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Water rocket

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Not to be confused with black powder poweredbottle rockets.

Water rocket launch

A water rocket is a type ofmodel rocket using wateras its reaction mass. The pressure vessel

the engine of the rocketis usually a used plastic soft drinkbottle. The water is forced out by apressurized gas, typically compressed air.

The term "aquajet" has been used in parts of Europe in place of the more common "water rocket"and in some places they are also referred to as "bottle rockets" (which can be confusing as this

term refers to a fireworkin other places).

Contents

[hide]

y 1 Operation

y 2 Multi-bottle rockets and multi-stage rockets

y 3 Sources of gasy 4 Fins

y 5 Nozzlesy 6 Launch tubes

y 7 Safety concernsy 8 Water rocket competitions

y 9 World Recordy 10 Hot water rockets


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y 11 Bibliography

y 12 Referencesy 13 External links

[edit] Operation

Simplified animation of how a water rocket works. 1) compressed air is added which creates a

bubble that floats up through the water and then pressurizes the air volume in the top of thebottle. 2) The bottle is released from the pump. 3) The water is pushed out the nozzle by the

compressed air. 4) The bottle moves away from the water because it follows Newton's ThirdLaw.

The bottle is partly filled with water and sealed. The bottle is then pressurized with a gas, usually

air compressed from abicycle pump, air compressor, or cylinderup to 125 psi, butsometimes CO2 ornitrogen from a cylinder.

Students test a water rocket.

Water and gas are used in combination, with the gas providing a means to store potential energy,

as it is compressible, and the water increasing the mass fraction and providing greater

momentum when ejected from the rocket's nozzle. Sometimes additives are combined with thewater to enhance performance in different ways. For example: salt can be added to increase the

density of the reaction mass resulting in a higherspecific impulse. Soap is also sometimes used


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to create a dense foam in the rocket which lowers the density of the expelled reaction mass butincreases the duration of thrust. It is speculated that foam acts as a compressible liquid and

enhances the thrust when used with De Laval nozzles.

The seal on the nozzle of the rocket is then released and rapid expulsion of water occurs at high

speeds until the propellant has been used up and the air pressure inside the rocket drops toatmospheric pressure. There is a net force created on the rocket in accordance withNewton'sthird law. The expulsion of the water thus can cause the rocket to leap a considerable distance

into the air.

In addition to aerodynamic considerations, altitude and flight duration are dependent upon thevolume of water, the initial pressure, the rocket nozzle's size, and the unloaded weight of the

rocket. The relationship between these factors is complex and several simulators have beenwritten by enthusiasts to explore these and other factors.

[1][2][3]

Often the pressure vessel is built from one or more used plastic soft drink bottles, but

polycarbonate fluorescent tube covers, plastic pipes, and other light-weight pressure-resistantcylindrical vessels have also been used.

Typically launch pressures vary from 75 to 150psi (500 to 1000kPa). The higher the pressure,the larger the stored energy.

[edit] Multi-bottle rockets and multi-stage rockets

Two multi-bottle rockets with a cat for scale.


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A larger multi bottle rocket with cylindrical fins.

Multi-bottle rockets are created by joining two or more bottles in any of several different ways;bottles can be connected via their nozzles, by cutting them apart and sliding the sections over

each other, or by connecting them opening to bottom, making a chain to increase volume.Increased volume leads to increased weight, but this should be offset by a commensurate

increase in the duration of the thrust of the rocket. Multi-bottle rockets can be unreliable, as anyfailure in sealing the rocket can cause the different sections to separate. To make sure the launch

goes well, pressure tests are performed beforehand, as safety is a concern. These are very good ifyou want to make the rocket go high however they are not very accurate and may veer off

course.

Multi-stage rockets are much more complicated. They involve two or more rockets stacked ontop of each other, designed to launch while in the air, much like the multi-stage rockets that are

used to send payloads into space. Methods to time the launches in correct order and at the righttime vary, but the crushing-sleeve method is quite popular.

[edit] Sources of gas

Several methods for pressurizing a rocket are used including:

y A standard bicycle/car tire pump, capable of reaching at least 75 psi (520 kPa).y An air compressor, like those used in workshops to powerpneumatic equipment and

tools. Modifying a high pressure (greater than 15 bar / 1500 kPa / 200 psi) compressor to

work as a water rocket power source can be dangerous, as can using high-pressure gasesin from cylinders.

y Compressed gases in bottles, like carbon dioxide (CO2), air, and nitrogen gas (N2).Examples include CO2 inpaintball cylinders and air in industrial and SCUBA cylinders.

