Questions and Answers about Recrystallized Propellant, Life, the Universe, and Everything.
Now I'm a pretty nice guy, for the most part.  

When I'm talking to other people, I strive to be pleasant, polite, caring, concerned, and pull it off pretty well most of the time despites occasional thoughts and feelings to the contrary.

But here I'm talking to myself, and that can get ugly.  I can tell it like it is.  At least like I think it is.  And because I'm not talking to anyone else, I can even be a bit insulting.  

If the truth hurts, wear it!

So no "42s" here... we are on to higher math!  
  1. Is the recrystallization process safe?
  2. How can I do it without getting hurt?  Arrested?  Sued?
  3. Where can I get Potassium Nitrate?
  4. My propellant doesn't burn right.  What's wrong?
  5. What can I use as a substitute for KNO3?
  6. What are the proportions if I use Sodium Nitrate
  7. How big a motor should I make? 
  8. How do I take up making APCP propellant?
  9. What metals can be used in sugar propellant other than titanium?
  10.  Phut--------phut-----phut--phut-Roar! Is this normal?
  11. Where to get Aerotech motors, nozzles?
  12. I got carried away and bought a bunch of motors.  What nozzle sizes should I use?


Q:  Is this SAFE?

A:  Hell NO, it's not safe!  If you choose to do this stuff, you gotta MAKE IT SAFE.  
It's part of LIFE, and I hate to be the bearer of bad news, but life invariably ends in death.  Sorry.  Please accept my apologies for bringing it up, but it's relevant.  Any activity could bring that dreaded, magical event closer.   Or push it back.  Or make life more enjoyable and meaningful in the meantime.  Or make it worse, even unbearable.  You have choices to make, and must make good ones to live a right and proper life.  

Amateur rocketry is right in the middle of all these things.  It has enormous potential for learning and enjoyment.  It has equal potential for harm.  One must be ever-vigilant of the risks attendant to any activity, to account for and moderate those risks so that the whole enterprise stays in the light and does not venture to the dark side.  This arena especially so.  Not because it is inherently more dangerous than say, driving a motor vehicle, but it is beyond common understanding, so that many of the dangers are not readily apparent and thus not easily anticipated.  

Laxity in the area of safety could make the experimenter a candidate for a Darwin Award in a heartbeat.  Or lack of a heartbeat.  One does not have to be stupid to do dumb things - I have proven that many times.  One must become aware of one's own mental processes that could lead to ignorance of a risk.  

A connundrum:  This is "experimental rocketry."  If you knew exactly what would happen every time, it wouldn't be an experiment, would it?  So one must learn from experiments.... er, experience, right?  Sometimes experience is the ONLY teacher.  Problem with learning by experience is that you get the test first, then the lesson* but wrong answers can lead to the loss of body parts, so one must not flail about unknowingly.  I recommend read the instructions first, study the cautionary tales, then design every experiment so that accidents will cause only acceptable consequences.  To quote my favorite pyrotechnist:  "it might spoil your day, but it won't ruin your life."

* Anyone know where this jewel came from?  

I can provide an overview of some of the risks and ways of mitigating them.  But this is Experimental Rocketry, where new things are tried, old things are done in different ways, thus new risks pop up all the time.  

So to be safe, one must adopt an attitude that safety ranks as a top priority.  Some say it should be THE top priority, but that is false.  If safety were THE top priority, one would not be doing rocketry at all.  Or driving a car.  Or eating fatty foods.  Or reading the newspaper.  One would have to live in a Tupperware(r) box with a steady supply of well-filtered, sterilized, humidified air and a tube supplying nutritious bland paste fed under light pressure directly into the gullet.  Too many people have choked to death while eating.  Oh, and I guess you need some device to remove the body waste, but our medical community has a good selection of devices for that purpose.  Safe?  Not me, thanks.  I like life.  Chills, thrills, fermented vegetable products, a good steak now and then, with butter AND sour cream on the baked potato.

At some point, the quest for safety becomes counter-productive to itself.  Total safety is a fate worse than death, so we move on to greater issues.  Such as the big question:   "Is my life worth living?"  If safety is your only goal, then the answer could be "no."  Every meaningful activity entails some risk.  Safety alone is the specter of the dark side.  Mr. Safety needs some company.  He needs Mr. Excitement, Ms. Sex, Mr. Enterprise, Ms. Passion to fill the hole in his soul.  To tell jokes, to make him smile, to give him a reason to be.  Safety is the counterpoint to Freedom.  All of either is nothing.  It is death.  Life involves some of both.

So one of the lessons of rocketry is:  Life is worth living, in spite of all the risks and hardships.  Life is worth preserving, even if it means avoiding some risks that could be fun.  The unexamined life might still be worth living, but if one does amateur rocketry it will not last long.  

Brother Safety and must learn to dance with Sister Freedom.

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Q:  So how can I do this "safely?"

Answer1.1:  There is no single answer to this issue, as each activity will entail its own peculiar risks, and the nature and extent of the risk will vary from place to place, situation to situation.  Example:  I can safely static test sizeable motors in the hole in my 10 acre field.  To do such tests in a suburban backyard would probably bring on the cops, and rightly so.  

A1.2  Each activity must be assessed for its risks.  That means identifying the possible outcomes, assigning a risk value, and making sure that any risk that could cause unacceptable damage is mitigated by appropriate procedures.  Like wearing protective clothing when making propellant or packing grains.  Like making tiny quantities when a new ingredient or technique is tested.  Like finding acceptable sites for static tests and launches.  Like angling the launch rod away from the crowd, even if it means lower altitude and a longer walk.  

