R-Candy additives

[JMan]

Hi. I've been wondering about some of the specific effects of certain additives in R-Candy (the standard 7:13 mix 65:35 fir scaled up) I've tried red iron oxide and aluminum (taken from rusting car rotors and shavings from coke cans) I've added 1, 3, and 5 grams of each and I've noticed/measured no difference in thrust or preformance.

 

Is it wrong to acquire aluminum or rust from these places or is the enhancement so minor it's not noticeable. Also what other additives have any of you guys found which change the characteristics of r-candy. I know of Krow to make it less brittle but other than that?

[NeighborJ]

The RIO I use is milled to airfloat and makes a huge difference in burn speed. The other thing I've noticed is temperature has a huge influence on burn speed and ignitability. On a 100f day the motors often would CATO but in the winter the motors always flew with sluggish ignition. If you have a pottery or ceramics supply near you they carry finely milled RIO or any pyro supply will have it,cheap.

[JMan]

So maybe the most effective is heating/cooling my motor before launch? And I'm also guessing RIO increases the burn speed. What does that stand for anyways?

[JMan]

Red iron oxide never mind

[MadMat]

Do you have a problem with your RCandy? One other thing, I wouldn't add the aluminum, just the RIO. If you are having problems, how are you actually making your RCandy?

[NeighborJ]

Sometimes adding a catylist isn't what the doctor ordered. In a lot of cases a rocket will fly better and travel farther with the slow and steady push of an uncatylized motor, the catylized motors have more thrust but burn out much quicker, this can cause the rocket to spiral or ungulate during lift which wastes a whole lot of the thrust.

I've even added a negative catylist to some motors and made longer cores or smaller nozzles to create a longer burn at reduced thrust. They do fly better and have been more reliable.

Addressing the brittle grain problem: this can happen from over cooking past dry. But a few percent of corn syrup helps to reduce the chance of flakey fuel.

[MadMat]

Agreed. I usually only add RIO to end burners for that matter.

[JMan]

I'm not looking to quicken burn time specifically, rather how to change the burn rate or other charastics of the fuel. I was thinking of trying to make a nice modified end burner and thought "maybe something increases pressure but not fuel consumption" I've also had problems with nozzle less motors and Cato. I'm simply looking for ways to change the fuels charastics such as "would it be better to shorten the core and make a modified end burner to help Cato or should I try an inhibitor?" I just want to know all the options that rcandy has

[Mumbles]

Ungulate

 

Undulate

 

Spelling is important, unless your rockets really act like hoofed animals.

[NeighborJ]

The two most common reasons for endburners failing are sidewall burnthrus or nozzle and bulkhead blowout. Neither are technically a CATO but if it is a CATO the problem is usually caused from fire migrating between the casing wall and the fuel. It is quite difficult to prevent this from happening without using a press to load the fuel securely against the tube wall. Using pvc or aluminum for endburners are less than ideal because oxidisers will consume them as fuel causing burnthrus. Believe it or not high quality cardboard tubes are the best option because it gets consumed slow enough to ensure adequate structural integrity during the entire burn. It also allows a pressed clay nozzle and bulkhead to bite into the walls securely enough to prevent blowouts.

Any fuel only has a given amount of energy, if case pressure is increased it will burn faster and for less time. If case pressure is reduced, it will burn for longer. Burn rate modifiers do nothing that a nozzle size change or core length adjustments can't do, technically they displace fuel and the resulting motor will have slightly less potential energy than a non catylized fuel. Some fuels may need a catylist in order to even out the burn and prevent chuffing but sugar rockets are perfectly happy without any. The one type of motor which could benefit most from a catylist is a nozzleless coreburner. They have a dramatic drop in case pressure shortly after ignition so a faster burning fuel will help keep the pressure up a little bit longer.

It is difficult to find general rules which encompasses every situation unless we can pick one specific motor design and review it's composition, construction methods, and materials to find what will work in that scenario and what can be improved.

[stix]

Yeah, you're pretty much on the money there NJ.

 

The way I look at it is that unless you're making big motors, RIO in a core burner is a recipe for CATO. I've used it before in a small end burner with a short port drilled approx. 5mm up the nozzle end and it took off with heaps of power - it worked great

 

I'm not looking to quicken burn time specifically, rather how to change the burn rate or other charastics of the fuel. I was thinking of trying to make a nice modified end burner and thought "maybe something increases pressure but not fuel consumption" I've also had problems with nozzle less motors and Cato. I'm simply looking for ways to change the fuels charastics such as "would it be better to shorten the core and make a modified end burner to help Cato or should I try an inhibitor?" I just want to know all the options that rcandy has

 

JMan, are you sure you're making your r-candy properly? I think sometimes people for whatever reason have an issue when making r-candy (ie. burns too slow) and then try to rectify it by adding RIO. It may well work ok, but it's probably best to work out what went wrong with the base mix and work on your methods etc. Consistency is it's OWN reward!

