QUESTION #156

Is it easier for an airplane to travel East to West or West to East?

Asked by: Andy McGlen

Answer

The ease with which an airplane may travel east or west depends on your definition of 'ease'. In all cases, the key is the direction of the airplane relative to the wind.

In terms of safety, both scenarios are equally safe during normal flight at cruising altitude. It is safer to land and takeoff, however, into the wind - more lift is provided at a given ground speed, which is advantageous for the relatively low ground speeds at which planes take off and land.

In terms of time and expense of travel at a given air speed, it is clearly advantageous to travel with the wind, since airplanes expend energy pushing backwards against the air through which they are flying but progress towards their destination is measured relative to the ground. An airplane with an airspeed of 550 mph traveling in a 100 mph tailwind is traveling 650 mph relative to the ground, allowing it to reach its destination more economically. Conversely, traveling into a headwind at a given airspeed is more expensive. It also takes more time at a given airspeed (there is a maximum airspeed determined by law and/or air traffic controllers that may not be exceeded on commercial flights).

The prevailing winds are from west to east for most locations in the United States. Therefore, it is more economical to fly to the east, taking advantage of the prevailing tail winds, for a cheaper and faster flight over a given distance.

By the way - Since the earth rotates about 1000 mph near the equator and about 700 mph at 45 degrees latitude, from west to east, it may be tempting to think that this affects the relative ease with which the plane may travel in a particular direction. However, the airplane has inertia, one interpretation of which means the airplane assumes the earth's frame of reference, moving right along with the earth's surface, and does not gain any advantage from this motion in travel to another point within this same frame of reference. However, rockets being launched into orbit AROUND the earth do gain an energetic advantage from this rotation, and are therefore launched towards the east almost without exception. Have you ever noticed that the space shuttle always curves out over the Atlantic, to the east, shortly after its initially vertical take-off?
Answered by: Tyler Gruber, Ph.D. Adjunct Professor of Physics, Louisiana Tech U.