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A water rocket is a type of model rocket using water as its reaction mass. The pressure vessel (the engine of the rocket) is constructed from thin plastic or other non metallic materials (usually a used plastic soft drink bottle) weighing 1,500 grams or less. The water is forced out by compressed air. It is an example of Newton's third law of motion.

Use of Bottled air

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Re: Use of Bottled air

Post by Tim Chen » Fri Jun 06, 2008 2:33 pm

Spaceman Spiff wrote:
The Mooseheads wrote:I think a simple solution to even the playing field would be to stipulate that anybody using a tank must fill the rocket and then wait a predetermined time (based on pressure) before launching. They would show this in a raw unedited ground camera video as proof.

Would this be an acceptable solution?


I'd go along with that. I'd love to see if anyone was really being put off by the compressor requirement. It's always been a hot topic.
That sounds quite reasonable. I've got a little bit of anxiety over the "stomp" rocket situation. I think it's not fair to make people using tanks have to use a small nozzle or short launch tube. These are things that can change the flight performance of the rocket and are not related to the filling system. We have to get rid of things which are going to change the rocket.

I propose that people filling with tanks have to use a small diameter hose between the tank and the rocket. At the minimum 50 feet distance, the hose would have enough friction to dash any hopes of using the tank to fire a stomp rocket.


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Re: Use of Bottled air

Post by Mark Chen » Fri Jun 06, 2008 5:27 pm

Tim Chen wrote:
Spaceman Spiff wrote:
The Mooseheads wrote:I think a simple solution to even the playing field would be to stipulate that anybody using a tank must fill the rocket and then wait a predetermined time (based on pressure) before launching. They would show this in a raw unedited ground camera video as proof.

Would this be an acceptable solution?


I'd go along with that. I'd love to see if anyone was really being put off by the compressor requirement. It's always been a hot topic.
That sounds quite reasonable. I've got a little bit of anxiety over the "stomp" rocket situation. I think it's not fair to make people using tanks have to use a small nozzle or short launch tube. These are things that can change the flight performance of the rocket and are not related to the filling system. We have to get rid of things which are going to change the rocket.

I propose that people filling with tanks have to use a small diameter hose between the tank and the rocket. At the minimum 50 feet distance, the hose would have enough friction to dash any hopes of using the tank to fire a stomp rocket.
WE came up with that idea together, bro! :lol:


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Re: Use of Bottled air

Post by Andromeda » Sat Jun 07, 2008 12:22 am

I am enjoying to see you guys putting so much thought into keeping everything fair. Thanks moderators for filtering out the bad seed. I wish I had ideas to contribute but I can't think of any at this moment but I did want to say I appreciate all the work you guys are doing. Well none indeed.


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Re: Use of Bottled air

Post by Tim Chen » Sat Jun 07, 2008 12:44 pm

Andromeda wrote:I am enjoying to see you guys putting so much thought into keeping everything fair. Thanks moderators for filtering out the bad seed. I wish I had ideas to contribute but I can't think of any at this moment but I did want to say I appreciate all the work you guys are doing. Well none indeed.
We're just brainstorming right now, which is fun and rewarding at the same time. I hope we get something formalized to present to everyone, but life is keeping me busy at the moment too. Thanks for the encouragement though! 8)


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Re: Use of Bottled air

Post by sporter2k5 » Sat Jun 07, 2008 2:01 pm

Do you guys think we need explanations for the rules governing pressurized air tanks (or other items for that matter) within the rules themselves in the form of the rule followed by the reasoning, or should the rules be just listed in clear statements and the reasoning for them listed in the separate rules FAQ?


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Re: Use of Bottled air

Post by U.S. Water Rockets1 » Sat Jun 07, 2008 9:18 pm

Hey Guys,
Nice work so far on the ammended rules proposals. You've touched on pretty reasonable solutions for all of the advantages as well as the dangers of using tanks. We're pleased to see co-operation and consensus on such a controversial subject, instead of arguments and criticizing.
If this is approved it won't force any of the established teams like us to have to change our equipment, so you probably won't see any objections. We really like our setup and don't want to invest in changing our equipment or getting certifications to do it any other way, so your ideas won't make it necessary for us to have to change anything. This is exactly what we would want. Everyone will have to work around the exact same issues, regardless of their pressure supply. We will be watching how this plays out. Keep up the good work!


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Re: Use of Bottled air

Post by Bellarossa » Sun Jun 08, 2008 5:15 am

I am interested too. Great!


