Sorta crappy attempt at sugar/kno3 rocket, few questions....

[NickC]

I took a piece of 8" x 3/4" cpvc pipe and plugged one end with 3/4" dowel and then packed it with powder form 40%sugar/60%kno3, i also think the middle of the mixture wasn't packed as tightly as the end. I cored the whole thing with a wooden shishkabob skewer in a drill. Then I drilled a 3/16" hole in some 3/4" dowel and pounded it the end of the pipe as a nozzle. I put the fuse all the way into the rocket, like from the nozzle all the way till it hit the end cap. I set it up horizontally against a piece of wood, then light it. It made the loud explosion, I've ever heard and blew out the nozzle. This all happened so fat I didn't see anything. I think I saw a little flame come out of the back for liek a split second like it was going to make thrust then just BANG! and it left a big black explosion burn mark from where the nozzle used to be. I think my next attempt will be with melted rcandy and in a stouter design, and with tighter dowel....

so what would cause this? and what dimensions do you guys use?

[Ray]

Start here. Read the whole website, understand it, then come back to ask the questions that you still have.

Something that I posted to another person in the forum, it bears repeating...

You'll find that people are a lot more helpful about sharing knowledge with you if you ask intelligent questions...ones that demostrate that you have the basic background to support the answers.

Non-intellegent question;
How do I make a rocket motor?

Intelligent question;
I've noticed that the amount a combustion calalyst effects the burn rate is not linear, is there a way to calculate the effect of a specific combustion catalyst and make the burn rate changes more predictable?

In the first question, no knowledge of the subject matter is demonstrated, and the answer will likely be an emphatic NO!

The second shows that you have done some experimentation, you understand the nature of a combustion catalyst and that your results were not what you expected. You have come to someone more knowledgable and experienced than you to try to understand one specific portion of the whole. You are more likely to gain the knowlege you seek and a meaningful dialog can take place.

Remember that knowledge should ALWAYS preceed experimentation. When you perform an experiment, you should have a good concept of what the results will be. If the results don't match the predictions, then you go back, study the results and try to understand what was wrong about your experiment, or your knowledge, correct for the error, and experiment again.

Energetic chemistry is dangerous, people, even those with extensive knowledge of it, have been killed doing this. Please approach this with knowledge and caution before proceeding.

[Najm]

Did you leave space for any of the accumulated gases to escape?If you blocked the whole nozzle or most of it or made it too small for the motor then the rocket motor will explode due to overpressure, no matter what type of fuel oxidiser mixture you use.
Richard Nakka's site(as mentioned above) is a very useful in rocketry and check out the rocketry software section it has got software for designing a rocket motor and checking how it performs very useful.

[NickC]

i've read nakka's site. I may go over it again for dimensions and stuff. This was just an experiment, and was wondering what exactly went wrong. I think the nozzle may have been to small, but was going to run it by the forum.

and Ray, your last name wouldn't happen to be charles? You appear to be too blind to have read my post, because your response has next to nothing to do with it.

[pablo]

despite i've only made a few rockets, i think the possible problem is that, since the mix was not melted or had a binder, when you lit it the grain lost its shape, blocked the nozzle and bang!

replacing the sugar with a bit of glucose (1/4) is helpful while melting and moulding, you get a lighter (almost white instead of yellow) fuel that gives you more working time.

my 2 cents

Pablo

[Zippiot]

To the best of my knowledge:
When the sugar is melted is coats the potassium nitrate, which is key in proper kn ratios. Black powder is similar, as the potassium nitrate is coated with charcoal and then mixed with sulfur, gound for a long time. Sugar cannot coat the potassium nitrate like charcoal, so for a good combustion it *must* be melted first.

Also the losing shape thing.

[Ray]

If you had read the site as I directed, you would have discovered your problem.

If you read the site, read it again.

Specifically what when wrong? You overpressurized the motor casing. More specifically, you exceeded the material strength of the CPVC "casing" you had. I'll bet it was a hoop failure. Study and tell me why the overpressurization occured.

I'll give you direction on which way to go.

I see many things wrong with what you did.

