A letter from water-rokets@yahoogroups.com

Sesuatu yang boleh dicuba dan dieksperimenkan oleh pelajar2....

To: water-rockets@yahoogroups.com
From: air.command@yahoo.com.au
Date: Thu, 31 Mar 2011 21:20:02 +0000
Subject: [water-rockets] 10 Challenges



Hi Guys,

I've been thinking about putting together a list of 10 tough water rocket challenges that would encourage broader innovation in the water rocket community. The main idea is that the challenges don't have complex rules, no judges, just very simple goals. The challenge achievements would be self-awarded purely on an honour system. It would be up to the individuals to choose how they interpret the few rules and how they present their achievements. Anyone can claim they have achieved a particular challenge, but without convincing evidence others in the community would probably remain skeptical.

There would be no ranking and no prizes awarded, though I was thinking that there could be a different badge for each challenge that people could put on their blogs or websites when they believe they have satisfied the spirit of a challenge.

I'm trying to exclude two specific challenges "Highest altitude" and "Longest hang time" as these are what most people concentrate on already. These 10 challenges are aimed at getting people thinking about designing their rockets and launchers in different ways.

Here are some ideas for a few of the challenges, but wanted to hear from others what people considered to be tough but achievable challenges. What should the challenges be?

In no particular order:

Precision - Fly a rocket that will not spin more than 90 degrees from launch to apogee. You can fly any water rocket you like, but will need show that it did not turn more than 90 degrees.

Accuracy - Land a rocket repeatably in the same spot. Or fly the same trajectory?

Durability - Fly a rocket 100 times without any repairs. Rocket must fly a minimum 100 feet on each launch that will be counted.  The rocket does not have to fly 100 times consecutively or even on the same day. Flights that don't reach 100 feet are not counted.

Power - Lift a 100Kg mass 10m.

Complexity - Launch a 5 stage rocket.

Speed - Launch the same rocket 10 times in 30 minutes.

Reusability - ?

Repeatability -?


The idea is that the less rules there are the broader the approach people can take to achieve the challenge.

Time to put your thinking caps on, all comments and suggestions are welcome. :)


- George

Bottle Rocket Designs...?

Q: In science class we are using 1.5 liter bottles for bottle rockets. We have to add on to the bottle (nose cone, fins, ect.) to make it stay in the air longer. Any suggestions? And what kind of material should each thing be built out of?


Also, how much water should the bottle be filled with?

Answer
This is fun. I just helped my son with his bottle rocket for science. Two critical areas of the rocket for success are the nose cone/parachute and the stability (getting the center of mass well forward of the center of aerodynamic drag. There is an easy test you can perform to check drag. Of course, fins are one method of moving the aerodynamic drag back and the nose cone moves the center of balance forward.



The biggest advance we found was using a compression plate for the nose cone. We used a cottage cheese container lid glued onto the base of the bottle to set the nose cone into. My son had concerns about the edge of the lip of the lid catching the air and pressurizing the nose cone as the rocket ascended, so we made exhaust holes to match up with the relief between the bumps on the bottom of the bottle. This makes use of the venturi effect to keep the nose cone firmly locked on until the rocket reaches its apex.


The nose cone has to be constructed so that it will tip off at less than a 45 degree tip angle. W placed 6 pennies (hot glued into the lid of the nose cone for additional mass forward and to help tip the nose cone off. His competition required that the nose cone, parachute and all parts of the rocket remain together is less than linear ft of length when deployed. So the nose cone also has a line tethering it to the rocket, as does the parachute. But we used an elastic shock cord to reduced damage to the rocket and parachute. This shock cord is tied through the compression plate.


For the parachute we used the thinnest clear trash bag we could find. Cut a 42" circle with a 2" circular vent in the center. This helps the efficiency o the parachute by keeping air flowing through the parachute but with lots of drag. If you don't have the vent, you can get a pillow of stale air stuck under the parachute and the whole thing comes down too quickly.


For stability, first you want to find the center of mass. Tape the nose cone with the parachute onto the rocket. Take a string and tie it around your rocket. Slide the string toward the nose or tail until the balance point is found and the rocket hangs horizontal to the ground. Mark this point with a permanent marker +M. Now to locate the aerodynamic center of drag. This is a bit more difficult. The rocket needs to be held horizontal over a pivot point. A short piece of wood trim with a 2-3 ft. dowel put in the middle of it forming an upside-down "T" works well. Hang the trim piece by a short string at the end of the dowel. Now you need a large fan. Using scotch tape, tape the rocket body horizontally attached to the trip piece with the location of your best guess of the aerodynamic center of drag located at the dowel point. now suspend the rocket in front of the airflow of the fan 5-8 ft from the fan. The rocket will likely tent to turn in the airflow. If the nose turns to the fan, then reposition the rocket a bit further forward on the pivot. If the tail turns toward the fan, reposition the rocket further back on the pivot. When the rocket is neutral in the air flow and has no tendency to turn toward or away, or just spins freely in the airflow then you have located the center of aerodynamic drag.


This point can be marked with a "+A" The +M should be at least 3-4" forward of the +A for good stability. Adding fins will

move the aerodynamic center of drag to the rear of the rocket. You can now do a quick check of the stability of your rocket. tie the same string you used for the center of mass test at the center of mass so the rocket hangs horizontal. Then put the rocket in front of the same fan you used previously. The rocket should point into the fan in a very stable fashion.


You will likely need to add fins. Be careful a this point. There should be constraints on where the fins can be. Check with your teacher. Thin plastic,as used in these cheap disposable cutting boards works well. Or if you can get thin balsa wood at a craft store you can cut any shape of fin that you want. Keep in mind that you want as much of the area of the fins as far back as possible. Unfortunately, the curve of the bottle near the neck makes mounting the fins challenging. That is why sloped or angled fins may work best. They will mount just forward of the curve of the bottle, but extend well to the rear of the curved part of the bottle all the way to the mouth of the bottle. Again, be careful of the constraints for clearances for the launch pad and pressure fitting. We had to keep out of the curved area of the bottle within the cylinder defined by the rest of the bottle, and the fins could not extend beyond the opening of the bottle.


Adhesive for the fins is critical. You cannot use hot glues or any solvent glues that molecularly bond with the plastic of the bottle. This could compromise the strength of the bottle and cause an explosion hazard on the launch pad when the bottle gets pressurized.

Good luck and have fun!

