PVC Water Bottle Rocket Launcher Design Components

Seal and Release Mechanism

PLEASE NOTE: PARENTAL SUPERVISION IS REQUIRED. Ensure the safety of children and others while operating this project. Be sure children are old enough to stay out of the way of the bottle rocket and take any other precautions you feel are necessary to keep everyone safe.

The Water Bottle Rockets are always a big hit with kids. We have gone through numerous water bottle rocket launcher designs derived from other designs we found and those we created ourselves. The launcher shown in the above image is the easiest, most cost-effective, and most reliable PVC pipe version thus far. The launcher is based on the PVC launcher detailed at Walking Mountains How to Build a Soda Bottle Launcher, with variations on certain components.

Design Components

Launch Tube Seal 

The most varied component of the PVC launchers is the seal between the launch tube and the mouth of the 2-liter bottle. The Walking Mountains Science Center version listed above does not detail what type of seal is used and other designs also omit this in their instructions. Some versions use O-rings or electrical tape around a threaded male connector. We tried these designs and found neither created a tight enough seal nor lasted long and the O-ring seals are too difficult to make.

The least complicated type that consistently created a good seal for our purposes is the bulge seal. This is made by using a candle flame to heat and soften the PVC pipe enough to compress it to make a slight bulge. It is important to keep constant pressure until it cools down enough to harden the bulge in place. This is not a kid-friendly method, but it does work well and is fast. Always keep safety in mind when doing this. Unsure where we originally found this technique, but the following video shows how it is done How to Build a Water Rocket | This Old House.

Release Mechanism

The other tricky part of the rocket launcher is the release mechanism. We tried just using a friction seal, surprised to find numerous online instructional sites use this method. With this method, the air pressure builds up enough to overcome the friction from the seal of the neck of the bottle on the PVC tube and propels the bottle up. The unexpectedness of when the bottle is launched seemed unsafe and could potentially scare kids, it really scared the adults testing this design.

Using a release mechanism allows us to verbally count down the launch forewarning everyone in close proximity. Ian Clark's popular Clark Cable Tie Release Mechanism is what the Walking Mountains Science Center, This Old House, and many others use, and we use it in our design as well.

                

The left photo shows the zip ties without the bottle in place. The darkened ring around the pipe indicates the bulged seal made from heating the pipe. In the right photo, you can see the bottle sitting right above that aforementioned darkened ring. The zip ties were secured in place so that the heads rest on the flange of the bottle.

Spring

The difference between the Walking Mountains', US Water Rockets', and our release mechanism is we use a spring underneath the release collar to keep it in place over the zip tie heads and not friction to keep the collar over the zip ties. This Old House's design also uses a spring, but it is made out of a plastic bottle. We found using zip ties is just as effective and doesn't reduce our supply of hard-to-get carbonated beverage plastic bottles. Unsure where we first saw this type of spring, but several PVC launcher designs use zip ties as a spring. There were some issues we found with the cut plastic bottle spring, if the cut holes are not smooth the edges can catch on the tape that secures the zip ties in place, and it seems the constant compression of the plastic bottle spring will require it to be replaced more often than the zip ties.

              

The photos above show the release collar (1.25" PVC coupler cut in half) and holes drilled for the large zip ties for springs and nylon string to which we attach a long trigger string to. The photo on the right shows how the collar is pushed up around the bottleneck holding the bottle in place by the black zip ties. 


The video below shows the two different spring mechanisms in action (not launching bottles).

  

The above landscape pins fit over the PVC tube and connectors to hold the launcher in place when used on grass.

References and Sources

Below is a list of sites we referenced while making the water bottle rocket launchers and other informative sites.

• https://www.walkingmountains.org/wp-content/uploads/2012/05/How-to-Build-a-Soda-Bottle-Launcher.pdf - detailed instructions on building launcher base
• http://www.aircommandrockets.com/construction_9.htm - uses zip ties for the spring and they detail the various seals of PVC launcher.
• soda-bottle-rocket (ucsc.edu)
• How to Build a Water Rocket | This Old House -Includes how-to video of making their handheld launcher includes the seal bulge technique and Clark Cable tie release mechanism as well as detailed instructions on how to make a handheld launcher with parts list, diagrams, etc.
• Rockets Educator Guide | NASA - water bottle rocket launcher (pg.87) is complicated, but the resource guide has a lot of great lesson plans and activities on rockets.
• Ian Clark's popular Clark Cable Tie Release Mechanism on USWaterRockets.com website