Description:
This is a building event. Teams will build ahead of time up to 2 water rockets using a 2 LITER (or less) CARBONATED BEVERAGE BOTTLE pressure vessel. At the competition, teams will have up to 10 minutes to launch their rocket(s) for the greatest time aloft. Only one launch is allowed per rocket, so teams only bringing one rocket will only be allowed one launch. No logs are required for this event.
*** MAJOR ISSUE: It has recently been brought to our attention that some soda manufacturers have recently changed the size of the neck of their bottles. Please make sure the inner diameter of your bottle neck is still 2.2 cm, not the new reduced size of 2.1 cm. 2.1 cm necks will not fit on the launcher.***
Materials:
Teams MUST bring safety glasses and their rocket(s). If bottle labels have been removed, teams must also bring those. Teams may also bring a funnel for the water and any materials required to adjust or prepare the rocket.
Event leaders will provide water, the official scoresheet, and launching equipment.
Scoring:
High score wins. The greatest time aloft for a single rocket will determine the winner. Ties are broken by the greatest launch time of the team's other rocket.
Common Mistakes:
- The number one mistake made by teams is not using a CARBONATED bottle for the pressure vessel (the part you put the water in and pump up with air). Carbonated bottles are required because they are pressure tested by the manufacturer against defects. Non-carbonated bottles are NOT tested, and are NOT allowed, even if they come in a 1 liter size. Other parts of the rocket such as nosecones and fins may be made from non-carbonated bottles, but the pressure vessel MUST be carbonated. This is a serious safety issue, and rockets that violate this requirement will not be allowed to launch at all. It is a safety disqualification that will NOT be arbitrated.
- Be sure that the pressure bottle remains intact. If you are unsure of what a glue will do to your pressure vessel, test it on an identical bottle first. Also, repeated testing and hard landings can damage your pressure bottle. Check it frequently for scratches and weak spots that may be compromising the structural integrity, and replace the bottle as needed.
- Find the ideal water level for your rocket. While 100% air will give you the maximum potential energy, it has very little mass and therefore very little momentum to carry the rocket. Likewise, 100% water will have great mass, but very little potential energy to give it momentum. Don't wait til the day of the competition to decide how much water to use!
- If you remove the label from your pressure bottle, be sure to bring it to the competition or you will not be allowed to launch the rocket.
- Remember, only one launch is allowed per rocket! If you want to use both launch attempts and maximize your chances, you must bring a second rocket!
Recommendations:
- Safety goggles (the chemical splash kind that most schools have) have a tendency to fog up, making it hard to see. This event only requires safety spectacles, meaning the kind that look like sunglasses will work just fine. These are MUCH easier to see out of. Your local home improvement store carries cheap versions for under $4.
- For transporting rockets with less risk of damage, glue/screw a bottlecap to a wood or cardboard base and simply screw your rocket onto it to make it stand up. For added protection, place this entire setup inside a 5 gallon bucket to protect fins, etc.
- If you are concerned about the integrity of a bottle that you have found to use for your pressure vessel (It looks unaltered but you're just not sure) you can pressure test it. To do this, fill the bottle completely with water. This ensures that the amount of air (and potential energy) inside is minimal, so that if the bottle does fail it should simply rupture and not explode. Then pressurize it to 1 1/2 times the competition psi (competition requires 60 psi, so test to 90 psi). While this is not a way to bypass safety regulations, it can give you peace of mind and save you a lot of build time by preventing building on a damaged bottle.
- Rather than trying to cut holes through your rocket's non- pressurized plastic components, use a hot nail or hot ice pick to poke a hole with smooth, rounded edges.
- Launching a plain bottle with nothing on it can achieve times of 3-4 seconds. Make sure you improve on this time when you start adding fins, nosecone, etc.
Fast Facts:
- The driving force behind a rocket launch is the combination of air and water under pressure. The air that you pump into the bottle compresses, giving you a higher pressure (60 psi in this year's rules). When the rocket is released the air expands rapidly, which forces the water out of the neck of the bottle and propels the rocket.
- Angling your fins slightly to one side will cause the rocket to spiral on its way up, creating stability much like throwing a football in a spiral.
A successful backslider design. The rocket is balanced so when it reaches apogee it turns sideways and floats slowly back down.
Getting rockets ready to launch. This footage is from the Egg-O-Naut event, which required the safe launch and recovery of an egg astronuat within the rocket, and also allowed parachutes.
Demo of rocket launched with no water. Time in the air will also be affected by the weight of any nosecones, fins, etc. you attach, the perfect amount of water will vary from rocket to rocket.
