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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.

Launch tube question

Discussion about Compressors, hose, pipes, fittings, launchers, release mechanisms, and launch tubes.
Scorpion_XIII
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Re: Launch tube question

Post by Scorpion_XIII » Sun May 24, 2009 7:57 am

Hello from Germany,

it ist great that the discussion goes around the world :)

From our (German roketrys) point of view, uses a waterrocket the thrust from the water to fly.
That means the compressed air inside the rocket presses the water through the nozzle and thats the 'thrust'. But the 'world record' from USA does not really use this princip.
We don't know the measurements of your rocket and launchtube diameter, but it seems that your rockets use not that 'waterrocket-princip'.

If the outer-diameter of the launch tube and the inner diameter of the rocket are nearly the same, than you have a zylinder! And that is not a waterrocket ;)

Our launchtubes are 15mm thick and the rockets are at minimum normally around 60mm thick.
Only the nozzles have a diameter of 15mm (or 9mm or 22mm).
So there is the feeling of a rocket when it starts. (Water comes out... :))

To the point of the 'complicated' rules of launchtubes:
The use of a launchtube is a good thing, as someone mentioned it, it gives stability in the first phase of the flight. So we allowed a launchtube. But to prevent such 'zylinder-rockets' the maximum diameter is limited to 15mm. Because some people use cable tie launchers and they have a short launchtube of 22mm there a this special rules.
But the rules are not fix, so there might be some changes in next time ;)

I hope some questions are solved, if not ask :)

Greetings
Scorpion_XIII



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U.S. Water Rockets1
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Re: Launch tube question

Post by U.S. Water Rockets1 » Sun May 24, 2009 10:38 pm

Scorpion_XIII wrote:Hello from Germany,

it ist great that the discussion goes around the world :)

From our (German roketrys) point of view, uses a waterrocket the thrust from the water to fly.
That means the compressed air inside the rocket presses the water through the nozzle and thats the 'thrust'. But the 'world record' from USA does not really use this princip.
We don't know the measurements of your rocket and launchtube diameter, but it seems that your rockets use not that 'waterrocket-princip'.

If the outer-diameter of the launch tube and the inner diameter of the rocket are nearly the same, than you have a zylinder! And that is not a waterrocket ;)

Our launchtubes are 15mm thick and the rockets are at minimum normally around 60mm thick.
Only the nozzles have a diameter of 15mm (or 9mm or 22mm).
So there is the feeling of a rocket when it starts. (Water comes out... :))

To the point of the 'complicated' rules of launchtubes:
The use of a launchtube is a good thing, as someone mentioned it, it gives stability in the first phase of the flight. So we allowed a launchtube. But to prevent such 'zylinder-rockets' the maximum diameter is limited to 15mm. Because some people use cable tie launchers and they have a short launchtube of 22mm there a this special rules.
But the rules are not fix, so there might be some changes in next time ;)

I hope some questions are solved, if not ask :)

Greetings
Scorpion_XIII
Now the issue is clear! Thank you for explaining the mis-communication. It appears that you have confused our water rocket with the rocket known as "Insane Air" which was flown by Robert Youens. His design used compressed CO2 to fire a FTC rocket over 1,000 feet with this method.

The rules which we agreed to follow (http://wra2.org/WRA2_Class_A_Rules.php) has several requirements which would make an "insane air" style rocket illegal to compete:

I. Water Rocket General Class ‘A’ World Record Design Parameters
...
2) Rocket must use Water as its primary reaction mass.
...
5) Rocket must be launched from a stationary position on a fixed launcher. (Slingshots, trebuchets, catapults, cannons, and all other forms of launcher boost assist are forbidden). Launch tubes are allowed as long as the internal pressure of the rocket is the only supply of energy.
...
V. Reaction Mass Rules
1) Reaction Mass must be primarily ordinary tap water.
2) Thrust must come from expelling reaction mass, not from air discharge. That would be considered an Air Cannon projectile.
3) Water Reaction Mass must fill a minimum of 20% of the volume of the Pressure Vessel. Token amounts of water added in an attempt to qualify an air cannon projectile as a water rocket are not allowed.
...


