cyrusabdollahi said:
http://video.search.yahoo.com/video/view?&h=240&w=320&type=msmedia&rurl=www.eng.uah.edu%2F%7Efrederic%2FBuffer&vurl=www.eng.uah.edu%2F%7Efrederic%2FBuffer%2Fbottle%2520rocket.wmv&back=p%3Dbottle%2Brocket%26ei%3DUTF-8%26fr%3Dslv1-&turl=re2.mm-so.yimg.com%2Fimage%2F1849296965&name=<b>bottle%20rocket</b>.wmv&no=1&tt=143&p=bottle+rocket&size=1.9MB&dur=68"
that looks fake as hell if you ask me.
Definitely.
Here's the problem with the experiment, as they did it. They have no attitude control. The thrust from each bottle should come pretty much straight out of the bottle. Any imbalance in the thrust will mean one side of the rocket will accelerate at a greater rate than the other - in other words, the imbalance induces a torque which causes the object to start spinning. As soon as the object starts spinning, none of the bottles are providing a force in the proper direction. Which is why you would expect the mannequin to routinely do face plants (the center of mass is always below the line of thrust since the bottles are strapped to the man's back)
The video shows the bottles did produce a torque which starts to rotate the man, but the off-line thrust doesn't affect his trajectory. Additionally, his pitch goes bad right off the bat, but instead of continuing to pitch end over end, his pitch more or less restores itself. The yaw acts the way you would expect - once you've started rotation about the yaw, there's nothing to slow it down.
The trajectory violates the laws of motion. The guy should experience a constant acceleration towards the ground. Instead the guy appears to experience a constant velocity towards the ground. He almost appears to float, but I think that's an optical illusion based on what we expect his trajectory to be.
First of all, the bottles need to be as close as possible to providing thrust in alignment with the center of mass. Instead of strapping many bottles to his back, a few bottles with very high pressure need to be strapped between his legs. A feedback system needs to be designed so the amount of thrust from one bottle controls how "open" the opposite bottle is. That way, if one bottle is providing more thrust than it's opposite counterpart, it's thrust provides a larger opening in the opposite bottle than the opposite bottle provides for it - imbalances become self correcting before the torques build up.
Edit: Actually, mounting the bottles on a cross frame and duct taping the man's hands to the frame and allowing him to trail the bottles will be a more stable configuration. A four fin configuration can be strapped around his bound ankles. Since the feedback system will require thrust from the opposite bottle to control the opening of each bottle, when there is no more thrust, all the bottles will remain closed, providing bouyancy once the man lands. Then he can be retrieved by boat and untied.