FLIGHT OF A WATER ROCKET

Flying model rockets is a relatively safe and inexpensive way for students to learn the basics of forces and the response of a vehicle to external forces. A model rocket is subjected to four forces in flight; weight, thrust, and the aerodynamic forces, lift and drag. The relative magnitude and direction of the forces determines the flight trajectory of the rocket.

On this page we show the events in the flight of a water rocket. Water rockets are among the simplest type of rocket that a student encounters. The body of the rocket is an empty, plastic, two-liter soda bottle. Cardboard or plastic file fins are attached to the bottom of the bottle for stability, and a fairing and nose cone are added to the top as a payload.

Prior to launch, the body of the rocket is filled with water to some desired amount, normally about 1/3 of the volume. The rocket is then mounted on a launch tube which is quite similar to that used by a compressed air rocket. Air is pumped into the bottle rocket to pressurize the bottle and thrust is generated when the water is expelled from the rocket through the nozzle at the bottom. Like a full scale rocket, the weight of the bottle rocket is constantly changing during the powered ascent, because the water is leaving the rocket. As the water leaves the rocket, the volume occupied by the pressurized air increases. The increasing air volume decreases the pressure of the air, which decreases the mass flow rate of water through the nozzle, and decreases the amount of thrust being produced. Weight and thrust are constantly changing during the powered portion of the flight. When all of the water has been expelled, there may be a difference in pressure between the air inside the bottle and the external, free stream pressure. The difference in pressure produces an additional small amount of thrust as the pressure inside the bottle decreases to ambient pressure. When the pressures equalize, there is no longer any thrust produced by the rocket, and the rocket begins a coasting ascent.

The remainder of the flight is quite similar to the flight of a ballistic shell, or a bullet fired from a gun, except that aerodynamic drag alters the flight trajectory. The vehicle slows down under the action of the weight and drag and eventually reaches some maximum altitude which you can determine using some simple length and angle measurements and trigonometry. The rocket then begins to fall back to earth under the power of gravity. Bottle rockets may include a recovery system like a parachute, or a simple detachment of the payload section, as shown in the figure. After recovering the rocket, you can fly again.

On the graphic, we show the flight path as a large arc through the sky. Ideally, the flight path would be straight up and down; this provides the largest maximum altitude. But water rockets often turn into the wind during flight because of an effect called weather cocking. The effect is the result of aerodynamic forces on the rocket and cause the maximum altitude to be slightly less than the optimum. The parabolic arc trajectory also occurs if the launch platform is tilted and the rocket is launched at an angle from the vertical.

Sumber : NASA water rocket article.

Here are some great links that I came across, and specifically why I liked them. Please feel free to recommend other sites to me. contact me.

http://www.et.byu.edu/~wheeler/benchtop/gallery.php  Amazing high speed video (slowed down) of water rocket launches! Elsewhere on the site, great tips for getting useful video of launches, quirky ideas like putting a water balloon inside the bottle and some thrust curve math.

http://home.people.net.au/~aircommand/index.htm When you're ready for advanced water rocketry, this is the place to go. Sending video camperas up in rockets, splicing bottles together, great video instructions...it's all here;

http://waterocket.explorer.free.fr/index.html The Water Rocket Explorer site shows what happens when an engineer and his sons encounter water rockets. Not only is there is lots of practical information for building simple to complex (parachute) rockets, but also facinating tangential stuff like the section on rockets reaching escape velocity from the Earth. Truly inspired and high quality. And don't miss the research page http://waterocket.explorer.free.fr/research.htm which has slow-motion video clips, pressure/volume curves and links to useful data.

http://homepage.ntlworld.com/telescope/Rocketweb/Launcher.htm  Jay Morgan, Cubmaster of Pack 327 (Texas) alerted me to this free-thinking European site. I believe the person running it is James Hardy, but I have not been able to find any contact information. Instead of making a bump in the PVC pipe to make the pressure seal, he wraps PTFE tape (Teflon thread-seal tape)--not so it forms a big bump to jam the bottle against, but rather enough so the bottle neck fits fully over the tape. So you don't have to be quite so precise about where the bottle is on the pipe. However, I am getting some feedback that the Teflon tape rips after one or two launches. Also on this site, a "spring"--just a section of plastic bottle--that pushes up a little on the trigger collar. So it does not depend just on friction to keep from launching. It's a great idea which I will incorproate onto my design. Also instructions for sending up a tiny video camera, and resultant airial videos.

http://www.ast.leeds.ac.uk/~knapp/rockets/ The Univeristy of Leeds Water Rocket page has the most amazing images, both still and video. You can see the still pictures by scrolling down the home page. Click "Slow motion movies" or
http://www.ast.leeds.ac.uk/~knapp/rockets/rocketmovies.html to see these amazing sequences (also seen on the waterrocketexplorer site). Also check out the "Quick Time Movie of the first manned water rocket launch" or
http://www.ast.leeds.ac.uk/~knapp/rockets/1.mov Thanks to Dr. Johannes Knapp of Leeds U.

http://ourworld.compuserve.com/homepages/pagrosse/h2oRocketIndex.htm The Water Rocket Index is a serious site by Paul Grosse that has everything up to and including recovery systems and aerial photography. Wow!

http://hazchem.smoke.com.au/~ic/water-rocket.html This is Ian Clark's water rocket site. Ian is the one who came up with idea of using cable ties to make a release mechanism.

The Wikipedia "water rocket" entry is very interesting. http://en.wikipedia.org/wiki/Water_rocket

http://www.geocities.com/rocketroos/ You can tell by the name (...roos) they're from Australia. With Coke can rockets and multiple rockets, they are definately thinking "outside the box."

Khas buat Guru2 Penasihat....roket H2O

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sila klik pautan di sini

semoga dapat membantu cikgu2 mengajar pelajar2 membina roket h2o yang baik.