Care must be taken with bottled gases: as the compressed gas expands, it cools (see gas


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laws) and rocket components cool as well. Some materials, such as PVC and ABS, canbecome brittle and weak when severely cooled. Long air hoses are used to maintain a safe

distance, and pressure gauges (known as manometers) and safety valves are typicallyutilized on launcher installations to avoid over-pressurizing rockets and having them

explode before they can be launched. Highly pressurized gases such as those in diving

cylinders or vessels from industrial gas suppliers should only be used by trainedoperators, and the gas should be delivered to the rocket via a regulator device (e.g. aSCUBA first-stage). All compressed gas containers are subject to local, state and national

laws in most countries and must be safety tested periodically by a certified test center.y Ignition of a mixture of explosive gases above the water in the bottle; the explosion

creates the pressure to launch the rocket into the air.[4]

[edit] Fins

As the propellant level in the rocket goes down, it can be shown that the center of mass initially

moves backwards before finally moving forwards again as the propellant is depleted. However

this initial movement reduces stability and tends to cause water rockets to start tumbling endover end, greatly decreasing the maximum speed and thus the length of glide (time that therocket is flying under its own momentum). To lower the center of pressure and add stability, fins

can be added which bring the center of drag further back, well behind the center of mass at alltimes, ensuring stability.

However, stabilizing fins cause the rocket to fall with a significantly higher velocity, possibly

damaging the rocket or whatever it strikes upon landing. This is noteworthy if the rocket has noparachute or other recovery system or it has one which malfunctions. This should be taken into

account when designing rockets. Rubberbumpers, Crumple zones, and safe launch practices canbe utilized to minimize damage or injury caused by a falling rocket.

In the case of custom-made rockets, where the rocket nozzle is not perfectly positioned, the bentnozzle 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 stabilizeris a straight cylindrical section from another plasticbottle. 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 rocketwill be stabilized.

Another possible recovery system involves using the rocket's fins to slow its descent and is

sometimes called backward sliding. By increasing fin size, more drag is generated. If the centerof mass is placed forward of the fins, the rocket will nose dive. In the case of super-roc or back-

gliding rockets, the rocket is designed such that the relationship between center of gravity andthe center of pressure of the empty rocket causes the fin-induced tendency of the rocket to tip

nose down to be counteracted by the air resistance of the long body which would cause it to falltail down, and resulting in the rocket falling sideways, slowly.


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[edit] Nozzles

Water rocket nozzles differ from conventional combustion rocket nozzles in that they do nothave a divergent section such as in a De Laval nozzle. Because water is essentially

incompressible the divergent section does not contribute to efficiency and actually can make

performance worse.

There are two main classes of water rocket nozzles:

y Open also sometimes referred to as "standard" or "full-bore" having an inside diameter of~22mm which is the standard soda bottle neck opening.

y Restricted which is anything smaller than the "standard". A popular restricted nozzle has

an inside diameter of9mm and is known as a "Gardena nozzle" named after a commongarden hose quick connector used to make them.

The size of the nozzle affects the thrust produced by the rocket. Larger diameter nozzles providefaster acceleration with a shorter thrust phase, while smaller nozzles provide lower acceleration

with a longer thrust phase.

It can be shown that the equation for the instantaneous thrust of a nozzle is simply:[5]

F= 2PAt

where F is the thrust, P is the pressure and At is area of the nozzle.

Different nozzle types generally require different launcher arrangements.

[edit] Launch tubes

Some water rocket launchers use launch tubes. A launch tube fits inside the nozzle of the rocketand extends upward toward the nose. The launch tube is anchored to the ground. As the rocket

begins accelerating upward, the launch tube blocks the nozzle, and very little water is ejecteduntil the rocket leaves the launch tube. This allows almost perfectly efficient conversion of the

potential energy in the compressed air to kinetic energy and gravitational potential energy of therocket and water. The high efficiency during the initial phase of the launch is important, because

rocket engines are least efficient at low speeds. A launch tube therefore significantly increases

the speed and height attained by the rocket. Launch tubes are most effective when used with longrockets, which can accommodate long launch tubes.

[edit] Safety concerns

Water rockets employ considerable amounts of energy and can be dangerous if handledimproperly or in cases of faulty construction or material failure. Certain safety procedures are

observed by experienced water rocket enthusiasts:


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y When a rocket is built, it is pressure tested. This is done by filling the rocket completelywith water, and then pressurizing it to at least 50% higher than anticipated pressures. If

the bottle ruptures, the amount of compressed air inside it (and thus the potential energy)will be very small, and the bottle will not explode.

y Using metal parts on the pressurized portion of the rocket is strongly discouraged because

in the event of a rupture, they can become harmful projectiles. Metal parts can also shortout power lines.y While pressurizing and launching the rocket, bystanders are kept at a safe distance.

