Putting it simply,
if the earth were still and a flight takes 8 hrs…
What are the differences in flight time along the direction of rotation and opposite the direction of rotation ? What about straight up and down longitudinally ?
There were similar questions in the forum years ago, but I can’t find them unfortunately.
I find that my head too starts spinning when I put more thought into this at work. : )
The rotation itself has no direct effect on flight times (though it will have an effect on the times listed on the ticket for takeoff and landing, because you’re crossing time zones). Wind direction does make a difference to flight times, and that’s largely indirectly a result of rotation. But which way the prevailing winds blow depends on latitude and altitude, and planes will usually seek out the more favorable winds (either weaker headwinds or stronger tailwinds).
I think the most important thing to clarify is that when you move up above the Earth’s surface, the atmosphere is all rotating with the Earth, and you just keep rotating with it.
But note that this complex causal relationship to the Earth’s rotation is not at all the simplistic notion that the atmosphere is “lagging”, i.e. spinning around more slowly than the Earth. There is no sense in which, as you fly up from the surface of the Earth, you are moving into atmosphere that is not also rotating. In fact, the jet streams are predominantly Westerly, in the same direction as the rotation, so the air in the jet streams where aircraft fly is rotating slightly faster than the surface below.
So when you fly “along the direction of rotation” i.e. you fly east, when you’re at a latitude with jet streams, you usually get there faster, contrary to what I think you are expecting.
Chronos basically nailed it. The atmosphere more or less rotates with the earth, but due to effects like convection and Coriolis forces there do tend to be prevailing winds. In most of the northern latitudes in which many of us live, they tend to be westerlies. I frequently track flights on the various flight tracking sites, and it’s amazing how much faster the ground speed is when travelling west to east instead of the other way around. Sometimes you’ll see the plane change altitude and gain a significant amount of increased ground speed. I’ve even noticed this when driving long distances. Returning from a visit to an eastern location, heading west, I’d often feel and hear strong headwinds. But it’s the opposite at comparable latitudes south of the equator.
Wherever jet streams occur in either hemisphere, they are predominantly westerly, in the same direction as the Earth’s rotation, with the air in the jet stream rotating faster than the surface below. It’s ultimately conservation of the momentum of the faster-rotating air above the equator (faster-rotating because the equator is moving faster, furthest from the axis of rotation) as warming air rises and moves either N or S away from the equator.
Yes, my last statement was incorrect. At latitudes comparable to North America and Europe south of the equator, the prevailing winds also tend to be westerlies. However the trade winds closer to the equator are opposite, and tend to be easterly.
You’re confusing things even more now. The trade winds are surface winds. That whole diagram is a map of surface winds (and cells), it does not show jet streams. There are no jet streams anywhere that are easterly. Since the equator is warmer, the air at the equator rises and then at altitude diverges N and S. In both N & S hemispheres it is then deflected E (relative to the surface) by the Coriolis force, i.e. it maintains its faster equatorial momentum in the direction of the Earth’s rotation, W to E. So all jet streams, wherever they occur, are predominantly westerly (W to E relative to the surface).
Relevant illustration from Wiki:
All four streaming from west to east (although wiggling a little north and south).
A plane is itself subject to the Corriolis force. If a plane was somehow flying in perfectly still air it would see a EW force on it proportional to a function of its NS velocity and its latitude.
So it would steer a heading very slightly different to the desired course. In actual weather this is going to be lost in the noise. But still there.
I got the impression that the OP was based on the common misconception that when you fly upward from the rotating Earth, somehow you stop rotating and the Earth rotates under you. Or the similar misconception that the atmosphere is not rotating along with the Earth.
To a first approximation, everything just continues rotating together, so it doesn’t matter which direction you fly with respect to the Earth’s rotation.
We’ve been talking about more subtle effects that are superimposed on that.
I got the same impression.
I had this impression as a kid and a book resolved it very effectively for me. It gave an example of a balloon. If indeed the earth was spinning and the atmosphere was not, one would only need a balloon to go up and stay at a place for few hours for international travel.
Rotational Frame dragging would seem to apply but be so negligible as be damm hard to measure. Basically gravity itself rotates at the same speed as the object (earth). The aircraft is thus moving in a rotation gravitational field, thus causing some spacetime relativist effects which end up speeding up or slowing down the aircraft depending on if it’s going with or against rotation. The aircraft would also weight more anti-spin, perhaps consuming a bit more fuel, but again it would be so small at this scale it may be impossible or very difficult to measure.
Ah but a vehicle in the atmosphere has to be correcting its direction of travel, its even got skew, as in the fuselage is aimed slightly differently to the actual direction of travel . So its not like they can just hold the fuselage to a fixed bearing.
So there was a second question…
What if you try to do a polar orbit ? Go up over the pole and come down the other side ?
Well in the atmosphere ( thats not an orbit, but its the attempt to replicate a polar orbit down low. ) winds are far more effect, and you will never notice the earth rotating under you. However, from your location at maybe 40 or 50 north, you have quite some easterly velocity but by the time you get to the pole,. thats going to have to be gone or you will have missed the pole and gone totally way off . such as going around the Arctic or Antarctica circle. some huge error. But the correction to wipe off your “around the latitude” speed is continuously happening as you move during the 4 hours to the pole you wipe it out, and rather gain a rotation(increase of skew) speed at the pole, tiny but its there, and and then as you leave the pole you have to add “along the latitude” speed, but in the four hours you do it gradually so its a very tiny acceleration to the side for that whole time. So you could follow 50 west longitude up to the pole and 130 east down the other side. Or at the pole, pick your longitude and follow that down. Its not the shortest route in any case, we are just doing it to demonstrate earth moving under you, if you don’t correct for it.
and the earth moving under you is why there is no polar orbit that works in space to keep you tracking a line of longitude. Unless you can do correcting thrusts for the whole way … ok that could be done, but its like the aeroplane steering to correct for winds right ?
Orbits would be far better if they were unpowered and stayed on desired track, right ? Can’t track a longitude in a polar orbit. or any orbit. Not unless the planet isn’t rotating.
You can have an equatorial orbit thats fiine. you can go up to near geostrationary altitude, and spend 8 hours and drop down again, thats a good way to get an 8 hour flight that remains pretty much on the one trajectory that we feel is “aimed toward the destination”… albiet going a long way further than mininum distance ,all the way out to geostationary altitude and back. You are climbing Mount Everest to get over the eiffel tower, but thats one way to waste 8 hours.
Ok so if you don’t need to waste 8 hours, then you can just shot up into space and drop down , a halk hour is the quoted time for half way around the earth.
If you do need to spend 8 hours up at very low earth orbit, you can just shoot around the earth multiple times. The only way to keep a straight line is equatorial. … Otherwise you have some messy sinusoidal track, and in 8 hours you go on five or six wobbles/squiggles around the earth, each time passing over new locations, and then drop down at your destination, with the general path and wobble size variable even for the same destination.