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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.

My first project.....

Discussions about rockets, construction materials, adhesives, nozzles, nosecones and fin design.
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Braaainz
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My first project.....

Post by Braaainz » Sat Aug 11, 2018 4:52 am

I built simple 2 liter water bottle rockets since the 90's with soft nosecones for a simple lawn dart recovery.

For my first project with modern water rocket tech, I've got a ftc T-12 tube attached to a 1 liter bottle via a tornado tube. Atop that, I have a Tommy timer with rubber band mechanism to release the parachute. Nosecone is a large plastic Easter egg. Nozzle is going to be Gardena type.

I used a heat gun to form fit my end caps. In hindsight, I should have created a mold to shrink over. The end caps are a little off center, but the rocket appears straight when put together.

I'm using corrugated plastic for fins and attaching via Velcro stickers.

Questions:

1. What pressure can an ftc T-12 tube usually hold?
2. What about a 1 liter bottle? Back in the 90's, I just used 100 lbs of pressure without any problem for my 2 liter bottles.

When I created my end caps, I didn't trim them down much, thinking more surface area would result in a better seal between the ends and the ftc.
3. Other than added weight, will that be a problem?

4. In my reading on the forum, I saw how FTC tubes flex. Will my 1 liter on top with another module holding the payload package and Tommy timer be too much weight for the tube under acceleration?



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retrotec29
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Re: My first project.....

Post by retrotec29 » Sat Aug 11, 2018 1:03 pm

Sounds cool. I hope you can post some pictures. The T-12 tube can handle quite a bit a pressure. I have ventured to 125psi with a few of my rockets. I have heard of a few others going much higher. Big problem is the joint. When you create the slip fit the adhesive should not get all squeezed out. Also a good rough surface on the insert and tube is necessary. Adding length to the inset will certainly help help the joint. A far as the weight of your deployment pod being a problem that is a complex question. The pressure and mass inside the booster will increase its rigidity. Big factor is the G's when it jumps off the pad. Using a Gardena nozzle will help. Lower initial yield but longer burn. Hope this helps. Good luck.


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anachronist
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Re: My first project.....

Post by anachronist » Sat Aug 11, 2018 2:12 pm

A gardena nozzle also adds significant weight, but it does reduce the G forces. I'd try instead to ensure that the equipment stays in place.



Braaainz
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Re: My first project.....

Post by Braaainz » Wed Aug 15, 2018 10:59 pm

First launch.
I made a couple quick pool tube topped rockets with Stratolauncher fins and gardena nozzles, so we could launch those if my main rocket failed.

First one was perfectly balanced for a tumble recovery. It used a 1.5 liter Seltzer bottle. Had great height and launched it 4 times total. Last 3 launches were at 120 psi. :D

Second bottle was a 1 liter bottle. It was not balanced correctly and reached only about 40 feet before tumbling. :?

Now, the main rocket. :(

First problem: I didn't realize I'd need to add washers to my tornado tube. We managed to launch at around 60 psi while leaking air constantly. DOH:
Second problem: No launch rail. The height and weight of the rocket was too much for it without one.
Third problem: Tommy timer had too long of a delay.

So, I was pumping like crazy to keep the rocket at pressure. I had the timer set for 15 seconds, hoping to give us a 10 second count down.
Without the launch rail, the rocket started to tip, but the launcher was secured with tent stakes. When it hit about a 45 degree angle, my Gardena nozzle remained secured to the launcher, but the main rocket broke free and it launched on its own with the regular bottle nozzle. EK:

It looked really impressive, even going at a 45 degree launch angle. It soared out of our designated launch/recovery area and into a fenced off field.

Because the launch was premature, the Tommy timer didn't have time to release and deploy the parachute, so the rocket lawn darted well before release could happen.

The Easter egg nosecone shattered and the payload area crumpled at each end (I had built an extra long payload area just in case if lawn darting happened). I had two bottle caps I'd cemented together break, ripping the plastic cover on them as well.

Luckily, the FTC body survived unscathed; which, after the heat shrinking of the end caps and cementing, I'm very happy about.

We tested the main FTC body afterwards (using just a bottle cap instead of the 1 liter reservoir chamber and payload bay), and it held pressure without a problem. We launched at about 40 psi, half filled with water, and it had a very slow and beautiful launch with tumble recovery after reaching about 50 feet in height (I didn't want to push for higher because I didn't want to damage it).

Next launch will be using the FTC body with a radial deploy using a small T12 diameter payload area and parachute... but it will be at least a day before I finish the new payload bay.

So you guys know if good resources on building/using launch rails?



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anachronist
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Re: My first project.....

Post by anachronist » Thu Aug 16, 2018 1:35 am

Well, for launch rails there's this: https://www.apogeerockets.com/Launch_Ac ... l_Standard

You might also consider a launch tower that falls away, or tilts back when you pull a string, just before launch. That would be just like a real rocket launch then. It wouldn't be attached to the rocket, just touching it to keep it in place.



Braaainz
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Re: My first project.....

Post by Braaainz » Thu Aug 16, 2018 2:11 am

anachronist wrote:
Thu Aug 16, 2018 1:35 am
Well, for launch rails there's this: https://www.apogeerockets.com/Launch_Ac ... l_Standard

You might also consider a launch tower that falls away, or tilts back when you pull a string, just before launch. That would be just like a real rocket launch then. It wouldn't be attached to the rocket, just touching it to keep it in place.
Thanks for the quick reply.
Alas, $70+ for a launch rail is WAY outside my miniscule budget. Buying an altimeter and splurging on a pre-built launcher were my big purchases and I'm hoping to nickel and dime it from here on out.

