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View Full Version : Why does it take longer to fly west to east than east to west?


mayong12002
04-17-2004, 09:44 PM
When flying by plane, east to west flights always take longer than west to east flights. Why?

mayong12002
04-17-2004, 09:48 PM
When flying by plane, east to west flights always take longer than west to east flights. Why?

No text

gazpacho
04-17-2004, 09:49 PM
The jet stream moves from west to east. it is around 100 miles per hour. When going west you have a head wind east has a tail wind.

lektrikpuke
04-17-2004, 09:50 PM
I think it's because the earth, spinning on its axis at approximately 1,000 mph (at the equator) helps in one direction and hinders in the other. It's kind of like having a 1,000 mph headwind or tailwind, depending on your direction of travel. :)

5cents
04-17-2004, 09:51 PM
When flying by plane, east to west flights always take longer than west to east flights. Why?

Headwinds. They change with the season (and the region), too. When you are flying, the plane's speed is its airspeed. Let's say that the airliner you are on is cruising at 450 knots indicated air speed. Assuming a 50 knot headwind, you're travelling 400 knots in relation to the ground. With a 50 knot tailwind you're travelling 500 knots in relation to the ground.

lektrikpuke
04-17-2004, 09:53 PM
Scratch that. Getting to smart for my own good. Forgot that its all relative (as we start out at the same speed). I suppose the air, not being fixed to the ground, would slip a little (be a little slower than the earth) in general. But, other than that, ? :)

Chefguy
04-17-2004, 09:55 PM
You get the same effect flying from Anchorage to Seattle and back. Down is about 3 hours or so, back is usually closer to four because of the prevailing winds.

mayong12002
04-17-2004, 10:15 PM
Thanks for clearing that one up for me! Like most science books written from their ivory towers of academia, always neglecting to factor in wind resistance...

JimMacMillan
04-17-2004, 10:23 PM
The single biggest effect is known as Coriolis Force or the Coriolis Effect. Instead of reciting my own understanding of it from flight school here is a plagiarized explanation.

The Coriolis deflection relates to the motion of the object, the motion of the Earth, and the latitude. For this reason, the magnitude of the effect is given by 2 sin , in which is the velocity of the object, is the angular velocity of the Earth, and is the latitude.

So basically LektrikPuke was close. However Coriolis Force also has a direct effect on our air patterns. Don't ask me to go into the three air cells that sit above and below the equator.

Jim Mac Millan

Quack
04-17-2004, 10:53 PM
I always thought that the primary reason an east-to-west flight was faster was that the Earth was rotating so your western destination was moving toward you and the opposite was true of west-to-east flights. Is it really due more to winds than it is to the rotation?

The Flying Dutchman
04-17-2004, 11:08 PM
The Coriolis effect is mostly* relevant to north-south travel. For example the eastern surface velocity of Anchorage is less than that of Seattle and even less than that of San Diego. So when travelling from Anchorage to Seattle in a southeastern direction, we are getting an assist from the increasing rotational eastern surface velocity. However going back, we have to overcome the initial higher eastern surface velocity of Seattle compared to Anchorage.

If Seattle were directly south of Anchorage, then the Coriolis effect does not apply to the time differential between back and forth flights. The Coriolis effect however does make north south flight times longer than east west (given no other influences) flights for any given surface distance.

Noone Really
04-17-2004, 11:17 PM
gaspacho is correct in that the jetstream is responsible for the head wind and subsequent time differences. The jetstream doesn't exactly flow west to east, rather it swirls around. A nice picture showing the direction of the current jetstream over North America is at the following site:

http://www.weatherimages.org/data/imag192.html

A better site showing more information including wind strength for anywhere in the world can be found at:

http://squall.sfsu.edu/crws/jetstream.html

Hope this helps.

elfbabe
04-17-2004, 11:57 PM
I always thought that the primary reason an east-to-west flight was faster...

It takes longer to fly from JFK to LAX than it takes to fly from LAX to JFK. (Judging by scheduled flight times on American Airlines' 767s, LAX -> JFK is about an hour shorter.) So an east-to-west flight is slower than a west-to-east flight. The title of the thread is t'other way 'round, but the OP corrected it.

MonkeyMensch
04-18-2004, 02:11 AM
Let's say that the airliner you are on is cruising at 450 knots indicated air speed. Assuming a 50 knot headwind, you're travelling 400 knots in relation to the ground. With a 50 knot tailwind you're travelling 500 knots in relation to the ground.

What airliner are you flying in? Nobody, outside of a Concorde, indicates 450k at altitude. Don't confuse indicated airspeed with true airspeed.

That said, Coriolis forces don't enter into consideration with respect east-west flights re the OP. And gazpacho and 5cents have pegged it: It's prevailing Westerlies.

David Simmons
04-18-2004, 02:25 AM
I always thought that the primary reason an east-to-west flight was faster was that the Earth was rotating so your western destination was moving toward you and the opposite was true of west-to-east flights. Is it really due more to winds than it is to the rotation?

It takes less clock time to go from New York to Los Angeles than vice versa. When you leave New York at noon it is only 9:00 am in Los Angeles. The flight is about 5-1/2 hrs. so you arrive in LA by the clock at 2:30 pm. An elapsed clock time of 2-1/2 hrs. Going the other way noon in LA is 3:00 pm in NY, add 5 hrs for the flight and you arrive in NY at 8:00 pm for an elapsed clock time of 8 hrs.

However the rotation of the earth has nothing to do with the actual flight time except that the rotation causes the prevailing winds to be generally westerly. Others have pointed out that you have tail winds going east and head winds going west. Simple.

