Skinny core, higher chance of CATO?

[ORMDale]

Of the three CATOs I've had so far, two were when experimenting with narrower cores.

Had this one last night: (1lb sugar rocket)

Edited March 16, 2015 by ORMDale

[ORMDale]

It will not allow me to embed. Media tags?

 

Edit: Thank you WonderBoy

Edited March 16, 2015 by ORMDale

[WonderBoy]

Do your rockets have a nozzle?

 

Not sure if there's a better way, but if you use the URL from the address bar instead of the "Share" URL, it will generally embed on it's own.

 

 

WB

[ORMDale]

Nozzled yes. This one I made the nozzle throat the regular size (1/4") and only made the core narrower.

[stix]

What are your specs? ie. core length, core diameter, nozzle diameter.

Are you using powdered or melted sugar fuel?

Case bound or inserted bates grains?

Casing material, ie. pvc, Al, cardboard?

Are you igniting deep into the core or at the nozzle end?

etc... etc...

 

The more info you can give, the more likely your cato issues can be resolved.

 

btw. There is little point making the core diam. smaller than the nozzle diam.

 

Cheers

[dagabu]

Stix,

 

I'm headed off to work now so I will have to dig into the archives later when I get home but there has been much discussion about "stepped" spindles over the years and with actual data from several designs, some of which reduce the throat right after the clay nozzle giving the propellant only the smaller throat and therefore, higher pressures before the cavity opened up to the nozzle width.

 

This ultimately led to more propellant to be pressed into the tube and a higher pressure start allowing for an initial boost off the pad and the sustaining portion to be used for lift further into the burn cycle resulting in a higher apogee.

 

That said, in this case, the nozzle was reduced but it sounds as if the core length was not reduced resulting in a casing over pressure and resultant CATO. How to fix this? Open the nozzle and make sure your grain isnt cracking, a few drops of real corn syrup in the R-candy (if that is what you are using) can make for a much more flexible grain.

[ORMDale]

My fuel is 65/35, both blade milled as fine as I can them, plus 2% red iron oxide, mixed dry and pressed at very high pressure into waxed tubes.

 

My core length extends about 3.5" above the nozzle. My normal nozzle throat and core diameter is 1/4". The first time I tried to go narrower, I drilled both the nozzle and core at 7/32", to see if the increased pressure would give me any more thrust, and it popped. The second time I tried to go smaller, in the video above, I drilled the nozzle 1/4" and then the rest of the core 7/32". My thinking was along the lines of what Dagabu said above, the narrower core would leave me with more fuel in the rocket.

 

I am top lighting, using Visco with a 3" length of heat shrink tubing applied, leaving about 1" of exposed fuse at the end, which is folded in half to hold it securely in the core.

 

I am starting to wonder if my fusing method might be to blame. I can picture a soft, gooey, half-melted length of heat shrink becoming a pretty effective plug, instead of being blown cleanly out, especially with a more narrow core.

[dagabu]

Try masking tape instead, standard 1"masking tape needs about 6-8 layers to fire proof it, cut a piece 1/2 shorter than the Visco and roll the fuse tightly along the length then add a second piece and roll it tightly. Test a section for burn through before using it in an actual rocket.

 

If top lighting pops rockets, pull the fuse down 1/2 way and try again.

 

Incidentally, that is my favorite way to make sugar rockets too.

[ORMDale]

I very much appreciate the replies. I just tested some fuses done both ways on a brick in the back yard, and I'm now even more convinced that my heat shrink tubing idea might be causing my problems. While it for the most part prevents any burn through, it really is soft and gooey afterwards. Two layers of masking tape prevent any burn through, and it's still stiff and straight, and will be easily ejected.

 

It will probably be tomorrow night before I have a chance to go launch a couple, but I have a good feeling about this. And should I have any more pop on me, I will try lighting lower in the core. Thanks again.

[stix]

Stix,

 

I'm headed off to work now so I will have to dig into the archives later when I get home but there has been much discussion about "stepped" spindles over the years and with actual data from several designs, some of which reduce the throat right after the clay nozzle giving the propellant only the smaller throat and therefore, higher pressures before the cavity opened up to the nozzle width.

 

This ultimately led to more propellant to be pressed into the tube and a higher pressure start allowing for an initial boost off the pad and the sustaining portion to be used for lift further into the burn cycle resulting in a higher apogee.

