Test casting.

My ultra sensitive and ultra cheap scales have arrived at last!

I celebrated by immediately making a test casting of inert rocket proppellant i.e. propellant that can not be ignited and will not burn (well, it'll burn worse than sugar. Sugar is safe, isn't it? isn't it?! :O).

It is important to note here that the way I treat the inert propellant must not be applied to the handling of the real deal. The inert fuel I'm using is dextrose and table salt. So it is almost like KNDX but instead of potassium nitrate, we use table salt instead. So: NaCl + C6H12O6.

I was previously misinformed about the local regulations regarding rocket candy, so now I know that this country has some really crappy laws that prohibits nice guys like me to do things like this that I am most passionate about.

No, seriously. It is good with these laws since they prohibits evil people (terrorists) to demolish our beautiful country. It's like walking on a tightrope. On one hand safety is important but are we really enjoying ourself being safe all the time? Do we all benifit from being locked up in our houses, or even better, in isolation cells. That would be very safe. No one gets hurt. But how fun would that be?? Hmm.. perhaps I should make a huge raft and sail it out to the middle of the atlantic and proclaim it to be a new nation. The amateur rocketry nation!

Anyways... I've updated my disclaimer. So until I have gotten a waiver or license I'll not make any real propellant. After all I'm a nice guy, remember?

Ok. Here goes. First I started out by purchasing dextrose. As I've mentioned in an earlier post, it can be bought in supermarkets. It is often waterbound so do as Nakka says and bake it for 2h in the oven on 80 centigrades:

Ok, so here's what you do: After baking it for about an hour, the dextrose will cake itself into a hard sugary plate. Break it up into pieces (probably not necessary, but this was how I did it). I did this once in a while and eventually, after two ours I weighed it out to see if the water was gone. However, back then (2-3 weeks ago) I didn't have a digital scale at home, but a crappy analogous scale that showed different results everytime I put something on it :P.

Anyhow, see that 9% mass is gone (hopefully) and when that is done, put it in a mortar and grind it to a fine powder (warning, tedious). Nakka suggests an electric coffee grinder. Perhaps easier.

Then put the stuff in a sealed container. The more sealed off from the air outside the better. Best wood be a vacuum packer device thingy. This stuff is said to be hygroscopic, so keep it away from air if possible.

So, fast forwarding to friday this weekend. I wanted to mix this stuff with table salt and cast it into a mold (another 16mm VP-pipe). Ok, found an extremely old electromagnetic toy I constructed when I was in elementary school and thought physics was easy and I didn't know how to calculate on magnetic fields :D.



I remember it was supposed to produce a powerful magnetic field that would fire out this little metal rod to the side (also coil-wire on it) with a high velocity. Never succeeded though. Naturally.

Stripped it down to this:



Made a plastic plug to be plugged in from the bottom, stopping the rcandy to sip through the bottom.





The funnel idea wasn't very good or didn't work well for me:










My first cast was horrendous:



The candy was too hard when pouring it into the mold so I had to heat it up again. I heated it far too much (150 centigrades) which should be fine with the water driven off, but somehow this was too much. Maybe I didn't get rid of the crystal water after all?
So poured the rest into the mold and it got this ugly turd. :P



Since I'm fore a conical shape at the bottom I started making a plug with a positively conical shape to get a negative conical impression in my propellant. The plug melted however, but I got some nice result now:







I succeeded to fill the complete mold this time!






Here's the plug afterwards. It melted of course. (I'm such a idiot).
Anyways, it did it job, sort of.






Beautiful, isn't it? Ok, it wasn't perfect, but much better than my previous attempt.






Anoter view.
As you can see it has air bubbles in it.
Air bubbles are bad since they produce a sudden increase in burning area.


All in all, I'm satisfied with my experimentation, however noting that this grian design along with the motor design will not be feasible. I noted that the VP-pipe quickly started getting sloppy at degrees higher than 100 centigrades (or maybe lower?). How on earth will it hold for 1703 K in 0.17 s or 1 second evenso??? Ok, maybe 0.17 s might work. But that is too quick for me. I need at least 1 second burn time (don't want to wreck my model rocket). An endburner will be too slow I think, and the pressure buildup will probably take too long. Hence, VP-pipe "myth" is "busted"!

I think I will focus on metal-based motor designs henceforth. Much more reliable IMHO.
I will see if I can make a motor chamber out of aluminum and a nozzle out of graphite (or possibly aluminum, but it will probably erode to fast due to the aluminum being prone to erosion/oxidation). Stay tuned!