AI
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Flight Times East To West & West To East

Thu Apr 28, 2011 10:53 pm

Hi all,
Have always wondered the difference in flight duration when flying east to west & west to east.

If we look at long routes for eg DXB to JFK, according to EK website,
DXB to JFK is 13.40 hrs &
JFK to DXB is 12.45 hrs.

The earth rotates from west to east. So as the flight takes off from DXB & flies west towards JFK, the earth is rotating from west to east & hence JFK is getting closer to the flight.

While flying JFK to DXB, as the flight takes off from JFK & flies eastwards, the earth continues to rotate towards the east & DXB is getting farther away from the flight &

hence I think that it should take longer to fly from west to east & quicker to fly from east to west, but its the opposite.

So why is that ?

Thanks in advance,

AI.
 
oly720man
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RE: Flight Times East To West & West To East

Thu Apr 28, 2011 11:32 pm

Quoting AI (Thread starter):
So why is that ?

The wind. In the northern hemisphere there is a prevailing flow from west to east so westbound flights typically take longer. In the extreme, there can be a 3hr difference in flights from the UK to New York, for example. A few years ago a MAN-JFK flight I was on took the best part of 8hrs whereas the return was around 5 hrs.

This is probably one of the reasons for the SIN-EWR-SIN flight going round the world eastwards.

Note also that inbound and outbound flights don't always fly the same routes, due to the prevailing winds.
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timz
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RE: Flight Times East To West & West To East

Thu Apr 28, 2011 11:57 pm

Quoting AI (Thread starter):
hence JFK is getting closer to the flight.

The flight is likely not moving at all-- the earth beneath it is moving eastward faster than the plane's airspeed. So the plane just hangs in the air and waits for JFK to reach it.
 
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Starlionblue
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RE: Flight Times East To West & West To East

Fri Apr 29, 2011 2:57 am

Relativity dictates that the aircraft is already in the Earth's frame of reference. It is already moving at the same speed as the Earth's rotation just sitting on the ground. You can thus ignore the Earth's rotation for this calculation.

As oly720man says, it has to do with winds. Now, Coriolis effects do generate many prevailing wind patterns, and they are in fact caused by rotation of the Earth.

BTW Earth's rotational speed already being built in is why orbital launches use less fuel closer to the equator, and why they go east after launch (barring polar orbits and such).

Quoting timz (Reply 2):
Quoting AI (Thread starter):
hence JFK is getting closer to the flight.

The flight is likely not moving at all-- the earth beneath it is moving eastward faster than the plane's airspeed. So the plane just hangs in the air and waits for JFK to reach it.

  .
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
InnocuousFox
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RE: Flight Times East To West & West To East

Sat Apr 30, 2011 2:17 am

So if the earth is moving, but the atmosphere that the plane is flying in is not, why don't we have 500-1000 kt winds all the time? It would have to be blowing pretty fast to get all the way around the world in 24 hours!
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Starlionblue
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RE: Flight Times East To West & West To East

Sat Apr 30, 2011 2:27 am

Quoting InnocuousFox (Reply 4):
So if the earth is moving, but the atmosphere that the plane is flying in is not, why don't we have 500-1000 kt winds all the time? It would have to be blowing pretty fast to get all the way around the world in 24 hours!

The atmosphere is also moving with the Earth. However since it is a fluid, it is not in perfect sync with the surface of the Earth. Since the rotational speed of the surface of the Earth is higher near the equator than near the poles (due to differing distance from the axis) the atmosphere is "dragged along" at different speeds depending on latitude. This leads to winds caused by Coriolis effects and other fun stuffs. But it is not that simple. The dynamics of the atmosphere are very complex since the surface of the Earth is not even (mountains and oceans) and the temperature of the surface is not even either, leading to a myriad currents, drafts, winds, and so forth..

Also remember about frames of reference. There is no "privileged" frame of reference that is absolute, so you can't say something is moving and something is not in this context. It's all relative. The Earth's surface is moving relative to, say, space around the Earth. However relative to a person standing on the ground it is not.

[Edited 2011-04-29 19:31:20]
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
star_world
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RE: Flight Times East To West & West To East

Sat Apr 30, 2011 4:33 pm

As others have already said - the earth's rotation does not play a role in the difference, it is related to the winds over the Atlantic which are generally eastbound.

By your logic all Olympic long jump events would be set up in a westerly direction to maximise the length of the jumps   Even a quick jump into the air in the safety of your home could result in a nasty bump against the nearest wall as it rapidly approached you the moment you left the ground.
 
InnocuousFox
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RE: Flight Times East To West & West To East

Sun May 01, 2011 3:19 pm

Quoting Starlionblue (Reply 5):
The atmosphere is also moving with the Earth.

Dude... I know. I was trying to perpetuate the silliness of the earth/atmosphere rotation fallacy.
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Starlionblue
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RE: Flight Times East To West & West To East

Sun May 01, 2011 3:35 pm

Quoting InnocuousFox (Reply 7):
Dude... I know. I was trying to perpetuate the silliness of the earth/atmosphere rotation fallacy.

Sorry I get very literal when I'm tired and sick. Which I was at the time. 

I also have this pet peeve about physics and once I get going it is hard to stop and look at the tone of the question. Sorry again!
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
474218
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RE: Flight Times East To West & West To East

Sun May 01, 2011 5:35 pm

Quoting star_world (Reply 6):
As others have already said - the earth's rotation does not play a role in the difference, it is related to the winds over the Atlantic which are generally eastbound.


I not sure about that: SR-71 set the speed record between New York to London 1 hr. 55 min. average speed 1817 mph. However, its record London to Los Angles is 3 hrs. 47 min. average speed 1448 mph. Each flight required only one refueling so something caused the west to east direction to be much quicker than the east to west? I am not sure what the prevailing winds are like a 80,000 feet.
 
InnocuousFox
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RE: Flight Times East To West & West To East

Sun May 01, 2011 5:55 pm

Quoting 474218 (Reply 9):
I am not sure what the prevailing winds are like a 80,000 feet.

There's actually not a lot of air at 80k. At that point, it WOULD be more of a function of the rotation of the earth.
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