A1.3  Like reading up on any new chemical or procedure as much as possible before using it.  By reading everyone's safety tips and following all those that apply to your experiments.  

A1.4  Most especially, by adopting an attitude of respect and appreciation for anyone who suggests that your activities might entail some hazard.  This is a good way to learn about risks of which you might not be aware.  It is very cost-effective.  But it may not be "egonomic."  The ego tends to preserve itself, often to an irrational degree.  Thus we have a tendency to reject suggestions for additional risk-mitigation, even when they are well-meaning.  They usually are.  

A2.0  Two attitudes facilitate safety:
    2.1:  Pyronoia.  This is the sneaking suspicion that flammable things will burn, and do not need your permission to do so.  One must arrange procedures and environment so that if the propellant caught fire at any time, the damage would be within acceptable limits.  A burned-up pot?  Acceptable.  A burned-up face?  Not acceptable.  A smoked-up workshop?  Acceptable.  A burned-down apartment building?  Not acceptable -Not to me, to the police, the residents, and hopefully not to you either.


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Q:  Where can I get Potassium Nitrate?

A:  Good sources are Skylighter (www.skylighter.com) and FireFox (www.firefox-fx.com)  Both of whom offer high-purity KNO3 at moderate cost.

Another source is SVRC (www.pvconly.com) who offers a technical grade at low cost.  This KNO3 requires slightly modified processing in the recrystallization method, but when done correctly yields good propellant.

There are many other possible sources.

KNO3 is often used as a fertilizer.  It is a very good one, prized by greenskeepers and hydroponic growers.  It is completely water-soluble, and offers megadoses of nitrogen and potassium, 2 of the 3 primary plant nutrients.  So one can often find fertilizer-grade KNO3 at feed-and-seed stores, or especially any any suppliers who cater to hydroponic growers.  Sometimes fertilizer grades are not pure, and may need to be "cleaned" before use.  

KNO3 is also used as stump remover.  There are several brands of stump remover that are almost entirely KNO3.  Richard Nakka has illustrated its use in some of his pages.   Beware, there are other stump removers that are not KNO3, so do look at the label.

Drugstores may still carry USP-grade KNO3, where it is sold as "saltpeter."  It has been used as a diuretic.  Less so nowdays because more effective diuretics are available.  It will probably not be on the counter where you can pick it up and take it to checkout - you will have to ask the pharmacist, and they will probably want to know what you will use it for.  If you say "rocket propellant," they might not sell it to you.  Or they might have you followed....  This might be better pursued with a druggist you know, personally or professionally.

Meat packers use KNO3 as a curing agent for meat products.  It is often used for curing bacon or making sausage.  Thus one of the major markets for "food-grade" KNO3.  So you might find it at a market that caters to sausage-makers.

I once found packets of KNO3 at an Oriental market.  They were labeled "Niter granules."  I bought a couple of packets and used some to make propellant, and the result was exactly like the drugstore-grade KNO3 I had been using, so I'm sure that's what it is.  Click Here for a photo of the packet.  It was not cheap, I recall about $0.89 for a 2-ounce packet, but it was a very good grade.  

If all else fails, you might be able to make KNO3.  It is done with manure and wood ashes.  This page includes a description of how it has been made in the past.  Might be done that way again.


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Q:  My propellant burns funny.  What's wrong?

A1.1  Many possibilities.  First questions are:  Did you use the specified ingredients?  Did you follow the recommended procedures?  Did anything funny happen during processing?  Any variation can make a big difference.  

In many cases, the experimenter says:  "I followed your recipe... but it didn't work."  Most often, upon questioning I find that they did not follow the recipe exactly, but assumed that their variations would not make a difference.  That is often the result of wishful thinking, and usually wrong.

For instance, I had a correspondent who could not find corn syrup, so he "made his own" by mixing sucrose in water.  It did not work - the propellant was grainy and crumbly.  Sucrose in water may look and taste somewhat like corn syrup, but it is not the same.  Corn syrup is a thick solution of glucose and fructose, and the use of different sugars prevents large crystal formation, making the mix a cohesive, amorphous solid.  Adding sucrose syrup simply adds more sucrose, and does not texturize the mix properly.  There are some good substitutes for corn syrup, but sucrose in water is not one of them.

Neither is table salt a good substitute for potassium nitrate.  Yes, it looks about the same, but it is definately not the same.  Taste it and see*.

(*Only if you have high grade KNO3:  NF-grade, USP-grade, ACS-grade...those which meet FDA standards for human consumption.  Lower grades might contain nasty stuff.)

A couple of other folks bought what they were told was "potassium nitrate" but got sodium nitrate instead.  Sodium nitrate can be used to make propellant, but the process is different.  It cannot be simply substituted for potassium nitrate.  If your propellant sputters and burns with BRIGHT yellow flashes, then your "KNO3" might actually be NaNO3.  I have hopes of developing a process for using sodium nitrate in the future, but have not yet done so.  Feel free to beat me to it, but if you are following the existing recipe using NaNO3, it won't work as advertised.

The confusion stems from the use of both potassium nitrate and sodium nitrate in meat curing.  They are used more-or-less interchangably in that endeavor.  So curatives intended for meat packing may simply say "saltpeter" on the label without specifying KNO3 or NaNO3.  If you look at the "nutrional informaton" it might offer a clue, as it might list the sodium content vs. the potassium content.  

Another test is to mix a little "saltpeter" roughly with an equal volume of sugar and light it.  Outside, of course.  KNO3/sucrose will burn with a purple flame tinged with dull carbon-yellow.  NaNO3 will burn with a bright-yellow flame, tinged with carbon yellow.  


