Update (6/10/2011): About bringing your own launcher: short answer, no. We view this as an engineering challenge – you do the best you can with the launchers you are provided. In this case, you may have the resources to build a launcher to replace ours, but when you scale up, it won’t be able to replace components you don’t like, as it will be too expensive to do so (or possibly in case of government contract, impossible). This is a reality of life, so start practicing!
Update (6/3/2011): We’ve had some questions about the propulsion of the rockets, so here’s some clarification. We provide a rocket launcher for all of you. So we don’t want anything in your bottles that might gunk up our launcher. This means nothing but water and air in the bottle. Secondly, the only source of propulsion for the bottle rockets should be the pressure in the bottle. No turbofan engines, solid rocket boosters, or other added propulsion. Thanks!
The task is to build a water bottle rocket out of a standard 2 liter soda bottle. The winner will be determined by the longest length of time the rocket is airborne.
Effective water bottle rockets take into account many of the same considerations as “real” rockets. Just as with “real” rockets, students should take into consideration propellant mass fraction, stability of flight, and engineering an effective reentry system.
The water bottle rocket launcher (pictured below) will be provided . You must use a standard 2 liter soda bottle with a neck of the same measurement as pictured in the second picture below. You will fill your rocket with the desired amount of water, and place it on the launcher. You, or someone appointed by you, will then use the bicycle pump to fill the launcher with the desired pressure (between 70 and 110psi), and release it when ready. The amount of water, the exact pressure, and all external attachments (which must be deemed safely secured by the judges), is left up to the discretion of the participants. Time in flight will be timed by the judges and will begin when the rocket leaves the launcher and finishes at the point of contact with the ground. If the rocket lands on a surface other than that of the ground (i.e. tree, roof), the timer will be stopped at the time of contact and will be considered its landing time. You will be allowed 3 launches, no exceptions. Judging will be based on the longest time in flight. Participants are encouraged to make modifications to the bottle so long as these modifications adhere to the guidelines set forth and does not jeopardize the safety of anyone involved.
Specifications for the bottle:
The bottle body must be a 2 liter bottle. The lip of the bottle should be 1.6-1.8cm, which should be standard for a two liter bottle. Other than this, there are no materials limitations.