Please correct my wrong thinking

[Merlin]

In terms of power BP is the least compared to hybrid or straight whistle.

I made 75/15/10 BP with 2% mineral oil to aid in pressing. I pressed a 8 oz tube with a clay nozzle and small increments of fuel to 6500 psi. The rocket went up about 20 feet and boom. I have had this before (rammed) with 75/15/10 but I thought 8 oz was small enough to use straight BP. I know one answer is to add more charcoal. But this is my question. If 75/15/10 catos why on earth wouldnt a even more powerful mix like hybrid or whistle not also cato? Because there is no clay nozzle on whistle? The tooling I am using is universal/hybrid but I put a bentonite nozzle and bulk head in place. I also expected the mineral oil to slow the BP down avoiding cato. The tube was not waxed.

[calebkessinger]

It's probably just not pressed hard enough. Hand ramming pretty much changes everything. When you start supporting the tube and pressing the fuel grain solid at high pressure it slows the burn and removes all the voids.

 

I too have had hand rammed nozzled rockets fail in the same manner. They work fine for me when pressed.

 

Just slow your fuel down a bit and have fun. Or if it's that hot of fuel just leave the nozzle out and fly them nozzle less

[AzoMittle]

In terms of power BP is the least compared to hybrid or straight whistle.

I pressed a 8 oz tube with a clay nozzle and small increments of fuel to 6500 psi. The rocket went up about 20 feet and boom.

 

I'm more of a shell guy but it sounds like you had voids/cracks/pockets in your grain; or, your nozzle was too tight for the grain design and it created more pressure inside than the propellant/casing were able to handle (meaning the pressure created cracks which further raised the pressure creating more cracks and so on until it catos). It could also be due to storage, are the motors/casings going through multiple heat/cold cycles or are they being bounced around/vibrated during storage/transport (even the vibration of a car going down the road)? Based off what you're saying about adding more charcoal and/or nozzleless working fine I'm leaning towards too much internal pressure. Try either using a more open nozzle, a cooler fuel, or else a shorter or narrower core.

 

For any rocket it is a combination of propellant composition, grain/core/sliver geometry, nozzle geometry and material, and case geometry/materials. You can absolutely use a more powerful propellant with a similar nozzle by changing grain geometry, or you can use more powerful propellant and grain geometry by varying the nozzle, etc etc. Think of a garden hose with your thumb over the end, you can change the pressure of the water coming out by either opening the tap more or covering the end with your thumb more, same idea but the nozzle is your thumb and the tap is the burning surface of the propellant.

 

Does that answer your question?

Edited May 14, 2016 by AzoMittle

[Merlin]

 

Does that answer your question?

 

Thanks. I am new to rockets but I have rammed several BP rockets on this same tooling and they worked fine- until I made the BP too hot. That was likely the case here but I thought the mineral oil would slow down the BP. If so it didnt slow it enough. Also, this was my first attempt at pressing rather than ramming. I want to learn to press well with BP before trying hybrid or whistle.

[OldMarine]

What tubes are you using? I'd try waxing them before trying anything else.

 

Afterthought: Did you use a tube support?

Edited May 14, 2016 by OldMarine

[mikeee]

A good quality tube support will resolve a number of issues with different fueled motors.

You can have success with one motor and the next one can fail when not using a tube support.

Every time you add a measure of fuel and press it, you can create flaws in the tube wall that you can not see.

When using a quality tube support the tube wall does not see the stresses of an unsupported tube.

A good quality tube support will also assure the spindle stays centered in the motor during pressing.

[Seymour]

I've had many BP + Flash end burners work and then plain BP ones using the same geometry (and pressing pressure) explode.

 

I've also been able to make end burners with BP + flash and plain whistle with smaller nozzle holes than I can with plain BP.

 

Perhaps BP + Flash and plain whistle press better at lower pressures than plain BP? There must be some reason why this is the case because these are not one off occasions, I've had this be the case again and again.