Rocket H2O -Tips For Students In Science Rocket Challenge // Tip berkaitan roket H20

Special thanks to the author....(I'm sorry....do not know, who wrote this article. I got this article from my friend)

1. Stiff fins are the best fins. Flexibility decreases the effectiveness of a fin.

2. To trace the bottle's shape on the fin material, place the bottle directly under a light source.

3. Place the grain of the fin perpendicular to the bottle. This will make the fin stiffer and stronger.

4. Do not sand the bottle prior to gluing. It will get you disqualified and is not necessary.

5. Best glues for fins: PL Premium - available at Home Depot or Lowes, Goop - available at most hardware stores, Shoe Gu - available at shoe stores and sporting good stores, 100% GE Silicone Glue - available everywhere. All hold well, PL Premium is the stiffest, probably the most toxic, Shoe Gu and Goop are both fairly stiff, GE Silicone is less toxic, but more flexible. Contact Cement or Rubber Cement can be used to glue on paper fins. You should be in a well-ventilated area and wear latex gloves when using PL Premium, Shoe Gu, and Goop. It will usually take fins about 2 hours to cure enough to put on
another fin and about 2 days before launching.

6. "Swing Testing" is a quick way to determine if a rocket has reasonable stability. This test is done by tying a string around the rocket at its CG and swinging the rocket around.

7. Fins cause very little drag and do not weigh very much. A non-stable rocket that is flying sideways is creating a lot of drag. Non stable rockets have a lot of problems with pre-deployment of their parachute.

8. The cost of non-vertical flight is tremendous. A flight that is 5 degrees off vertical can loose 10% of its potential altitude.

9. Parachutes are more efficient with more shroud lines. Shroud lines hold the shape of the parachute and keep air from burping from the chute.

10. Parachutes should be as large as possible while still meeting overall length requirements and efficiency standards.

11. Parachute efficiency is improved by using the correct shroud length. Shroud lengths should be between 1.2 to 1.5 times the parachute diameter.

12. The best parachute material that I have found is dry cleaner bags. If you request the bags used by commercial cleaner for drapes or wedding dresses you may find one large enough for your parachute.

13. The best material for shroud line is nylon upholstery thread.

14. How much water? 1/3 of the capacity of the bottle will get you close. Use simulator listed on page 4.

15. When humidity is low and there is no chance of rain, you can use talc to keep the chute from having static cling.

16. The best folding technique for passive deployment is to zig zag fold the cute, starting from the top to bottom. When you fold the chute to the shroud lines, gently make a couple of wraps with the lines. You want to use as few wraps as possible so that the chute will deploy quickly.

17. The parachute should be attached securely to the rocket. It can be glue or tied. If glued, you should reinforce the bond with fiberglass reinforced packing tape. This also applies to the cord that attaches the cone to the bottle.

18. Deployment at apogee and a quick opening parachute are essential to increasing hang time.

19. If the rocket arches through apogee and does not slow down, wind drag will not allow the cone and body to separate even with active deployment.

20. Make sure that your cone sits securely on the rocket. I have seen numerous rockets disqualified due to cones shifting during pressurization or by being blown off by the wind.

21. The rules no longer allow for a wind block to be used by a competitor to shield the rocket from wind gusts during launch.

22. Beware, bottles expand under pressure. The expansion can upset a cone if the rocket is not designed to deal with this problem.

23. You can design a cone that fits loosely on the bottle. It will need to be supported by a ring or pegs. Both pegs and rings (butter tub seal) can be glued to the rocket with PL Premium.

24. Many competitors use poster board paper or banner paper to make their cone.
See: http://hometown.aol.com/powerdeployment, for procedure to make a simple cone.

25. If you use pegs to sit the cone on, make sure to use Bass Wood (not balsa) and turn the grain so that the G-forces of take off will not cause the cone to cut through the peg.

26. Another simple method of controlling expansion and creating a ledge for the cone to sit on is to wrap fiberglass reinforced packing tape around the top of the bottle until it has created a ledge.

27. Practice many times in all conditions including rain.

28. Have a written procedure and follow it every time. The teams I coach follow step by step through their checklist everytime even though they know it by heart. Airline pilots and surgeons both use checklists, shouldn't you? Laminate your checklist!

29. How heavy should my rocket be? That is a good question. The weight that would give the rocket the best loft may not allow it to reach the highest altitude. Go for stability first, loft second, altitude third. Try to reach a good compromise.

30. How much air pressure do I use? Easy question, all that is allowed. The more stored energy, the higher you go.

31. Use this flight simulator to determine the best amount of water. http://homes.managesoft.com.au/~cjh/rockets/simulation/

32. Check the opening of your bottle, a standard piece of 1/2 inch, Schedule 40 PVC pipe through the nozzle of your rocket.  If it will pass through the opening, it will launch from any standard launcher.

33. With rocket designs where a tall cone sits loosely on the bottle, the cone mass can do little to correct an initial flight stability issue. Why? Because when the fins attempt to correct the instability, the rocket can bend in the middle where the cone sits on the bottle. If you notice that you are getting a lot of pre-deployments, you may attempt to move some of your cone mass toward the base of the cone or you may choose to shorten your cone.

34. Make sure that you have a waterproof box to store your rocket and supplies. Also make sure you have an umbrella to cover the rocket while staging and before launch. Bring rain gear for yourself. The last 2 years at nationals we have had intense rain and many rockets were damaged.

35. Try not to use paper, cardboard or wood components in the rocket. If you do, attempt to waterproof them.

36. Bring too much clothing. You don’t have to wear it, may want to. When cold or wet it is hard to concentrate.

37. Know the launcher that will be used at the event you are going to attend. This is a particular concern for rockets that have fins that are swept below the flange on the bottleneck. Many launchers including the typical "Bent Fork Launchers" and the NERDS launcher will not launch rockets with swept fins. If you plan to use a swept fin rocket, I recommend that you
contact the event supervisor or event director to determine what type of launcher will be used. In the past at nationals a launcher that is capable of launching all typical rocket fin configurations has been used, but it still doesn’t hurt to check.

38. I recommend a fin jig be used for installing fins with precision. A fin jig is a necessity when using slow set glues. You can see my fin jig at my rocket web site: http://hometown.aol.com/powerdeployment

39. To measure your water, build you own custom measuring device from a 1 Liter Bottle. Mark it for just the right amount of water for your rocket. This will help eliminate measuring mistakes.

