How are Zero G planes able to simulate weightlessness?

[pr1de]

how do "zero g" planes work?

As the title says, I'm curious about how Zero G planes work. They can't get into orbit , because there's no way they're engines could provide thrust for such speed, and they don't really leave the atmosphere. I've read that they way it's done is by simulating sort of a elevator drop effect, going up... and then dropping , and the persons inside it are floating in free fall. i understand it so far, but when the plane is dropping, and the people are in mid air.. how come the plane's back doesn't smash into them? they would have to be at the exact same velocity ( the human and plane). right?

 

[mgb_phys]

Yes - everything falls at the same speed.
So a plane dropping out of the sky and the people inside it are falling at the same rate and so feel weightless, exactly the same as in a falling elevator.

In practice it's a little trickier, the plane feels the drag of the air around it so wouldn't fall as fast as the people inside - it has to actually power into a particular dive to compensate

 

[rcgldr]

The pilot builds up speed, pulls upwards, then places the plane into a "parabolic" path, which is technically elliptical relative to Earth's' center, adjusting pitch and throttle control to maintain the path. In the NASA version, the plane would pull up into a 45 degree climb, then follow a zero g path until a 30 degree descent, where it needed to pull out to avoid excess speed and loss of altitude. You'd get about 25 seconds of "zero g" every 65 second cycle.

http://en.wikipedia.org/wiki/Vomit_Comet

 

[Rasalhague]

The pilot builds up speed, pulls upwards, then places the plane into a "parabolic" path, which is technically elliptical relative to Earth's' center

If the path is technically elliptical, why is it called parabolic and how can it be described using a parabolic equation? Is it because the path approximates a parabola when there's no great change of distance to the Earth's centre of mass but would be seen to be elliptical if it was possible to follow it through the Earth without impediment?

 

[pr1de]

thank you for the answers

 

[rcgldr]

If the path is technically elliptical, why is it called parabolic and how can it be described using a parabolic equation? Is it because the path approximates a parabola when there's no great change of distance to the Earth's centre of mass but would be seen to be elliptical if it was possible to follow it through the Earth without impediment?

A parabolic path would occur if the Earth was flat and an infinitely large disk or plane. A relatively low alititudes, and short horizontal distance traveled, the "flat earth" model is close enough. As you mentioned the relative distance traveled relative to the center of Earth would be small. The horizontal distance traveled versus curvature of the Earth would also need to be small.