 

That said, in this case, the nozzle was reduced but it sounds as if the core length was not reduced resulting in a casing over pressure and resultant CATO. How to fix this? Open the nozzle and make sure your grain isnt cracking, a few drops of real corn syrup in the R-candy (if that is what you are using) can make for a much more flexible grain.

 

Very interesting info Dags, and appreciated - but once again I have a differing opinion. Oh dear, looks like I'm stepping onto the "carousel of pink undies again" . Yes, I get that a smaller core can cause a "spike" in initial thrust to get the motor off the ground but why introduce potential issues?

 

My solution for greater initial thrust is a "wider" core. More fuel surface area burning = larger Kn's = more pressure = more thrust. If there is a worry about packing more fuel in "just make the bloody grain longer!!". With a larger core there is less chance of cato's due to the igniter getting blocked, which may be compounding ORMDale's current problem.

 

My fuel is 65/35, both blade milled as fine as I can them, plus 2% red iron oxide, mixed dry and pressed at very high pressure into waxed tubes.

 

My core length extends about 3.5" above the nozzle. My normal nozzle throat and core diameter is 1/4". The first time I tried to go narrower, I drilled both the nozzle and core at 7/32", to see if the increased pressure would give me any more thrust, and it popped. The second time I tried to go smaller, in the video above, I drilled the nozzle 1/4" and then the rest of the core 7/32". My thinking was along the lines of what Dagabu said above, the narrower core would leave me with more fuel in the rocket.

 

I am top lighting, using Visco with a 3" length of heat shrink tubing applied, leaving about 1" of exposed fuse at the end, which is folded in half to hold it securely in the core.

 

I am starting to wonder if my fusing method might be to blame. I can picture a soft, gooey, half-melted length of heat shrink becoming a pretty effective plug, instead of being blown cleanly out, especially with a more narrow core.

 

Sounds like you've put a lot of thought, effort and time into making your fuel and pressing the motors. How are you dry mixing it?

 

The addition of red iron oxide is great for increasing the burn rate, it can be used to enhance a substandard fuel production method - not so good if you are making your fuel properly - it can then burn too fast and result in cato (for core burners). Which could be an alternate reason for your cato's??

 

My specs for my core burner motors are very similar to yours, except that my nozzle and core are a bit bigger (less pressure) and I make my fuel burn slower (on purpose!!). I would NEVER use red iron oxide for my core burners otherwise boom booms!

 

I very much appreciate the replies. I just tested some fuses done both ways on a brick in the back yard, and I'm now even more convinced that my heat shrink tubing idea might be causing my problems. While it for the most part prevents any burn through, it really is soft and gooey afterwards. Two layers of masking tape prevent any burn through, and it's still stiff and straight, and will be easily ejected.

 

It will probably be tomorrow night before I have a chance to go launch a couple, but I have a good feeling about this. And should I have any more pop on me, I will try lighting lower in the core. Thanks again.

 

My opinion is that there is possibly two compounding issues. You can also try igniting at the nozzle base or drilling the core out bigger or dropping the RIO completely. There may be varied discussions and opinions on processes and methods on this forum but rest assured, we also want to see a fellow rocket enthusiast succeed!!

 

[EDIT] btw. I do agree with dags masking tape method as the fuse inhibitor rather than the heat shrink.

 

Cheers.

Edited March 18, 2015 by stix

[dagabu]

Godspeed Dale!

[ORMDale]

 

Sounds like you've put a lot of thought, effort and time into making your fuel and pressing the motors. How are you dry mixing it?

 

The addition of red iron oxide is great for increasing the burn rate, it can be used to enhance a substandard fuel production method - not so good if you are making your fuel properly - it can then burn too fast and result in cato (for core burners). Which could be an alternate reason for your cato's??

 

My specs for my core burner motors are very similar to yours, except that my nozzle and core are a bit bigger (less pressure) and I make my fuel burn slower (on purpose!!). I would NEVER use red iron oxide for my core burners otherwise boom booms!

 

That's very kind of you to say, Stix. Thank you. As far as mixing my fuel, I mill both parts as fine as I can get them, with the iron oxide getting tossed in with the sugar before milling. Both then getting dumped into a ziplock freezer bag and sealed with as much dry air as I can get and then shook like Shake & Bake until well mixed. The nice thing about milling the rust with the sugar is that I can then see when the sugar and the KN03 are fully mixed.

