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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.

Simple new staging mechanism

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SaskAlex
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Simple new staging mechanism

Post by SaskAlex » Wed Apr 22, 2009 11:44 pm

Well I'm new around here, so I'm not sure if this is new. From what I can tell though, most people seem to have fairly intricate stagers, and I think mine is unique. I've been developing this idea for a while, and I finally have a working staging mechansim. I've only launched with it twice and it worked both times. There really is no way that it won't separate. What I'm not sure of is how much pressure it will hold before it leaks. So far I've only had it up to about 80 psi and there were no leaks. I'm hoping to get it up to about 150 pretty soon. Personally, I make fairly low-volume rockets and can pump them up quite fast, so I'm not concerned if I get a slow leak. However, I think this will still hold a lot of pressure without leaking if I drill a hole tight enough.

I think the pictures are pretty self-explanatory, but let me know if you have questions. Basically, the shrink wrap makes an air-tight seal with both the top cap of the booster and the sustainer nozzle, letting air pass between them. When the booster takes off the string pulls the shrink wrap out of both caps. After the booster is done thrusting the stages just fall apart.

Oh, and after you see the pictures you might wonder what stops water from the sustainer from falling into the booster. The answer is, nothing really. The shrink wrap is just small enough that water can't go down and air up at the same time. In testing, a little squirt of water did make it down from time to time, but it was nothing really. It won't take much work to add a one-way valve to the booster side of the shrink wrap either, and this might be necessary if larger diameter shrink wrap is used.

I'm also trying one out with a larger (diameter) peice of shrink wrap. The holes in the caps for that one are 9/64". I've had it up to 50 psi in the shop with only a negligible leak (tiny bubbles very slowly appearing when submerged in water) but haven't launched with it yet.

So here it is, the stupidly simple stager:
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rockets-in-brighton
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Re: Simple new staging mechanism

Post by rockets-in-brighton » Thu Apr 23, 2009 4:45 am

This looks really ingenious, thanks for sharing it. It seems to be a very pared-down variation on the crushing sleeve. I assume that the sustainer is prevented from premature release on the launcher by the expansion of the shrink wrap tube during pressurisation, which is then whipped out at launch by the string. So how have you attached the string to the launch tube without anything sticking out of the side?


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SaskAlex
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Re: Simple new staging mechanism

Post by SaskAlex » Thu Apr 23, 2009 10:16 am

Actually, it's even simpler than that. It's just friction that keeps the sustainer from taking off prematurely. So you can see how important it is to get a nice hole that the heat shrink just fits into. I figured this would be possible when I realized just how small the nozzles were that people use in their sustainers. That's not to say you need to use a tiny hole, though. When I first got into water rocketry I didn't know anything about it, or that anyone else did it. I came up with a friction fit stopper (like the cork release) that fit in a 1/4 nozzle and didn't even leak at 150 psi. It had to be yanked out to release the bottle.

As for the string, I've built myself an internal grip launcher (http://www.geocities.com/af_wr/) that has a nice bolt on the inside of the launch tube that I can just tie the string too. But I think it would be pretty easy to glue a little hook on the inside of a launch tube to tie the string to, or even glue the string itself.

Alex



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Re: Simple new staging mechanism

Post by dongfang » Thu Apr 23, 2009 10:26 am

Hi,

Very nice design!! I'm going to build and test one when I have a chance, except that I am going to fill it up with aluminium pipes and O-rings as usual, instead of shrink wrap . . . I particularly like the absence of stuff that can fail to trigger.

To keep the 2 caps centered on each other, you could just find a piece of plastic / aluminium / epoxy reinforced cardboard tube that just fits over both caps.

Yes the booster makes the speed; the sustainer sustains it :)

Regards
Soren



SaskAlex
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Re: Simple new staging mechanism

Post by SaskAlex » Thu Apr 23, 2009 11:56 am

Hi Soren,
I didn't use a tube to fit over the caps for two reasons. First of all, I have tons of old tire tube lying around and some great two-sided tape, so this was actually the easiest method. Secondly, if I get around to making a more refined two-stage rocket this summer the sustainer will probably have a tapered aerodynamic fairing that goes right down to, or a little passed, the bottle cap. Good luck with your version, and try to get some pictures.