Typically, mechanisms for releasing the rocket at a distance (with a piece of string, forexample) are used. This ensures that if the rocket veers off in an unexpected direction, it

is less likely to hit the operator or bystanders.y Water rockets should only be launched in large open areas, away from structures or other

people, in order to prevent damage to property and people.y The water jet from a water rocket is sufficiently fast that it can break fingers, thus hands

should not be near the rocket upon launch.y As water rockets are capable of breaking bones upon impact, they should neverbe fired

at people, property, or animals.y Safety goggles or a face shield are typically used.

y A typical two-liter soda bottle can generally reach the pressure of100 psi (690 kPa)safely, but preparations must be made for the eventuality that the bottle unexpectedly

ruptures.y Glue used to put together parts of water rockets must be suitable to use on plastics, or else

the glue will chemically "eat" away the bottle, which may then fail catastrophically andcan harm bystanders when the rocket is launched.

[edit] Water rocket competitions

The Oscar Swigelhoffer Trophy is an Aquajet (Water Rocket) competition held at the AnnualInternational Rocket Week

[6]in Largs, Scotland and organized by STAAR Research

[7]through

John Bonsor. The competition goes back to the mid-1980s, organized by the Paisley Rocketeerswho have been active in amateur rocketry since the 1930s. The trophy is named after the late

founder of ASTRA,[8]

Oscar Swiglehoffer, who was also a personal friend and student ofHermann 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 greaterdistance 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 2007 was ASTRA. 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 PhysicalLaboratory's annual Water Rocket Challenge.[9] 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 avariety of "works" and private teams, some traveling from abroad. The rules and goals of the

competition vary from year to year.


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The Water Rocket Achievement World Record Association 1000 Foot Challenge.[10]

Teamscompete to be the first to fly a water rocket over1000feet (305meters),

The oldest and most popular water rocket competition in Germany is the Freestyle-Physics

Water Rocket Competition.[11]

The competition is one part of a larger part of a student physics

competition, where students are tasked to construct various machines and enter them incompetitive contests.

Science Olympiad also has had a Water Rocket event in past years.

[edit] World Record

Apogee photograph taken by the onboard video camera from U.S. Water Rockets' record

breaking X-12 Water Rocket at an altitude of2,068 feet (630 m).

Most water rockets launched simultaneously, by Gotta Launch [12]

The Guinness World Record of launching most water rockets simultaneously is in hands of GottaLaunch,[13] when on June 19, 2009 they launched 213 of them at the same time, together with

students of the Delft University of Technology.

The current record for greatest height achieved by a water and air propelled rocket is 2044feet(623meters), held by U.S. Water Rockets

[14]on June 14, 2007. This altitude was calculated by

averaging two flights. The first flight achieved 2068feet (630meters) and the second 2020feet(615.7meters). The rocket also carried an onboard video camera on both flights.

[edit] Hot water rockets


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Main article: Hot water rocket

A hot water rocket (orsteam rocket) is a water rocket which uses hot blast wateras its

propellant. Water is kept in the rocket under pressure, at below its boiling point at that pressure.

As it exits through a rocket nozzle, the pressure drops and the water instantly boils and expands

against the nozzle and this greatly increases the exhaust speed and thrust.

Wesley's Water Rockets & Rocket Derby

Water rockets are a great activity to do with the family, your Scouting group, and in the classroom.They are fun to make and launch, and are also educational. I have taught Scout leaders how toincorporate simple rockets, including water rockets, in their Scouting program. See myPowWowRockets Handoutto learn more about these rockets. There is an Engineering professor at MIT thatuses water rockets to examine the principles of thermodynamics.

Water rockets are perfect for younger children because they are relatively safe, are easy to build,and do not require permits to launch. Leave the solid fuel rockets to the older kids and parents.They also help the environment since the rockets can be made from recycled materials. A wellconstructed water rocket can go over 100 feet.

The Water Rocket Derby Rocket (using Mailing Tube)

The rocket that we use for our Water Rocket Derby consists of an 18" mailing tube, a 20 oz. sodabottle, fins and a nosecone. The rocket is constructed from the materials listed below. You will alsoneed a roll of 2" wide clear packing tape. Color paper, stickers and markers can be used fordecorating the rocket.18" cardboard mailing tube (3" wide) with tube cap


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Small quantities of mailing tubes can be purchased from the post office or mailing supply stores(Mailboxes Etc.). Bulk quantities can be ordered from packing supply companies on the internetsuch as Papermart.com . Cut the tube into a 12" section and 6" section.