1. You experimented without understanding what the results would be.

2. You used powder instead of a solid grain.

3. The "core" you made was not a precise dimension

4. The nozzle material is totally wrong

5. You used a fuse to light the motor

6. You didn't restrain the motor in any significant way.

7. Your fuel/oxidizer ratio is off, but it will work.

8. You didn't protect the PVC in any way.

9. You didn't take enough care in the preperation of the "grain"

10. I'm betting your KN ratio was WAY off

11. You ask a question that showed you didn't have a clue as to what you are doing.

SO, now you have some of your answers. There is enough information in what I have pointed out to make corrections to your motor. Now, go read the site I directed you to until you can at least answer some of your own questions.

I haven't done any sugar motors...nor do I plan too. I have successfully tested and flown AP/HTPB motors into the "M" class. One had 560 lbs of thrust for approximately 3 seconds.

I feel that I have some knowledge to offer you, but if you continue to insult me, you won't get any of it in the future. If you had read the post carefully, it all applied. After asking a question as you did, why do you expect that you deserve a direct answer? I have invested a lot of time and money into this hobby. You blowing up motors isn't doing the hobby that I love any good. I pointed out where you could find the knowledge that you are seeking. Handing it to you does nothing for your education. The old adage about "teach a man to fish" comes to mind.

NEVER FORGET, you are PLAYING with energetic chemistry. You can DIE from this stuff. Stop playing, start studying...it can be done with reasonable safety, but it will never be totally safe.

[Ray]

To the best of my knowledge:
When the sugar is melted is coats the potassium nitrate, which is key in proper kn ratios. Black powder is similar, as the potassium nitrate is coated with charcoal and then mixed with sulfur, gound for a long time. Sugar cannot coat the potassium nitrate like charcoal, so for a good combustion it *must* be melted first.

Also the losing shape thing.

The coating of the KNO3 has nothing to do with proper KN ratios...it does have everything to do with stable burning. You want a nice slow stable burn inside a rocket motor. If you have areas where the fuel and oxidizer are not completely mixed, you'll have an unstable burn. When the burn isn't stable you can't predict pressures inside a motor. When you can't predict pressures, you'll CATO.

Surface area to throat area are the keys to proper KN ratios. Powder has more surface area than monolithic grains...another clue for NickC...

[marksteamnz]

I'll say it again. Anyone who lights fuses to ignite rocket motors should be banned. Use a remote electric igniter, no ifs, no buts, no maybes. Anything else is asking to be a west coast sawmiller. (It's a kiwi saying, they are all missing fingers)

[El-Kablooey]

and Ray, your last name wouldn't happen to be charles? You appear to be too blind to have read my post, because your response has next to nothing to do with it.

Dude, what the hell is wrong with you? Ray took time to write you a helpful reply. It was perfectly relevant to your post. You showed you had absolutely no idea what you were doing, he directed you to a great source of information. He did this because he doesn't want you to injure yourself, which is very likely. Even after your childish insult he is still trying to help, Ray is a better man that I, because I would have thought "well go blow yourself up then", and ignored any of your future posts.

[NickC]

I'll say it again. Anyone who lights fuses to ignite rocket motors should be banned. Use a remote electric igniter, no ifs, no buts, no maybes. Anything else is asking to be a west coast sawmiller. (It's a kiwi saying, they are all missing fingers)

whats the difference with the fuse?

[Tom]

whats the difference with the fuse?

1. Fuses can't be stopped. Electrical ignition can be called off at the last microsecond, should a problem arise, which sods law says will happen sooner or later.

2. They are highly unreliable in burn time, enough to the point where no sane person would trust them with something like a rocket motor on the other end of it.

Not to mention such things are banned by UKRA in the UK.

Tom

[Ray]

another problem with fuses, they light the motor from the bottom. You want to light a motor from the TOP.

They are used sometimes in air starting rocket motors in clustered rockets...they usually put them in a teflon tube to ensure they light the motor from the top.

[Greg O'Bryant]

Once in high school for a tech class we all made rockets that fired an Estes c sized engine. We would lite the rockets with fuse. When one guy lit his rocket it instantly took off! The fuse was defective and was lightning quick. Fortunately nobody got hit by the rocket. His hand was a different story. When the rocket took off it was directly under the blast from the engine. He missed a few days of school and when he cam back had second and third degree burns over most of the palm of his hand and fingers!


This was the "good" American made green hobby fuse!

[NickC]

i used the thick blue chinese fuse, it's pretty reliable and i left a good bit of it between me and the rocket and it was at an angle so my hand was never behind it.