Nova Water Rocket - Part 1 of 3 - Pressure Chamber 

Thanks Laurence.

Thanks!

Great! I'll have to check out any photos/videos from the launches. The more water rockets the better! :) NSWRA usually doesn't fly in December and then restarts again at the end of January.

@@AirCommandRockets Well that might be something to suggest to them, or you could come down to Canberra :)

Cheers Sandeep.

Cheers. :) Yup, we have the three videos for this rocket ready. It flew a couple of weeks ago. We'll release them each week while we work on the Horizon project.

@@AirCommandRockets that will be grate

The philosophy here is we can test it to destruction on the launch pad trying to launch it. The safety margins are a lot lower in rockets simply to conserve weight. Hydro testing only gives you a part of the picture, as it doesn't take into account the compression heating of the air during pressurisation that can weaken the epoxy. It also doesn't take into account the dynamic load applied to the bottom of the pressure chamber under acceleration. A 50G launch can exert quite a bit of force from the water that is still in the rocket. The payload on top of the pressure chamber can also apply compressive loading on the top of the pressure chamber during high acceleration. Here is a good example of a rocket being destroyed by the dynamic loads after launch. The pressure chamber was hydro-tested before launch. ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-465jLsotDyA.html

Cheers. :) The problem in doing it in the final shape is that you wouldn't be able to extract the mandrel. You may be able to get away with shaping one end, but then you would have trouble removing the tube because the baking paper wouldn't be able to shape itself over the end well and you would get wrinkles.

@@AirCommandRockets I admit that would be a problem ! :-) I can see from your methods that you have so many things well thought out, the engineering you are applying is fantastic!

Really good question. We had plenty of PLA on hand, and because it is such a common printing material that a lot of people have, we wanted to see if it would work with it. I'm sure if you are really trying to push the limits of the design you probably would want something a little stronger.

That's something that could be feasible. I'm not sure what equipment would be needed to make that happen in terms of heating the preforms and then making the molds so they don't come appart when blowing into the preform, and do that at the full length of the rocket. My guess is it would only be economically viable if you were making dozens and dozens of them.

@@AirCommandRockets A new family business, time to retire from that boring job that pays the bills to do something to ruin your love of your hobby :) I would think you could 3D print the outside blow mold in sections that split vertically and would be bolted together. Obviously the entire central body would be pretty much identical with the ends for the nozzle and head cap being different. Maybe even use a piece of tubing to form the central cylindrical section blow mold and just split it lengthwise and use outside clamping brackets made from normal pipe hanging hardware or 3D printed ones.

We use 105 resin and the 206 slow hardener to give us enough work time. The cure time depends on ambient temperature. On hot days it cures a lot faster than on cold days. Normally we wait around 10 hours before removing it from the molds/mandrels, but it is still very slightly soft. I always wait at least 3 days before testing it with any loads. In terms of safety equipment, we just use gloves, the epoxy doesn't give off any odours like polyester so no need to wear a mask.

Greetings from Sydney François :)

That's a really good question. It would certainly be worth investigating by doing a small test pressure chamber. The major concern is the higher pressures and the larger diameter that Horizon uses.

Yes vacuum bagging would definitely help improve the strength to weight ratio. We don't have the equipment to do that .... yet. :)

@@AirCommandRockets What about peel ply? it gets close to vacuum bagged results, without any equipment, just a extra step of layup.

It is actual baking paper that has a waxy coating. They are not all created equal though, Glad Bake is recommended by many club members.

@@AirCommandRockets Just needed an Australian to English translation :)

The best part about 3D printing is you can work on something else at the same time that it's printing.

@@AirCommandRockets indeed

All STL files are available here: www.thingiverse.com/thing:5502347

The mandrel is 60mm

He mentions in the video that they are using West Systems epoxy. As another West Systems customer, I expect they are using 105 resin and 206 hardener, for its increased working time over the 205 hardener. Or possibly even the extra slow 208 hardener. More info available at www.westsystem.com

Challenge accepted. No parachute: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-QDZJdNnQRvY.html ... also no glue or tape or anything else. :)

Thank you

That's true. but the size of the hole here is 7mm so it is difficult to get the vortex going to let air pass through it and drain at the same time.

We use a scuba tank with an adjustable pressure valve to fill our rockets.

It is stronger and easy to machine. Weight reduction isn't an issue since it stays on the ground. For us also it is cheaper because we have lots of brass stock on hand.

1 meter.

No, we have not.

60mm

That's a good question. As the video says this rocket was specifically designed to fly within the permissible altitude range for our launch site in Sydney. Club rules state that we have to keep to around 1000 feet so making it go higher really wasn't an option. So then if we can go that high with a big or small nozzle. we chose to go with the small nozzle in order to keep the acceleration and stresses down on the rocket. The slower take-off is also easier to film. A small nozzle also means that it is easier to hold the rocket down on the pad at higher pressures.

@@AirCommandRockets And if you use a bigger nozzle like 10-12mm and lower pressures like 18-23bar ? Also, with a smaller nozzle you can’t use a launch tube right ?

Liquid CO2 would certainly be worth investigating. I can imagine icing at the nozzle would need careful attention.