Cluster Launcher

[chemdude118]

I wanted to build a cluster launcher that allows for 3 boosters. My dad and I don't have a lathe or any fancy equipment. We were going to have the boosters full bore on 1/2 inch PVC with an o-ring to seal the pressure. The main bottle will be locked in place with a Gardena release head. We would appreciate any tips or suggestions that we may have overlooked.

[air.command]

I wanted to build a cluster launcher that allows for 3 boosters. My dad and I don't have a lathe or any fancy equipment. We were going to have the boosters full bore on 1/2 inch PVC with an o-ring to seal the pressure. The main bottle will be locked in place with a Gardena release head. We would appreciate any tips or suggestions that we may have overlooked.

Hi Chemdude118,
What pressure are you expecting to launch the rocket at? One of your biggest problems is going to be holding down the main stage with the gardena release head. If for example you are using 120psi, then the force on the Gardena quick connector will be roughly 215 pounds from the boosters alone + another ~20ponds from the main stage. A plastic Gardena release head will likely fail. We use a brass release head with steel ball bearings (rather than the plastic tabs) on an aluminium nozzle to take the strain (and we're not even using full bore on the boosters). We've done tests where we suspended a weight on a plastic nozzle in a plastic gardena quick connector and IIRC anything over around 90Kg damaged the inside of the connector.

When designing the placement of the o-ring groove for the boosters, get the o-ring to be as far up into the nozzle as possible so it still seals when sitting on the pad. When you start pressurising the boosters will want to move upwards (how much depends on the slack you have in your booster retention clips) this will allow the boosters to move up a little and still seal. If the o-ring groove is too low then there is a chance the booster will move up too far and pop the o-ring out of the nozzle and leak.

Good luck with the build.

- George

[chemdude118]

Thanks Air Command,
We were planning to use a brass release head because we have always used them on our other launchers. The information about the o-ring placement is very useful and I will be sure to place the groove high enough to allow for the slack in the booster clips.
Thanks,
chemdude118

[SaskAlex]

Hi chemdude. As George points out, holding the boosters down by the main stage results in a lot of force on one release. If you can handle the forces involved, it probably is the simplest solution. The other option is to have a release mechanism for each bottle, and activate them simultaneously. Several people have had success with this. See the launcher I made for my JP-2 rocket here http://www.wra2.org/forum/viewtopic.php?f=53&t=1044 (near the bottom of the thread). I saw somewhere a cluster launcher with gardenas that was similar. The creator (can't remember who) modified the female gardenas so they always wanted to release, and the retention rings had to be held up, like on my launcher. You could try something like mine, with this type of modified gardena in the middle for your main stage. Just another option.

Alex

[U.S. Water Rockets1]

Hi chemdude. As George points out, holding the boosters down by the main stage results in a lot of force on one release. If you can handle the forces involved, it probably is the simplest solution. The other option is to have a release mechanism for each bottle, and activate them simultaneously. Several people have had success with this. See the launcher I made for my JP-2 rocket here http://www.wra2.org/forum/viewtopic.php?f=53&t=1044 (near the bottom of the thread). I saw somewhere a cluster launcher with gardenas that was similar. The creator (can't remember who) modified the female gardenas so they always wanted to release, and the retention rings had to be held up, like on my launcher. You could try something like mine, with this type of modified gardena in the middle for your main stage. Just another option.

Alex

As shown by the Mythbusters Episode #42, you should avoid trying to go crazy with simultaneous releases. Use fewer if you can get away with it because simultaneous release really is not that easy.