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. For 2016, Div B rockets must not change shape (aka no parachutes). Div C rockets ARE allowed to have parachutes.
*** MAJOR ISSUE: It has 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. The easiest way to test this is by sliding a piece of 1/2 inch PVC into the bottle. If it fits loosely, the bottle will go on the launcher. If the PVC sticks and you have to apply any force to slide the PVC in, the bottle will not go on the launcher***
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, grade A large chicken egg (marked with sharpie), the official scoresheet, and launching equipment.
High score wins. The greatest time aloft for both rockets combined will determine the winner. Ties are broken by the greatest launch time a team's single rocket.
- 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. 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!
- 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.
- 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.
- 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.
About Launchers: In our opinion, the best launcher out there is made by Nerds, Inc. It is the only launcher we will recommend for both safety and durability. We use the fully pneumatic ultimate launch package at tournaments, you can buy a non-pneumatic version for $129 (price checked 9/5/14). You will need a bike pump or air compressor that has a regulator gauge on it so you know what pressure you're at, or else buy the Nerds regulator gauge attachment. If the o-rings wear out or need to be replaced, go to a home improvement store. They are in the sink repair section, size #12 o-rings. You can get a 10 pack for a few dollars.
Launching Rockets - Several styles of launcher are shown in these pictures. The silver metal launcher shown in most pictures is the pneumatic launcher from Nerds, Inc that is used at most NC competitions. The white PVC launcher is by Pitsco and has stability problems, the small boxlike one is a homemade launcher from plans off the internet.
What NOT to do. Pointed nose cones, metal parts, spray painting, etc. on the pressure vessel are all against the rules.
A successful backslider design. The rocket is balanced so when it reaches apogee it turns sideways and floats slowly back down.
To help parachutes deploy more efficiently, dust it with baby powder so it doesn't cling to itself.
When folding a parachute for a bottle rocket, you want it done neatly so it doesn't get tangled, not so tight that it doesn't open, but also not so loose that it gets stuck inside the rocket.
You can test your bottle rocket's recovery system even without a launcher. Find a high location, then toss the rocket straight up a few feet to simulate the peak, or apogee, of the flight. As it begins to fall you'll get an idea of how well your parachute works, if it will deploy or not, if you packed the parachute well, etc. This method does not take into account the forces that act upon the rocket at launch, which may affect your rocket on it's ascent or it's ability to deploy the parachute after apogee.
You can test your backslider rocket if you don't have a launcher by finding a high spot, then tossing it up to simulate the peak, or apogee, of the flight. Pay attention to how it falls after that- is it balanced or unbalanced? See NC Science Olympiad: Balancing a Backslider for info on how to balance your rocket if it is nosediving or coming down bottle first. The first toss of this rocket is heavy on the bottle end. The second toss is slightly overcorrected, and begins to nosedive right at the end. This method does not take into account the force of the launch or how straight the rocket will fly with it's fins, but it can give you an idea of how well your recovery will work.
Backslider rockets work great if you can get them to properly balance so they float gently (and slowly) back down after launching. If your rocket is nosediving or coming down bottle first, try to balance it out.
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.