When we first formed our team to set the world record altitude for water rockets, we decided it was very important to follow a set of standard rules which would eliminate the possibility for people to cheat by using "non water rocket" ideas to try and set records, and protect us from anyone accusing us of doing this ourselves.

The rules further require the following:

VI. Filing a Record Claim
1) All record claims must be filed to the WRA2 Contest Submissions for public review.
2) Items required:
-Onboard video for both flights.
-Ground videos for both flights
...


By providing these videos, it is easy for peers to confirm that the rules are being followed. Having these videos available can also show that the assumptions some have made about our launch tube are not correct. If you look at our world record videos:

[youtube][/youtube]

[youtube][/youtube]

You can clearly see that our launch tube is a lot narrower than our rocket body. You can also see that water is being used to propel the rocket. It is clear from the videos that water is used for thrust.

It could be possible that the typical water rocket person would expect to see a neat stream of water and spray of droplets coming from the rocket, but at extreme pressures the water comes out in a fine mist of atomized drops.

We have a video taken from another launch which shows a view of our water column as well as the "air burst" which any water rocket person will instantly recognize as the trademark of a water rocket (which would be missing from a "piston" rocket). If you look at this video, you will observe the water very clearly:

[youtube][/youtube]

Hopefully, you can show this to your friends who mistook our design and the example will help you and your friends to design rules which will allow you to use launch tubes of some sort.

One important use for launch tubes is to prevent the water from draining back into the pressure supply. By putting the air inlet at the tip of the launch tube the air can be safely removed from the rocket in case of an emergency. Another one of the rules we follow requires a way to remove the air if there is a problem. If you do not allow any launch tubes in your contest, people will have to put a one-way valve in their rocket to keep the water from draining back into the hose. This will make it more difficult to release the air pressure. Keep this in mind when you decided on your rules.

Oh yes... one more thing.... until 2009, the WRA2 rules forbid the use of any source of air other than a compressor to power a rocket. All of our records were set using a compressor, which shows that our rockets are used as the pressure source, and the rocket is not powered by external air pressure into a "cylinder".

Thanks for explaining the situation. Hopefully, we have explained our design clearer now.


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Scorpion_XIII
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Re: Launch tube question

Post by Scorpion_XIII » Mon May 25, 2009 5:09 am

Hi,

thanks for that description. The rules have changed by time? At the beginning there were less rules?
For me your rules are a bit complicated ;) A restriction to a 15mm Launchtube might be enough...
Launchtubes are a good thing, the positive aspects (water does not go back to pump, removing air safely...) are known. We use still launchtubes but the diameter is restricted.

To take a onboard video is nice, but we think it is not so important. The data from the altimeter is the main point. From the onboard video it is hard to say if the rocket is 500m or 600m high ;)

Greetings
Scorpion_XIII



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Spaceman Spiff
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Re: Launch tube question

Post by Spaceman Spiff » Mon May 25, 2009 10:31 am

Scorpion_XIII wrote:Hi,

thanks for that description. The rules have changed by time? At the beginning there were less rules?
For me your rules are a bit complicated ;) A restriction to a 15mm Launchtube might be enough...
Launchtubes are a good thing, the positive aspects (water does not go back to pump, removing air safely...) are known. We use still launchtubes but the diameter is restricted.

To take a onboard video is nice, but we think it is not so important. The data from the altimeter is the main point. From the onboard video it is hard to say if the rocket is 500m or 600m high ;)

Greetings
Scorpion_XIII
I think you and the WRA are trying to have the same rule but with different ways to specify the same thing. You want to limit the LT to 15mm and they want to lame the LT a fraction of the volume of the rocket.

