# How long can the 'vomit comet' aircraft produce the conditions of free fall?

25 seconds I thought it would be longer. The free-fall speed of the human body is 120mph. So, the aircraft has to dive and reach a vertical speed of 120mph. If you run the calculations with the a/c starting at 45,000 feet altitude, you would expect the aircraft could "fall" for 4 minutes. But, of course, you have to allow time for the aircraft to pull out of the dive and a little margin for safety. Then there are structural limitations on the aircraft. What is amazing is that the weight-less scenes in the movie "Apollo 13" were filmed using a "vomit comet". This required them to fly over 58,000 dives. The weightlessness is not caused by diving, but by flying upward into a curve (I believe it is called a hyperbolic curve). This curve essentially imitates what a body would do projected upward into a similar curve. I'm sure it's a great deal safer and less stressful (on body and plane) than any "dive" method.

Zero G conditions are achieved just before, during, and after the top of the above mentioned curve. For a informative diagram of this phenomena see the Web Link to the left.