Rocket Propellants

[DIYMark]

Hi all,

 

I'm opening this thread to discuss/debate KNSU and BP fuel used in rocketry.

 

I'm not sure for the rest of you guys, but I make my charcoal and even then its a messy job which I don't like too much, and soon realizing how much BP I go through making rockets its just annoying (making lots of charcoal).

 

So having that said I turned to Sucrose based propellants. R-Candy is great...if you have to time so when i refer to KNSU I'm referring to dry mix. The main deciding factor for me between BP or KNSU is impulse. I don't mind the extra work to make charcoal - that is if I get more performance from it than KNSU.

 

So I did some basic calculations...

 

Say I have 2 batches of fuel. One BP and one KNSU and both weigh 100 grams. So in the BP case it would be the typical 75:15:10 and in the case of KNSU it would be 65:35 (not including the 1% Fe2O3 catalyst). These ratios are chosen because they are generally the "default" ratio and both equal 100 parts/grams all up.

 

So next thing is the energy content for the fuels. Sucrose has an energy content of 17Kj per gram and charcoal has an energy content of 29Kj per gram (Approx.)

 

Now in a 100 gram batch of BP we typically have 15 grams of charcoal so that equates to 435Kj of energy while in a typical 100 gram batch of KNSU fuel we have 35 grams of sucrose which equates to 595Kj. This means that gram for gram KNSU fuel has 36.8% more energy in it than BP.

 

Okay, the other part. Power as we all knows is expressed in physics as Energy over time. So the faster you use the energy the more power.

 

This is my issue. KNSU (Catalysed) has about the same burn time as BP in an equivalent engine so having said this the KNSU propellant has more power seeing as it uses more energy of a slightly longer time.

 

What do you guys think? Or know?

 

Is anyone else tossing up between the two propellants?

 

Would anyone be able to confirm my calculations (If you’d call them that)?

[Swede]

I wish I knew the answer, but I will be following this thread very closely. My own limited experience with ball-milled KNO3 + Sucrose has been disappointing, perhaps due to moisture problems. I personally have no desire to cast propellants. I'm wondering if it is the casting vs. a dry mixture that truly makes the K-Suc fuel a success.

 

Any advantage to alternate sugars? From what I've read, using sugars other than sucrose may help with the energy, but may not be worth the additional expense.

[psyco_1322]

Well I was bored one day and decide Id try some of my KNO3/Sugar/Sulfur fuel with my 4oz bp core burner tooling. Its a fuel I have used for some small 3/8" rockets with success over and over again, it was pulled from the big pyro comp file thats around and then tweaked a bit because it burned with some KNO3 dross left over. I made it burn nice and clean:D and added a bit of catalyst. Though my little rockets had a small, long core to make up for the fuels low impulse I thought I might be able to use it in plass for bp. Well it kinda worked. The rocket was slow on take off and arced over in mid air. Not quite suitable for a replacement in my opinion. A spindle that was maybe a 1/3 more smaller would probably produce some nice rockets.

 

On the note of RCandy, mmade a bunch up once, made one good 3/4" rocket. It flew fantastic but was such a pain in the ass to make. Heat up fuel, burn fingers trying to get a bit in the case then heat some more.....must have took me all day. It was back in my noobish days, I looked at the stick it lugged up and was quite impressed. Considering it was a big tank ass rocket made of PVC pipe with PVC end caps, one being the nozzle. Plus it was held on by 3 zip ties and JB Weld. It was also burning the un-catalysted fuel cause I thought that that nozzle was way too small for a fuel burning 3 times as fast. I gave up on them rockets and just burnt up the rest of the fuel as smoke bombs just playing with it. Of coarse the was after about a year of storage and it was still good after being kept in a plastic chemical tub.

[asilentbob]

You have to remember that sucrose and charcoal form different amounts of gas when they burn and at different temperatures. I feel like BP would expel hotter gas, though less of it, meaning more thrust than KNSU... but thats just how I feel. Also the sucrose in KNSU might have a tendency to not burn up as completely. Consider that sucrose burning gives off CO2 AND H2O... Comps giving off H2O tend to be burning at a relatively low temperature.