A1.2  It's overcooked.  If you cook the propellant until it is brown, or even a dark tan, it may burn very slowly at 1 atmosphere, and it might not even sustain its own combustion.  This is not necessarily a bad thing, as larger motors benefit from slower-burning propellant.  But it will be difficult to ignite, especially in smaller motors.  

Solution?  1.2.1 Don't overcook it, for starters.  Use the skillet method, watch carefully, and stir often.  A light-colored, fast-burning propellant can thus be obtained.  
Solution 1.2.2 - Catalyze it.  A little red iron oxide should restore a fast burn rate to dark propellant.  Just reheat it until soft, and mix in 1 percent or so.  Other substances also speed combustion, like yellow iron oxide, black iron oxide sodium disilicate (ultramarine) and carbon black.  


Q:  My propellant is crumbly.  It never gets to the "putty" stage.  What is wrong?

A:  First off, you ARE using the recrystallization method, right?  And you ARE using corn syrup or one of the other approved substitutes, right?  The old-fashioned melt/casting method using just sugar and KNO3 often yields crumbly propellant.  That's one of the reasons it is not used much anymore.

The most common causes of crumbly propellant are:

1.  Failure to use corn syrup.  Sucrose by itself IS crumbly.  Solution?  Follow the recipe.  Corn syrup is not trivial, it is necessary.  Oh, there are substitutes, but if you don't use corn syrup, you must use something else to get the right texture.  Glucose syrup is a close approximation of corn syrup, more available outside the US.  I have not tried it but have been told that it works very well.  Or you can add a little dextrose and fructose which is a pretty good simulation of corn syrup - might even be better as it provides a closer measure of the total sugar in the propellant.  

2.  Cooking it too dry.  This propellant needs a little moisture to obtain a good working texture.  In the skillet method in particular, it is easy to get it too dry.  

Solution:  
A.  Don't overcook it.  Stop cooking as soon as a cooled disk is very stiff.  Reduce temperature to 250 degrees in the skillet (working temp) or to 200 or 225 to hold it for a long time.  The propellant will continue to dry at 250 degrees, but slowly.  
B.  Reheating/kneading.  If allowed to cool undisturbed from the final cooking temperature of 280 degrees or so, this propellant will become a hard, crumbly mass.  It is necessary to work it at lower temperatures to obtain/retain its pliable nature (quick approach) or to heat it gently under close cover for a long time (slow approach.)  By close cover, I mean to find a heatproof lid that fits inside your cooking pan, sealing in heat and moisture.  I have some glass lids that serve this purppose pretty well.  Alternatively, long heating in an oven at 200 degrees will often improve the propellant's texture greatly.  It does not dry quickly in an oven, it does dry quickly in an electric skillet.
B.  Add a little water or more corn syrup to the mix.  You might have to heat it back to 275 degrees to get it soft enough to incorporate the new water, and you will have to add a bit too much because some of it will evaporate immediately.  Then stir like crazy, mashing out all the lumps.  Reduce temp to 250 degrees and stir again.  

3.  Using impure KNO3.  
Oven recrystallization is difficult-to-impossible with some grades of KNO3, including fertilizer-grade.  Skillet recrystallization can be done, but often results in a crumbly texture, despite large amounts of corn syrup being added.  

Solution?  Acidify the mix.  Fertilizer-grade KNO3 is often a bit caustic, and this seems to somehow interfere with the recrystallization process, making a crumbly and non-cohesive propellant.  So far I have tried using boric acid and citric acid to reduce the alkalinity, but the best, easiest, cheapest and smelliest solution is to use vinegar.  In working with the technical grade of KNO3 from SVRC (www.pvconly.com) using half vinegar/half water to dissolve the other ingredients seemed adequate.  So for a batch using 100g KNO3, 50g sugar and 20g corn syrup, I would add 50ml water and 50ml white vinegar, rather than 100ml water.  



Responses to e-mail querys:


March 14, 2007

Mr. Yawn,

Now that I'm back at school I've finally had a chance to mess around with those two excel spreadsheets (BatesCALC and U-Calc) that you had sent to me. They seem like they could be extremely useful but I just have a a couple of questions. To maximize thrust from your motor, do you necessarily have to maximize the pressure (and Kn max I think?) in your rocket motor? Say there are two motors that are each the same length but different inside diameters. If you mess around with the spreadsheet and set it up so each have the same Kn max, will both motors produce the same thrust even though one is bigger and contains more propelllant? And is it possible to make a motor with more thrust at lower Kn than at maximum Kn? Thanks for all the help!

KDG


Dear K:  I'm glad you find the spreadsheets useful.  But as I'm sure you are aware, they don't tell the whole story.  Your questions suggest that you are considering a bigger picture than they can convey.  

Pressure is one way to maximize thrust.  There are other factors, but whenever solid propellant burns at low pressure, it generates less total energy than when it burns at high pressure.  There are two reasons for this.  One is that the propellant itself burns more completely and efficiently at high pressure, thus more of its potential energy is extracted.  The other is that rocket motors work most efficiently at higher exhaust velocity, and the higher the pressure, the higher the velocity.  

(It's similar in gasoline engines - a high compression engine has higher efficiency, generally translated into more pep.  I guess that's why you still see Premium gasoline being sold - the Porches and other hot cars often have high compression motors, and need it to keep the motor from "pinging" at high.  A turbocharger turns a normal motor into a high compression motor, so any car with a turbocharger is likely to require premium gasoline.)

