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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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Direct fire air rocket

Discussions about rockets, construction materials, adhesives, nozzles, nosecones and fin design.
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vinni
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Direct fire air rocket

Post by vinni » Mon May 09, 2016 10:05 am

For my thesis I'm designing a direct fire rocket using water rocket technologies (just without the water). Before anyone has a fit about the recklessness of such a heinous act: Safety is the most important aspect of the thesis.
The idea is to have a launcher setup that could be used as artillery or direct-fire device in airsoft or paintball anti-vehicle or anti-fortification roles. Having some experience in the sport, I can assure you I've paid the utmost care to err on the side of caution whenever the situation arose. It wouldn't be the first time someone doesn't pay attention to what you're shooting and stroll right into the projectile's flight path.

It is constructed around the Gardena launcher system and uses a ring fin in order to fit into a launch tube (which is both for guidance as well as safety, it is a thin-walled pressure vessel after all). The nosecone is made of foam and is hemispherical, with a layer of foam between nosecone and bottle as a buffer zone.

The entire rocket prototype weighs in at just a smidge under 100 grams, and has a maximum velocity at burnout of about 37 m/s if pressurised to the max pressure of 6 atmospheres(depending on the launch angle, that is). The maximum pressure stems from impact safety precautions, not bottle burst limits.

Here's a video of the latest test fire:
https://www.youtube.com/watch?v=juVdNt7 ... e=youtu.be

The rear end of the launch tube has holes drilled into it to prevent the buildup of pressure behind the rocket as that might cause it to exceed the safe speed limits, but I think it needs more holes as it flies almost 5m further than calculations indicate.


As most of the experts on the combination of PET bottles and rocketry reside on this part of the internet, I'd thought this would be a good place to share :)



vinni
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Re: Direct fire air rocket

Post by vinni » Mon May 09, 2016 10:07 am

Also: I'm new here, hi :mrgreen:



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anoymous
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Re: Direct fire air rocket

Post by anoymous » Sun May 15, 2016 8:32 am

Nog een Belg!
Yeuy!


"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former."
- Albert Einstein

Sorry for malconstructions in my sentences, I am Belgian. And I was never good at making easy sentences.

Killer11b
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Re: Direct fire air rocket

Post by Killer11b » Sun Jul 24, 2016 1:22 am

Interesting Concept



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Blenderite
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Re: Direct fire air rocket

Post by Blenderite » Fri Sep 02, 2016 9:44 am

Here in 'Merica, there is no such thing as a rocket going to quick!

On a serious note, that is a very interesting idea you have going there! Good job!


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"Get it right, then go for GREATNESS!"

vinni
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Re: Direct fire air rocket

Post by vinni » Wed Nov 09, 2016 10:23 am

Thank guys :)

Currently still looking to optimise the nosecone. Safetywise I can't go more pointy than a hemispherical cone, but there is room to play with the material as the spring constant of the contact surface is the major factor in risk of injury.

Anyone got any ideas? Or perhaps some links where I can get some datasheets on A+B foam? :)

PS: zijn de belgen dan zo ondervertegenwoordigd hier? :o



mini feebas
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Re: Direct fire air rocket

Post by mini feebas » Wed Nov 30, 2016 9:37 am

vinni wrote:Thank guys :)

Currently still looking to optimise the nosecone. Safetywise I can't go more pointy than a hemispherical cone, but there is room to play with the material as the spring constant of the contact surface is the major factor in risk of injury.

Anyone got any ideas? Or perhaps some links where I can get some datasheets on A+B foam? :)

PS: zijn de belgen dan zo ondervertegenwoordigd hier? :o
To optimize the nosecone, you should go a little more pointy, i think. If i recall corectly, a parabole is better. But if you think that's already too dangerous, i think a perfect hemisphere will be your best option.
Ps: voor zo ver ik weet, zijn jij, discovery waterrockets en ik (ik ben trouwens anoymous, mijn ander account krijgt een browserfout bij het inloggen)



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China_WaterRocket
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Re: Direct fire air rocket

Post by China_WaterRocket » Thu Mar 02, 2017 1:24 am



I come from China, do not understand English, your information I use the translation software to view. I like water rockets, technology is the same, I hope we can become friends.

vinni
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Re: Direct fire air rocket

Post by vinni » Thu Aug 17, 2017 1:05 pm

So someone was kind enough to let me shoot their tank.

https://m.youtube.com/watch?sns=fb&v=7HFqHyf7SYI

The drift to the left is due to fin misalignment and/or side winds, not quite sure yet.

PS: In hindsight we were MASSIVE IDIOTS not to wear any eyepro, but the range was kept clear of passer-bys (this was at a reenactment event hence the tigerstripes and ODs).



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anachronist
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Re: Direct fire air rocket

Post by anachronist » Fri Aug 18, 2017 2:39 am

vinni wrote:So someone was kind enough to let me shoot their tank.
Thanks, that made me chuckle.
By the way, to answer a previous post in this thread, a pointy foam rubber nose cone would be safer than a hemispherical one due to the longer crush zone.

Does the launch tube seal around the body of the rocket? If it did, you'd probably get significantly more velocity out of it. Basically you try to make the launch tube act like a pneumatic cannon. You may have to do something with fins that fold. Otherwise keep the fins sticking out and use a split sabot (perhaps made of styrofoam) around the rocket that separates when it leaves the tube as in this video (see the last few seconds, good footage of sabot coming off after launch).



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