[evilducky]

1st Post here. Woo. Anyway earlier this year, I saw someone do a dry ice bomb (ie. subliming dry ice in a soda bottle till it goes pop). Not very impressive on its own, but it got me thinking. So i went out, got a length of PVC pipe, an end cap and a valve, and created what I called "The dry ice cannon."
See http://www.spudfiles.com/forums/viewtopic,p,243398.html#243398

It could shoot small objects about 50m. Soon after that I realised that PVC and very cold don't go together (i could easily have filled my self with tiny shards of exploded pvc pipe), so built my second version made out of galvenised iron. Knowing that pressure was no longer an issue, I packed tonnes of dry ice in there, and could then shoot lemons more than 100m.
See http://www.spudfiles.com/forums/viewtopic,p,251335.html#251335
and http://www.youtube.com/watch?v=rw_qsoQ-3Rg

As you can see from the video, this thing really flies. It also weighs 6kg. So there's a lot oh umph there. So this..., and some forum comments... got me thinking: this could be a rocket.

Here's my idea:

Pack the large chamber (2L total) with dry ice. Seal it. Wait for the pressure to reach eqillibrium. Then heat it up to room temperature or even higher. The dry ice will then melt (and possibly go to supercritical fluid). Turn it upside down. Release the valve. The initial 850ish PSI gives me lift off, and the liquid carbon dioxide immediately turns to gas (because the pressure has been removed). And woosh.

I know it will work if the chemistry does. Unfortunately super critical fluids or thermodynamics arent covered at high school level. Yay me. So here I am.
Can anyone tell me if this will work or not?

Ducky

[billnotgatez]

There are so many things that could go wrong, I do not have the time to write them all and I probably would not remember them all. But here are a few to get you started

I assume you have no experience in rocketry so you do not know how many rockets have decided to go sideways after just going a few feet up. Even ones with fins will do this depending on conditions.

I assume you do not know the failure point of the tube you are using, so you do not know how much pressure it will take and you probably do not have a pressure relief valve to protect the system. Finding out the hard way could make you a member of the Darwin award.

[evilducky]

Going sideways might be a problem... but.... most of the weight is at the base of the rocket, and the idea is to fire it not directly straight up (i.e. going for distance) so starting at a 50-60 degree incline. I'm predicting no more than 5 seconds burn time so hopefully I could get a parabolic path with that. But yeah research into rockets might help 

As for the system failing. At 850ish PSI (it'll depend on temperature), dry ice ceases to sublime. This places an upper limit on the pressure that can be created in the tube. This is also galvenised iron, rated for several thousand PSI. So in that regard I'm safe. Its also the reason I moved away from PVC.

I acknowledge that this is potentially stupid. If I'm gonna set this off it will be in a very deserted field. And I will set it off from afar. very afar.

[Borek]

I think it won't be too effective. Amount of energy stored in the pressurized tank is much lower than amount of energy stored in chemical propellents. Your rocket - to sustain pressure - must be massive, exhaust gase are relatively light, so from moment conservation you won't fly fast. These things can be calculated, don't worry about super critical fluids, try to assume it is just an ideal gas.

[billnotgatez]

I remember when reading
Handbook of Model Rocketry (Paperback) by G. Harry Stine (Author)
that putting the center of gravity at the bottom of the rocket did not always give the intended result. There are a lot of rocket kits a lot cheaper than your stuff that would be good to practice on first. These kits are safer and give better results than what you are doing.

Just curious == what size pipe are you using (diameter, length).

I find it interesting that you are trusting the transition point pressure, but not interesting enough for me to condone it.

[kem]

you will not be able to make heat flow into liquid or solid CO2 fast enough to produce any kind of thrust.

if you are going to try to build a rocket that runs on pressurized CO2, you will find that the more pressure you want it to hold, the heavier it will be, which means it will get less oomf out of its payload

here you can see someone made a projectile out of the gas cylinder they put in pellet guns - http://www.youtube.com/watch?v=JK6lx1oUyR4

what you are attempting is potentially dangerous, especially the "charging" phase of your rocket

[hobobot]

Old topic I know.
But I was wondering if you ever tried anything new with this?
Maybe a quick-release solenoid instead of a simple valve? This is way too awesome not to follow up on.