# Earth Rotation & Flight Time

Currently having an argument with said genius. Is an aircrafts flight time effected directly by the rotation of the earth? Would an aircraft flying east to west have a shorter flight time compared to the same flight west to east?

Actually, flights are faster going West-to-East because that is the direction of the jet stream and most weather patterns flow I this direaction.

That said, maybe the direction the earth is moving is WHY the Jet Stream behaves as it does, so maybe that guess is indirectly correct, just getting the directions wrong?

Any weather buffs in the house?

Yer pal,
Satan

The earth’s spin affect airplane flight times, but not in a very direct way. The simple answer is, earth rotation doesn’t directly affect flight times because the atmosphere rotates more or less with the earth.

A more complex answer, which I am only halfway-qualified to give, is that wind pattern heavily influence airplane flight times, and the earth’s rotation affects prevailing winds. My textbook Biogeochemistry: An Analyis of Global Change by William Schlesinger, says

Then there are a bunch of cool three-D charts showing how this contributes to direct Hadley cells, cyclonic storm systems, and a bunch of other stuff that doesn’t directly address our question.

In any case, I think the earth’s rotation produces the jet streams, which pilots seek out (or avoid if they’re going the other direction) in order to save time and fuel. At different altitudes, the jet streams made not be present at all. So the spinning earth doesn’t necessarily speed or slow down a plane going in a particular direction, but it does create the atmosphere patterns.

If we ever have commercial sub-orbital flights, then the Earth’s rotation would affect times in different directions.

And sub-orbital polar flights would really take some planning.

This is an attempt at this question that may assist or inspire someone who understands physics and engineering better than me to provide a superior reply.

The airliner’s power is used to overcome gravity and air resistance and it is able to get off the ground and travel at around 600 MPH in a constant struggle against those two forces. It never breaks free from gravity and air resistance enough to allow the world to twirl past at a much higher speed. Even though it is off the ground it is still within the air mass which is moving at the same speed as the ground and the airliner never breaks free from, or goes faster than, the air mass.
It would be convenient and fuel efficient if air travellers could just go straight up in a balloon and wait for their destination to rotate underneath them but they are suspended in an air mass that is very solid and tangible and is moving at the same speed as the Earth’s rotation.

We had some fun with a question similar to this a few months ago regarding a helicopter hovering “in place” while the world rotated beneath it.

The simple answer to your question, blueboy, is that the only effect on an aircraft’s flight time is, as Satan stated, due to jet stream patterns (less airtime if flying with the stream, more airtime if flying against the stream). In this respect, it’s no different than trying to paddle a canoe a given distance upstream - it takes longer than paddling the same distance downstream.
But now for a little academic mind game:

While the plane’s airtime is independent of its travel direction (taking into account aforementioned jet streams), its speed does indeed change - at least if looked at it in a certain way.

Imagine yourself as an observer in space, situated above Earth’s equator with absolutely no motion relative to the planet spinning beneath you. With your super vision, you watch a plane preparing to take off on an east-west journey. From your vantage point, the earth is rotating in the opposite direction of the plane’s intended flight motion, in a west-east direction.

So from your stationary vantage point high above the earth, the grounded plane seems to be slipping past you, moving from your left to your right. Since the plane’s nose is pointed west in the direction of its intended travel, the plane appears to you to be moving backward - and at a fairly rapid pace too. The earth’s circumference is approximately 24,000 miles, and it makes a complete revolution once in 24 hours. So the plane - and every other grounded object - seems to be whizzing by you at a speed of 1,000 mph.

Once the plane becomes airborne, it’s still under the effect of the 1,000 mph speed imparted to it while grounded. Now things get a little tricky, and the plane’s speed depends on your vantage point. If you were on the plane, you’d say it was moving forward at 600 mph. But from your motionless vantage point above the earth, you can see that the plane is not moving forward at all; indeed, it is still moving backward - but now at a much slower speed.

