stationary helicopter

[rwwaite]

For an observer in a helicopter, does the earth appear to revolve under it if it hovers for a long time or does it remain over the same spot???
i.e. does it follow the rotation of the earth or.........

[ChuckFickens]

it's a point of reference thing.

You would be hovering above the earth so that is your only point of reference as to what stationary is so you would actually be moving in space to compensate for the earths rotation and remaining fixed above one point on the earth

If the helicopter was to genuinely remain stationary in space then yes the earth would appear to move under it.

[splenn10]

The helicopter takes off from a revolving earth into an atmosphere that is revolving with the earth. There would be no forces present to stop the helicopter revolving with the earth and the atmosphere. Therefore it would continue revolving with the earth and atmosphere and remain in an apparently stationary position above the ground

[brachiopod]

The rotation of the Earth is irrelevant, in the same way that if you jump vertically, you don't land 30 meters away from where you jumped because you and the air you jump in are moving with the Earth.

What is more important is the movement of the air the helicopter hovers in. If a pilot hovers over a fixed point in a 20 knot headwind, he will actually be moving forward into the wind at 20 knots. The forward motion is cancelled out by the wind so he will appear to hover in one place.

Similarly, if you were swimming in a river and wanted to remain over a certain point of the river bed, you would have to actually swim against the current in order to stay in the same place - if you just 'trod water' you would drifft downstream with the current.

Both air and water are fluids, so this is analogous to the helicopter pilot hovering in the air.

[brachiopod]

Sorry, splenn - I didn't intend to appear to contradict or knock your answer - it wasn't there when I started - but due to kids interrupting, mine took ages to post!

[Clanad]

I certainly understand your intent, 'pod, but you mis-interpolated your two examples. While the second concerning the swimmer is accurate, the first contradicts that, unintentionally, I suspect. If the helicopter is hovering in a 20 knot headwind and makes no corrections, such as power or cyclic control changes, it, just like the swimmer, will drift downwind at about 20 knots.
Asa pedantic point, helicopter pilots rarely hover their aircraft more than just a few feet off the ground and that's usually during the final stages of the landing approach. A rule of thumb is that the forward motion of the craft must equal the distance, i.e., twenty feet off the ground requires 20 knots forward speed, 10 feet high, 10 knots, etc. The purpose is, should an emergency landing be required (known as an Auto rotation) the forward airpseed will keep the main rotor turning with enough velocity to effect the landing, usually safely... well, sometimes safely... actually, the outcome is seriously in question...