View Full Version : Silly Helicopter Question

06-02-1999, 05:59 PM
I know it's not possible for helicopters to continuously run for several hours (fuel concerns) but IF IT WERE...

Imagine you boarded a copter, fired it up and hovered for several hours (overnight, for example)...when morning came would you be in a different spot then where you boarded, the earth having theoretically rotated beneath the hovering helicopter?

"My hovercraft is full of eels."

06-02-1999, 06:28 PM
The helicopter is in the Earth's atmosphere. As you may have noticed, the air tends to spin around with the Earth.

06-02-1999, 07:00 PM
Theoretically, yes, but not by lifting "straight" up. Simply being aloft does not divorce you from the forces that were acting on you before liftoff. When your helicopter was sitting on the launch pad, it was apparently motionless, right? But in reality, it was sitting on a globe whizzing around with a rotational speed of approximately 1,000 miles per hour.

So when you lift "straight" off, you are still subject to the same 1,000 mph rotational velocity that you were when on the ground. Without compensating for this, the result is a curving arc: slight motion in the Y direction as you lift off, but breakneck speed in the X direction.

This curving trajectory of an object launched from a rotating object is what’s known as the Coriolis effect, and is what makes launching a rocket "rocket science." The rocket doesn’t just go straight up to its intended target (be it the moon, Mars, or Earth orbit), but instead – just like your helicopter – curves to the side as well.

So in order to stay "motionless" with respect to space, you’ve got to overcome that high-velocity send-off. To do so, you’d have to fly your helicopter in the opposite direction of Earth’s spin, which would give you a relative ground speed of 1,000 mph.

From the point of view of a motionless outside observer somewhere in space, you would then indeed seem stationary, but to you, inside the helicopter, it would seem like you’re cruising away at nearly twice the speed of sound!

Hope that helps.

~ Complacency is far more dangerous than outrage ~

06-02-1999, 07:04 PM
Wouldn't be able to sit there very long. Eventually it would push away the air that holds it up, and it would fall down.

06-02-1999, 07:36 PM
The great inventor Nikola Tesla once speculated that a great mode of transportation would be if you could construct a hollow ring around the earth, unaffected by its rotational forces. By transporting yourself to this ring, you could travel 1000 mph anywhere you wanted to go, with almost no energy required.
If you are having trouble with the helicopter question, try looking at it this way: if you throw a baseball straight up, it comes straight back down, it doesnt fly away at 1000 mph

06-03-1999, 01:37 PM
To expand on this topic a bit:

Does an airliner flying from LA to NY actually travel a greater distance than one would flying from NY to LA?

If so, shouldn't they be adjusting frequent flyer miles?

06-04-1999, 09:15 AM
Sly: in a way, yes, a plane does travel farther in the LA to NY direction.

Obviously, the amount of terrestrial miles traveled is the same, but looked at from the point of view of an observer in space, the number of ... uh, call them celestial miles is greater east to west than from west to east.

And even if we could convince all the airlines to switch over to counting frequent flier bonuses in celestial miles, it still wouldn't do you any good. While the celestial miles would be great LA to NY, you'd get screwed on the return trip.

It's kind of like mountain driving: lousy mileage on the way up, killer mileage back down, but it all evens out in the end.

~ Complacency is far more dangerous than outrage ~

06-04-1999, 11:19 AM
If you can argue that the rotation of the Earth is a large factor in prevailing winds, then the oposite is true. Atmosphericly the trip from LA to NY is shorter. If two airliners taking off at the same time (one from LA and the other from NY) each maintain an airspeed (as opposed to ground speed) of 500 miles, the LA plane will land in NY before the NY plane lands in LA.