Instructables
video Splicing bottles for water rockets
Splicing bottles together is technique often employed by water rocketeers to increase the volume of their rockets. Splicing involves gluing sections of bottles together to make a longer pressure vessel.

Because of the forces involved inside a typical rocket, and because PET plastic is very hard to glue, there are only a few existing glues that are suitable for the job. The most commonly used is PL Premium construction adhesive, but VISE and a small number of others can also be used.

Splicing is not as easy as joining bottles using a Robinson coupling, is permanent and is less predictable at which pressure it will fail, but it has the advantages of virtually unrestricted internal flow and potentially long pressure bodies can be made this way.

The technique presented here is based on previous work done by other rocketeers:

http://wrockets.trib-design.com/index.php?project=nick&page=splicing

In the following video tutorial we present a technique called 'symmetrical splicing' for joining two bottles. The same technique can be used for making much longer bodies. The join is just repeated for each section.

For more water rocket instructions visit: http://www.AirCommandRockets.com
mattman22 years ago
ya could just melt it
Lftndbt5 years ago
Very nice explanation. Any idea shich Sika product in AU would be most suitable. There seems to be hundreds.
air.command (author)  Lftndbt5 years ago
Your best bet is probably Sikaflex 11FC.
Hmmm, no clear available at bun nings. Oh well looks like black splices for me. I am starting to see the benefits of bottles over FTC and pressure pipe. My two stage rocket with drop away boosters is boardering on the same drag co-efficiency as a bottle rocket due to the drop away. I am thinking now a third stage done in bottles would give me a little more bang and air volume.
air.command (author)  Lftndbt5 years ago
If the main stage has a similar burn time to the boosters, then the boosters will not necessarily give you greater altitude, but will be able to lift a heavier weight to the same altitude compared to the main stage alone. This is good for lifting a bigger second stage. -> more volume and more water in your sustainer. Do you have any pictures of your rockets?
This rocket have a custom quick change mech for the fins. I don't know if you have spotted these little clips/holders in any stationary stores but they make a great fixing method for the fins. They bite onto boards, especially celled boards commonly used for fins very well. It takes a great deal of force to remove the fin but it will pull out at an angle under great physical force.
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Kaiven Lftndbt5 years ago
How did you splice your bottles together?
air.command (author)  Lftndbt5 years ago
That's not a bad idea for attaching fins. Certainly makes it easier to swap fins between rockets or replace damaged ones. I can see transportation of the rocket also being a lot easier if you can remove a fin. Have you tried them with a full open nozzle where acceleration is a maximum? My only concern would be that the high G loads on take off could either move a fin or loose it entirely. Perhaps a safety piece of wire through the fin and the clamp would make sure the fin does not move. Cool stuff though!
Yes I would definatley think that at a max G launch they would shift. Just looking for a identical fixing method that can replicate. They almost guarantee a perpendicular mount. If your ever in Bunnings they are the holders to the bay item signs. We hit them regularly with machines and the sign always breaks (which is hard plastic) before the clip releases the sign. I still intend on either applying a glue to set the fins or a method like you suggested.
Not as yet, but i'll post pic of my pressure pipe rocket when it's done. I just finished a 7L spliced rocket body using the Sika 11FC. No neck to necks just straight through mid sections. That black Sika (as you would know) has a great advantage when a light is shown from behind it. You can easily see where you have spread the glue to thin or if you have missed a section... Now to just wait 5 days... hmmpppfffhhh!!!
Which sika do you use? I have found a range of the stuff in Mitre 10 in town :-).
Air.command is like the jesus of water rockets, I see he answered your question. I use sika 11FC black.
Ok great. That's off the shelf stuff. Tops!! Thanks.

Just as an estimated guess. What would you think this MOSS branded quad garden fitting would rate to? It appears to be cast steel coated in a golden layer. Ball valves look good. I was hoping around the 150PSI-200PSI mark.