Ask your local eating establishment or office building with a soda bottle vending machine if you

can collect their empty soda bottles. For large quantities, try your recycling center.Get these in a variety of bright colors for the nosecone.Poster board

This is the thick cardboard used for framing pictures and photos. Some framing stores sell theirscrap pieces for very low prices. Matte board is used for the fins.Matte board

This can be purchased at craft supply stores, such as Michaels. The fun foam is cut into strips, andused to make a tight seal around the bottle when inserted into the tube.Fun Foam

Santa Clara County Council Water Rocket DerbyOur water rocket derby began as a district-level event in 2002, as a project for my Wood badgeticket. Prior to that, I had organized a couple of rocket derbies for my Pack, and taught some basicrocketry classes at Cub Scout Pow Wow. The council water rocket derby is one of the most popularevents in the council, and is sold out each year. The 2006 rocket derby was featured in an articletitled "Ready, Set, Launch!" in the Scouting Magazine Nov-Dec 2006issue.

We use four launch pads in our derby, and can handle up to 150 scouts. We provide the rocket kitsand the materials to build the rockets. See our2007 Rocket Derby program for our event scheduleand an illustrated construction guide.

Water Rocket DerbyThe 2007 rocket derby was written up in the May 4, 2007 issue of the West San Jose Resident, oneof our local community/residental newspapers in Silicon Valley.Awards and RecognitionAll scouts who attend our rocket derby receive a derby patch and a participation ribbon. The top 3winners (rockets with longest flight times) from each rank also receive a medal. The derby patchesare custom designed and are different each year. Your local Scout shop can order custom patches.I have also ordered custom patches from Stadri Emblems. The medals were purchased from CrownAwards, and the ribbons were custom ordered from H & R Trophies.


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8. After the second launch, hand the scorecard to the head timekeeper for the official tally. If timepermits and you are

using multiple launchers, the third launch can be for fun (not timed), where multiple rockets arelaunched simultaneously.9. Call up the next group of participants, and repeat steps 3-8.

Water Rocket LinksThere are many websites devoted to water rockets, some simple ones and some very sophisticatedones. Some people are very serious about their rockets - the world's record height for a waterrocket is over 2000 feet! Some sites sell launch pads, and some explore the science behind therockets. Here are some of my favorite water rocket links:

Peter Grosse's Water Rocket Site:http://ourworld.compuserve.com/homepages/pagrosse/h2oRocketIndex.htm

Gary Ensmenger's Water Rocket Site:http://www.h2orocket.com

Jim Gallant's Water Rocket Site:http://www.outsideconnection.com/rockets4-H Club activity sponsored by Ohio State University:http://www.ag.ohio-state.edu/~rockets

Leeds University Water Rocket Page:http://www.ast.leeds.ac.uk/~knapp/rockets

Mike Passerotti's Rocket Pop! Site:

http://www.waterrocketpop.comhttp://mpassero.tripod.com/rocket

Water Rocket Car:http://www.outsideconnection.com/rockets/rocketcar.htm

Please sign my Guestbook if you have enjoyed this website or the article in Scouting magazine, orplan to do water rockets with your group.


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Copyright 2006-2009, Wesley Wong, All Rights reservedScouting Magazine cover image used by permission of Scouting Magazine.

Previous Site | Join the Webring | Index of Sites | Next Site

Feel free to contact me, if you have any questions on water rockets, or how to run a water rocketderby.

Den & Pack Activities with RocketsIn addition to an organized Rocket Derby, water rockets can also be used in your den program tofulfill Wolf, Bear and Webelos badge requirements, or as a fun Pack Spring or Summertime activity.

They are also great for recruitment!

Den Activities:Wolf Elective 5g: Make a model rocketBear Achieveient 21f: Make a model of a rocketBear Elective 1d: Build a model of a rocket or space satellite

Webelos Scientist 5: Show the effects of air pressureWebelos Scientist 6: Show the effects of watr & air pressureWebelos Scientist 7: Build and launch a model rocket

Additional Activities:- Rockets can be used to teach the scientific method. Experiment with different amounts of

water and chart the launch

times verses water level, to determine the optimum water level. Experiment with different findesigns and see which

ones give the best flight.


