Skinny core, higher chance of CATO?

[dagabu]

Whatever you decide to do with this one, make sure to record it well in a log so that you can work down the list of common denominators to determine what went wrong. It is very likely you are dealing with a tube fracture if you press it really hard, R-candy and sugar propellants don't take a whole lot of pressure to press into a nice grain but are more fluid and can cause ruptures easier in paper tubes.

[chand]

Which onone is better placing ignitor in middle or at end in a core burning rocket

[chand]

Guys I am sorry for misbehave with everyone specialy mrb

[stix]

Sorry guys. I sure didn't mean to start a ruckus in here. But, like like Caleb said, it truly has made for some educational reading.

 

Also, sorry for disappearing. Between work and some family stuff, I've not had much time to make and launch rockets. Since my last post, I've only been able to do one, and it also popped. It was drilled 1/4", nozzle and the entire core, so it really surprised (and scared the shit out of) me.

 

 

I have given this a lot of thought, and what I come up with is that, as my techniques for making these things improve, so do the number of explosions. When I was pounding them out with a dead blow hammer, they always flew. Since then, I got myself a little six ton A-frame type press from Harbor Freight, and with a little welding and a bunch of drilling, I was able to increase it's usable working height to about 11". I then had to go buy a bag of hose clamps and slit a piece of PVC to make a tube support, and I am now able to really compress the hell out of my fuel. What I am thinking is that is that dry sugar fuel really likes to be compressed, and the harder you lay into it, the hotter it gets. I just pressed one tonight, and I'm going to try drilling the whole thing at 1/4", and then go back in and open up the nozzle and the first inch or so of the core to 9/32". If all goes well I will be able to run out tomorrow night and light it and see what happens.

 

Edit:

 

No, scratch that, I'm gonna leave it at 1/4" and takes Dave's advice and light it a little lower. Wish me luck.

 

Wow ORM's, that really freaked me out so much I had to watch it over and over and over and over I enjoyed it, but please be careful though.

 

Don't worry about the apparent ruckus you've caused - ya bastard! - it's all your fault .

 

As suggested, it's always a good idea to log what you've done. I've had a f*ck up myself very recently by not recording past compositions and dates. It certainly brought me back down to earth. The stored sugar motors I made were around 2yrs old, they didn't ignite and I assumed the fuel had degraded. Fortunately I did have some others (even older) that worked perfectly, and with some recorded data, I confirmed I must have screwed up the composition - possibly by mixing up the KNO3 and Sugar ratio?? I'll never know.

 

What made it all much worse is that I made 4 motors with various "cast in place" nozzle formulas that I had spent months perfecting. The purpose was to test the nozzles, the motors were secondary and were a known quantity (I thought). A lot of work has gone to waste as I'll never know how the nozzles may have performed. Very pissed off!!! bla bla bla bla bla.

 

I think I've already suggested previously to drop the red iron oxide. I say this some good experience. A good "pyro buddy" of mine uses a highly compressed powder technique similar to your own and the motor dimensions are around the same spec. In competition with him, I use the melted method. After much testing It has worked out and agreed that the performance is essentially the same.

 

At NO stage with these motors has RIO ever been used - it is simply NOT necessary, no NEED. Not with "nozzled" motors that have well made/incorporated fuel. IMHO there are only four reasons to use red iron oxide:

• Your roughly powdered pressed fuel is "hammer rammed" and you need faster burning fuel to compensate
• You are not using a nozzle, ie. "Nozzle-less"
• You like making short-arsed motors
• You love CATO's

I do enjoy a good CATO just like the next bloke , but not with what I'm wanting to achieve. I want a reliable sugar rocket motor because I'm hoping to use them as a vehicle to launch some pyrotechnic shells. I don't want to spend a lot of time making stars, then a shell, only for it to not lift and cause a possible CATO, not to mention the safety implications.

 

Anyway, If you can be bothered at some time in the future, just try a mix without rio and do everything "exactly" the same as you are doing now. If it CATO's... well I'll go... um... be surprised! Then you could look at the casing as the failure point.

 

The reality is that if you have a casing that never fails and a nozzle that won't blow out, then the power of the fuel you put in it, for all intents and purposes, is "limitless". The reality is, there is a "balance" that must be reached. You can back off on the "hot" fuel or strengthen your casing.

 

I purposefully over engineer my motors and accept a performance loss of 20%. Yeah, less than Ideal, but for safety reasons and reliability I'll go with it - except for the ones that f*ck up of course .

 

Cheers.

 

[EDIT] I am talking about core or internal burners - with end burners RIO is probably necessary and with a short bore.

Edited April 2, 2015 by stix

[ORMDale]

I very much appreciate all the replies, lots of good stuff posted to think on. I apologize for disappearing. Been dealing with some medical and family stuff and have had no real time to make rockets. We're also in a drought out here, and now things are starting to get dry, I'm gonna have to drive a lot further to test, but plan to in the next week or so, and will report back. Much thanks, you guys.

[stix]

Sorry to hear about any medical or family issues. If you, or any of your family have medical problems, that will always be number one. It certainly puts things into perspective and re-focuses your priorities.

 

Hope it all works out well.

 

Best wishes - Stix.

[ORMDale]

For what it's worth, I just didn't want you guys to think I had lost interest or given up on the hobby. The truth is, I've not been able to try and send one up since my last post. I live in an S & S state that suffers horrible wildfires every year, and is currently suffering it's worst drought in history. I have to wait until it starts raining again, and everything is good and damp. To light a rocket now would be insanely negligent. It's killing me. Tomorrow is gonna be another 94 degree day. Please let it rain, and soon..

[dagabu]

Sorry to hear about the dry conditions, I have a friend that lost his house, horses and a barns in the Valley Fire this past August. With the El Niño, you should have more rain than you can handle!

 

Can you draw out your nozzle in relation to the motor core and OD?

[ORMDale]

Thanks for the reply, Dag. Yeah, it's really bad out here. Residents have died in the wildfires, property damage in the untold millions, and lots of animals lost. We're all praying for rain and hoping for El Niño.

 

But as far as my rockets, I think the problems I started having were due to a few different points you kind folks raised in this thread. This is all conjecture until I can go light one, but I think it comes down to this:

 

1. My cores were getting longer without increasing the aperture of my nozzles.(and yes, I was breaking the most basic rule, and was making more than one change at a time in regards to total length and core lenght)

2. I took a little too much material out when I slit the PVC for my tube support. There was a good 1/8" gap all the way up. I took a good look at one of the last ones I pressed with that support, and there was a perfect 1/8" lump all the way up. I'm pretty sure my tubes were compromised.by that carelessness.

3. I should probably have taken stix advice, and backed off with the red iron oxide until I figured it out.

 

Going forward, I've sworn off drilling nozzles and cores. I bought an absolutely beautiful custom 1lb core burner set from Caleb for 7" tubes, and also had him turn me a second slightly shorter spindle, just in case. I've also cut a virtually gapless (tit hair, gnat's wing gap) tube support. Oh, and I upgraded my press from a heavily modified but still crooked and wobbly Harbor Freight, to a ten ton Dake.

 

I've got damn near a dozen pressed, sitting in an ammo can with a little cup of desiccant, waiting for the weather to change and start testing.

Edited October 17, 2015 by ORMDale