 

As far as even adding the red iron oxide and making the mix that much hotter, well I just can't help myself there. I reckon I am one of those people that's gotta get as close to redline as possible. Only about 20% of mine cato so far. There's just something about seeing 40 grams of very hot flash light up a full second before you hear it that moves me.

[ORMDale]

Godspeed Dale!

 

Thank you, kind Sir. I had really hoped to get out and test tonight, but it's a bit of a drive and it just didn't work out tonight. I will for sure light and report back as soon as I get the chance.

[dagabu]

 

Very interesting info Dags, ....... Yes, I get that a smaller core can cause a "spike" in initial thrust to get the motor off the ground but why introduce potential issues?

 

My solution for greater initial thrust is a "wider" core. More fuel surface area burning = larger Kn's = more pressure = more thrust. If there is a worry about packing more fuel in "just make the bloody grain longer!!". With a larger core there is less chance of cato's due to the igniter getting blocked, which may be compounding ORMDale's current problem.

 

 

 

 

I appreciate the work on thinking up hypothesis that may solve the CATO problem, I do think perhaps that you will lose actual lifting power as you "just make the bloody grain longer!!" or have a large core. The gents making those 2 million pound 'O thrust motors use special tooling to make a "star" shaped core that keeps the actual burning surface nearly identical throughout the entire burn. To just open the throat, as it were will give a short but powerful shot of thrust but certainly not greater overall impulse.

Edited March 18, 2015 by dagabu

[stix]

I appreciate the work on thinking up hypothesis that may solve the CATO problem, I do think perhaps that you will lose actual lifting power as you "just make the bloody grain longer!!" or have a large core. The gents making those 2 million pound 'O thrust motors use special tooling to make a "star" shaped core that keeps the actual burning surface nearly identical throughout the entire burn. To just open the throat, as it were will give a short but powerful shot of thrust but certainly not greater overall impulse.

 

Hey Dags my man, I do enjoy our robust and humourous discussions but some of your points above just don't add up - so lets clarify some things. Perhaps we are misunderstanding and/or assuming the wrong things?

 

So to set things straight, in my view these are the (ideal) constants:

• The motors we are talking about have nozzles <tick>
• They are cylindrical core burners (no fancy star or any other shaped geometry) <tick>
• The fuel grain is either inserted or 'case bound', inhibited externally and at both ends <tick>
• The fuel has been made/rammed/pressed or cast properly to ensure a consistent burn <tick>

 

Also, for simplicity sake, let's assume we are testing the motor on a thrust meter/load cell, therefore g's and drag are not a distracting issue. <tick>

 

Some facts:

• If the above constants are accepted, then it follows that this type of motor will be "progressive" ie. the thrust will increase over the burn period - that is a FACT!
• From that, we can deduce that more fuel burning = more thrust. (or cato) that's a FACT!
• Restricting the nozzle via either a fuse or small nozzle opening can result in cato - FACT!
• I know this not by just reading books and doing some math, but from a build up of testing and practical experience - FACT!

So, my analysis and response your above post:

 

Dags - "I appreciate the work on thinking up hypothesis that may solve the CATO problem"

Thanks, but it's not just hypothesis, it's years of practical experience as well.

 

Dags - "I do think perhaps that you will lose actual lifting power as you "just make the bloody grain longer!!" or have a large core."

No you won't lose lifting power, Here's why: Instead of making the nozzle smaller, extending the length lets the motor "breathe". You will have more fuel burning = more thrust and less pressure on the overall casing structure. Having a wider core to begin with is just like starting the motor off at a later period in time of it's normal "progression", the downside is burn time which I'll address later - Why waste fuel if the motor doesn't produce enough thrust?.

 

Dags - "The gents making those 2 million pound 'O thrust motors use special tooling to make a "star" shaped core that keeps the actual burning surface nearly identical throughout the entire burn."

Yes, all fine. But for all practical purposes we aren't making star shapes are we?. I have actually done this about 15+ years back using AP and a rubber binder which I cannot remember right now. But so what? that is not important for basic rocket motors of which we a discussing.

 

Why do you think the SRB's of the ex space shuttle, and the newer ones are long and thin? They are not short and fat are they? There are good reasons for that, as I have eluded to above.

 

There is an inter-relationship between enough pressure and not too much, also burn rate of your fuel and nozzle and core size. If you change one, then you have to start at square one. It's a process that can be measured, if effort and time are taken. Scientific careful testing methods is one way to understanding other than looking at just scientific formulae.