40. Mark your rocket with the correct water level as a double check. If you are going to be launching off a launcher where you will have to tip your rocket, rather than the launcher tip ping for loading, always put in a little too much water. As you tip your rocket you will always lose a little water.
You can lift up on your rocket gently to let out a little water while on the pad. (Don't get too bent out of shape if  you don't have exactly the correct amount of water, a few ml of water will not make that much difference)


Bottle Rocket Resources
(Bottle Rocket Are Commonly Referred To As Water Rockets)


Recovery:

Vertical, Horizontal Systems http://hometown.aol.com/powerdeployment&Passive

Dave Johnson Air Flap http://dogrocket.home.mindspring.com/WaterRockets/

Gary Ensmenger - Balloon http://www.h2orocket.com/topic/balloon/balloon.html

Nerds Recovery Systems http://tc.unl.edu/rbonnstetter/rockets/recovery.html

Paul Grosse http://ourworld.compuserve.com/homepages/pagrosse/h2orrecsys1.htm

Ulrich Hornstein http://home.t-online.de/home/u.hornstein/wr.htm

Aaron Allen - VDEN http://hometown.aol.com/a1allen/Aaronswaterrockets.html



Division C Backslider Recovery:

Robert Youens http://hometown.aol.com/powerdeployment

Always Brothers http://members.aol.com/petealway/srrg.htm

Ulrich Hornstein http://u.hornstein.bei.t-online.de/wr_backglide.htm



Links Site & Invaluable Sources For Information:

*Clifford Heath* (recommended) http://homes.managesoft.com.au/~cjh/rockets/links.html

A Good Science Olympiad Site http://www.scioly.org/eventpages/event.html



Launchers:

SO Nationals Launcher Last 2 Yrs: http://hometown.aol.com/waterrocketguy/solauncher.html



Simulator (Used to optimize variables)

Clifford Heath http://homes.managesoft.com.au/~cjh/rockets/simulation/



Great Book On Model Rocketry:

Model Rocketry by Timothy S. Van Milligan, available at hobby stores

Rocket Flight Simulation // Ujikaji yang boleh dilakukan bagi mendapatkan satu roket H2O yang baik.

Sila klik pautan di bawah

Pautan


semoga berjaya menghasilkan roket h2o yang baik

azmi j

Artikel berkaitan dengan roket H2O

The "Coney"

Backslider Water Rocket

By

Robert Youens

The cone is 2.5 feet long and made from paper twisted into the cone shape. The paper I used was labeled for use as school book covers. It is 15 inches wide and 20 foot long. The cone is simply taped to the bottle with scotch tape.

Reason may indicate that the Center of Gravity is way to far back on this rocket for it to have stable flight. It was discovered years ago that in long skinny rockets the relationship of the Center of Gravity and Center of Lateral Area can be very different than the required one caliber (dimeter) distance of Center of Gravity ahead of Center of Lateral Area.

A fellow name Barroman mathmatically calculated a new point which has become know as the Barrowman Center of Pressure. In long skinny rockets with the Center of Gravity located behind the Center of Lateral Area, stable flight is still possible as long as the Center of Gravity is ahead of the Barrowman Center of Pressure.

This rocket will fligh well and will maintain vertical flight to apogee. At apogee, rather that nose over and head for the ground, the rocket slides downward tail first. At a point the fins catch the air and put the rocket into a horizontal recovery. This ballance is maintained by the angle of the fin. If the tail is lifted up too much the fins stall and the back of the rocket goes back into the horizontal position until the fins catch enough air to get back into the horizontal glide angle.

It is a beautiful thing to watch and a dependable form of recovery.

This rocket has 4 fins which are almost too much surface area to keep the Center of Lateral Area ahead of the Center of Gravity. When you think about it, another fin or larger fins add little weight, but the additional cross sectional area does dramatically move the Center of Lateral Area backward while the Center of Gravity stays in place. When the Center of Lateral Area gets behind the Center of Gravity you are almost insured a nose down attitude as the rocket progresses through apogee. You may find if you used three fins or smaller fins you would get a smooth recovery with a slightly steeper backward glide angle.


Special thanks to Mr Robert Youens for above article.

Artikel berkaitan dengan roket H2O yang mengandungi banyak maklumat yang perlu diketahui

Special thanks to the author : Johanna De Witte

BOTTLE ROCKETS


The following information is the basic format that I used for my bottle rocket. Due to difficulties in getting parts I had to modify my launch pad. The valve stem I used was from a Tire shop and it sat nicely in a 1/2 " hole on the launch pad. There are drawings on the web site listed below. Good Luck, Johanna DeWitte

copyright February 1997 by Brigham Rees. Copies may be made by educational institutions. Otherwise contact

Brigham Rees,

1408 Dominique,

Austin, Texas 78753

http://www.onr.com/tso/br_man.html

Safety First

Even bare bottle experiments can be dangerous, but a finely tuned rocket can reach speeds in excess of 150 miles per hour. Major league baseball pitchers pitch fastballs between 80 and 95 miles per hour (Bob Feller was clocked at 145 feet per second--99 MPH.). Imagine getting hit without (or with) a helmet at speeds of that magnitude. Cars can be dented, windows broken, roofs damaged. The good news is that with some precautions bottle rockets are relatively safe, despite their awesome power.

0. Equipment. Reliable equipment is absolutely critical. Using poor equipment can not only damage your bottle rocket, launcher, houses, cars, or other property, it can also damage people. A bottle rocket is danger and power in a pop bottle. See the appendix on equipment and make sure yours is up to standard. Don't launch until your equipment is good enough.

1. Adult Supervision. Although not a guarantee of better precaution than youth, adults have had more years to add to their alarm systems. However, anyone's alarms, bells, and whistles should be enough to at least pause a launch for more consideration. A sanity check should be made before any rocket is pressurized. If you don't check your stuff before pressurization, you will almost be guarantied of having to deal with a dangerous situation sometime. Adults should be able to deal with emergencies. They should also familiarize themselves and the students with the following guidelines:

2. Tools. Some rocket ideas may require using tools the students are not trained to handle safely. Watch the students' abilities with tools. Either training the students or doing the part of tool usage that they cannot do may be in order. (For their sake, only the unsafe parts should be done for them, or they will not learn as much). Although individual parts of the rocket may need adult help, the overall rocket should be made and assembled by the student.

3. Metals and sharp objects. This is obviously an alarm bell because a bottle can explode, misfire, or have an errant flight path that would cause someone to get hurt or maimed. In addition, a rocket which has excellent flight characteristics and a good flight trajectory on the way up, may become very dangerous on the way down-especially if a parachute doesn't exist or fails to deploy. (Excellent flight characteristics will mean the rocket comes down almost as fast as it went up). See the huge precaution of the next to last paragraph of Inertia in Flight.

