Water Rocket Forum

In fact that is also a question that I have, because I can take the reinforcement from the rocket but I need an extra reinforcement for the cross-section of the nose-cone, and maybe the weigth difference will be minimal...

I don´t need 400 psi to say that this works, I only need to launch it above the burst point of the bottle.

Making the seal with the reinforcement of the cone will be hardest part of the design.

The one major problem is that during launch as soon as I break the seal around the nose cone, the water around the outside will depressurise rapidly. This will cause the rocket to overpressurise and explode before it makes it off the end of the launch tube.

I think the solution to this problem is to mesure the maximum expansion in diameter of the bottle before it bursts.
That expansion will be in milimeters, so the 0-ring in PVC tube must be deplaced in the bottle in a way that the distance that the bottle has to move up will be less than the expansion distance.

So if the burst distance of the expansion is 4mm, the 0-ring must be 2mm inside the bottle.

Probably the 0-ring must be made of teflon and I should put a teflon tape inside the bottle´s neck, that way less friction will help to launch the rocket faster than the expansion.

Here is the same idea, this time the launch tube is retractable (wich will be a technological challenge) before the launch.

This way it wont have the friction of the 0-ring wich would avoid the rocket to depressurise before it explodes.

I think it won´t explode because the resistance towards the 22mm hole is less than towards the walls of the rocket, so the air will move more quickly towards the nozzle than towards the wall.

That way the rocket will depressurise faster than the burst speed (I guess...).

What if you were to make a sabot the shape of your rocket that would hold the rocket in shape until it exits the launch tube.

We were just kicking around some ideas at out meeting and it was suggested you freeze the water in the launcher and the ice would shatter when the rocket swelled up as it exited the launch tube, but it should come out before the rocket could explode.

The reason that I had prefered a water-box instead a sabot is simple:

- more easy to make
- the sabot can´t cover the zone from were the fins born, so that sligth area might burst.
- with a sabot it will have virtual spaces around the rocket (mm, micro...) that might burst.

The freeze idea is cool but the problem are the fins, they will get stucked in the ice.

Maybe they should be retractable so after getting out they would expand...but I dought that the expanding speed would be more faster than the launch speed.

To break the ice the fins should be strong (carbon fiber) and very thin (like the ones from the X-12).

Fins that goes from the top of the rocket to below the rocket will slide trough the ice instead of having to crack the ice that is freezed in the superior part of the fins.

SaSkAlex said that my sealing mechanism must hold 3600lbs (= 1600kg) of pressure.
If so this project is already doomed, but I don´t know the carbon fiber strenght to hold this.

Here is an example of a Sabot Launch.

Any idea of a good material to make a mold from a 2 L bottle ?

I think the Sabot idea might work I just need to find a material to make the mold.