Water rocket tank

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Thomas235711

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Hello folks, I need help from an materials engineer or someone who knows about the materials strength laws. I first tried to make a rocket powered with rocket fuel, but this forum can't help-me with it cause I'm not american, and no one sends rocket motors international, so I am giving up with this fuel, but not with the Idea (I forgot to say that potassium nitrate is forbidden to buy in my country Brazil). I am making a high power water rocket, and its tank will be fueled with water and compressed air at 450-550psi. The tank will be 1,65m long and 70mm diameter. One observation is that its the ends will be capped with domed covers, welded to the tube (also made of aluminum) just like a propane tank. Now what I need help with : how can I calculate the needed wall thickness to resist 550 psi ? Thanks for attention
Obs: I am not pretty sure if this is the correct category for this topic, if not, tell me.

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I am not sure if it was on the NAR or Tripoli Facebook page, but I am pretty sure I saw a post from a Brazilian guy that does HPR. The launch site looked like your typical tropical paradise...


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TRF Member 'Evospider' is Brazilian, and lives in France. contact him, he is to be "coming home" sometime soon!

Thanks. I've just discovered that if I associate to BAR (it is like NAR, but the "B" means Brazilian) I'll be able to buy motors and ingredients to make by myself.


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I am not sure if it was on the NAR or Tripoli Facebook page, but I am pretty sure I saw a post from a Brazilian guy that does HPR. The launch site looked like your typical tropical paradise...


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Hehe, my country isn't a paradise, at least most of it isn't. There are good things and bad things. One of the good things in my opinion is that there are people who make a lot of effort to make their dreams reality (the model rocketry per example). People like me (I am 14 years old) who interest in rockets, and want to make their own. In my case is more difficult, there aren't much hobby stores, and I never saw any which sells things related to rocketry. I think that in the US there are lots of hobby stores and it's easy to buy rockets, am I right ?


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Can't help with with the materials question but aluminum isn't the best choice for a water rocket. Various plastics (FTC tubes, water bottles etc can be fiberglass reinforced to hand those pressured and you can also roll your own fiberglass pressure vessels. Here is a good resource https://www.aircommandrockets.com/

Here is a discussion of their current project, a 1000psi fiberglass design.
[video=youtube;q-8DWp1LqgQ]https://www.youtube.com/watch?v=q-8DWp1LqgQ[/video]
 
I thought in aluminum because It is lightweight, don't oxidize and (I think) resists high pressures


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Can't help with with the materials question but aluminum isn't the best choice for a water rocket. Various plastics (FTC tubes, water bottles etc can be fiberglass reinforced to hand those pressured and you can also roll your own fiberglass pressure vessels. Here is a good resource https://www.aircommandrockets.com/

Here is a discussion of their current project, a 1000psi fiberglass design.
[video=youtube;q-8DWp1LqgQ]https://www.youtube.com/watch?v=q-8DWp1LqgQ[/video]

I am thinking about using carbon fiber, but there are two issues : It's more expensive than aluminum and I didn't find any carbon fiber supplier in my city (which is the main city in my state). I only found it in São Paulo, but they don't send it to my city because it is too big. Another problem is that even if I use this material, I don't know the thickbess of the wall to resist 500 psi


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I am thinking about using carbon fiber, but there are two issues : It's more expensive than aluminum and I didn't find any carbon fiber supplier in my city (which is the main city in my state). I only found it in São Paulo, but they don't send it to my city because it is too big. Another problem is that even if I use this material, I don't know the thickbess of the wall to resist 500 psi


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Carbon fiber has its benefits but is more expensive than fiberglass and (edit: qualify with possibly) not necessary. (edit: I now see the Dark Shadow did use some carbon.) I am pretty sure the AirCommand folks discuss the process they used (type of fiber, number of wraps, etc ). You can always message them and ask. IIRC, USWaterRockets also have done similar things. I'm sure both will share with you.

Btw, I am not convinced you can easily get aluminum thin enough to approach fiberglass in weight. Maybe others can chime in.
 
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Thanks. This forum is great. Please tell me, I am learning english, and I wonder if I am writing everything correctly.


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English is a very difficult language to speak and write perfectly. Many English speaking people do not speak or write it correctly. However, English is great because you can speak it poorly and most people will still understand what you are trying to say.
 
English is a very difficult language to speak and write perfectly. Many English speaking people do not speak or write it correctly. However, English is great because you can speak it poorly and most people will still understand what you are trying to say.

That's true. I like to say that English is a live language.


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