 

And this isn't even considering the effect of the sulfur on the black powder. That adds a bit to the gas production to.

[DIYMark]

As far as I know - other sugars are only marginally better if not worse. James Yawn Clicky Here has done some tests with different fuels (sugars) and it seems that plain old sugar is great because of how cheap it and its performance.

 

I’m on the same page as most of people here; casting takes too much time. But I have noticed this. Well mixed/powdered (cant beat my $11 coffee grinder I got ) burns pretty clean with out any of that yellow solid crap left over that is typical of course dry mix. After I burn a small pile all that is left is the catalyst from the reaction. The KNO3 and sugar burnt very well.

 

One other note; if you haven’t made any tests with catalysed propellant; I urge you to! When I first used un-catalysed dry mix it was pretty pathetic. However once catalysed it burns as fast as meal powder made with a relatively poor grade charcoal (I'd know I made my charcoal before with hardwood scraps - now I’m hoping top try Balsa; What do you guys use or buy?)

 

Also in my KNSU fuelled rockets for catalysed mix I use a nozzle ID of around a third of the case ID, maybe smaller and around a quarter of the case ID for un-catalysed mix. So if you made 2 identical rockets, one with KNSU fuel and one with BP fuel. And made both on BP tooling the BP rocket will be better (as the KNSU requires a smaller nozzle - more pressure).

 

So maybe this is my answer? BP as fuel?

 

After all if the above "Test" was made the BP rocket would fly further because it’s more energetic (needs bigger nozzle) where as the KNSU fuel needs a smaller nozzle. The problems I see with KNSU fuel is how hydroscopic it is! It’s a real pain to store an engine.

 

Also good point aslientbob. However won t the H2O turn to steam and thus create more thrust?

 

LOL psyco_1322, I had the fun of “disposing” of some Rcandy batches too! I made them with glucose syrup (No corn syrup here) and I was misled by all the Rcandy videos of the Rcandy having to be a light Tan colour when in fact Rcandy made with glucose syrup should be white and pass the snap test! Otherwise if made with glucose syrup and cooked to a tan colour it would burn for a second or 2; then extinguish its self – weird!

 

So in the end I had the fun of burning about 1Kg of Rcandy (Hey at least it doesn’t extinguish its self if it’s in a huge amount)! Man that stuff can smoke out the block. Then we all were when the neighbours cut sick LOL.

 

Well, so far for me, BP fuel is looking to come out ahead of KNSU a bit because it’s easy to store and is more energetic (Needs bigger nozzle for an equivalent sized KNSU rocket). But once I think of KNSU I lean towards that because of how easy its to make.

 

At this point in time, I have this in mind.

 

BP Fuel....

Is better for fireworks (Nice charcoal sparks tail)

Isn’t hydroscopic

Apparently has more Power

Can be made Core or End burning

Uses pain in the ass Charcoal!

 

KNSU Fuel….

 

As hydroscopic as a sponge in water

Is easy to make

No messy charcoal

No huge variables like in BP (Charcoal)

Umm and that’s it hehe

 

So maybe BP fuel is better. Also once writing the above the fact that BP can be core or end burning is very appealing from a fireworks stand point which is what I’m aiming for.

 

Still, the biggest factor for me is charcoal. It’s a huge variable in BP! And the only decent wood I can get here for good charcoal is balsa – has anyone used this before? How were your results?

[mormanman]

I've read that if you put the KNSU in a like glad ware container and put it in the frig it help with the hydroscopity of it and I think that those silica gels in the shoe boxes would help too.

 

Other than that I have enjoyed this topic and hoping it continues.

[Mumbles]

Balsa is considered to be one of the hottest and most reactive charcoals. Willow, Alder, Cottonwood, Aspen, Poplar, and probably a few others I am forgetting, are also considered to be high on the scale of reactivity and burn speed.

 

You may be interested in Danny Creagan's tests of various charcoals.