I like the ratio way better because if you set a limit on the diameter of the LT then you are not fair to every type of rocket. A 15mm LT is huge for a T8 FTC rocket and 15mm is tiny for a 3 liter bottle rocket. I think WRA2 considered that so you do a ratio of volume to water then you can be fair to everyone.

I bet if you make 15mm the max LT size then someone would make a 15.5mm piston rocket just to set the record.


Spaceman Spiff
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Re: Launch tube question

Post by WRA2 Admin » Mon May 25, 2009 12:10 pm

Scorpion_XIII wrote:Hi,

thanks for that description. The rules have changed by time? At the beginning there were less rules?
The rules have been the same for about 5 years, with only minor clarifications added. The only change approved by a majority consensus on this very forum was to eliminate a rule banning bottled air by adding a rule describing the restrictions on its use.

The topic discussing the use of bottled air can be found here:

http://www.wra2.org/forum/viewtopic.php?f=15&t=254

One of the reasons we required a compressor was to eliminate those "piston rockets" or as we call them "stomp rockets".
Scorpion_XIII wrote:For me your rules are a bit complicated ;) A restriction to a 15mm Launchtube might be enough...
Launchtubes are a good thing, the positive aspects (water does not go back to pump, removing air safely...) are known. We use still launchtubes but the diameter is restricted.

To take a onboard video is nice, but we think it is not so important. The data from the altimeter is the main point. From the onboard video it is hard to say if the rocket is 500m or 600m high ;)?
The camera requirement is really not to measure altitude. For that we require a commercial logging altimeter. The videos from the camers serve several purposes. One is to verify that the flights occurred (and you did not just put the logging altimeter in a pyro rocket or fly the required 2 flights on different days) (or even different seasons or in 2 different locations). We can also compare the sky/ground/location from the video onboard to the ground video showing the rocket launching. The "altitude vs. time" graph from the altimeter can also be compared to the onboard video proving that the altimeter data came from that flight of the rocket shown. Time to apogee to touchdown can be compared to the altimeter data. Another is to promote the sport to new people. The onboard videos have drawn many new people to the sport. Video from one of our teams even was shown on a world wide television show (Mythbusters) A lot of our members mention that they were first interested in water rocketry when they saw the show.Flying a camera is now a lot easier then it was when we first formed the WRA2 6 years ago. The cost has come down and the capabilities of the cameras has increased over the time making it easier to fly one.
Low cost cameras are available everywhere.

Since you have an organized competition, you might want to propose that become a class in the WRA2. Just post (or have a representitive of the competition administration) post a list of the rules to our competition Q & A forum :

http://www.wra2.org/forum/viewforum.php?f=15

For membership disussion and approval. :WRA2:


David Walker
Administrator
The Water Rocket Achievement World Record Association

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Mark Chen
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Re: Launch tube question

Post by Mark Chen » Mon May 25, 2009 3:06 pm

Scorpion_XIII wrote:Hi,
To take a onboard video is nice, but we think it is not so important. The data from the altimeter is the main point. From the onboard video it is hard to say if the rocket is 500m or 600m high ;)
Greetings
Scorpion_XIII
The camera isn't used as the altimeter, they use it show the launch really took place. It looks way cool too! This means the onboard video allows WRA2 to have a World Wide Competition!

If you don't show a video from the rocket then you can't have a contest with a wide participation. The only way to prove you flew the rocket would be to have a launch where your competitors can observe your flight themselves. Very few people are going to want to spend thousands of dollars to see you launch. What happens if you have bad weather too? Imagine getting airline tickets to watch a competitor launch and they have to cancel because the weather was bad? You would lose your money from your travel and lodging and if that were me I would be very angry. The only alternative is to prove their record with onboard video. This is a small price to pay in exchange.

There's really no reason not to have an onboard video anymore, a camera adequate to do the job costs less than some of the gardena connectors people use.


Mark Chen
Team Enterprise

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