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How they work The bottle is partially filled with water (typically a third full), and then inverted so the nozzle points towards the ground. The bottle is then pressurized with air and then released. However, it should be noted that an excess of water will cause the maximum altitude of the rocket to decrease. Water and air are used in combination, with the air providing a means to store potential energy, as it is easily compressed, and the water providing momentum when ejected from the rocket's nozzle. Typically an air pressure of at least 80 (PSI) is required, although over 100 is usually used. If the pressure is too low, the water is not forced out fast enough, causing the rocket to use a lot of its energy to propel not only the rocket but the water propellent as well. This severely reduced achieved height. Parachutes Parachutes for water rockets can be made from many things, including simple dustbin liners (garbage bags). The difficulty lies in getting the rocket to release the parachute at the right moment. There are many methods for accomplishing this. The simplest is adding mass to the nose cone. The theory is that at the apex the nose cone will fall faster than the rocket body, which will be slowed down by drag, separating the two. Another method is an airspeed flap, which goes along the rocket's body. While the rocket is in flight, the flap is pushed down by the airflow. As it reaches the apex, the flap is no longer being pushed down and can swing upwards, releasing the nose cone. Some water rockets need a "Samuel" parachute. Drone parachutes are small parachutes which open very quickly because of their size, and aid a larger parachute out of the rocket. Most rocketiers put these parachutes on their water rockets for the first launch to make sure their deployment system works. Also drones are use to deploy big parachutes that would get stuck in the car body. As most bottle rockets launch at over 100mph, it is very likely that loose parts will be ripped off by wind shear. This can be dangerous to observers or operators, so securing everything properly is an important safety consideration. Parachutes are particularly likely to be ripped off if even slightly misplaced. Multi-bottle rockets and multi-stage rockets
Nose cone Hemispherical nose cones are considered to be better than conical or parabolic nose cones as they generate less drag. If fins are not used on a rocket, the cone should be made heavy so as to raise the centre of gravity (for stable flight, the centre of gravity should be above the centre of pressure by 1 - 2 rocket diameters). Sources of air pressure Several possible methods of pressurizing a rocket include: Fins As the rocket loses its thrust it has the tendency to start tumble end over end. This will decrease the length of its glide (time that the rocket is flying under its own momentum). To lower the center of pressure and add stability, fins can be added. However, stabilizing fins will cause the rocket to return with a significantly higher velocity, possibly damaging the rocket upon landing. This should be taken into account when designing rockets. Crumple zones or parachutes can be utilized to minimize this. In the case of custom-made rockets, where the rocket nozzle is not perfectly positioned, the bent nozzle can cause the rocket to veer off the vertical axis. The rocket can be made to spin by angling the fins, which reduces off course veering. Another simple and effective stabilizer is a straight cylindrical section from another plastic bottle. This section is placed behind the rocket nozzle with some wooden dowels or plastic tubing. The water exiting the nozzle will still be able to pass through the section, but the rocket will be stabilized. Another possible recovery system involves using the rocket's fins to slow its descent. By increasing fin size, more drag is generated. If the center of mass is placed forward of the fins, the rocket will nose dive. In the case of super-roc or backgliding rockets, the centre of gravity and the centre of pressure are as close as possible, so it spins around, which slows down its descent. Aerial photography Cameras and video cameras can be launched along with water rockets to take photographs in-flight. These aerial photographs can be taken in many ways and with many different types of cameras. Mechanised timers can be used to take photographs. Passive methods are also employed, such as strings that are pulled by flaps that respond to wind resistance. Microprocessor controllers can also be used. However, the rocket's speed and motion can lead to blurry photographs, and quickly changing lighting conditions as the rocket points from ground to sky can have an impact on video quality. Video frames can also be stitched together to create panoramas. As parachute systems tend to fail, cameras also need to be protected from impact with the ground. An example of a video taken from a water rocket can be seen here: Air Command Water Rockets - In-flight Video Safety concerns Water rockets employ considerable amounts of energy and can be dangerous if handled improperly