4. Launch area. Although the size of the launch area can be as small as a front yard for no wind and bare bottle experiments, once good flight characteristics are achieved, the launch area will need to be clear for the size of a football field size. If parachutes are added to a good rocket (you will get tired of making disposable nose cones.), a half mile or more of fairly clear field space may be needed, depending on the size of the chute. In any case, nothing should be overhead of the launch. Period.

5. Observer. The adult should be free to be observing during every launch to check for safe and unsafe practices and conditions. Any launch should be stopped immediately if any suspicion of an unsafe condition is observed.

7. Before pressurizing. Someone other than the one who pinned the rocket should check it. Although the launch pad and clamp design included at the end of this has yet to have a misfire due to bad pinning, anything is possible.

8. While pressurizing. The rocket and pad should be observed by the adult and the launching student for the first sign of any problems. 2-liter soda-pop bottles which have no modifications to the water/pressure chamber should solid above 90PSI, but I won't guarantee them. Soda-pop bottles have a rumored minimum specification of 90PSI and a few are valid to 150PSI or more. Water bottles have no known specification. Some appear to be exactly like soda bottles, but I had a sun bleached 20-oz water bottle (unknown time in the sun) explode on me at 55PSI. Sharp shards from the bottom didn't hit anyone, but upon examination, if they had... Any bottles that have not been pressurized previously should have a containment box over them with 20 lbs. or more of weight on top of the box. The box should be heavy duty cardboard (like an appliance box, but only a few inches to a foot taller than the rocket on the launch pad. This prevents the rocket from turning potential energy into dangerous kinetic energy. Leaning over a pressurized rocket or fooling around with one are obviously invitations for injury. Parents won't like any injuries. Any rocket which has multi-pressure-chamber bottles joined in any manner should be pressurized in increments of 5PSI with wait times of 10 seconds between each increment--(pressurized in the containment box). These may be dangerously explosive. The first signs of problems at pressures above 35 PSI may not have enough action time between the observation and the resulting explosion to do anything. Safety goggles are recommended.

9. Problems while pressurizing. If a leak is detected during pressurization, a blowout may be eminent. Stop pressurizing immediately. Clear the area immediately. The leak may be with the launcher or with the rocket. If the leak is at the launch-pad clamp of the design specified in the rear, it may be adjusted carefully. Otherwise, go directly into a launch procedure at the current pressure. The leak should be fixed before launching again.

10. After pressurizing. All other activities should stop. Everyone should be facing the rocket without the sun in their eyes.. Permission to launch should be asked for, permission given, and a countdown started. Everyone should understand that until the blastoff is reached, the countdown can be stopped by anyone.

11. No one catches rocket parts after a launch. Bare bottles have no need to be caught, and other rockets have the possibility of good flight characteristics. They are dangerous on the way up or down.

12. Launch failure. I have never seen this happen with our launch pads. One book recommended the adult jiggle the rocket 3 with a long stick to cause it to release. Maybe a plastic bucket over the rocket would be better (hold on tight. During the first moments no kinetic energy level of danger has been reached, but loosing grip on the bucket may allow that to happen.). Some other procedure may be better still. I have no experience with this and don't believe it happens with this launch pad design, but I welcome inputs.

Up In ;Smoke: Money

The glamour of bottle rockets is that they are something fun to do with an item that is normally trash or, at best, recyclable material. It is possible to spend a lot of money for fancy parts for rockets, but we have achieved best-of-class results from refuse items. An open eye while looking at trash, packaging material, etc. will provide phenomenal results using plastic material that is normally thrown away. After this has been achieved, you will know what a few dollars may possibly achieve towards the super-phenomenal. Don't send your money up in rocket vapor. The most expensive items we have spent money on so far are the launch pad and air compressor. You would be wise to do likewise. See the equipment appendix.

Work and Energy

What makes a bottle rocket fly? (Water and Air Pressure)

If some water and air pressure works, will a lot of water and-or air pressure work better? (Yes and no.)

The water has no magic. It is just a convenient material to push out the bottom of a bottle. Bottles without any water will still fly, just not as far. Adding water gives us a much larger transfer of mass as well as a pressurized container. Let's look at the bottle as the water escapes. We will look at the first little piece that comes out. (You are right, it flows out smoothly, not in pieces, but if we make our pieces small enough we get down to the molecule level.) But I can't draw pictures that small, so we will look at bigger pieces.



A. When the first piece of water comes out of the rocket at a tremendous velocity, it has an equal and opposite reaction on the rocket mass (including other water). But since the other stuff is so big, the little mass only causes a small velocity change to the whole mass. The other possibility is that it could have a full reaction on a singular piece of the large mass. That would involve a small piece pumping up through the water at a high velocity. Imagine a small piece hitting the top inside of the rocket at full force. In all reality, this idea of what happens is more realistic since water is fluid. But the water friction, viscosity and air pressure on the water mass transfer the velocity to the whole mass. Viscosity is how &127;sticky&127; the fluid is with itself. Honey is more viscous than water.

B. After the first little masses have left, 2 things are happening. The big mass is beginning to pick up speed. As it does, the little masses are already traveling in the up direction, so their down velocity coming out of the bottle is less. This is their relative velocity with the rocket. In addition, as more water escapes, the air volume gets bigger. So the pressure on the water decreases in proportion to the increase in volume. This has a direct bearing on the question of whether a lot of water (D.) would be better than a little.

C. As the last water leaves, it is approaching a one-to-one mass transfer with the water left behind. Only the weight of the bottle prevents it from that ratio. And the force imparted may still be very high if the proper water ratio was used in the beginning. 4

D. If the bottle is filled almost full, the amount of air volume needed to get a high pressure is very small. And as the air expands as the water leaves, the pressure drops dramatically. This is still an interesting experiment to do, and has interesting results.

Determining the best water volume. Experiment # 1:

Since we want to determine the best water volume, we must only vary water volume. We can check our results by doing the experiment on another bottle. The first set of experiments might be done using a 2-liter bottle pressurized at 75PSI. A second set might be done using a 20-oz. bottle. We want to know which one reaches a maximum height. We could use a sighting method to determine height, but the best result will be timing the bare bottle from the moment it is launched to the moment it hits the ground.

Typical bare bottle times for a two liter bottle at 75PSI are in the 5 to 6 second range for optimal water volume. We simply put a mark and its number with a permanent marks-a-lot on the side of the bottle before each launch. Then you can go back and number other lines after you see the probable best volume.

