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CuriousAmateur 03-03-2018 07:05 PM

Newbie failures - sugar rockets
 
Hello,

We are new to rocketry, and it shows from our results. I'm wondering if anyone has any advice. We are trying to make a basic (sugar) rocket motor. The results of which have thus far been smoke "bombs." If you have stopped groaning at another failing newbie and are still interested in helping, here are the details:

We're using 33% confectioners sugar and 66% Potassium Nitrate. Our sugar is pure, but I cannot verify the same for my KNO3. We're getting it from Gordon's stump remover, which we know contains a good concentration of KNO3, but we are strangely unable to find the MSDS info in it. We grind it up, and bake it to dry it out before mixing.

We then pack it into a 3/4'' PVC pipe, with a 3/4'' clay plug on each end and drill a 7/32'' nozzle through one plug, set it up, and light it off at the nozzle. It has a nice hot, fast burn, with a good amount of gas output. However, it comes in waves rather than a steady burn. It burns for probably about 20-40 seconds (we never timed) but never lifts off. It also has a small amount of white discharge which comes out liquid and quickly hardens into a hard, crumbly material. As expected, there is also a lot of white smoke. We originally thought that the white discharge might by melted PVC, but it is strange that it is crumbly.

As a couple other notes, we are not crystallizing the KNO3 before use; we don't know if that is needed or not, since we can't find the MSDS info. It does seem to act about right, except there is never enough thrust from rockets. We are packing the powders FIRMLY into the pipe, since it should be oxidized and not much matter. The nozzle is drilled all the way through the white mix to increase surface area though. On the first try, we had 1.5'' of fuel (not sure how many grains that comes to), and on the second attempt, we doubled it to 3'' of fuel, with the same 3/4'' plugs on each end. There is a fair amount of weight to the finished rocket, though we haven't thought to weight the finished product yet. The first one was 3'' long in total, and the second was 4.5''.

Any thought on what we should try? We've thought of perhaps packing it less tightly, but even as it is, some fuel tends to spill out when the nozzle is turned downward, multiple times after the hole is drilled. We've also thought of mixing in a little sulfur to the fuel, and also had it recommended elsewhere that a little iron oxide mixed in could help.

Any thoughts? Does anyone know if Gordon's stump remover is even a pure source? Thank you!

neil_w 03-03-2018 09:35 PM

I am not a motor builder myself so I can't help you out with your chemistry questions, but I do know enough to say that you should not use PVC as a casing, since it shatters unpleasantly.

CuriousAmateur 03-03-2018 10:39 PM

Quote:
Originally Posted by neil_w
I am not a motor builder myself so I can't help you out with your chemistry questions, but I do know enough to say that you should not use PVC as a casing, since it shatters unpleasantly.


Okay, good to know--any thoughts on what I should be using? Cardboard just isn't going to cut it.

jadebox 03-03-2018 10:40 PM

If you want to learn how to safely and legally make rocket motors that actually work, visit Jimmy Yawn's web site at:

http://www.jamesyawn.net

CuriousAmateur 03-04-2018 11:11 PM

Quote:
Originally Posted by jadebox
If you want to learn how to safely and legally make rocket motors that actually work, visit Jimmy Yawn's web site at:

http://www.jamesyawn.net


Thanks for the tip. He is making some very high-grade propellants, which I 'm sure are good. I will read through more of his material later.
To be honest, though, we don't need high-quality fuels, as long as they can provide a short burst of thrust. Perhaps we'll need to try a zinc/sulfur mix instead.

neil_w 03-05-2018 09:17 AM

Quote:
Originally Posted by CuriousAmateur
Okay, good to know--any thoughts on what I should be using? Cardboard just isn't going to cut it.

There are vendors out there selling cases, often aluminum.

Anyway, I'll bow out of this because although I've seen people say over, and over, and over, not to use PVC as a motor case, it looks like lots of sugar motor builders (that link Roger provided sure is a fun rabbit hole to go down) are in fact using PVC. So... I dunno, as I said I don't do it myself so I won't comment any further.

tbzep 03-05-2018 09:39 AM

I've made sugar motors in old cardboard motor casings. They are stronger than you think. Just don't use cardboard tubes that weren't designed for motors. Start small and work up.

ghrocketman 03-05-2018 11:46 AM

I have made sugar motors as well in old used 18mm and 24mm cardboard casings, and in used 29mm plastic/phenolic casings as well.
Many use PVC for sugar motors as well due to ease of availability; I have no comment on safety of using said PVC.

Don't mess around with zinc-sulfur aka "micrograin" propellants.

jadebox 03-06-2018 09:45 AM

As you can see on his web site, Jimmy Yawn has done some experimenting with using PVC to make motors, but he wouldn't recommend that for others. PVC is frangible. It breaks into small pieces when it fails.

The motors he actually uses to launch rockets use non-frangible metal casings as required by the Tripoli Research Safety code.

tmacklin 03-06-2018 10:20 AM

You might try your hand at rolling your own convolute wound paper tubes using Elmer's white glue. If you want a super strong tube, try West Systems epoxy which will produce a maple hard tube that you can drive nails with...almost. Like everything else in life there is a learning curve to be mastered.

If you want to buy some excellent paper tubes, here's a link:

http://www.hobbyhorse.com/pyro_tubes.shtml


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