But in rocket motors, the difference may be minor, depending.  When I burn sugar propellant in my model rocket motors at Kn 120 or so, it generates pressures of about 300 psi and I get delivered ISP's in the 80's to 90's.  In PVC motors, with Kn's up to 200, pressures from 600 to700 psi, I get ISPs around 115.  In aluminum motors with Kn up to 300, pressure up to 1200 psi, ISP reaches 130 or a little above.  

But Kn/pressure is not the only determinant of ISP - a good motor design helps, smooth nozzle, proper converging and diverging cones, etc.  My model rocket motors have very "poor" nozzles from an efficiency standpoint - I might get a few more ISP points by improving them a little.  I might experiment with that some day.  But the power of these little motors is quite adequate for their purpose, and better nozzles will be much more trouble.  So for the moment I'll stay with the quick-and-dirty nozzle which only takes a minute or two to make.

Two motors of same length but different diameters will be very unlikely to produce the same thrust.  Unless, perhaps you do some trick like use the same sized propellant grain in the larger motor as the smaller, or use a less powerful propellant in the larger one.  I will assume you are filling the case with propellant, and using the same propellant in each case.

With the same grain design, the larger diameter motor will have slightly higher thrust, and a longer burn time.  By clever tailoring of the grains, you might arrange for both motors to have the same thrust levels, but the larger motor will still burn longer, creating more total thrust.  Web thickness is the key here - the thickness of the propellant wall from the core to the inhibitor.  Since the grains burn from the inside out (BATES grains, at least) the thicker web means a longer burn.  

Alternatively, you could tailor the grain design so that the motors have the same burn time, but the larger motor will have higher thrust.  

So the general rule stands:  larger motor = more propellant = more thrust.

You can twist this rule with some effort, but the more you deviate from it, the sillier things become.  For instance, you might make the larger motor's grains with a really large core, such that the motors contain the same amount of propellant, and the thrust will be about the same.   The larger motor will still have slightly higher thrust because of the greater surface area, but with careful tweaking of the grain geometry or propellant characteristics, you might get the two motors to behave the same.  But you will be "wasting" some of the capacity of the larger motor, and why did you make it larger if you don't want more thrust?  Well, there may be some very good reasons, but it will be these reasons that dictate the final design.

Making a motor with more thrust at lower Kn than higher is theoretically possible, as there are some propellants that don't follow the rule.  But I don't know of anyone who has done it.  Any particular reason you would want to do this?  

Your questions are good ones.  They can be taken as intellectual exercises and thus useful in understanding motor design.  But this is also the kind of thing engineers at Morton Thiokol and ATK spend their days doing, to tailor rocket motors for specific purposes in space flights and military applications.  

Hope this is interesting, if not useful!

Jimmy Yawn
jyawn@sfcc.net

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Substitutes for KNO3?

A.D. wrote::
Could you use another substitute instead KNO3? (Potassium Chloride, Magnesium Oxide, etc.)

Jimmy replies: Many things have been tried as substitutes for KNO3.  Some can be made to work, but have serious disadvantages - none are commonly used as KNO3 is clearly the best oxidizer for sugar propellants.  

Sodium nitrate can be used, and in theory could be even better.  But that theory has not been realized in practice.  It is more difficult to work, harder to make into propellant. The result is slow-burning, and very hygroscopic.  So no one currently uses it, although I entertain the hope that it can be developed at some point.  I've done a few tests with it, and some have worked OK, but not as good as with KNO3.  

Ammonium nitrate has been tried.  It is even worse than sodium nitrate, at least with sugar propellants.

The reason most chemicals won't work is because solid rocket propellant needs a good oxidizer.  When nitrates and perchlorates are heated, they give off oxygen.  Most substances do not.  Nitrogen and chlorine bind loosely with oxygen, so it only takes a bit of heat to break the oxygen off, freeing it up to burn with the fuel.  

That's how a solid propellant works.  A fuel (like sugar) starts to burn, giving off heat.  The oxidizer molecule next to it gets hot, releases it's oxygen, allowing more of the fuel to burn.  That's how a propellant can pack a lot of self-contained fire in a tight casing.  The oxygen is bound to other elements.  I call it "powdered air."  

Potassium chloride is the potassium equivalent of table salt, and is inert.  

Magnesium oxide will not work.  It contains oxygen, but tightly bound to the magnesium so the energy needed to break it free will be greater than the energy released by the fuel for a net loss of energy.  Rocket propellant has to put out energy, not suck it up.  

Perchlorates can be used in rocket propellants, but are not used with sugar.  Ammonium perchlorate is used in professional rocketry, but it is bound with polybutadiene (essentially tire rubber) which serves as both fuel and binder.  

Potassium perchlorate has been used with polybutadiene, but is not used much nowdays becasue ammonium perchlorate is more efficient and better-behaved. 

Potassium perchlorate has been mixed with asphalt to make Galcit propellant, not used much anymore because ammonium perchlorate/polybutadiene propellant is much more effective.

Chlorates should be avoided at all cost!  Potassium chlorate, sodium chlorate, and barium chlorate are very dangerous.  Besides, they do not make good propellants.  These are the chemicals people used to blow off their hands in years past, and where the term "basement bomber" came from. 

Some pyrotechnists use them, but with extreme care.  I hesitate to even mention chlorates because some fool might think I'm recommending them, try it, blow their eyes out, and claim that "Jimmy said chlorates are OK" when in fact I said over and over that they are BAD.  

I will not converse with anyone I know or suspect to be using chlorates, lest I be considered to blame when they lose body parts.

I wrote a treatise on this last year:  http://www.jamesyawn.com/kclo3/notes.html

OK, rant mode off.  Just don't use chlorates.  If you must, don't talk to me.  

Potassium nitrate is the "right stuff" and well worth the trouble to obtain.

