Expert: Roberto Gomes - 9/16/2004

Question
Hello sir,
 You recently helped with a Visa/Passport question, I gave you highest marks.
 I have rather an unusual question regarding air travel and weather.
 I've only been on 2 international flights.  Both times from Los Angeles (where I live) to China and back.  As you know, on planes they have that lcd screen in front of you for movies, but also a ongoing "gps" style report of the planes location superimposed on a map.  Both times I've traveled I went to China (once to Beijing and the other to Guongzhou, a great distance apart), the plane TO took a highly curved path over Alaska and into Russian airspace, and down to CHina.  Appx 16 hours.  Both times on the way back the flight path that I could see on the red line was much closer to a straight line, however still slightly curved northwards, but over the ocean the whole way back to LAX. Appx 12 hours.
 Why is this?  It's not just me, I've asked my parents (I'm Chinese) and they say its the same way all the time.  Why not a straight line?  Why the much more, land hugging, north curved path to rather than back?  

 I've asked around for ideas and Ive heard only one.  The earth spins counter-clockwise from an overhead/Norht pole view.  Thus they say the "to" trip is highly curved in order to avoid excessive air turbulence (headwind) caused by the spinning of the earth.  However, I don't buy this, because in physics, we know from Galileo's experiments (and common sense) that if you're on a car, and you toss a ball in the air, the ball goes straight up and down because you and the ball are moving with the car (or open boat, etc.)  Now from an outsider's perspective, of course the ball is moving at an angle.  Now, the earth is spinning sure, but isnt the complete atmosphere being "dragged" along with it?  Thus the plane would not feel any turbulence due to the fact that the plane and the air are both equally in the "frame" effect of the earth's gravitational pull.  Otherwise every building, tree, mountain would be sheared away from winds blowing at close to a thousand miles an hour.
  What am I missing here?
 I have myself thought of something else.  On the LCD screen, the world map is of cousre 2 dimensional.  But the earth is not.  Thus a slighty curved path on the LCD is in actuality a straight line on the planet's surface area.  Thus the ride home that shows as a slight curve really is a straight line. Is this true?



Thank you for reading this long email.
Tim  

Answer
Dear Tim,

Most airlines would endeavor to use the shortest routes between 2 points.   These are naned Great Circle routes and appear curved on the map in the TV screens on board most modern airliners today.

Airlines will endeavor to fly the nearest air route to save cost, a straight line like how a crow will fly, so to speak.  Transcontinental flights are never curved but appears to be so on maps found on the Cabin TV screens or magazines because all the maps you see are not the real representation of the globe.  A real and correct representation between two points is the air routes found on a globe map.  The next time you see a curve route, tell yourself that it is actually a distorted representation only - it is in fact the shortest possible air route flown!  Of course, some routes are slightly curved due to the nature of the routes, mainly because it was designed to avoid or take advantage of strong jet streams, especially those air routes across the Atlantic Ocean.
 
Your description of the journey from LA to China appears to be normal because, the airline was attempting to fly a Great Circle route, which is the nearest route between two destinations on the earth.  It would be uneconomical to deliberately fly a longer route.
 
Do you know that when you first did Geography in school, many people were not aware that the basic world map was a distorted representation of the earth's surface.  Only those countries around the Equatorial regions are truly represented by its size. Those nearer to the poles are highly magnified.  The basic world map is similar to a ball being stretched so that its shape is made to fit into a piece of paper.  The most accurate map is in fact the map on a globe.

The shortest distance between LAX and Asia is in fact a straight line between these two cities.  So if you place a string on a globe between LAX and Taipe for example, you would see that the shortest distance is in fact the one that head further north and then south to LAX.  Because the map you so often used or see is in fact a distorted map, the shortest route now appears like a curve on the map in the airline magazine.

Regards,
R. Gomes