I'm using this unit on this Quad metal launcher
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air.command (author)  Lftndbt5 years ago
Hard to tell from the photos. It's unlikely to be steel, perhaps brass? You should be able to contact the manufacturer and ask for the rating. From the looks of it, you should be okay with 150-200psi. But hydro test it first and stay well away while testing.
Perhaps brass coated, but not solid. Will certainly take your advice, in regards to pressure testing it.
Any chance I could convince you to do some of your write ups on Instructables?
The water rocketing community is in need of some good info.
I am sure everyone would love a write-up on how to build Polaron IV.

I was actually going to email you to request if I could use a shot of Polaron IV as the picture for my new water rocket group. Water rockets
air.command (author)  Lftndbt5 years ago
I'll consider writing it up, unfortunately I don't have any spare time over the next few months.
Kaiven5 years ago
Hmm... I'm getting back into this stuff again. But how can I use this type method with only the same type bottles? I can't find any bottles wider than my 2L bottle.
air.command (author)  Kaiven5 years ago
You can actually heat shrink the bottles before curling the edge so that you can use the same bottle type for the sleeve. This is best done in a saucepan full of hot water ~70C. Fill it up with enough water to a depth of half the length of the splice. After removing the bottom of the bottle and neatly trimming the edge, submerge it in the saucepan for a few seconds and the bottle will shrink a little. (make sure there is no cap on the bottle) Test fit it into the sleeve, if it still does not fit, repeat the procedure. Don't leave it in there for too long otherwise the bottle will shrink too much. With a little practice you can get a good yield of bottles shrunk the correct size. You can then curl the edge as normal and splice the bottles together. Hope that helps - George
Oh! That's a really good idea. I might try that... and what about JB weld instead of the glue you use? It's strong and can hold hundreds (maybe thousands?) of PSI, and I think it will bond the bottle splice together well.
air.command (author)  Kaiven5 years ago
You could try JB, but I am not sure it will work well. You really want a glue that has a flexible bond rather than a rigid bond like JB or epoxies in general. As the bottles stretch under pressure a rigid bond can crack and leak. The other issue is adhesion to PET. Most glues are unsuitable for PET plastic. The most successful ones have be polyurethane based (like PL). But by all means give a test and see how things go. If you only use lower pressures you may be able to get away with it.
I guess I will try the Gardena launcher with small soda bottles spliced together with JB weld before I try large scale.
microman1715 years ago
Hey Mate :-) You're Aussie I take it? I'm Kiwi. I was wondering on what I could use for glue. I've never seen this PL or sikaflex stuff... How about regular epoxy? The 3min cheapo stuff? Or super glue? I can get super glue real cheap at $2 shops..
air.command (author)  microman1715 years ago
Hi there, yup I'm just from across the pond ... in Sydney. The problem with gluing bottles is that very few glues actually bond well to PET. Rigid bond glues like epoxy also crack when pressure is applied because the bottles stretch considerably. While super glue should work, the amount of glue you need and super glue's work time make it difficult to use for splicing, and its difficult to properly sealing the joints. The best glues are polyurethane based, such as PL or Sikaflex. PL is by far the best, but sikaflex is good for up to around 100psi. There is also a glue here in oz called VISE which may be available in NZ. It is a bit runny but works well. If you thicken it up then that is a good alternative. All these glues cure with a flexible bond allowing the bottles to stretch somewhat while still providing a good seal. Hope that helps :) - George
Thanks mate, will keep a look out. I really wanna build a rocket like one of your's, they look so cool!
Mattrox5 years ago
Wow is saw one of your videos on metacafe you people are awesome
macrumpton5 years ago
Exceptional instructable! I am not sure why you are using a sleeve rather than just cutting the bottoms off the bottles and sliding one over the other.
air.command (author)  macrumpton5 years ago
The problem is that same diameter bottles will not slide into each other without buckling. You need a little more room for the glue as well. If there is any buckling the splice will leak. A fully pressurised spliced pair has as much as half a tonne pulling it apart so you need a very good bond = large overlap.

Also sliding them over each other gives you less volume.
Kryptonite5 years ago
Wow, that is done so professionally, thanks for posting. My speakers are currently broken so the writing in the video made it an exceptional video. Damn, that makes the way I did it look terrible, I'm envious now...
Kaiven5 years ago
Wooooooooooooow. A lot of work, but nice job!