Alex



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Tim Chen
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Re: Simple new staging mechanism

Post by Tim Chen » Thu Apr 23, 2009 1:17 pm

Wow! What a great idea! I like the fact that it's so simple and really doesn't have any parts or mechanical pieces to fail.

Thank you for sharing the concept! Great job!


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U.S. Water Rockets1
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Re: Simple new staging mechanism

Post by U.S. Water Rockets1 » Sat Apr 25, 2009 10:17 pm

Hey that is a great and simple design! Good work!!! It's not something that would probably adapt well to the pressures we use but nevertheless it's a really brilliant idea! 8)


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runnin_rocket_maker
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Re: Simple new staging mechanism

Post by runnin_rocket_maker » Tue Oct 20, 2009 8:45 pm

What a great idea, simple yet eloquent. I may have to try this myself, have you gotten the opportunity to test launch yet?



SaskAlex
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Re: Simple new staging mechanism

Post by SaskAlex » Wed Oct 21, 2009 12:16 am

Yes, I've launched with it. It works very well. Unfortunately, some other aspects of my two-stage rockets don't, and I don't have the time to make a real good one at the moment. I have tested the seal in the shop and it held up to 160 psi. That's all I got it up to, but I think it could go even higher. Good luck if you give it a shot!



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Jelo
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Re: Simple new staging mechanism

Post by Jelo » Mon Oct 26, 2009 6:52 pm

i dont get how it works...


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SaskAlex
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Re: Simple new staging mechanism

Post by SaskAlex » Tue Oct 27, 2009 6:34 pm

Jelo wrote:i dont get how it works...
Alright, here is a very rough diagram of the launch sequence. First note that this stager does nothing to keep the booster and sustainer aligned. In the rocket above, the trailing fin of the sustainer kept it in line with the booster.

1. While on the launcher, the shrink wrap lets air from the booster flow into the sustainer. Water doesn't flow from the sustainer into the booster because the shrink wrap is so small. The only force trying to separate the stages is (the area of the hole in the bottle caps) x (the pressure in the rocket). The weight of the sustainer and the friction between the shrink wrap and the bottles caps is much greater, so they don't separate.

2. When the booster is released the shrink wrap is pulled out of the caps by the string. The stages stay together because the acceleration caused by the booster is much greater than that caused by the sustainer (because the sustainer's nozzle is so small). A little bit of water from the sustainer shoots into the booster. This isn't a big deal.

3. When the booster is done thrusting, it decelerates rapidly due to gravity and air resistance. The sustainer keeps going because it is still expelling water. With nothing to keep them together, the stages separate flawlessly.

Hope that helps.
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Jelo
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Re: Simple new staging mechanism

Post by Jelo » Wed Oct 28, 2009 11:33 am

oh right yeah i get it...but you cant use it on 9mm nozzles....


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Rocket Man97
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Re: Simple new staging mechanism

Post by Rocket Man97 » Thu Jul 01, 2010 11:33 pm

How is this a stager? The way your drawing shows it, it looks like the bottom bottle isn't all the way off the launcher before the string is pulled out. I thought multi stage rockets were supposed to get off the launcher and go quite a few feet before the bottles separated.



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U.S. Water Rockets1
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Re: Simple new staging mechanism

Post by U.S. Water Rockets1 » Sat Jul 03, 2010 10:43 pm

Rocket Man97 wrote:How is this a stager? The way your drawing shows it, it looks like the bottom bottle isn't all the way off the launcher before the string is pulled out. I thought multi stage rockets were supposed to get off the launcher and go quite a few feet before the bottles separated.
The thrust of the first stage should be powerful enough to keep the upper stage from separating until the first stage is exhausted even though the release is pulled.


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srowe
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Re: Simple new staging mechanism

Post by srowe » Wed Jul 13, 2011 5:52 am

cant see pictures. guess i dont have enough posts yet.



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