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Re: Use of Bottled air

Post by sporter2k5 » Tue Jun 10, 2008 1:43 pm

I hope to get something written up this week. Thanks for contributing to my proposal everybody!


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Re: Use of Bottled air

Post by Spaceman Spiff » Fri Jun 13, 2008 12:17 pm

I was just thinking last night when I couldn't fall asleep that it would be a good thing if these idea were written up sooner rather than later. The more I think about it, the more I believe there's probably people who want to join up but don't like the way that tanks are prohibited. If 50% of all people want to use a tank then the roster could double in size in a very short period.


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Re: Use of Bottled air

Post by air.command » Thu Jul 10, 2008 5:42 am

Hello All,

I realise that I am not very welcome here, but Lisa asked for my comments on bottled air so I'm happy to offer some. I have observed that the "bottled air" discussion is a very contentious issue so I don't want to throw more fuel on the fire. I'm also not an expert on compressed air, but have been around it most of my life with dad's profession.

For what it is worth, my opinion on the subject is that WRA2 can set their own rules how they like and if bottled air is prohibited in the competition then it is prohibited for the stated reasons.

Potential competitors, however, see the prohibition of bottled air as a deterent because for altitude records high pressures are required. To achieve higher pressures good quality high pressure equipment is necessary and is harder to obtain. This includes hand pumps, compressors or bottled air.

Bottled air as I understand it is prohibited within the competitions because:

1) It is dangerous.

2) It could give the rocket a kick like a stomp rocket.

3) The type of gas used in a tank cannot be verified and potentially give an unfair advantage to a competitor.

4) Being able to fill the rocket faster compared to competitors using hand pumps or compressors.

5) Too expensive and not widely available.



1) Bottled air IS dangerous. I believe the main concern here is that the tank could explode with very unpleasant consequences. Explosive accidents in reality are extremly rare. Consider the use of compressed gasses in everyday life: oxy welders, people breathing oxygen with lung problems, mountain climbers, paint ball games, Clowns at fairs blowing up helium balloons, firefighters entering burning buildings with breathing equipment, CO2 fire extenguishers in people's cars and homes and tens of thousands of scuba divers who strap one to their back every day.

Cylindres of their own do not spontaneously explode. They are designed to withstand a certain amount of punishment. Take SCUBA tanks for example that generally cop a lot of abuse on dive boats getting knocked around. They are also designed to not explode when hit by a bullet. (Look at the mythbusters episode). The main valves are designed to withstand a certain amount of impact when knocked over.

This is not an endorsement for mishandling tanks and they need to be treated with utmost care and common sense.

All tanks always need to be filled by professionals who check the "last tested" stamps on the tank before filling and only fill the tank with the appropriate gas.

The next issue are the things that connect to the cylinder. Pressure regulators, gauges and hoses. People could try to cut corners and build ones themselves, (we would recommend highly AGAINST this) as that can be extremely dangerous. Only commercial regulators and gauges should be used at all times and only those designed for the specific gas. Greasy fittings and pure oxygen are a dangerous combination for example.

This ,however, isn't a "bottled air" problem specifically, it is a problem no matter what the source of air. One needs to consider the workmanship of equipment of the entire path of air from the air supply to the rocket. Not only do you have to consider a pressure regulator, but gauge connections, non-return valves, hoses, launcher fittings etc. Because you are away from the launcher when it is pressurised does not mean you can use sub par materials or bad construction techniques in its construction. You may have a compressor or one of those high pressure hand pumps that is connected to a dodgy manifold or substandard hose. When you build up 500psi in it even with a hand pump you will still get a nasty surprise if it fails.

Water rocketry is inherently a dangerous sport as we have encountered a number of times ourselves, and as strongly advocated by USWR safety should be at the top of the list.



2) This issue may be easily resolved. A rule amendment can simply say that before launch the air line to the air supply has to be disconnected with a quick release fitting. This can be (somewhat) verified in the required ground footage of the launch. This prevents any advantage from a "kick" whether from a tank, a running compressor or a very eager rocketeer on a handpump during launch.



3) This is not an easy one to resolve. Perhaps competition judges can take the word of the competitor in good faith, and if indeed a record is broken then a record can be published with an annotation saying that "Gas could not be verified but atmospheric air is suspected". It is then left up to the reader to decide based upon the presented evidence.



