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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.


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Air Supply question

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bugwubber
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Air Supply question

Post by bugwubber » Fri Sep 20, 2013 11:10 pm

Is a compressor with a tank attached still considered a compressor under the rules or is it considered to be a bottled air source?

Thanks, just wanted to clarify

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Re: Air Supply question

Post by WRA2 » Sat Sep 21, 2013 4:35 pm

bugwubber wrote:Is a compressor with a tank attached still considered a compressor under the rules or is it considered to be a bottled air source?

Thanks, just wanted to clarify

Bugwubber
The original intent of the rule was to prevent people from making a stomp rocket, so tanks were not allowed at all.

There were a couple of people who really objected to this rule, and in the spirit of water rocket unity, it was decided to allow people to use tanks, if they could show that they were filling the rocket with the tank and then holding the pressure for 10 minutes.

We've been considering making changes to the rule so that it is less restrictive. For example. We were thinking of setting up pressure classes and making the lower classes more open by saying you can fill the rocket any way you want if the max pressure is less than 150PSI.The unreinforced bottle class would be a good example for that.

One proposal that was made is that for higher pressure classes we would need to see that you didn't fill the rocket faster than 25% of the volume per minute. Another would be to use a small diameter fill hose to restrict the flow to the rocket while pressurizing thus forcing a "slow fill".

As the rule currently stands, a compressor and tank would be considered a compressor only If the tank was not pre-pressurized and you filled the built in tankattached to the compressor and the rocket at the same time.

We normally do our proposed rules changes during November-January and we will be holding discussions in the WRA2 association business forum. Any suggestions would be welcome. The goal is to allow the use of bottled air but prevent a team from flying a "stomp rocket" which could be conceivably be built lighter as it would not need to withstand launch pressure (or even pressures near launch pressure for an extended period of time like if the rocket was filled slowly with a compressor).


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Re: Air Supply question

Post by bugwubber » Sat Sep 21, 2013 10:04 pm

Thanks,

I'll most likely just use my 12v compressor for our record attempt but I wanted to be sure what procedure I should follow if I needed to use my big compressor.

The tank definitely allows faster fill but it would take longer to fill a 32gal tank + rocket to 100psi.

My opinion would be to eliminate the difference for "specified material" competitions. If you are controlling what the pressure bottle is made of, then the stomp rocket issue becomes a moot point. As far as speed to fill giving an advantage, well there is already a ton of time built in so just that eliminates any benefit at these lower pressures. At higher pressures and larger rockets, yeah I see the advantage to having a 2500psi bottle vs a LVHP pump.

My two cents anyway.

Thanks,

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Re: Air Supply question

Post by bugwubber » Sun Sep 22, 2013 1:25 am

bugwubber wrote: The tank definitely allows faster fill but it would take longer to fill a 32gal tank + rocket to 100psi.
Meant to finish that with "...than my 12v compressor just filling the rocket"

This was in response to the thought of allowing a tanked compressor to start filling from empty.

No need to discuss that further now.

One last question- do I need to isolate the launcher from the tank/compressor prior to launch?

Thanks,

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Re: Air Supply question

Post by WRA2 » Sun Sep 22, 2013 5:53 pm

bugwubber wrote:
bugwubber wrote: The tank definitely allows faster fill but it would take longer to fill a 32gal tank + rocket to 100psi.
Meant to finish that with "...than my 12v compressor just filling the rocket"

This was in response to the thought of allowing a tanked compressor to start filling from empty.

No need to discuss that further now.

One last question- do I need to isolate the launcher from the tank/compressor prior to launch?

Thanks,

Bugwubber
Well a 32 gallon tank would definitely count as bottled air.Probably the best thing you could do if you wanted the option of filling the tank or the rocket would be to install valves to give you the choice of either filling the rocket, tank or both.

What do you mean by isolate from the compressor/tank? Are you saying to shut off the air supply prior to launching? It does not matter either way. A team could have a pressure regulator set to the launch pressure and the valve open from the tank (thus maintaining launch pressure should there be leaks). The drawback would be that you would lose air from your supply after the rocket launched and the launch operator closed the valve. As far as being rules compliant, it would not matter.


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Re: Air Supply question

Post by bugwubber » Mon Sep 23, 2013 12:46 am

WRA2 wrote:
bugwubber wrote:
bugwubber wrote: The tank definitely allows faster fill but it would take longer to fill a 32gal tank + rocket to 100psi.
Meant to finish that with "...than my 12v compressor just filling the rocket"

This was in response to the thought of allowing a tanked compressor to start filling from empty.

No need to discuss that further now.

One last question- do I need to isolate the launcher from the tank/compressor prior to launch?

Thanks,

Bugwubber
Well a 32 gallon tank would definitely count as bottled air.Probably the best thing you could do if you wanted the option of filling the tank or the rocket would be to install valves to give you the choice of either filling the rocket, tank or both.

What do you mean by isolate from the compressor/tank? Are you saying to shut off the air supply prior to launching? It does not matter either way. A team could have a pressure regulator set to the launch pressure and the valve open from the tank (thus maintaining launch pressure should there be leaks). The drawback would be that you would lose air from your supply after the rocket launched and the launch operator closed the valve. As far as being rules compliant, it would not matter.
Ok thanks. If I need to use my big compressor I will just follow the bottled air rules except I won't have any certifications or filling station receipts. I've already lost one 12v compressor when my kids dropped it just right so it's best for me to be prepared.

Thanks,

Bugwubber


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