 

http://www.wichitabuggywhip.com/fireworks/...2.html#charcoal

http://www.wichitabuggywhip.com/fireworks/...coal_tests.html

[DIYMark]

Thanks for the links Mumbles; after reading the results, its pretty interesting to say the least!

 

Balsa charcoal based BP seemed to be the most powerful which is what I'm after. This is because I would prefer to make end burners apposed to core burners any day (Easier to machine tooling, easier to pack and easier to remove spindle ). Also I wont need a delay. However, eventually I will most likely make a core burner set of tooling for the hell of it.

 

So this weekend if I have to time I may end up making Balsa charcoal

[Swede]

There's SO much room to experiment with rockets. You can go cored vs end burning, differing nozzle shapes, opening diameter, tamping pressures, binders, etc. I am going to try and find one size casing (right now it's 3/4" OD, 1/2" ID X 3.75") and learn how to optimize it. Once optimized, and notes taken, then maybe I'll move on to something bigger.

 

Cored vs. end burners, in particular, is worth looking at. If you can get rid of the core tooling, you'll have a much easier time of it. Yes, you'll get less thrust, but perhaps that can be handled by a slightly smaller nozzle ID. You also get to load more fuel by weight, and that in theory should get you higher. But if your fuel is not hot enough, then it may not even get airborne, whereas a cored engine with the same fuel might. So it really looks like each and every setup can be a bit different, and might require some tinkering.

 

It looks like KNSU vs BP will require different tooling and different techniques, and that makes it tough to do a proper comparison.

[Sylar]

The only fair comparison would be the same weight propellant in the same casing.

 

Nozzle diameter and core lenght can be adjusted freely to optimize results for the specific fuel.

 

 

My money is on KNO3+sugar. Stochiometric optimised with possibly sulfur and a iron oxide catalyst.

[Mumbles]

I think it depends what you're looking for in a rocket as to which will be optimal.

 

If you want to make display rockets, you can't get away from black powder. To me KNSU just doesn't have the right look. I personally like core burners better. Better lifting capacity for headers, and many more delay effects can be used. There is more room to tweak the fuel for better tail and such as opposed to end burners.

 

If you're going for height, it's up in the air. (pun not intentional) I'd say KNSU as much more experimentation has been done in larger sizes and and with more model rocketry type of things.

 

If you're trying to lift a payload, cored black powder I believe will be the best, as far as max payload, and height per weight of propellant.

 

If going for consistency, I'd say end burners. KNSU is hygroscopic, core burners are much easier to cato. With end burners, you just make hot meal and launch away.

[DIYMark]

Thats what is detering me from making tests.

 

Each rocket will have to be "custom made" with the only link between them is that they both have thee same mass of fuel. So then I'd need to optimise 2 separate rocekts. Which will take a fair bit of messing around

 

I guess the easy way would be to know each fuels impulse - would any one here know what BP and KNSU impulses are?

 

Furthermore, for me personally, its the fuel with the most versatility that will be the best. Like with BP you can make core and end burners where as with KNSU you can make core burners but there isnt any end burners that I have seen yet (and I doubt there will be - unless it has really poor payload carrying abilities).

 

As of now I and holding by BP (I will try to make balsa charcoal this weekend). However if I were into amuter rocketry (Large Scale) you cant go wrong with R Candy. Cheap and easy to use for rockets.

[Mumbles]

Actually, many amateur rocketry clubs ban the use of sucrose. Requiring dextrose or sorbitol. The burn characteristics are actually quite variable with sucrose for some reason.

 

KN Sugar is cheap, easy, and pretty over the counter. BP is also cheap, but some of the easiness and OTC is sacraficed with the need to ball mill, and use special charcoal. Core burners though can use very crappy charcoal, and really only needs to be screened.

[DIYMark]

Intresting you mention the ban on sucrose in Rocket Clubs.

 

Recently I read that "Sugar" isnt jsut sucrose and In fact the sucrose content can vary greatly so maybe this is why the ban?

[Mumbles]

Table sugar should be 100% sucrose or very close, containing only minor anti-cake components. Brown sugar has some molasses in it. "Sugar" on it's own is an entire class of compounds though. Much the same as "salt" or "metal" really defined a broad selection of things.