or in cases of faulty construction or material failure. Certain safety procedures are observed by experienced water rocket enthusiasts: Competitions The sport of Water Rocketry has been growing at a fast pace in recent years, which has led to an escalating competitive spirit. Founded in 2003 The Water Rocket Achievement World Record Association (WRA2) was established as the first officially sanctioned set of rules for world record competitions. The WRA2 Class ‘A’ Water Rocket World Record Rules set forth the guidelines for world record competition. These guidelines were created to ensure a level playing field and safety for all competitors hoping to claim the water rocket world altitude record. This class of rockets, powered by an air compressor and water, are completely fabricated from ordinary materials, such as soda bottles and balsa wood. The Oscar Swigelhoffer Trophy is an Aquajet (Water Rocket) competition held at the Annual International Rocket Week in Largs, Scotland and organised by STAAR Research through John Bonsor. The competition goes back to the mid-1980s, organised by the Paisley Rocketeers who have been active in amateur rocketry since the 1930s. The trophy is named after the late founder of ASTRA, Oscar Swiglehoffer, who was also a personal friend and student of Hermann Oberth, one of the founding fathers of rocketry. The competition involves team distance flying of water rockets under an agreed pressure and angle of flight. Each team consists of six rockets, which are flown in two flights. The greater distance for each rocket over the two flights is recorded, and the final team distances are collated, with the winning team having the greatest distance. The winner in 1996 was ASTRA after regaining it from the Sheffield Rocketry Association. The competition has been regularly dominated over the last 20 years by the Paisley Rocketeers. The United Kingdom's largest water rocket competition is currently the National Physical Laboratory's annual Water Rocket Challenge. The competition was first opened to the public in 2001 and is limited to around 60 teams. It has schools and open categories, and is attended by a variety of "works" and private teams, some travelling from abroad. The rules and goals of the competition vary from year to year. Records The overall record holders are: The people at U.S. Water Rockets have the current overall world record for height achieved by a water and air propelled rocket. Their design flew to an amazing 582 meters (1909 feet) (2 flight average as required by the WRA2 altitude record rules). They flew an onboard video camera as payload and used an air compressor as a pressure source for the water reaction mass. They used a carbon fiber reinforced fluorescent lamp cover (FTC), and a special low friction large nozzle shape to lift the heavy payload. (This data is not verifiable except by reference to a web site which is maintained and edited by the claimants of the record - see http://en.wikipedia.org/wiki/Wikipedia:Verifiability for clarification on acceptable Verification). Previous world records The current second highest altitude is Antigravity Research company. On 17 July, 2003, the rocket flown by Antigravity Research company reached 378.5 meters (1242 feet). Their rocket was made using an ordinary 2-liter soda bottle with carbon for reinforcement, allowing a pressure of 1150 psi to be achieved using compressed nitrogen. They also used soapy water, creating a foam reaction mass that more evenly distributed the weight in the rocket and allowing the use of a nozzle to use the energy stored in the rocket more efficiently. The current third highest altitude holder is Sam Mulock with his Red Arrow III, a 12-liter water rocket constructed from standard soft drink bottles reinforced with Kevlar fabric. His 1230 foot (375 meter) flight on November 7, 2004 was achieved using compressed air with a water reaction mass. Mulock has flown a camera to altitudes of 1131 feet (345 meters) during his photo flights. The current fourth highest altitude is Robert Youens with Insane Air, an ultra lightweight design made from a fluorescent lamp cover (FTC) which achieved an altitude of 1105 feet (336.8 meters) using only compressed CO2 at a pressure of 130 psi, and no water or other reaction mass at all, on the 22nd of June 2002. Specifications, flight data, construction details and other explanations can be seen on his website. The current fifth highest altitude is Bruce Berggren with his two-stage Millennium VIII rocket reaching 1060 feet (323 meters) on 3 July, 1998. His former world record holding rocket was constructed combining both a fluorescent lamp tube cover and ordinary soft-drink bottles. He used compressed air and water, and all parts used to build the rocket were standard, off the shelf components available to anyone with access to a good hardware store. This rocket was the first to break the 1000 foot (314 m) altitude. The 8th rocket in the millennium series (the name indicates the altitude goal of 1000 feet) was built with the following constraints: See also | ||||||||||||
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