[lloyd]

Or -- perhaps you've not yet learnt to make them, considering their specific pressure gradients and constraints!

BP motors should be 'first' for every geometry and configuration. Once you learn them through-and-through, you have the ammunition to assault the more-difficult materials with some modicum of understanding.

 

Um... (respectfully) understanding I think is lacking here.

 

Lloyd

[Seymour]

I am quite aware that I usually press rockets WAY lower than the ideal. I do this to avoid changing the pressure over from fountains and to avoid using tube supports.

 

With the rockets I normally work they are very reliable. Many types have NEVER blown up with the geometries I use.

 

Is there actually anything wrong with me doing it like this? Am I actually misunderstanding anything? Am I actually failing to understand anything significant?

 

There are times that I do use the tube supports and press harder, and I mean tens of times higher pressure.

 

But Lloyd, can you really criticise my understanding if I choose to use a lower pressure often because it works in that particular situation and it does so reliably?

 

My overall point is that BP might be expected to never explode in a situation which whistle works, but this is not always the case. And yes I am very much aware that the most obvious reaction to this situation is to press harder, and support the tube.

 

If you think that if you have two rockets with the same geometry and pressing pressure, one whistle, and one BP, and the whistle one flies and the BP one explodes, this means that BOTH should be pressed much harder, then you agree with me, because this is what I also think.

 

However I personally like to explore the limits of different fuels. I find it really interesting, and I do this more than I make reliable rockets. It has been many years since I have had a rocket explode and thought "oh my god why did that happen? why can't I make rockets work?", because if I wanted a reliable rocket then there is damn near zero chance it would blow up, because I'd make a reliable motor, not an "experimental" one.

 

You might think I'm a fool for playing around with a range of pressures and being interested in experimental motors pressed at fountain pressure, and since this is a situation where different opinions are valid you might be right, to and extent.

 

Lloyd, you are a mine of information but a minefield to deal with! you are pretty damn quick to criticise and I am often the same. I feel like we both end up making ourselves look like fools. Respect is there, but only partial respect, obviously.

Edited May 15, 2016 by Seymour

[lloyd]

Is there actually anything wrong with me doing it like this? Am I actually misunderstanding anything? Am I actually failing to understand anything significant?

----------------------

Yeah, Seymore, there is. You fail to recognize that you should employ the most-consistent and most-reliable method of assembly of any particular device, whether it be star, comet, lance, rocket, or gerb.

 

What you propose is to use whatever method is 'convenient' for each sort, then to condemn as 'excessively critical' anyone who proposes more-reliable methods.

 

Yeah... I _am_ a critical sort of fellow.

 

First -- It has to do with 'livelihood'. I do this stuff for a living. You don't survive in this arena unless you are HYPERcritical of each and every method.

Second -- I've helped a LOT of people past hurdles by being honest (sometimes painfully) about what's right and what's wrong. If you don't want me to honestly evaluate your methods, I'm good with that, too. I will gladly abstain. Just say the word. I certainly do NOT want to interfere with your "freedom of expression"!

 

LLoyd

[Seymour]

 

 

You fail to recognize that you should employ the most-consistent and most-reliable method of assembly of any particular device, whether it be star, comet, lance, rocket, or gerb.

 

With no exceptions? For commercial situations, or when there will be public nearby sure, I fully agree... but can I not break this rule of yours during experimentation. Deliberately lowering the standard of a variable seems to me to be a great way to get more information about the variable to me. Note that I do not think that lowering standards is something that should be done when it compromises safety. However pressing a rocket at a lower pressure and having a good chance of it blowing up in the middle of a field does not seem to be a safety issue to me.

 

 

 

First -- It has to do with 'livelihood'. I do this stuff for a living. You don't survive in this arena unless you are HYPERcritical of each and every method.

 

It is my livelihood too. Not for nearly as long as you but it won't be long until I've been a decade earning my bread from my old (and current) hobby.