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- Foster creativity and exploration (for older boys). Give materials to the boys without anydirections, and have them put

together a rocket they think will fly the highest. Explore options for recovery systems suchas parachutes.

- Attach glow sticks to your rockets for some cool night launches. Get the thin kind that areused for glow bracelets.

- To make your rocket spin during the flight up, attach all the fins at the same angle slightly offvertical.

I have a few extra rocket derby patches, for any interested scouters.


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Paper Wrapped RocketsThe two rockets on the left were made by wrapping heavy paper around two 20-ounce soda bottles.The red one is 19" long. Two 20-ounce bottles are placed end-to-end and taped together. Then a12"x10" sheet of colored poster board is wrapped around and taped to the bottles. The 3" finpattern from the handout is used for this rocket.

The white one is 28" long. A 26"x20" sheet of heavy-stock paper (at least 80-lb stock) is wrappedaround the two 20-ounce bottles that are taped to one side of the sheet and rolled, so that about 2-1/2" of each bottle extends beyond each edge of the sheet. The 4-1/2" fin pattern from the handout

is used for this rocket. If you make this rocket longer, it will actually float down (good scienceproject to determine optimal length). The longer rocket (white one), may require two people to assemble (a Cub Scout and his buddy oradult partner). Since it is longer than the red rocket, it will be more stable and fly straighter than thered one. The red rocket will flip in flight, but is simpler to make.and looks just as cool. Click onimage of rockets to see enlarged view.All Plastic Rocket (Barbie Rocket)The rocket on the right is made by taping two 20-ounce bottles to the ends of a plastic mailingtube. The fins are cut from a sheet of heavy plastic mylar. I was able to find some recycled plasticsheets that I cut out and doubled over for the fins. The top bottle is the nosecone.and is sealed witha bottle cap. You can place an object (payload) in the top bottle, or in the mailing tube before it is

taped to the bottles. You will notce that this rocket has a passenger (a small Barbie doll from aMcDonalds happy meal).

This rocket appeals to the girls and the Moms, as well as the boys. The boys think that Barbie willblow up. Barbie has survived over 50 flights! Because the rocket is all plastic, it is very light, andflies very high. It also lands harder than the all paper rockets, so you will need a larger and softerlanding area. When the nosecone becomes too mangled, it is replaced with a new bottle. This is thesecond generation of the Barbie Rocket.


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Pack Activities:

- Space Theme

- Space Derby or Rocket Derby

- Pack Picnic or barbecue

- Scout-O-Ramas

- Camporees, Webelos-ree

- Summer Day Camp / Family Camp

- Cub Scout Roundup or RecruitmentTypes & Sizes of BottlesYou have probably noticed that I have only mentioned 20-ounce soda bottles for my rockets. Canother types of bottles, and other sizes (such as 16-oz) be used? That depends... Plastic bottles

come in many varieties: water bottles, soda bottles, juice bottles, etc. Soda bottles make the bestwater rockets, because they all have fairly uniform openings (to fit standard screw caps), and arerated to withstand high pressures (carbonation process). The openings of the soda bottle fit nicelyonto the launch tube of the launch pad. Water bottles made by water companies (Crystal Geyser,Alhambra) will work, but they are not rated as high as soda bottles. These water bottles have ashorter cap depth and narrower rim. Some water bottles (Aquafina) are actually made by sodabottlers - these are OK. Stay away from juice bottles with the wide mouth (Sunny Delight), becausethese are too wide for the launch tube. So what brand of soda bottle works best? I try to collect asmany bottles as I can, and test the openings with my launch tube after rinsing out the bottles. Thereis enough variation in the openings that some bottle may not slide onto the launch tube. I havefound that the Pepsi and Aquafina bottles tended to fit the best.

Rocket Derby Photos(requires Java run-time engine)


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Bottles come in a variety of sizes, from very small (8-oz) to jumbo (5-gallon). What size bottle youuse depends on your launch system, and how you plan to use it. I prefer the 20-oz bottles becasethat is the most common type of soda bottle to collect from recycling areas, and they fit the bestinside the 3" mailing tubes. They are the ideal size for the Cub Scouts and the rocket derby. For the

paper wrapped rockets described above, bottles other than 20-oz size (such as 16-oz, 25-oz, 0.5liter, 1-liter) will work, but you may need to adjust your launch pad to fit the opening. 2-liter bottlesmake nice bottle rockets, but they should be saved for the older boys, because they require moreair to pressurize (can be tiring with a bicycle pump). What about the 5-gallon bottle? That's waybeyond my league - Only for the diehard water rocket fanatic (


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watr roket repaired)

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