Newton's Laws of motion: Mass transfer .vs. Gravity

Once the ideal volume of water for the best thrust .vs. mass transfer ratio has been found, it would be nice to know what forces are acting on the rocket in order to optimize performance.

The sum of all the forces on any object equals zero, so Fv + Fg + Fr = 0. This section will be completed later.

Fins in the Air Stream

It would now be great to begin improving the rocket performance. The first thing the students invariably suggest is to install fins. We began with paper fins, then went to paper with lamination over them. Then came cardboard fins, then cardboard with lamination over them. We devised a method of marking our bottle with perfectly vertical lines which were used as guides to have highly tuned fins. Rockets still tumbled tremendously in the air stream. This was obviously not yet the answer to good flight.

In our fin quest, we discovered a very convenient and cheap fin material that is easy to cut and attach. The plastic in which many store items are packaged is a fairly tough plastic that must be cut with scissors to get the part out of the package. Usually there is a small side and a much larger side at right angles to it. The right angle makes it easy to tape it to the rocket. Duck tape works, but clear packing tape can give a clean smooth edge. A little finesse with the tape yields beautiful fins. This is even easier than the 5-minute epoxy method we originally used with plastic fins. But since this is not yet the answer to good flight, why bother mentioning it now? Because it is time for experiment number 2.

Cut fins and tape them onto the bare bottle, then do a time test. More importantly, do an observation test. I have yet to see a bottle that performs any better with only fins attached, but who knows, maybe someone will surprise me. If it does, share your fin design with me. In any case, fins aren't yet the answer, so rip them off and proceed to experiment #3.

Inertia in Flight

Experiment number 3 involves a wooden meter stick or other thin &127;pole&127; to which you tape some large object. It should not be large enough to bend or break the stick when the taped object is on top and the bottom of the stick is on the floor. It should be as heavy as (or heavier than) a large apple. See the diagram. Now get the students to guess whether it is easier 5 to balance the stick with the weight on their finger, or the bottom of the stick on their finger. The mind naturally moves toward the big end down. Now let them try it.

This is a quick fun experiment of inertia. Your hand is racing to move either the stick or the weight before gravity can get past you. Now ask yourself. Which is easier to move: your dad's car in neutral or a little tricycle? The car is very massive and takes more effort, even though its rolling friction is more efficient than the tricycle. The reason is called inertia. So it takes more effort for you to move the heavy object, and gravity can move the yardstick rather easily. But if you let gravity try to move the heavy object and leave yourself with the easier job of moving less mass, you can easily outperform gravity. Now you know how a circus acrobat can balance a man on a chair on his head. And the heavier the man, the easier it gets (up to the point where the man on the bottom gets crushed, anyway).

So what does this have to do with our rocket? We are trying to balance it in the air stream. This is why spears have a big heavy head on the front and a relatively thin staff behind them. This is why arrows have arrowheads. Get the big guy moving and the rest will trail behind.

We can actually find out how balanced our rocket is by finding the center of mass in relation to the &127;center of pressure&127;. The next experiment must now move to a football size field. No one can get in the way of the rocket coming down. Nothing should be on the football field that can be dented, broken, or destroyed.

Put a small handful of clay on the top end of a bare bottle rocket. (The top end of a bottle rocket is not the nozzle end.) Shape it as symmetrically as you care to. Alternately, tape a small handful of dirt onto the end of the bottle. Blast it off. It should bring some form of stability to your rocket, although probably not a perfect result that would be desired. The tail end (nozzle end) probably began oscillating in the wind, but never swung to the top side of the now heavy top end. Now you have managed to orient it into the wind, what can be done to keep it straight so it doesn't oscillate?

Yes, bring out the largest fins you made and tape them on again. Six inches is a large enough fin, but not the optimum size. Use a smaller pressure of 40 or 45 PSI, because poor fin design makes for rockets that zig and zag like balloons and may be very dangerous. Check the wind. If there is anything more than a whisper, move your launch closer toward the windward side of your &127;football field&127;. Do not launch in heavy winds. For this launch, everyone should be paying strict attention to the rocket and be able to keep it in sight throughout the entire flight. This rocket will go 5 to 10 times higher than any rocket you have launched. It will come down almost as fast as it went up and can dent cars, break windows, damage houses, and maim people. From here on out you must not launch your rockets anywhere but clear areas larger than football fields.

Now go and experiment with fin sizes. Find out how small they can be and still be effective. Do they need to be bigger in length or width? Neither? Two fins? Three fins? Four fins? More fins? The answers fit within the laws of flight, but you will be required to find these on your own. Too small a fin causes a balloon zig/zag kind of flight; too large a fin drags too much head wind if even slightly misaligned, and always catches the wrong amount of side wind.

Velocity Calculations and Height

Now you will be wanting to know just how high that rocket went. We will assume it has virtually no air resistance. If your round-trip time exceeded 10 seconds for a one bottle rocket at 75PSI, you are close enough. Calculations will be made over the distance traveled coming down from the top. Only gravity affected the rocket, so it is a constant acceleration problem. Suppose your flight was 10 seconds round trip (up and down). We can only calculate from the peak of flight down, since that is the distance gravity moved the rocket by itself. So gravity had a &127;pull&127; time t = 5 seconds on the rocket.

distance: y = (1/2)gt**2 ; g = 9.8meters/sec**2

y = (1/2)(9.8meters/sec**2)(5sec)**2

y = (4.9meters/sec**2)(25sec**2) = (4.9meters)(25)

y = 122.5 meters = 401.9 feet 6

velocity: v = gt = (9.8meters/sec**2)(5 sec) = 49meters/sec = 160.8 feet/sec = 109.6miles/hour

As promised, this rocket will fly faster than a baseball form a major league pro pitcher. Now let's see how trigonometry compares with calculations.

Height from Trigonometry

Trigonometry in this case is simply a tangential calculation. We need to step back 300 feet from the launch site sideways from any wind. Otherwise our angles will carry an error of windage. A protractor can be used to site the rocket at the top of flight and find the height angle at 300 feet. Since the rocket slows to zero velocity at the top of flight, then accelerates with our tuned design, this will be much easier than with bare bottles or finned-only bottles. Those rockets stop much more abruptly due to misalignment with the air stream.