Since the plane is flying at 600 mph against the spin of the earth’s 1,000 mph backward speed, the net effect is that to you the plane now seems to move backward at only 400 mph.
Now switch the direction of the plane’s travel to fly with the spin of the earth. From your motionless point of view, the plane now seems to be going forward at 1,000 mph, plus an additional 600 mph the plane is providing. The net effect is that to you it now seems to be rushing past at 1,600 mph.

## So to sum up, while the plane’s airtime and speed as measured from the plane are constant regardless of the direction flying (again discounting the effects of the jet stream), its speed can change dramatically (from 400 mph to 1,600 mph) as viewed from a motionless vantage point in space. Honestly, now, does all that make sense? Or did I just spend a lotta time writing gobbledy gook?

~ Complacency is far more dangerous than outrage ~

I think you pretty much got it there, STARK. It’s all frame of reference. Another way to look at it is that a plane on the runway in Ecuador is already going 1100 mph. If it wants to head due west, it travels at 1100 mph - airspeed. Due east, 1100 mph + airspeed.

This is also why ESA likes to launch its rockets from Guiana, and why the U.S. has its main launch facility in Florida instead of New England. The closer one gets to the Equator, the higher one’s initial rotational energy. That means less fuel is required, and more payload can be carried.

Naturally, this benefit applies mainly to equatorial orbits in space, where you’re trying to throw an object just hard enough so that it falls constantly, but not enough to reenter the atmosphere (you have to throw harder to get a polar or retrograde orbit). Left to its own devices, an airplane will fall too, but since it is travelling much slower and within the high-friction atmosphere (or it wouldn’t fly at all), sooner or later the path of its fall will intersect with the ground. Sometimes, that can be a bad thing.

Sofa King:

Really? I thought it was so they’d have warm weather year-round.

Why haven’t they built any launch facilities in Hawaii?

Chaim Mattis Keller
ckeller@schicktech.com

“Sherlock Holmes once said that once you have eliminated the
impossible, whatever remains, however improbable, must be
the answer. I, however, do not like to eliminate the impossible.
The impossible often has a kind of integrity to it that the merely improbable lacks.”
– Douglas Adams’s Dirk Gently, Holistic Detective

***cmkeller: Really? I thought it was so they’d have warm weather year-round.

Why haven’t they built any launch facilities in Hawaii?***

[ul][li]cheaper to ship materials to Florida vs. Hawaii[/li][li]terrain is more level (for hauling shuttles to their pads)[/li]weather around Florida is less volitile; also, it rains almost daily in Hawaii (they don’t mention that in the travel brochures)[/ul]

Hawaii is a bit on the small side, you know those things explode sometimes…

Whatever happened to planes flying over the Artic to save time?

Planes still do fly over the poles to save time, but this isn’t a rotational thing. The shortest distance between two points which are both equally northerly, will always jog northwards somewhat. (This route is not changing course - it is our latitude lines which are not straight.) So two points, both in the northern hemisphere, but very far apart (say, Nebraska and Siberia) will cross the pole.

It’s not easy to figure out what the shortest route is on a lot of maps. The only sure-fire way is to take a globe, and some thread, and put one end of the thread at your starting point, and the other thread at your ending point, and then to pull it taught. What looks great on a globe will look really curvy on a Mercator Projection.

Incidentally, this is why Titanic and most transatlantic ships go through such northerly waters.

It’s easy enough to figure out true directions to and from Point A on an azimuthal equidistant projection with Point A as the centre point. The shortest route is just a straight line outwards from Point A to wherever. Imagine a polar projection of a hemisphere (or the entire globe) with your Point A as the north (or south) pole.

The large aerospace firm I work for just participated in a launch of a satellite from the equator to take maximum advantage of the earth’s rotation. The project is called SeaLaunch and it’s a consortium of Russian (rockets), Norwegian (launch platform) and American (payload, ground support) companies. They launch from a modified oil drilling platform and had their first successful launch just a week or so ago.

I’m fuzzy on this other item but they either did have or planned to have a launch site in Hawaii, on the southern tip of the Big Island (the southernmost point in the U.S.). But, as mentioned above, the additional cost of operations offset any fuel savings. IIRC, water was actually a primary deal-breaker --not enough fresh water on the island to support the additional load the launch site demanded.

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