 

Note that I do not think the fact that I make my money from making pyro makes me any good at it, or knowledgeable. In my experience, most in the industry have no prior experience and quite little understanding, compared to experienced amateurs. However I see potential ways that I could be killed or maimed by explosives around me every day at work and think how to avoid these things from ever happening. I understand the paramount importance of safety, and how the stakes are just much higher in commercial manufacture compared to hobby pyro.

 

 

 

Second -- I've helped a LOT of people past hurdles by being honest (sometimes painfully) about what's right and what's wrong. If you don't want me to honestly evaluate your methods, I'm good with that, too. I will gladly abstain. Just say the word. I certainly do NOT want to interfere with your "freedom of expression"!

 

 

Oh no! I don't want you to stop evaluating and criticising my methods, but I won't lie, I think you were too quick to state that I lack understanding with what I am doing.

 

Overall I just think that you throw too many personal comments in to your criticism. Even if they are true, they are not necessary, and I think they don't make people more interested in taking you seriously. Considering the big issue of safety, I feel like it's important to not push people away with what may be considered personal insults when questioning someones ability is (usually) in no way necessary when it comes to pointing out safety issues.

 

I also think that it is your duty, or at least right, to criticise my methods regardless of if I want you to, when it comes to safety. I expect you will agree that safety is more important than being offended. But I think that the more diplomatic the approach, the more good can be done, when it comes to all issues including safety. People are much better at listening when they don't feel misunderstood or dismissed or attacked.

 

One really big reason that I often press BP + Flash rockets at a lower pressure is that I hate pressing "experimental" fuels in a steel sleeve. I'm not sure how far though a blast shield they might go, or what kind of damage they could do after a ricochet. Perhaps this is me being naive (lacking in understanding, yes, I'll admit this is quite possible), but I just personally prefer to press them at a lower pressure and not have a steel tube in the equation. Here I may be wrong and if I am wrong I'd like you to explain why without telling me that the problem is me lacking understanding. However I'm not insisting that you reply or that you become more diplomatic, but this is my opinion.

Edited May 15, 2016 by Seymour

[lloyd]

I guess I'll end the discussion by asking, "What's wrong with an aluminum sleeve, instead of steel?"

 

It's JUST that sort of question I answer every day. A sort, it seems, you've never asked yourself.

 

Yeah... I will stop criticizing your work, because I do not wish to offend. You're WAY too "into this" to accept criticism of the sort that will keep you alive.

 

(Of course, that's only MY opinion. But that's the only opinion I need to make such a decision!)

 

Lloyd

[Seymour]

I'm working with the tools provided for me, which are steel. They are not mine and they are not Aluminium, but I guess there is no reason I cannot change this by sourcing them on my own.

 

I'm still baffled as to why you consider me under pressing a motor and then risking it to be exploding on the ground as a safety hazard, and aparrantly telling me that I'm lacking in understanding in a way that is unsafe. Consider that the explosions I referred to in my original comment was me trying to push the fuels to see how far you could get them to still work even with low pressures and excessively small holes, I personally see this is finding out what the limits are when they get pushed. If a fuel goes off like flash or not when it explodes at this limit is something I personally see as relevant, if not the most important to know. I've made many thousands of rockets in my time and some of them have been made to test limits. Some of these limits might be not that important, and you might even think I'm stupid for trying to explore in this direction, but I do not see how it is a safety issue.

 

 

"You're WAY too "into this" to accept criticism of the sort that will keep you alive. " I guess I'll just let you believe that. I'm sad that you've got to the point that you see me as off limits because I don't like the insults you add to your otherwise excellent comments, and have on occasion stated this.

 

It might also be relevant to note that the last week I've been in a very quickly deteriorating relationship and that has been quite messy. I'd love to say this has not affected how I've behaved on here, but the reality is that I'm constantly bracing for the next abuse and unfortunately this tension can come out unfairly. I apologise for how you have been on the receiving end of this frustration Lloyd, which of course has nothing to do with you.