I worked on my second attempt tonight. My simple payload bay is completed. I had a harder time getting the Tommy timer to release properly, but finally shortened my retaining pin enough that I was able to do four consecutive dry releases without mishap.

My parachute is 24", bigger than my old Estes rocket parachutes.



Braaainz
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Re: My first project.....

Post by Braaainz » Thu Aug 16, 2018 9:30 pm

Okay, the Mark 2 launched 3 times today.

First launch, 100psi. Parachute deployment was just after apogee. Went well, but didn't go as high as I would have hoped.

Second flight, 120psi. Parachute again deployed just after apogee, but did not unfurl. Not sure why. Luckily, the balance of the rocket was such that it landed near horizontally. No apparent damage to the rocket.

Final launch, launched vertically and it seemed to really get the height I wanted/expected. Parachute deployment went perfectly at apogee and it unfurled without a problem.

Of course though, it fell into the only tree in the immediate vicinity.
We tried throwing a basketball, my shoes, and a tree branch at it.
End result, the rocket is still in the tree, hanging off the end on just one long branch (seriously, even a couple of feet difference and it would've missed the tree). Both my shoes got stuck in the tree, although I got one back. One of the thrown tree branches bounced on the pavement, and in a weird set of odds, flipped onto my second toe, breaking it.

End result: 2 great launches, 1 okay launch, 1 broken toe, 1 missing shoe, 1 rocket out of commission.

Still fun was had and I'm very happy my parachute deployment worked so well.

I learned a lot and expect my new rocket body (also either a T-12 or T-8 body) to be far better.



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anachronist
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Re: My first project.....

Post by anachronist » Thu Aug 16, 2018 10:13 pm

Oh, my. I hope you didn't have an altimeter in there. How high up is your stuck rocket?
Maybe a long pole with a pruning saw on the end would help cut it down.

There are possible lessons to be learned.... Set your timer so that the parachute deploys after apogee, as low to the ground as you dare. And launch well downwind of any trees.



Braaainz
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Re: My first project.....

Post by Braaainz » Fri Aug 17, 2018 2:53 am

The wind direction must have been different at height because the rocket shouldn't have drifted anywhere near it. I subscribe to the theory that trees just draw kites, rockets, and frisbees thru some unknown physical law.

Luckily, I didn't install my electronics package. It's unreachable right now. Although I'm sure a strong wind will bring it and my shoe back quickly.

Another lesson is to put my phone number in the payload bay.

I'm not too heart broken. I learned a lot and my next rocket will be far better in design and looks. I do regret the loss of the Tommy timer and my Gardena nozzle though.

I also need to build a better launcher. I'm thinking simple PVC with interchangeable head to switch between Gardena and regular bottle nozzle. Any advice on making one that also works with boosters? (ie distance between launcher heads, how to equalize pressure, etc?



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anachronist
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Re: My first project.....

Post by anachronist » Fri Aug 17, 2018 4:14 am

A shotgun might get it down. :)

I've never done boosters. I've thought about a launcher for drop-away boosters, but I have never figured out a good way to get the distance between the tubes just right. Ideally I'd want some sort of hinged pipes that doen't leak, to let me set the heads where I want.

If all the launcher heads have an air path between them, the pressure always be equalized. I wouldn't want to pressurize the different parts separately.

With boosters, you probably want a wider nozzle. Gardena on the main rocket body and a regular bottle opening on the boosters, so they'll drop away before the rocket's water is exhausted.



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retrotec29
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Re: My first project.....

Post by retrotec29 » Fri Aug 17, 2018 10:37 am

Air Command Water Rockets is a great place to get some ideas for a staging coupler. I have had some success with a modified version of his design. A one way valve in the coupler allows the booster to pressurize the sustainer. When the booster is depleted it will drag separate allowing full pressure to be available in the sustainer. A little heavy but it can be quite reliable.
F30C1533-757F-463D-941E-DF5042168A0E.jpeg
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retrotec29
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Re: My first project.....

Post by retrotec29 » Fri Aug 17, 2018 10:53 am

As far as launchers go it is all up to your imagination. I use a brass quick connecter and project specific launch tubes. Bigger the rocket longer the launch tube.
491418FE-6DA4-4014-87C1-EBD1F95FE8DC.jpeg
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retrotec29
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Re: My first project.....

Post by retrotec29 » Fri Aug 17, 2018 2:29 pm

Here is my basic park launcher. I like tripods. I will admit they have there quirks. But every system does. Two legs are filled with sand. The third has a treaded rod for elevation adjustment. Everything is slip fit for easy takedown. My big FLT and muti stage rockets fly from a much larger version. That one has mounts for rails or rods.

490E8836-59BF-49CF-876A-4B57646C2027.jpeg
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retrotec29
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Re: My first project.....

Post by retrotec29 » Fri Aug 17, 2018 2:31 pm

Ready for transport.
40411D7E-C7DB-4219-A9C8-54232CC3EAB5.jpeg
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Braaainz
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Re: My first project.....

Post by Braaainz » Fri Aug 17, 2018 6:48 pm

Retrotec29,
How are you using the pump sprayer? I've got a two gallon one I've been experimenting with in an unrelated project (for making ginormous soap bubbles).

I'm planning on doing a two stager next spring if all goes well. I want to do the new method of using clamps that are kept closed with a radial deploy mechanism. When the deploy activates, clamps fall open and second stage launches.



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