Only the part of the protractor that goes from 0 to 90 as shown is needed. If your protractor doesn't number like this, you can subtract your reading from 90degrees to get the height angle. Or use the co-tangent instead of the tangent. So in our example time of 10 seconds of flight, the height was 401.9 feet. So the angle we should measure will have a tangent = 401.9feet / 300 feet = 1.33967. This angle is about 53degrees, so if we had made an observation of 53 degrees we could calculate the height:

tangent 53 degrees = 1.327 = y/x = y/300feet , y = (1.327)(300feet) = 398 feet

If we had been off by 3 degrees (and measured 50 degrees) when we sighted, the calculations would be made by looking up the tangent of 50 degrees either in a trigonometry table or by using a scientific calculator:

tangent 50 degrees = 1.1918 = y/x = y/300feet , y = (1.1918)(300feet) = 357.5 feet

The amount of error can be lessened with larger protractors or smaller tangent angles. Stepping back far enough to keep the angle under 30 degrees will lessen the amount that a site error affects the calculation. This is because the tangent has smaller increments at those angles.

Hang Time

Increasing height is a big challenge, and you will want to experiment with nose cones as well as the fins and &127;spearhead&127;. Nose &127;cones&127; can be an form of symmetry: round, cone, split point, ... Cutting either nozzle end or the bottom end of bottles is a valid thing to experiment with. Taping nose weight inside them is an easy thing to do. Use tape to balance the nose &127;cone&127; and the amount of nose weight until the balance point you have discovered is correct. Then tape the weighted nose cone down solidly to the rocket. The challenge will be to find a nose cone/weight that provides a great round-trip time. But soon after getting the rocket to time well, you will get tired of crashing nose cones with each flight. Finding a way to put a parachute on it and maintain rocket dynamics will be a challenge. Usually this involves making a nose cone that will come off at the top of flight (and not before), when the rocket changes direction. And inside that nose cone would be something to return the rocket to earth without wrecking the nose cone. Finding a way to put a parachute in it, maintain rocket dynamics, and not deploy the nose cone too early will be a challenge. Most of our problems with nose cones come from having the cone deploying early or having it throw our rocket dynamics off balance. Maximum air pressure may not be best for your nose cone design. A proper nose cone and parachute will not throw the rocket off course nor pop off before normal peak height. The gauntlet is down. Let the quest begin.

But I suppose you would like a few hints about parachutes. When I was a kid with Moses, we used to take dry cleaner bags, split them squarely from the large opening on the bottom to the shoulder with a smooth pass of sharp scissors. Then we 7 folded them in half diagonally. This allowed for an easy guide to cut a square. Cutting the corners off equally yielded an octagon. This is a good parachute start. Checking into real parachutes and determining how to duplicate them in very thin plastic is more design work the students will be able to jump into. And then improving them for bottle rockets will be the next challenge.

Toward New Heights

When you reach for new heights, you will probably want to try to hook more than one bottle together to reach for the stars. Although this is tempting, I would like to tell you that I have seen a one bottle rocket go almost as high as 2-bottle rockets. Getting a good rocket flight is more important than 2-bottles. Now if you have plenty of time left to mess around with 2-bottles, the cautions are simple. I have yet to see a rocket that was cut on the outside cylinder hold up to 75PSI. I have heard rumors, but actual proof is lacking. I have seen 4 different successful versions of rockets that have been joined end to end in some fashion. All of them had mechanical means of joining the bottles, with another method of sealing the chambers. I have not yet seen a successful joint based solely on glue.

Now for safety concerns. Never pressurize a joined chamber without the new bottle containment box mentioned in safety rule #8. Pressurize it to 85PSI and wait 5 minutes. If it doesn't explode, tilt the pad over sideways with someone holding the containment box in place over the pad. Unfasten the air hose and release some of the pressure. Tilt the box back upright and carefully remove the containment box. Now you may launch. If the rocket works properly and doesn't crash (the parachute works right), you may perform future launches without doing a pressure test. After any crash, check the rocket, then do a containment test before putting it back in service.

Equipment Appendix

Air pumps: A handheld bicycle pump with a built-in pressure gauge runs anywhere from $40 to $80. We have found a sealed cell battery operated pump that hold up very well at Walmart. A Campbell-Hausfeld portable air compressor launched 60 rockets at our state tournament, then worked every Saturday for the next 9 weeks for 3 to 7 launches. The only caution is that it is powered by a sealed cell lead-acid battery. Unlike ni-cad batteries, they don't have memories, so recharging them too soon is not a problem. Running on low charge too long is a problem and can short out the battery cells. This unit ran about $40 to $60, depending on the model. The rocker switches were the weakest part of the design. I wound up popping the pump switch out after it broke and simply held the wires together on the weekend it broke. I put in longer wires and a push-button switch. Not good for a 3-minute tire inflation, but fine for a 15 second rocket pressurization. The rocker switches may have been replaced with better slide switches since then.

Launch Pads: We took the information from the Nationals Coaches Manual and Rules page and did some ingenious modifications. We used a plastic short rework electrical box, turned it upside down, and used an adjustable hole cutter to cut a 1-3/4-inch hole in it. This provided the ability to slip the rocket pin yoke under the hole edge, then wiggle it into the holes without any difficult struggle. One of our coaches suggested adding an o-ring to the valve stem. This helps provide an easier seal. Additionally, a custom valve stem (the ones used for Mag wheels) was used as the valve stem. This gave a further advantage. With a little adjustment to the washer nut, the o-ring tension could be made to just the right amount. The valve stem could then be fitted to the bottles right side up. When the bottle was turned upside down, none of the water leaked out even if the valve stem was let go of. This makes water measurements very accurate, and allows for easy guiding of the rocket over a launch guide rod if desired. The launch platform size is not specified, and when it is built large enough and passive restraints are used, it becomes stable enough to have no need of being staked down to the ground.

Assembly time of all components is about 4 to 6 hours. Mass production cuts that down somewhat. Parts alone run about $7-$9. Completed launch pads can be obtained for $25 from the authors (unpainted). (Not including shipping.) I have sold 7 launchers at the 1996 Cen-Tex Regional Tournament, and am just publishing this paper, so I haven't yet had to determine how much it would cost to ship the pad. My guess would be between $6 and $10. Paint $5 extra. Specify or sample color.