 

So, I'll end with my original response to Dale's question: "Skinny core, higher chance of CATO?"... YES there is!... and you know why, so don't bother with making the core smaller to pack more fuel in, It's of little value. Make the core longer and open it out a bit if you want to see better results. Which you have already been there from your other posts. ie. you have had good success rates.

 

(sorry if this has dragged on, but you guys only had to read it - I had to write the bloody thing! )

 

Cheers.

[calebkessinger]

You guys keep hashing this out... we are learning plenty by watching .

[dagabu]

Stix,

 

Lets take a step back and flesh out each one of the issues one at a time but with little less emotion and lets use some data to back up the hypothesis. I came from the HPR side, I was a team member and did a lot of nozzle and grain design, we did R-Candy and Composite grains (C-Slot) along with a few Hybrid (N2O) motors that I would classify as "Interesting". The body and electronic guys were the real brains behind the group.

 

Lets go back and take on one single item at a time, feel free to disagree but keep the tone respectful please.

 

"So to set things straight, in my view these are the (ideal) constants:

• The motors we are talking about have nozzles <tick>
• They are cylindrical core burners (no fancy star or any other shaped geometry) <tick>
• The fuel grain is either inserted or 'case bound', inhibited externally and at both ends <tick>
• The fuel has been made/rammed/pressed or cast properly to ensure a consistent burn <tick>"

Agreed, nozzled motors with round spindle cavities, pressed into the tube (casebound).

• "If the above constants are accepted, then it follows that this type of motor will be "progressive" ie. the thrust will increase over the burn period - that is a FACT!"
• No complaints with that, all round cavity motor grains are progressive.
• "From that, we can deduce that more fuel burning = more thrust. (or cato) that's a FACT!"
• IF all given variables remain the same across the testing platform, then it is fact, change, remove or modify a single component or dimension, the result changes. For the sake of "facts", lets refer to Impulse instead of undefined "thrust". I can get an immense amount of "thrust" from flash in a solid billet of steel but it is worthless in flight.

"Restricting the nozzle via either a fuse or small nozzle opening can result in cato - FACT!"

Roger that Stix!

 

 

"I know this not by just reading books and doing some math, but from a build up of testing and practical experience - FACT!"

Ditto.

"Dags - "I appreciate the work on thinking up hypothesis that may solve the CATO problem"

Thanks, but it's not just hypothesis, it's years of practical experience as well."

noun, plural hypotheses [hahy-poth-uh-seez, hi-]

a proposition, or set of propositions, set forth as an explanation for the occurrence of some specified group of phenomena, either asserted merely as a provisional conjecture to guide investigation (working hypothesis) or accepted as highly probable in the light of established facts.

Sorry, without data and proven, working experiments, its still hypotheses.

"Dags - "I do think perhaps that you will lose actual lifting power as you "just make the bloody grain longer!!" or have a large core."

No you won't lose lifting power, Here's why: Instead of making the nozzle smaller, extending the length lets the motor "breathe". You will have more fuel burning = more thrust and less pressure on the overall casing structure. Having a wider core to begin with is just like starting the motor off at a later period in time of it's normal "progression", the downside is burn time which I'll address later - Why waste fuel if the motor doesn't produce enough thrust?."

In reply to the making the grain longer: As you add more propellant, you add weight, you have to use a more robust casing and since we are focusing on paper housings, the paper has to be thicker. I don't recall making the nozzle smaller, just the core. The nozzle should be a consistent size and shape for testing, changing that variable changes the whole data stream. You don't get something for nothing, you pay a hefty inertia bill with longer motors and history proves time and again that about X10 is as long as BP will go and R-Candy follows the same rules, there is a maximum length at which paper just will never be enough to hold the pressure. Then there is the "large core" hypothesis. Yes, a larger core (same size nozzle) will result in the exact same thrust at that single point as any motor same to the same dimensions with the same propellant as one with a smaller core. When the propellant burns away to the same size core that your hypothesis emphasizes, the thrust will be identical. The downside is that the burn is shorter and there will be less impulse as a result, therefore, lesser usable thrust.

"Dags - "The gents making those 2 million pound 'O thrust motors use special tooling to make a "star" shaped core that keeps the actual burning surface nearly identical throughout the entire burn."