Jimmy

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Question:  How big a motor should I make?  

Jimmy, how can I tell what a size a motor is that I may make or rather would like to develop. Maybe this isn't a simple question as maybe I need a way to measure thrust? I suppose nozzle diameter being one of many variables? Maybe just the amount of propellant is how motors are rated. I have been searching around for software to download to calculate this. The "rasareo" software is pretty thorough but they go by published motors and or historic motors, motors that are in production.


Jimmy writes: 

A couple of other questions must be answered before determining the size of the motor, mostly what kind of rocket do you want to launch and to what altitude?
By "kind of rocket" I mean it's mass, diameter and coefficient of drag.  That will determine the altitude it will reach on a given amount of thrust.

Then you can consider that sugar propellant, in a good motor, will have an ISP of 130 or so.  That means that each gram of propellant will generate 1.3 Newton-seconds of thrust.

With this input, you can reverse-engineer a flight using an altitude-prediction program like RocCAD, EZAlt, or RASAERO, to determine what total thrust will send such a rocket to the desired altitude.  Divide the needed thrust (Newton-Seconds) by 1.3 to get the amount of sugar propellant needed (grams.)

Then you can start designing the motor so that it will include this much propellant and burn it in a timely manner.

There are many fine points to consider, but this should get you in the ballpark.

Example:  Say we build a 3-inch diameter rocket weighing 4 lbs and we want to send to 2000 feet.  Assume it has a COD of 0.5

I run the altitude prediction component of ROCCAD, input these values, and start with an arbitrary thrust of say, 200 Ns and a burn time of 1 second.  I'll need 154grams of propellant to generate 200Ns, which is 5.43 oz, so I input that starting value. 

Output tells me that this one will peak at 1420 feet, not quite high enough.

I re-run the sim and arbitrarily bump up the thrust to 250 Ns.  That would require 192 grams of sugar propellant, which is fed to RocCAD as 6.7 oz.  This puts apogee at 1966 feet. 

So we are in the ballpark, and can start thinking about a motor size that will contain this much propellant and fit in this rocket.  

I happen to know that a 38mm BATES grain contains about 50 grams of propellant.  So four of them should give us 200 grams, which should give us 260Ns total thrust and send the rocket to 2080 feet.

I also happen to know that a 54mm grain contains about 195 grams of propellant.  So a single-grain 54mm motor should do the trick.
I've taken a few shortcuts here, but this is just to get a first approximation so that we can tweak the design.  It is also an inelegant way to determine the amount of propellant needed - perhaps I should modify EZAlt to work in this direction.

Let me know where this leaves you.  No doubt I've missed a few bits and pieces, and will be happy to fill in the gaps.

Sincerely,
Jimmy Yawn
jyawn@sfcc.net

2/28/09

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Question:  I see that APCP has been ruled out as an explosive and from what i have read that I could find (lol),  it seems to be much easier to work with....My Q's are, What would be a good SIMPLE all around formula for APCP? Do u have to wrap the grains with an inhibitor for bates grain operation? I use scott' s bates grain calculator. Do u  still need to keep the KN factor roughly under 200 with APCP  such as with KNSU also? 

Answer:  Folks are a little more protective of their APCP recipes than sugar propellant, so you might not be able to find everything for free on the web.

APCP certainly has its virtues, not the least of which is that it is declared "not explosive" at the moment.  Sugar propellant is still iffy - I was hoping that the jury in the Megahed trial would declare sugar propellants "not explosive" and they sorta did, but not clearly enough to make me comfortable transporting the stuff w/o license. That one may have to go back to court, and I don't want to be the defendant! 

AP also has its limititations and hazards, and should not be taken on lightly.  AP is toxic, for starters.  So are many of the additives.  So you can't handle the propellant without gloves.  Fine metal powders must be handled carefully, especially Mg.  Face mask is usually required to prevent breathing of toxic dusts, and a heavy-duty mixer is almost a necessity for mixing the stuff up.  AP propellants take time to cure... you can't dream up an experiment in the morning and test it by noon like you can with rcandy.  Some require a hot box to cure, as they will not cure at room temperature.  

So when you say "It seems pretty easy..." place it in this context.  

Best approaches for learning APCP are to get Terry McCreary's book "Experimental Amateur Rocket Propellants" which describes the process in detail.  It's available from Loki at:  www.lokiresearch.com

Or you could take a Thunderflame course from Tom Henderson (He's in SC - where are you in GA?)  It costs a little bit, but Tom's course teaches how to make APCP, and after completing the course you can buy kits from him containing all the stuff you need to make propellant and to make it into rocket motor loads. 

Alternatively, you could order one of the propellant-making kits from FireFox (www.firefox-fx.com) which includes instructions. 


Kn ratios will differ.  How they differ will depend on a lot of things - every type of motor you make will require a simulation or two to make sure it is in the "reasonable zone."

 There are many recipes for APCP, some burn very fast, some very slow.  So the Kn ratio for a given motor will depend on propellant burn rate and several other factors, including the motor size, casing strength, and propellant grain design.

You can get a copy of BurnSim off the web (www.burnsim.com) which lets you simulate thrust and pressure curves for motors.  You can enter your own data, but it's kinda fun to play with the propellant parameters built into the program.  You can try out different prospective motors, and see if they are likely to chuff, explode, or go like crazy.

For most motors, you will want to keep the inhibitor on the propellant grain(s).  The BATES design requires an inhibitor.  Moonburners do too.  It is possible to use uninhibited grains too, but they are usually sub-optimal for flight motors. 

The uninhibited grain makes for a strong burn, but of very short duration.  I use them for propellant tests and in model-rocket motors.  They are a good way to test new propellants or motor casings.  But for larger flight motors I stick to the BATES and moonburner designs.