[lloyd]

Seymore, I have a son who recently went through a breakup, and I understand how it can affect one's outlook.

 

You entirely miss my points. I did not criticize you -- I questioned your methods as being (from my perspective) both unproductive and unsafe.

 

Although you defended your right to use such methods, you didn't defend the actions themselves, except as being somehow 'justified' in the broader scope of experimentation.

 

If you had a stated goal -- say, "To explore just how poorly compacted black powder motors can be, and still work properly", I'd say that was a lofty goal. Your statement that using lower pressures where possible might be beneficial is true.

 

But I didn't sense such altruism from your prior statements; rather, only that you had "gotten away with it" in some cases. Sorry if I misunderstood your motives. My opinions are colored by many folks I deal with on a consulting basis whose only goal is to "get done with it", and to Hell with quality, and to Blazes with safety.

 

LLoyd

[schroedinger]

Merlin you say you use hot 75/15/10 +2% mineral oil in a 8 oz nozzled rocket. That fuel is commonly used for nozzleless rockets. In nozzled rockets it can work, but also can be to strong.

 

What you experience sounds to me like your motor is blowing up at the end of the thrust phase, when the burning surface reaches it's max area.

This can have several reasons. As the tube survives until the end of the thrust phase the quality should be ok. If you don't wax your tubes, this is quite likely to solve the problem.

If you allready wax your tubes, you will need to decrease the burn speed of your powder (decrease the ammount of kno3 in the fuel) or use a tool with a larger exhaust hole (more complicated if you don't have a lathe). I would try to make a batch of 14/3/1

[Merlin]

The mineral oil is a bad idea. Made a end burning nozzle less yesterday. It lifted off about 2 feet and fell to the ground and continued till it burned out. The mineral oil BP will be used for crossettes. Today I made a end burner nozzled with 75/15/10 but it is not hot BP as it was made with commercial AF. It was originally intended for crossettes and rising effects on shells so I thought I would try it. I doubt it will Cato may just flop over and die like yesterday. It's supposed to rain here in the next couple days. Since I don't know what it will do I rather it not be so dry. Your suggestion sounds similar to the formulation for the Estes motor which is what I will try next. I made several rammed cored rockets last year that worked using 65%KNO3. But I am trying to learn to press rockets with BP. It is a learning curve if you have no experience. I am in doubt if I will ever be comfortable enough for whistle- certainly no time soon. I know large aerial shells are complex but I think pressing rockets is trickier to do successfully than small shells based on my experience.

By the way, I am waxing the tubes, using PVC sized to the tubes and reinforced with hose clamps top to bottom and pressing to 6500 psi. I have a sali tool set so I could use that spindle to increase the nozzle diameter I suppose?

Edited May 18, 2016 by Merlin

[schroedinger]

The sali whistle tool has a short core. Not what you want.

Maybe it would be better to get one rocket type working, then the next. Just makes things a lot easier to work.

 

For the endburner, 2% mineral oil isn't needed, but it still shut fly. The 2 feet rise and drop sounds like the little initial core had enouh of a thrust spike fo rais the rocket but the grain didn't have enough thrust to sustain the movement. Use plain 75/15/10 +2% dex (rice to -2mm) i a waxed tube. Core diameter 14 -1/5 of the tube id.

Also the reason for that loop can be to much weight on the rocket during the sustained thrust phase.

[Mumbles]

Merlin you say you use hot 75/15/10 +2% mineral oil in a 8 oz nozzled rocket. That fuel is commonly used for nozzleless rockets. In nozzled rockets it can work, but also can be to strong.

...

 

No such thing. If you think your BP is too hot, I will guarantee you're not compressing hard enough or the tubes suck.

[Merlin]

The rocket that fell back and burned was nozzelless with 75/15/10+ mineral oil. The tubes I use are from hobby horse I think they are good. But something you mentioned about it being heavy struck me. It was balanced right with the stick but it did seem particularly heavy. I pressed it all the way to the top leaving only room for the clay bulk head. The tube was 5 inches in length- it is possible to load too much powder? The fuel had no binder and was not granulated.