Yes, all fine. But for all practical purposes we aren't making star shapes are we?. I have actually done this about 15+ years back using AP and a rubber binder which I cannot remember right now. But so what? that is not important for basic rocket motors of which we a discussing."

Nope, we are not, I just answered the question that was posed is all.

"Why do you think the SRB's of the ex space shuttle, and the newer ones are long and thin? They are not short and fat are they? There are good reasons for that, as I have eluded to above."

Better materials, lighter weight, closer tolerances, better nozzle design, better technology to determine the broach position in making the star shaped cores (1mm of lateral movement to one side can effect the overall thrust curve at the end of the burn) allow for longer motors (QM-1) this one had 5 segments, the motor is not skinnier, just the housing is.

"There is an inter-relationship between enough pressure and not too much, also burn rate of your fuel and nozzle and core size. If you change one, then you have to start at square one. It's a process that can be measured, if effort and time are taken. Scientific careful testing methods is one way to understanding other than looking at just scientific formulae."

Agreed!

"So, I'll end with my original response to Dale's question: "Skinny core, higher chance of CATO?"... YES there is!... and you know why, so don't bother with making the core smaller to pack more fuel in, It's of little value. Make the core longer and open it out a bit if you want to see better results. Which you have already been there from your other posts. ie. you have had good success rates."

In the 1996 film Jerry Maguire, the phrase, "Show me the money!" became popularized and it has become infamous along with "Wheres the beef?" What that means is that making a statement, even with decades of experience will ultimately fall on it's face without proof. I hypothesize that a skinny core, NOT a skinny nozzle will, if not blocked, help the initial rise and reduce the propensity of CATO. I plan on testing that hypothesis on April 11th with video. Sorry but there are no video, test results or actual data to back up that claim, skinny spindles have been around a lot longer than you and I, keep the nozzle open to accepted dimensions (traditionally) and the skinny spindle cannot add to its propensity to CATO.

Conclusion: There seems to be some issue with nomenclature, the words core and nozzle seem to get used interchangeably and should not. We also see the use of the words thrust and impulse used interchangeably and should not. I have no K-9 in this rukus so I'll not respond again to inflamed emotions but I will add to the conversation if asked to do so.

Video proof of skinny spindles/cores.

Edited to make my reply in BOLD

Edited March 19, 2015 by dagabu

[stix]

Hey Dags, I'm at work atm so can't take in your reply fully, but I want to say from the outset that I didn't mean any disrespect to you - on the contrary, I respect and value your input on this forum. Thanks for letting me know about your experiences with HPR, it sounds like a lot of fun.

 

The "tone" of the written word can easily be misinterpreted by the reader. I can assure you that I wasn't sitting at my computer banging at the keys in some angry rant . A little frustrated perhaps, because I was getting confused about what was being said and wanted some clarity. Thanks for providing it.

 

I've had a quick look at what you've said and it all looks very positive to me. I can see where there could have been some misunderstandings. I'll have a good read when I get off work.

 

Cheers.

[dagabu]

Hey Dags, I'm at work atm so can't take in your reply fully, but I want to say from the outset that I didn't mean any disrespect to you - on the contrary, I respect and value your input on this forum. Thanks for letting me know about your experiences with HPR, it sounds like a lot of fun.

 

The "tone" of the written word can easily be misinterpreted by the reader. I can assure you that I wasn't sitting at my computer banging at the keys in some angry rant . A little frustrated perhaps, because I was getting confused about what was being said and wanted some clarity. Thanks for providing it.

 

I've had a quick look at what you've said and it all looks very positive to me. I can see where there could have been some misunderstandings. I'll have a good read when I get off work.

 

Cheers.

 

Stix, I feel the same way about posts, I write pretty darn straight, no inflection of humor or fooling around, not that I mean to do that, its just my engineering background. Technical writing shouldn't be happy and smiley, it should be strictly tab A to slot B stuff...

 

It's hard to disagree with someone over the forum, it does not mean one person is right and the other is wrong, its just different. Experience paints a different picture for everybody and in my own experiences, I have had different outcomes than others.

 

Yes, working with several others made launching a LDRS or a RTF rocket an affordable thing to do but diluted the knowledge base a lot for any one individual. The political environment of HPR became toxic to many in that time and then the BATFE dropped the hammer on APCP and my magazine went away because it no longer could simply be stored in my garage. I would love to go out to LDRS34 to watch but it's no fun being a mile away from the rockets. I almost got the wife to go because of the fingerlakes wine area but I lost out to a nieces wedding in Ohio....