Apologies for rattling on.  Please let me know where this leaves you, I'll be happy to continue! 

Jimmy Yawn

6/19/09

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Metals in Sugar Propellant


Question:  
Dear James.
For several years I am following your experimental rocketry site with great interest.
I want to have a 'sparking tail', but titanium is hard to get here (israel)
do you think magnesium flakes would work?  iron flakes? other metals?
 
Answer:  Please accept my apologies that I cannot offer an easy answer to this question.  Rest assured that if I did, it would be all over my web page by now.


I've tried Mg and a couple of other metals in sugar propellant, and some burn.  But the effect is not dramatic.  With Mg and Al dust, one gets a slightly brighter flame, but the difference is  barely noticeable at night, not at all during daytime.  Here's an example:  www.jamesyawn.net/tests/1-06/index.html#5-21-06D1

I've tried Mg lathe turnings, and get a spark here and there.  Again, if you were not looking for it, you would not notice it. 

A friend of mine, Jonathan Carter, experimented a bit with iron and obtained a reddish flame.  It's pretty, but it is not very bright. 

Ti is the only thing I've found that makes folks go "Wow!" 

I find that "flake" is the best form of Ti for sugar propellant. 

The flake form of Ti is considered non-hazardous here in the US.  Hopefully it is also considered non-hazardous there and thus might be obtainable if you can find someone who has it. 

But a quick web search did not turn up any vendors in your country, I am sad to see.

There are many metals I have not tried.  I have some copper powder and have not yet tried that... perhaps I will!  A green sparkle would be nice, although it would probably not be very bright.

Problem is in the nature of KNO3.  In reading Sutton and Biblarz, I searched for references to KNO3 in professional rocketry, and they are rare.  The only mention was that it is used in some military missiles as a "flame suppressant."  When burned with sugar, the major product of combustion is potassium carbonate.  It's all that white smoke you see.  And it is a military-grade flame suppressant.  In fact, potassium carbonate is used in many dry-chemical fire extinguishers.  It's really, really good at putting out fires.  So a sugar motor is, strangely enough, an excellent fire extinguisher. 

So you can put all kinds of color chemicals and flame effects in a sugar motor and get naught.  The potassium carbonate snuffs it. 

Ti is an exception only because the heavy particles are heated enough to burn and then thrown clear of the exhaust stream.  In observing Ti/sugar burns, I note that the Ti burns outside the smoke stream, for the most part, with only a few burning inside of it.  I believe this another advantage of Ti flake, as the flat flakes do not all fly in a straight line upon leaving the motor - many diverge from the ballistic path and encounter clean air outside of the fire extinguisher stream. 

So my best recommendation is to stay the course and try to find a vendor for Ti over there.  Failing that, one must enjoy the high thrust and beautiful smoke trail that sugar propellants love to provide.

I'll see if I can find my copper powder and give it a test.  I'll let you know if I have any positive results.

Hope to hear from you!

Jimmy
jyawn@sfcc.net

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Tight-Fitting Grain, Propellant Browning


Dear Mr. Yawn,

I have a number of comments and questions but I'd like to start with just two because I don't know how much time you have to answer questions from people you don't know.
I watched a series of videos you made showing how to make Rcandy using an electric skillet. In one of the episodes you put the finished grain into the cardboard tube (with the nozzle) and it seems to be a fairly snug fit. Since the grain was made from the same size tube along with the mold liner, wouldn't the grain fit loosely in the tube without a mold liner?
I made some Rcandy following your instructions and I noticed the batch started to go a bit darker - I guess it was 'carmelizing', so I quickly reduced the heat and continued on. Is this darkening something to avoid - does it have a large adverse effect on the Rcandy?

Thanks in advance for your response, 

(Name withheld)

Dear Namewitheld:  Because I hand-roll my own tubes, they vary somewhat in inside diameter.  The mold liner is thin, so it does not create a lot of leeway.
So I tend to choose a smallish tube to make the grain mold, but sometimes don't get it quite right.  But no biggie - tight grains work fine as long as they will go into the casing.  If a mold is too large, I can use another turn or two of mold liner to make it smaller.

I just looked at my movie again, and realize that I was using some commercially manufactured tubes at that time.  They tend to be fairly consistent in size, but still vary a bit.

Browning slows the burn rate of the propellant.  This is not necessarily a bad thing, as larger motors work better with slower propellant, and this stuff is pretty darned fast.  But little motors need fast-burning propellant, so unless you are making large ones, browning should be avoided.
It is possible to rescue browned propellant by adding red iron oxide or some other burn rate enhancer.  I use RIO routinely in my model rocket motors nowdays.  It helps them ignite quickly and completely.

Thanks for writing... I'd love to know what kind of rocketry you are doing or plan to do.

Hope to hear from you soon,

Jimmy Yawn
11/2/09

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Smoke Grains

Rocketeer wrote:
Jimmy,
   A smoke grain is over cooked r-candy with a little RIO added is it not? I would like to fill the 54mm Loki with a smoke grain so I can follow it as you suggested. I have a few cardboard tubes that come with the Aerotech G motors that fit perfectly in the well. Would I need any O rings around this tube and would I need a fiber washer between the propellant and smoke charge?

Rocketeer:  That is about right... slow propellant with a bit of RIO to make sure it stays burning.  Plain rcandy often self-extinguishes when the propellant grains burn out and the case pressure drops.  Problem with KN/SU is that it burns fast, so a short smoke grain does not burn for long.  Adding RIO makes it burn even faster.  