It's possible like Mumbles said they were not pressed hard enough. The 6500 psi is calculated using a ptof gauge I made and estimated pressure by the ram and spindle surface area on the comp. I do not have a true calibrated ptof to verify my guage with- though I did make a second one with a 4" gauge and the both read within 100 psi. I know they could both be wrong. I hand calculated it and verified my calculation with the pressure calculator on passfire.

Edited May 19, 2016 by Merlin

[dagabu]

Merlin,

 

I lit two motors yesterday (nozzleless), one was a #1 BP motor, 75:15:10, no binder or phlegmatizer, the other was a hybrid, 50/50 BP and Benny Whistle, also #1. The calculated thrust on these is better than #50 so there is (IMHO) something wrong with your powder.

[schroedinger]

Wait in #16 you say a endburner fell back to earth, and in #19 you say it was nozzleless. If that both is true, no wonder, such a setup won't produce any reasonable thrust.

 

Mumbles why do you say there is such thing as too hot bp in rocketry. Your propellant always has to match the rest of your setup. Of course you can use the fastet propellant as you want, but if your tube just can't handle the pressure, it doesn't help at all. Same with the old and new NEPT tubes, both good quality, but the new ones just can't handle as much as the old ones (sadly).

[Merlin]

That is correct. My first one nozzled Catoed. Then I made another without a nozzle which went 2 feet. I think now the first wasn't properly supported during pressing. I then fabricated a good support and made one nozzleless which went two feet. Now I have pressed a third with a nozzle and proper support- just waiting on rain in case it goes crazy. I honestly thought it would fly nozzless end burning with just BP.

I mentioned previously that the motor felt heavy at least compared to hand rammed. Can you press too much fuel or is there a rule of thumb on the number of increments in a endnburner?

[schroedinger]

Yes you can press to much fuel into an endburner, but that stops with a slower bp at 15 mm and 150 mm tubes. Those rockets tend more to hover around then to fly. But > 12mm with hot bp and 5x i.d. fuel grain everything should fly propper w/o a header.

 

And an endburner w/o header is what we normally call a spolette.

 

Also since you know have endburners and coreburners mixed in this thread, it would be nice to mention above what you are always talking, else it gets quite hard to sort over multiple pages.

[Merlin]

Sorry if I messed up I will be more careful. I have a lot to learn. Thanks for your help.

[FlaMtnBkr]

Endburners have much less surface area burning at once and basically burns end to end. A core burner has much more surface area and basically burns from the center out and the fuel is consumed much faster.

 

BP is not hot enough to be used in an end burner configuration without a nozzle. Some more powerful fuels like whistle can be used like this but doesn't have a ton of lifting capability until a small core is added. They also don't whistle if a nozzle is added to increase performance of an end burner.

 

For end burners and nozzle-less core burners, I use the hottest BP that I can make. The hotter, the better. If I want a sparks or a tail, I add a bit of coarse charcoal or metal which slows the burn rate slightly but still makes a high performance motor.

 

There are basically 3 ways to increase thrust in a rocket motor. Increase burning surface area, decrease nozzle diameter to increase pressure and exit velocity, and by using a more powerful fuel. You really want to adjust one at a time or you can quickly increase internal pressure to a level that the motor housing cannot support which causes rapid catastrophic deconstruction of the motor, aka, a CATO.

 

You probably know a lot of all that but it never hurts to think about a bit of what's happening when you have a problem. Keep asking questions if you aren't sure of something and keep making motors as practice helps perfect your method and your consistency which is important when making rockets. Also, smaller motors are more forgiving than their bigger counterparts, and also use less materials and are quicker to make. I actually really like 3/8" motors for those reasons and they are still quite impressive and much more high performance than any commercial fireworks. They can also be launched from smaller spaces and are just easy and fun.

 

Good luck and keep at it. It will all come together and 'click' at some point.