 

I'm not sure what you mean by ..."not looking to quicken burn time specifically, rather how to change the burn rate or other charastics"... If you're not looking to increase the burn rate then you must be looking to decrease it. If so, then I'm not sure either. I think you could probably use baking soda? NJ mentioned above that he has used a negative catylist, I'd be interested to know what it was.

 

What other "characteristic" of the fuel do you mean? Safe, easy to cast, flexible, hard, long/short set-up time, hygroscopicity, etc. etc. Or do you mean the "geometry" of the fuel, ie. length, core diam/shape etc. I think it's best to concentrate on getting the basic fuel mix and casting method working consistently before worrying about additives, otherwise you will be just chasing your tale and trying to fix something long after the horse has bolted. Hmmm... perhaps that's what is meant by "ungulated rockets"

 

JMan, you seem to be taking on too much all at once. Perhaps it may be best to take a step back and re-evaluate your goals. There are many on this forum willing to help especially if you ask clear questions.

 

btw. RIO can easily be purchased at a hardware store, usually in the cement section as it's commonly used as a colourant.

[NeighborJ]

Stix, in response to your question about negative catalysts: I've tried baking soda as a negative cat with differing results depending on the manufacturing method.

 

When heated with the fuel the baking soda releases CO2 and becomes washing soda and it does slow down the fuel, but I ended up having consistency problems because the water would not cook out of the batch at the same rate as the CO2. In fact it kept releasing moisture back into the fuel during cooking.

 

It does work well in uncooked hand rammed fuel in small ammounts (1-3%) because the excess gases produced during combustion add to the impulse slightly while slowing the burn rate. If too much baking soda is used it will start to chuff or even extinguish the motor mid flight.

 

For R candy I used titanium dioxide (white paint pigment) and was able to slow the burn rate in a consistent manor. It has almost unlimited versatility and can slow the burn rate beyond anything else I've tried. I use it in BP endburners for the delay portion, and at a mix of 50/50 BP, TiO2 I've managed to slow the fuel down to 8 seconds per inch and with a smooth and consistent rate.

 

I'm almost certain that "negative catalyst" is a misnomer, maybe burn rate modifier is more applicable because it is simply an inert substance used to replace a portion of the fuel in the effort to put the breaks on the reaction.

Edited April 11, 2017 by NeighborJ

[stix]

"I used titanium dioxide (white paint pigment)"

 

That's what I love about pyro - it does overlap into the world of the artist.

 

Can I please suggest that you break your text into paragraphs - It would make it much easier to read.

[lloyd]

Neighbor, it's also been incorrectly called a "phlegmatizer". I think the best term is probably "burn rate modifier".

 

Lloyd

[stix]

Yes Lloyd, and also "catalyst" is better described in this case as a "burn rate modifier".

 

So let us all be clear. Adding a chemical to the fuel should be described as a "burn rate modifier" regardless of whether it's positive or negative.?

[lloyd]

Stix, I believe that to be true. We ordinarily think of catalysts as being necessary to make the reaction occur, but not just to 'speed it up'.

 

Another correct implication when the term 'catalyst' is used is that even though it promotes the reaction to occur, it is not consumed IN the reaction... being left over afterwards, chemically (if not physically) intact. Such is NOT the case with most of the burn rate modifiers we use.

 

So... "positive burn rate modifier" and "negative burn rate modifier" seem to me to be more-appropriate terms.

 

Lloyd

[JMan]

I think NJ really explained what I needed. Modifying the core length is probably the best way to change pressure I realize now. And stix yes I'm sure I'm making it correct I've had many successful launches now from pvc casings to reused Estes casings. In fact I launched my fuel and Estes and (although less reliably) my fuel goes a little higher than Estes motors.

 

But yes NJ you hit it home instead of sticking with a 4 in x 1 in tube I might just want to cut different lengths and cores to get the burn I desire. I haven't tried an end burner but that's my next goal I just thought that adding something which causes it to burn at a higher temp (and therefore higher pressure) might help but maybe it needs no modification, and if so maybe it's just a small core like Estes has in it.

 

Thanks so much guys.