latitude. 

Further Reading:

East to west flight times by Doug Jackson, aeorspaceweb.org

Boing stratocruiser flight times by Doug Jackson, aeorspaceweb.org

Trade wind, Wikipedia

Jet stream, University of Illinois at Urbana-Champagne

(Answered May 9, 2006 ; updated Oct. 26, 2007)

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