If you are ambitious, here are my plans as complete as I can get them:

Cut a piece of 3/8 inch plywood. I built the first platforms 24inches by 24inches. For that size, I cut four 2inch by 2inch white pine studs to lengths of 22-1/2inches. Successful pads have also been cut 24inches by 18inches. (Cut two 2x2inch studs to 16-1/2inches, and two to 22-1/2inches.) The smaller pads seem to be as stable during launch as the larger sizes. I drilled and screwed the 2x2's to the platform and each other as shown, using &127;yellow&127; wood glue liberally in all the joints. You can also use Elmer's white glue. The glue makes the launcher more solid, for more reliable launches. Refer to the next page for a better visualization. I used 3inch &127;drywall&127; screws in the 2x2 corners, and 1-1/2inch drywall screws to hold the top of the pad to the 2x2's. Drilling 3/32inch holes for the screws prevents splitting the wood. Drywall screws aren't necessary, but drilling appropriate holes for nails also prevents splitting.

A plastic &127;rework&127; type electrical box is used for the launch site. It measures 2-1/2 x 3-1/2 inches x 1-1/4 inch deep. Two 5/16inch mounting tabs stick out on each long end. The ones I can get here are all made from blue PVC plastic. I'll call it a bluebox from now on, even though yours may be a different color. When the launch pad is dry (an hour should do), center the bluebox from side to side, but within 3 inches of one end of the platform. Make sure it is &127;squared&127; with the edges. (Meaning that each edge of the bluebox is parallel to each edge of the platform.) Draw on the pad around the bluebox, and draw a circle inside all four mounting tabs. Set the bluebox aside. On the pad, draw a diagonal from one of the mounting tab circle marks to the opposite mark. Then draw a diagonal from the a third mark to the last opposite (fourth) mark. Where the two diagonals cross is the center hole where the valve stem will go through the pad. Drill it with a 5/8inch bit. Drill the four mount tab holes with a 9/64th inch bit. However, you may find it easier to drill one hole; screw the blue box down with a 10-24 by 3/4inch screw through the pad wood (getting it started may be a little hard, but should not be too hard.); finally drilling the next holes using the bluebox as a hole guide, screwing each down in turn. If you are careful, you really don't need nuts on the back side of the wood as the wood will form sufficient &127;treads&127; to easily hold the 75PSI.

Now a 1-7/8inch hole must be cut in the bottom of the bluebox. Refer again to the next page. Depending on your hole cutter, the hole that comes out can be used in the valve stem assembly later. The side holes for the locking/release pin should be drilled so as to just barely miss the bottom of the blue box. They are 1-1/4inches center to center. Use a 1/4 inch drill and a round file to give them a smooth clearance of the 1/4 inch &127;locking/release&127; rod. Usually 1/4 inch rod comes in 3 or 4 foot lengths. Cut a foot of it, bend it carefully without pliers into a U shape. If you use pliers, you will leave scars on the rod that will not allow a smooth pull. I drilled a 3/8inch hole in a 2x4 stud and used the hole to bend with. As you start to complete the U, you will want to use a pop bottle to help get the proper diameter of the U. (Bend the last part around the pop bottle neck.) Work the U until it slides smoothly in and out of the bluebox locking holes (that are 1-1/4 inch center to center). You will probably want to file the U ends until they are round enough to smoothly enter the bluebox.

Now for the valve stem. Buy a straight chrome Hi-performance valve stem (They usually come blister-packed in a box of four.) Western Auto sells them for about $5.00 a box. They are used for chrome or Mag (&127;high performance wheels). We will not need the bottom rubber washer. Take off the other washer as well. It should have a &127;lip&127; on it. Cut it off as carefully as possible without cutting the surface it is on. It is now a flat washer. Now put the metal washer on the stem, followed by the flat washer you cut. Push them all the way to the top. You will need a metal fender washer with a 7/16inch hole, or the hole cut from the bluebox with a 7/16inch center hole. Use it as a pattern to cut a piece of an old inner tube. A standard paper hole punch will punch a sufficiently large hole in the inner tube. Stretch the inner tube over the valve stem, working it up all the way up to the flat washer. Put on the &127;fender&127; washer (or bluebox hole &127;washer&127;). Screw on the valve stem nut. Now comes the O-ring. Any hardware store should have these. Inside diameter is 9/16inch. Outside diameter is 3/4inch. They usually come in a box of six. They can pop off during launch, so get a box. Work it onto the top of the valve stem over the high-performance metal washer onto the flat rubber washer. This should now fit into a pop bottle very snugly. If not, loosen the valve stem nut a little. If you fill a bottle half-way with water and put the valve on tight, it should hold all 9 the water in the bottle when you turn the bottle upside-down. If not, tighten the valve stem nut a little until it does. Now you can do accurate experiments with water quantities. You should be able to lower the whole assembly (with a bottle rocket on the stem) into the bluebox, and clamp it to the pad with the U lock/release pin.

Now for safety. Learning a carefully aimed but swift pull might not result in any accidents from the U-pin hitting shins or other body parts, but a restraint would be advisable. A 2x2 stud secured to the top of the pad on the opposite end of the launch bluebox will do. Drill a 9/16inch hole towards the top side and smooth it out so it won't wear the rope out. Or make a passive restraint from two large strips of inner tube about 3 foot long each. screw each to opposite corners of the end away from the bluebox site. These allow you to not need to put stakes in the ground in the pull direction of the pad to guarantee that the box doesn't get pulled into the rocket on a good hard pull. (The solid 2x2 stud will catch the rope and U-pin solidly, and can pull the pad into the rocket). Inner tube strips will be used at Texas State Tournament 1997.

One last requirement. Unless you like building pads, take the bluebox off now. Paint the entire wood surface with high gloss outdoor latex paint. (It sheds very well). Let it dry for 2 days, then mount the bluebox again. May I suggest a half-pint of your school color. Happy launching.

If this sounds complicated, you may contact the author, or see him at one of the Texas tournaments about buying one pre-built. I do have water bottle launch pads. Since these are largely used by schools who prefer to paint it their school colors, the launch pad will be unpainted and should be painted in a good exterior gloss latex paint (or other good water-proof coating) before using. Otherwise it WILL warp. If the order request comes on school letterhead with a photocopy of a 1998 Science Olympiad Coaches Manual cover, the cost is $25 plus $5 shipping. Otherwise, it is $30 plus $5 shipping (continental U.S.). I am not in a business, so I cannot do charge card stuff.

You may order a launch pad by sending check or

money order to:

Brigham Rees

1408 Dominique

Austin, TX. 78753

Current supply will determine speed of delivery.