Coriolis effect is only a factor insofar as it affects wind direction.

Tokyo_Mann
04-18-2004, 02:43 AM
I always thought that the primary reason an east-to-west flight was faster was that the Earth was rotating so your western destination was moving toward you and the opposite was true of west-to-east flights. Is it really due more to winds than it is to the rotation?Think of flying in a hot air balloon. Once you leave the earth, the “resting point” is the speed and direction of the wind. If the air were moving exactly west-east at speeds which matched the rotation of the earth, (which means that the air would have to move faster at higher altitudes) then the balloon would float above the point where it was released. As David Simmons and others explain, the reason is the winds.

Chefguy
04-18-2004, 10:23 AM
The Coriolis effect is mostly* relevant to north-south travel. For example the eastern surface velocity of Anchorage is less than that of Seattle and even less than that of San Diego. So when travelling from Anchorage to Seattle in a southeastern direction, we are getting an assist from the increasing rotational eastern surface velocity. However going back, we have to overcome the initial higher eastern surface velocity of Seattle compared to Anchorage.

If Seattle were directly south of Anchorage, then the Coriolis effect does not apply to the time differential between back and forth flights. The Coriolis effect however does make north south flight times longer than east west (given no other influences) flights for any given surface distance.

Wouldn't this mean that the flight would always take longer? Because that's not always the case. What magnitude of delay is caused by coriolis?

David Simmons
04-18-2004, 10:53 AM
The Coriolis effect is mostly* relevant to north-south travel. For example the eastern surface velocity of Anchorage is less than that of Seattle and even less than that of San Diego. So when travelling from Anchorage to Seattle in a southeastern direction, we are getting an assist from the increasing rotational eastern surface velocity. However going back, we have to overcome the initial higher eastern surface velocity of Seattle compared to Anchorage.

Wouldn't this mean that the flight would always take longer? Because that's not always the case. What magnitude of delay is caused by coriolis?

Hmmmm. I'm not so sure about grienspace's claim. On a calm day the atmosphere above Anchorage is turning at the same velocity as Anchorage and that above Seattle is turning at the same rate as Seattle. So an airplane traveling from Anchorage to Seattle is constantly flying into an increasing crosswind from its right which boosts it along.

I know of no air navigation scheme that asks the pilot to account for Coriolis effect. When you determine your present location by visual means, or by GPS or any method you compute your heading to the next check point only by taking account of your true airspeed and the local wind, if known, and the magnetic variation (I guess it's called deviation now) in your area.

Chronos
04-18-2004, 02:14 PM
I suppose the air, not being fixed to the ground, would slip a little (be a little slower than the earth) in general.Nope. No "slippage" at all. What would cause the air to slip? Contrary to popular belief, there is no tendancy in the Universe for objects to be at rest rather than moving. If you have some sort of frictional force, then there is a tendancy for objects to be at rest relative to each other, but this is exactly what's causing the atmosphere to not slip relative to the Earth.

And Coriolis forces on the plane directly probably don't make much difference, but it's the Coriolis forces which cause the jetstream to go in the direction it does, and the jetstream (or other wind patterns, also determined by Coriolis) does have a significant effect on the plane.

David Simmons
04-18-2004, 03:50 PM
Nope. No "slippage" at all. What would cause the air to slip? Contrary to popular belief, there is no tendancy in the Universe for objects to be at rest rather than moving. If you have some sort of frictional force, then there is a tendancy for objects to be at rest relative to each other, but this is exactly what's causing the atmosphere to not slip relative to the Earth.

And Coriolis forces on the plane directly probably don't make much difference, but it's the Coriolis forces which cause the jetstream to go in the direction it does, and the jetstream (or other wind patterns, also determined by Coriolis) does have a significant effect on the plane.

As to Coreolis effect, I quote myself from a previous post, "However the rotation of the earth has nothing to do with the actual flight time except that the rotation causes the prevailing winds to be generally westerly." Once you factor in the effect of the wind you have accounted for the only effect that Coreolis has.

Let's get this straight. The plane is an aerodynamic object immersed in the air mass. As such it takes on the motion of the air mass, whatever it is. Superimposed on that is the motion relative to the air mass that the plane's propulstion gives it. The sum of the two motions is the plane's motion over the ground.

David Simmons
04-18-2004, 03:53 PM
And let's also get this straight: It is Coriolis and not Coreolis.

Chronos
04-18-2004, 03:58 PM
As to Coreolis effect, I quote myself from a previous postYes, I agree with you. I probably should have explicitly said so.

MonkeyMensch
04-18-2004, 07:26 PM
David Simmons has pegged it nicely. You don't need to make Coriolis corrections 'cause you're moving through an accelerating airmass.

And Chronos, I'm surprised at you. I think I know what you were trying to say re the slippage thing. But friction with the Earth and its rotating atmosphere is the whole point. Angular momentum will be conserved and most of the energy conserved, to boot. I know, I know.

There's a reason the prevailing winds won't blow North-South on the planet and I think I know what it is.

kniz
04-19-2004, 01:15 AM
The OP couldn't by any chance have been talking about the time zones. :rolleyes:

For instance and flight from Atlanta to Birmingham can leave at 1:30 and arrive at 1:31. That's just a minute. However, a flight from Birmingham to Atlanta would leave at 1:30 and arrive at 3:30. That flight took 2 hours.

A drunk at the Atlanta Airport goes to the ticket counter and asks when the flight is leaving for Birmingham. The ticket agent asks if he wants a ticket. The drunk replies "Hell no, I just want to watch it take off."

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