4) As Tim mentioned there is a definite advantage that bottled air can fill a rocket faster than a hand pump and a compressor is somewhere between the two. Filling a rocket too quickly, can cause other problems as well. Perhaps then if the potential record holder who uses a hand pump manages to achieve the record in 2 hours and 10 minutes, then again their record could be published with a note saying "Although the flights occured just outside the 2 hour mark a hand pump was used." If the same rocketeer manages the two launches in under 2 hours with a hand pump, then they earn the bragging rights that they managed to make a record with only a hand pump and the rules stay as they are.



5) Cost and availability is a potential issue, but no where in the rules is the real total cost of a record attempt mentioned. A high tech carbon fiber rocket with complex tracking electronics, sophisticated launcher probably costs a bit more than the price difference between a hired nitrogen tank and an expensive compressor. Again this can be an issue for bragging rights. "So-and-So managed to beat a record for only X dollars.

Compressed air tanks vary greatly in availability and price from place to place, but so is the availability of other rocket and launcher building materials.


These are perhaps some things to consider in using bottled air. I am not advocating that the rules be changed as it would disadvantage existing competitors who have factored the existing rules into their design. Perhaps those are some things to be considered in future competitions. Rules are always totally up to the discretion of the competition organisers.

I am not trying to encourage the use of bottled air over hand pumps or compressors and we recommend hand pumps or small battery operated compressors for new rocketeers to the sport. We use scuba tanks for our rockets and tests mostly for the convenience, ease of use and cost of refils.


There, my rant is over now it can be picked to pieces. :D


- George



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Re: Use of Bottled air

Post by WRA2 » Thu Jul 10, 2008 4:05 pm

air.command wrote:Hello All,

I realise that I am not very welcome here, but Lisa asked for my comments on bottled air so I'm happy to offer some. I have observed that the "bottled air" discussion is a very contentious issue so I don't want to throw more fuel on the fire. I'm also not an expert on compressed air, but have been around it most of my life with dad's profession.
Welcome to The Water Rocket Forum George, I think that you can make friends here once the people get to know you.
air.command wrote:All tanks always need to be filled by professionals who check the "last tested" stamps on the tank before filling and only fill the tank with the appropriate gas.
Our Thoughts on his were that the competitor would provide receipts from the filling station as part of their submission package.
air.command wrote:The next issue are the things that connect to the cylinder. Pressure regulators, gauges and hoses. People could try to cut corners and build ones themselves, (we would recommend highly AGAINST this) as that can be extremely dangerous. Only commercial regulators and gauges should be used at all times and only those designed for the specific gas. Greasy fittings and pure oxygen are a dangerous combination for example.

This ,however, isn't a "bottled air" problem specifically, it is a problem no matter what the source of air. One needs to consider the workmanship of equipment of the entire path of air from the air supply to the rocket. Not only do you have to consider a pressure regulator, but gauge connections, non-return valves, hoses, launcher fittings etc. Because you are away from the launcher when it is pressurised does not mean you can use sub par materials or bad construction techniques in its construction. You may have a compressor or one of those high pressure hand pumps that is connected to a dodgy manifold or substandard hose. When you build up 500psi in it even with a hand pump you will still get a nasty surprise if it fails.

Water rocketry is inherently a dangerous sport as we have encountered a number of times ourselves, and as strongly advocated by USWR safety should be at the top of the list.
Agreed, all fittings,hoses pipes and regulators should be the correct ones for the pressures and gas (air). This has been a problem in the past. Look at the discussions that have gone on in the old mailing lists on modifying regulators, filling tanks with other gasses, and other dangerous practices.

air.command wrote:2) This issue may be easily resolved. A rule amendment can simply say that before launch the air line to the air supply has to be disconnected with a quick release fitting. This can be (somewhat) verified in the required ground footage of the launch. This prevents any advantage from a "kick" whether from a tank, a running compressor or a very eager rocketeer on a handpump during launch.
Rick has the best solution to the "stomp rocket" issue. To have the competitor wait a predetermined amount of time after filling the rocket to full pressure or filling it slowly during that time. This would duplicate the long slow fill of a compressor and eliminate "stomp rockets". This can be verified using the ground video of the launch.