[Maserface]

I have never made a sugar rocket or a "high nose powered" rocket, so I wont comment on either of those. I found a skinnier spindle to increase the impulse of my rockets over fat spindles, because of the smaller exit path, the pressure is able to spike quickly (despite the reduced burn area), and due to the pressure sensitive nature of potassium perchlorate propellant, the skinny spindle makes for a hellofa rocket.

That being said, my tests only tell a very narrow (nopun) story- Skinny cores ABSOLUTELY increase the chance of cato

 

 

http://www.amateurpyro.com/forums/topic/10475-whistle-spindle-comparisons/

Edited March 20, 2015 by Maserface

[dagabu]

I have never made a sugar rocket or a "high nose powered" rocket, so I wont comment on either of those. I found a skinnier spindle to increase the impulse of my rockets over fat spindles, because of the smaller exit path, the pressure is able to spike quickly (despite the reduced burn area), and due to the pressure sensitive nature of potassium perchlorate propellant, the skinny spindle makes for a hellofa rocket.

 

That being said, my tests only tell a very narrow (nopun) story- Skinny cores ABSOLUTELY increase the chance of cato

 

 

http://www.amateurpyro.com/forums/topic/10475-whistle-spindle-comparisons/

 

Was that with BP too or just Perc based rockets?

[Maserface]

I havent tested BP just, I have tested a BP-ish propellant, but it contained perchlorate.

 

I have a couple pounds of Goex Xfine that I will be testing, maybe this weekend.

 

Looking back in Kentish, Lancaster, etc. the BP rocket spindle design really hasnt changed much, I suspect that the wider core was/is necessary for successful flights when using slow propellants (like Kentish would have had, or like TR uses), my gut tells me that a narrow cored rocket with slow propellant would want to leave the pad too slowly and lay over.


Wandering off topic though-

[dagabu]

Naw, that's a good point too, the propogation speed of the propellant has to be up to snuff as well. I bet it works the same with granular sugar propellant in opposition to R-candy as well.

[stix]

I got a bit sidetracked.

 

Has there been a reasonable and agreeable conclusion reached? - ORMDale hasn't come back yet with his final results which would be helpful if he did.

 

Anyway, after reading over all the posts again I realised there was something important that was not pointed out (on my part) where there could, and probably has, been a source of some misunderstanding.

 

My view is from dealing with small motors, like 1lb size or "E-class" whereas others may be looking at this from a 3lb motor and larger point of view. Therein lies the issue or potential problem area. My nozzle and core diam is around 5mm (less than 1/4") - there is no way I would make the fuel core smaller without being very concerned that the ignitor wouldn't exit the nozzle and therefore... CATO.

 

If you are looking at this from a "3 pounder" then those concerns are less of a problem. I would imagine a nozzle throat diameter of 7-8mm? and an ignitor exiting the nozzle is less of a problem and there is also room for experimentation to see how low (or thin) you can go. All good.

 

I have made "H class" motors but only tested on a load cell. They performed very well, and with my "Scale-up theory" the total impulse was correct. The issues for me is more about not having the correct tooling and making do with standard metal rods available.

 

With my "E" motors, they perform at around 80% of theoretical efficiency - ie. I get a specific impulse of around 100, whereas you could get 125-130 out of sugar rockets. No problems, I don't care. My motors have a built in "safety factor" and are reliable.

 

Although, if I wish to, I can easily increase the length - I use Aluminium tubing and I know (from actual testing) that the extra length will easily contribute to a higher total impulse. With larger motors the extra weight can become an issue, but not with mine.

 

Hopefully that's cleared a few things up. It would be good to have a consensus of opinion, not necessarily just for the sake of contributors of this thread to feel vindicated (like myself ), but for others in the future to read and come to a conclusion based on "actual worked models"

 

Perhaps along the lines of:

• Small motors (cores) may cause constriction and over-pressurisation when inserting the ignitor and result in CATO.
• Larger motors can be "tweaked" for optimum performance by reducing the fuel core diameter, resulting in higher total impulse.
• Safety, ie no CATO'S should always be of upmost consideration.
• CATO'S can be satisfying, providing no-one gets hurt and the authorities aren't alerted

 

Cheers.

 

 

 

[ORMDale]

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.

Edited April 1, 2015 by ORMDale