# Plane flying east/west

1. Jun 9, 2014

### Maxo

If a plane flies from point W due east to point E and then from E due west to W, does it take equally long? Why doesn't the rotation of the Earth makes it shorter going E to W?

2. Jun 9, 2014

### Bandersnatch

How does the plane's propulsion system work? Meaning, how does it fly? What does it "push" against?

3. Jun 9, 2014

### Maxo

Against the wind... which follows Earth's rotation. Could that be seen as like there is wind blowing in the direction of the plane when it goes W to E, and the plane flies with it? Then this wind is instead against the direction of the plane going E to W. So in other words these "winds" exactly cancel out the effects of the rotation?

4. Jun 9, 2014

### A.T.

Why a plane, and not a car? What do you think is diffenrent here in terms of Earths rotation effecfs?

5. Jun 9, 2014

### Bandersnatch

Yes. The atmosphere rotates at (very nearly)the same angular velocity as the rest of the Earth. Although these are not "winds" as these are normally defined as motions of air masses w/r to the surface. Here, rotation of the surface and air is the same(apart from Coriolis force, but that's another kettle of fish).
Best to think of it in terms of a rotating reference frame tied to the rotation of the Earth. As you normally do in your everyday life, without thinking or even noticing the (quite fast)rotation of the planet.

As usual, A.T.'s response is much more incisive, so better focus on that. It's not just a plane or a car, it's also you walking E or W. Can you sense any difference?

6. Jun 9, 2014

### A.T.

As a side note: The Earths rotation does have a small effect on westward vs. eastward flights. The vertical component of the Coriolis force affects the amount of required lift, and thus fuel consumption. Its a measurble effect, but small compared to jetstreams etc.

7. Jun 9, 2014

### Staff: Mentor

And another side note: when you hear someone talking about the "speed" of a powered aircraft, they nearly always mean the airspeed, the speed of aircraft relative to the air around it. There's a different term, "ground speed", which allows for the effect of headwinds and tailwinds.

8. Jun 10, 2014

### Maxo

Thanks for the explanations, very interesting.

Here's another (kind of) related question. If the mass of Earth would change, would that affect the banking of airplanes as they turn? If so, how? I don't see why it should. The banking of airplanes as they turn are dependant on the lift force of the engines, which is not connected to the mass of the Earth. Or?

9. Jun 10, 2014

### Staff: Mentor

In a bank, the lift force no longer points straight down; the vertical component keeps the plane in the air and the horizontal component changes its direction.

If the earth's gravity were stronger, the aircraft would have to generate more lift to stay aloft. Thus a shallower bank would be needed to generate the same horizontal component and turning force.

10. Jun 10, 2014

### Maxo

Very good explanation

11. Jun 10, 2014

### rcgldr

Last edited: Jun 10, 2014