air.command wrote:3) This is not an easy one to resolve. Perhaps competition judges can take the word of the competitor in good faith, and if indeed a record is broken then a record can be published with an annotation saying that "Gas could not be verified but atmospheric air is suspected". It is then left up to the reader to decide based upon the presented evidence.
The competitor would be required to provide electronic copies of the receipts from the filling station as part of their submission package.
air.command wrote:4) As Tim mentioned there is a definite advantage that bottled air can fill a rocket faster than a hand pump and a compressor is somewhere between the two. Filling a rocket too quickly, can cause other problems as well. Perhaps then if the potential record holder who uses a hand pump manages to achieve the record in 2 hours and 10 minutes, then again their record could be published with a note saying "Although the flights occured just outside the 2 hour mark a hand pump was used." If the same rocketeer manages the two launches in under 2 hours with a hand pump, then they earn the bragging rights that they managed to make a record with only a hand pump and the rules stay as they are.
We like the 2 hour rule as it stands. A record should be repeatable and not accomplished by luck or "perfect weather conditions". The 2 hours time can be verified from the ground and onboard videos. Teams have to consider this when designing their rockets and launchers.
air.command wrote:5) Cost and availability is a potential issue, but no where in the rules is the real total cost of a record attempt mentioned. A high tech carbon fiber rocket with complex tracking electronics, sophisticated launcher probably costs a bit more than the price difference between a hired nitrogen tank and an expensive compressor. Again this can be an issue for bragging rights. "So-and-So managed to beat a record for only X dollars.
The cost was never a consideration for our advanced classes as once AGR set the record and we formed our competition to beat them that an advanced rocket would be needed. When AGR set their record using a reinforced bottle the days of record rockets built with recycled household materials were over for good. We have a "Class C" that people can enter where cost was considered and strongly encourage beginners to start there.
air.command wrote:[Compressed air tanks vary greatly in availability and price from place to place, but so is the availability of other rocket and launcher building materials.


These are perhaps some things to consider in using bottled air. I am not advocating that the rules be changed as it would disadvantage existing competitors who have factored the existing rules into their design. Perhaps those are some things to be considered in future competitions. Rules are always totally up to the discretion of the competition organisers.

I am not trying to encourage the use of bottled air over hand pumps or compressors and we recommend hand pumps or small battery operated compressors for new rocketeers to the sport. We use scuba tanks for our rockets and tests mostly for the convenience, ease of use and cost of refils.


There, my rant is over now it can be picked to pieces. :D


- George
Once again, thanks for the input George.


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Re: Use of Bottled air

Post by Tim Chen » Thu Jul 10, 2008 11:18 pm

Hi George. Welcome.

That was a well thought set of suggestions. It's good to hear from someone who has experience with air tanks.


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Re: Use of Bottled air

Post by WRA2 » Fri Jul 11, 2008 10:09 am

I have another question for George,

What types of regulators are used on SCUBA tanks legally?


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Re: Use of Bottled air

Post by Team Seneca » Fri Jul 11, 2008 10:51 am

SCUBA is sooo "last week". I use a rebreather.


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Re: Use of Bottled air

Post by air.command » Sat Jul 12, 2008 7:25 am

WRA2 wrote:I have another question for George,

What types of regulators are used on SCUBA tanks legally?
From a legal point of view one can connect anything they like to an air tank whether it be a commercial regulator or something they build themselves. There is no law that prevents one from holding a rubber hose against the air outlet of a tank, or whether they add a fitting to make it easier, or add a piston and spring to make a simple regulator. Even commercially produced regulators are not governed by any "laws". However, it is in the interest of regulator manufacturers to adhere to materials and design standards and norms established by the industry. Selling products that are faulty or harmful will not keep them in business very long.

At least in Australia and in the USA SCUBA regulator manufacturers don't need to have any certifications to sell their regulators. Within the EU regulators require to be certified to get the 'CE' label in order to be sold. But after they are sold, there are no laws that prevent one from modifying them.

This is because laws never prevent you from doing harm to yourself. Laws are there to protect harm done to others and their property.

Where the law comes into it is if the results of your actions cause injuries to someone. This does not relate specifically to things that you connect to a tank, but ANYTHING you do. such as droping a hand pump on someone's foot. Then they can sue you for injury.

Therefore it is in the rocketeers best interest to use equipment that adheres to standards and follow best practices when doing anything associated with water rocketry in order to minimise the risk. My recommendation would be that if the rocketeer is not confident that something they've made is safe, then there are two options: Either keep themselves and others well away from it in case it fails, or not do it in the first place.

I must stress that this is not an endorsement for people to start buying any old tanks and attachments and adapting them for use with water rockets. There are commercially available adjustable pressure regulators, gauges and hoses that are suitable for water rocketry. This is what we use.



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