So I prefer to add a little Ti flake which keeps the candy burning but does not speed up the burn rate.  I suspect that the Ti flakes retain heat through the pressure transition and re-ignite the sugar propellant.  In watching the videos, I often notice that there is little or no smoke coming out of the motor right after burnout, but it picks up again a short time afterward.

If your head end closure has an opening, you will need O-rings somewhere to keep propellant gasses from rushing past the smoke grain. 

Personally, I prefer to use a solid, sealed head end plug with a smoke grain well so that there is no chance of leakage.  But I've used O-rings too when the smoke grain was used for delay: 

http://www.jamesyawn.net/motoreject/index.html

Some kind of washer should be used to support the delay grain, to keep it from coming loose from its well and allowing gas blow-by.  That said, in my 38mm Dr. Rocket motor tests I did not use a washer, and it worked fine... with a couple of exceptions, one of which was a premature ejection, likely caused by gas blow-by: 

http://www.jamesyawn.net/nefar10-8-05/index.html

It sure made for a nice photo, don't you think?

Does your Loki head end closure have a threaded hole, closed with a brass screw and an O-ring on the "wrong" side?  I've never quite figured out what that was for.
I use steel fender washers in my 38mm motors - they work well, and can be used many times.  I'm sure a similar washer could be used in the 54mm casings.
I think the smoke grain is even more likely to cause problems with a solid header unless it is held in place.  Several times I've had smoke grains get loose and cause trouble.  

So I had Jonathan Carter turn me a 54mm head end closure with a 2 inch long smoke grain well and an internal snap ring groove.  That way I can have positive retention of my loose-fitting smoke grain.  It doesn't need O-rings because there is nowhere for the gases to escape forward.  The grain is inhibited on the outside and the forward end, so a little gas leakage around it does not set other parts burning. 

Hope this helps!

Jimmy
11/2/09

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Using Sodium Nitrate

Someone wrote:
Hi James,

I have gone through your website http://www.jamesyawn.net/ and it's awesome.

I wanted to build a rocket but ran into some problem. At my place (New
Delhi, India) KNO3 is banned. So I purchased NaNO3 instead.
Also there is no corn syrup available. Dextrose is available though.
So I wanted to cook my r-candy using these components. i.e NaNO3 +
Sucrose + Dextrose. I need your help on the weight ratios of these
components. It would be a great help if you can tell me how much of
each component has to be used.

Thanks.

Dear Somone:  I am sad to hear that KNO3 is "banned" in India, but suspect that it is more complex than that.  There are a good number of fireworks manufacturers in India, most of which seem to be in the Sivakasi area.  A complete ban would make the production of fireworks impossible.  So I'm sure it is possible to obtain KNO3 there, somehow.  The question is how difficult it would be.  You may need a special license or permit to obtain or use it. 

But sodium nitrate can be used, as you have observed.  It has different properties, which make it challenging to use in the recrystallization process... it holds its water more closely, tales much longer to cook, and makes for very slow-burning propellant.

I have successfully used NaNO3 with the sugar syrup process, described at:

http://www.jamesyawn.net/syrup/

Here is a motor I made using sugar syrup with NaNO3:

http://www.jamesyawn.net/nano3/1-19-04c/index.html

In sugar propellant, the ratio of sugar to oxidizer is not critical.  For instance, my standard recipe is rather fuel-rich, and works very well.  You could just substitute NaNO3 for the KNO3 and have a good propellant, perhaps even a little better as it would be less fuel-rich.
The molecular weight of KNO3 is 101.1, the weight for NaNO3 is 85.
So to do a direct replacement, you would need 84% as much NaNO3 in a given mixture as you would KNO3.  In other words, if the formula calls for 100g of KNO3, you would only need 84g of NaNO3.

Using the "No Karo?  No Problem!" formula, a good mix might be:

84g NaNO3
30g sucrose
20g dextrose
50ml water

This would create the fuel-rich mixture I normally use, but may not be optimal for NaNO3 propellant since it burns so much more slowly.  So I'd suggest using the original recipe of 100g NaNO3, 30 sucrose, 20 dextrose to balance the O/F ratio a little better.
A possible advantage of NaNO3 - it is a bit lighter for the amount of oxygen it supplies.  So if the other issues can be worked out, it has the potential to make propellant with somewhat higher ISP than KNO3.

I hope this helps.  Please keep me posted on your progress!

Jimmy Yawn
jyawn@sfcc.net

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Chuffing

Tom wrote:
Hi there Jimmy.
First of all, I just love your site and have spent ages on in (my parents get really annoyed).
Secondly, I have just started making Rcandy and am having a problem with getting it to burn right.
When in the motor case it goes, phut--------phut-----phut--phut-Roar! Is it supposed to do this or am I doing something wrong?
And finally, with your 38mm Aerotech casing, Where did you get this from and is the nozzle reusable?
Keep up the great work 

Jimmy writes:

Tom:  This behavior is normal with rcandy, but not desirable.  And it can be avoided, with attention to a few details.

It's called chuffing, and it happens when the propellant grain gets partially ignited but not fully.  The motor oscillates between some pressure, no pressure, some pressure... then it goes like crazy.... most of the time.  Sometimes it just chuffs itself out.

You can avoid this issue by any of several methods.  I generally use more than one method in any given motor.

1.  Head-end ignition.  This is done with an electric igniter placed at the very head end of the propellant grain, as far from the nozzle as possible.  This is to ensure that once any part of the grain gets lit, the rest ignitesvery shortly thereafter.  It pretty much eliminates using fuse as an igniter.  If you are lighting your motors with fuse... well that's the problem.  They should be lit with an electric igniter placed at the head end.