[Pyrohawk]

I would vote in favor of Rcandy... I havn't done a lot of rocketry but I have shot a lot of BP rockets and some Rcandy. Rcandy is a lot of fun, its easy to use and can be scaled up pretty easily.

 

But if you want a boost in power. Try Jimmy Yawns recrystalized Rcandy. Its pretty cool stuff! And also if you want RCandy to look cool, just add Ti flakes. Ti is the only additive that I know of off the top of my head that works great. It looks awesome.

[DIYMark]

True, RCandy is good stuff but it takes time to make! Then time to make a Grain and time to heat the propellant to make the grain! Argh

 

However, after watching James Yawn's rocket videos he launched some C class equivilents with R candy and man they burnt fast! Faster than a C6 - 7 I say.

 

Ive got an Idea for R Candy though. I'm hoping to mount a shell on a rocket (This coming holidays) and load it with "RCandy Stars" so when it bursts it will make trails of thick white smoke ("Day time" shell). I reckon that would be cool. Better still would be to colour the smoke with some natural dyes

 

Also Ti flakes I think for like the "Only" metal that gives R Candy a good look. I dont think Al in nearly as good. However Ive never heard of MgAl being used - I wonder how that fares.

[psyco_1322]

Mumbles I believe that Cork ranks up there with Balsa on the reactivity list, or so Ive heard. No first hand exerience though.

[GalFisk]

Iron filings also give a nice tail to rcandy, though I don't know where it ranks compared to Ti and Al. I'll try my coated iron powder (added 2.5% paraffin wax from cheap candles) and compare it to Ti, FeTi and Al some time.

Does FeTi need to be coated against nitrate?

I've heard of grinding up rcandy and then ramming the powder, to get around the process of molding. Has anyone tried this?

[DIYMark]

Ive also heard that cork makes for very fast BP - I had a video of it but cant find it! Anyway Cork was the fastest out of the three (Others were willow and balsa charcoal)

 

Also Ground Up R candy should work pretty good I imagine however I think the Solid Grain would burn faster.

[Yankie]

I havent had much experience but i think KNSU rockets are better, they arent as fast but have a much longer burn time. I made some tiny bottle rockets one with KNSU and one with BP and the bp rocket shot up about 15 metres really quickly, the KNSU rocket however burned for about 3 times as long and went almost 35 metres. however it did make an arc whereas the BP did not. this is probably because i didn't ram the KNSU and just pressed it resulting in less power (I think)

I have 3 BP rockets (one willow two pine) and 2 KNSU rockets, i will test the out soon and will see which is better.

[DIYMark]

Thats what I have noticed. The KNSU rockets burn longer and tend to arc in their flight where as BP is short sharp and tend to not fly as high.

 

Please let us know of the test results

[Sylar]

That's why special cores have been made on KNSU propellants like star and hexagons. This creates a larger initial thrust through higher surface area.

 

On melting the propellant, I've experimented with sorbitol a long time ago and this is VERY easily molten, doesn't caramelise and is not as hygroscopic.

[psyco_1322]

Ive alwasys wanted to try sorbitol never could get my hands on any, never really tryed that hard either. I seen some at the 07 PGI convention and was going to buy a pound and it disappeared Its seems like it would be a lot easier to handle, just pour into your grains and done!

 

The problem with rcandy and other melt KNO3/sugar mixes is that there so freaking hygroscopic they turn into mush in a matter of hours if not sealed up. When I made that one rocket I described early I did seal up the casing with some Al foil tape and covered up the the nozzle and ended up careing it around in my car for a day or two and then it had a few days some other places too before I shot it.

[Swede]

For candy rockets, I think a good way to store them would be in one of those small ammo cans with one of those rechargeable silica bead dessicators. They are the size of a cell phone, are available at sporting goods stores, and do a great job. When saturated, the beads turn from blue to pink. Put it in an oven at 350 for 4 hours, and it'll recharge back to blue.

 

The ammo can will both seal and protect the motors.