That said, one can use fuse if certain precautions are taken to ensure that flame is carried forward to the head end of the grain immediately.  I've done that on occasion by placing a length of black match in the core of the grain.  Alternatively, to wrap the (uninhibited) grain in one turn of fuse paper often helps.

2.  Catalyze the propellant.  Using 1% red iron oxide makes the propellant much easier to ignite, and reduces chuffing greatly.  I regularly use a little RIO in my small motors nowdays.  Big motors don't need it, but little ones do.

Aerotech cases are available from a number of suppliers, including Aerotech, of all places!
http://www.aerotechstore.com/

.... but I had trouble just now finding anything except 29mm motors.

There are other places that carry these and compatible motors, like

http://www.apogeerockets.com/

Apogee is a very reliable supplier, I've used them many times.

My "Aerotech" motors were actually made by Dr. Rocket, since defunct.  Dr. Rocket made Aerotech "clone" motor casings, which were every bit as good as the orignials.  Rouse-Tech has taken up the torch and is making Aerotech-compatible "Monster" motors that are excellent.  I'm now using Rouse-Tech motors for my propellant static tests since I blew up my Dr. Rocket 38/240 casing earlier this year. 

Here is a link to Apogee's 38mm Rouse-Tech motors:

http://www.apogeerockets.com/Rouse-Tech_38mm_Motors.asp

The nozzles can be obtained from RCS (www.rocketmotorparts.com) which is actually a part of Aerotech.
I suggest you download their order form, which lists all the parts and prices:

http://www.rocketmotorparts.com/orderforms/rcs_ord_frm_6-30-09.pdf

The nozzle to use for 38mm motors is # 01550, with a nozzle throat of 0.219 inch.  This size will work with uninhibited grains in the 38-240 casing, with BATES grains in the 38/360 and 38/480 casings, and with moonburners in the 38/720 casing.
These are a heat-resistant plastic which can be used several times.  They will erode a bit each time, but can be drilled out and used with a larger casing and/or a more aggressive-burning propellant configuration.  Just be sure to calculate your Kn progressions and pressure levels before pushing the button.  (I'll send you the software to do these sims if you need it.)

Please let me know where this leaves you.  I'll be happy to pick up the ball at any point...

Jimmy Yawn
jyawn@sfcc.net 

11/28/09


Question:   I got carried away and purchased 2, 4, 6, 8' 10, 12, 14, & 16 Grain  38mm casings sized for 2" bates Gr. length (crazy)  I may never be able to use the longer casings but I really like rocket motors.

What nozzle sizes should I use with these motors?  I'm not much for math anymore, and the software is confusing.  Can you give me some hints?

Answer:  I've made some assumptions, and generated a table that may provide you a point of departure for these motors.

Assumptions are that you want the motor to ignite well, and the pressure stay under 1000psi.  Commercial aluminum motor cases can handle 1000psi with a good safety margin.

That means an initial Kn ratio of 200 or more, and a maximum Kn of 250 or so. 

Kn 250 results in a pressure of about 875 psi.  I use Richard Nakka's "design table" for KNO3/sucrose which shows the relationship of Kn ratio to pressure for this propellant.

For the 38mm motors I use, the actual grain diameter ends up being 1.25 inches.  That's because the case liner and inhibitor take up a bit of space in the case.

Grain diameter:  1.25 inches
Grain length:  2 inches

Number of grains 
Core diameter Nozzle throat diameter,
fractional inches
 Nozzle throat diameter,
decimal inches
 Initial Kn Kn Max Kn Final Mass of each grain
1
 .375
 11/64ths inch
 .171875
 198
 233
 190
 64g
2
 .375 15/64ths
 .234375 213
 251
 205
 64g
3
 .375 19/64ths
 .296875
 199
 234
 191
 64g
4
 .375 21/64ths
 .328125
 217
 256
 209
 64g
5
 .5
 3/8ths
 .375
 208
 245
 200
 58g
6
 .5
 13/32nds
 .40625
 212
 250
 204
 58g
7
 .625
 7/16ths
 .4375
 213
 252
 206
 52g
8
 .625
 15/32nds
 .46875 213
 251
 205
 52g
9
 .75
 1/2
 .5
 210
 248
 203
 44g
10
 .75 33/64ths
 .515625 220
 259
 218
 44g
                           
I'm using 64ths because it should be easy to find drill bits in any of these sizes.

Note that the core size increases as the motor gets longer and the nozzle throat gets larger.  The grain core must be larger than the nozzle throat, to prevent erosive burning from causing excessive pressure spikes. 

There are formulas for calculating the optimum core diameter, but I haven't used them here.  This is just my "rule of thumb."  So any of these motors might be tweaked for somewhat better performance, but this table should give you a ballpark figure.

I've only included up to 10 grains, because that is about the largest practical length for BATES grains of sugar propellant.  The longest I've made is an 6-grain motor. 

I believe your longer motors were intended for slow-burning AP or AN propellant.  With KN/sucrose, an 8-grain motor is balls-to-the-wall, and 10 grain really iffy, and anything beyond that truly experimental - fire it in a hole the first few times.

Also note that the larger core decreases your propellant loading density, decreasing overall performance.  There is a point of diminishing returns with long motors,and that point is about 8 grains with sugar. 

Those longer motors might work well with moonburner grains.  Moonburners are much less aggressive than BATES grains, and are a natural for long motors.

I suggest starting with the 2, 3, and 4 grain motors and get them working first.

I hope this helps - lemme know where it leaves you.  I'll be happy to pick up the ball at any point.

Jimmy Yawn
jyawn@sfcc.net
2/20/10



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