58 replies to this topic

[Pyropow3r]

Ive been doing pyrotechnics for at least 5 years now and have been specializing in mostly rockets. you name it ive made it end burners core burners black powder rockets sugar rockets r-candy rockets etc. But mainly i am focused on end burners i dont know why i just like em (maybe because of the long burn time). I have done at least a 1000+ launches with end burners.

But up until know i am starting to ask my self this question are end burners really better then core burners ? Well they must be because all the big names like quest and Estes use end burners right? Well i dont know

So i want to know what you guys think are end burners better than core burners. tell me what you think or know from your past experiences.


So hopefully this constructive argument can lead us all in the right direction in rocketry.


I want to know which of the two are better in terms of performance labour and dont forget the fun factor.

[Aneantis]

I'm in endburners to, always have been. I compare it with a drag race, a big powerful motor against a regular motor. The powerful motor is the fastest but it burns all his fuel in 100 meters but the regular motor can do hundreds of kilometers.

So I use a small core with super fast black powder

Hm, and I thought everyone was in making core-motors with slow fuel?

Edited by Aneantis, 05 September 2009 - 04:48 AM.

[Sambo]

But up until know i am starting to ask my self this question are end burners really better then core burners ? Well they must be because all the big names like quest and Estes use end burners right?

End burners are used because of their reliability and ease of manufacture, fast bp pressed into a tube, 2 drifts needed. While with core burners, the smallest thing such as slightly different mesh size of added charcoal can cause a CATO if your rockets are on the edge.

I find core burners have the ability to lift larger payloads to a good working height, while end burners can't lift the same weight they seem to lift lighter payloads out of sight!
I prefer core burners for lifting shells etc, although if I'm looking for a long flight with a pretty tail an end burner with a salute header is my fav.

[Pyropow3r]

I have always thought along those lines that the big names like Estes use end burners due to its simplicity ease of manufacture and reliability also perhaps due to performance as well ? Maybe we have hit the nail on its head early in this topic already.

But i still want to know what the rest of you guys think is better core burner or end burner. Perhaps i have overlooked something ?

[Eric70]

I have only done core-burners because you are not required to ball mill the BP.

The 1lb and up core-burners can lift a payload to a good height. Core-burner gives you a beautiful long orange tail (charcoal) and has a more aggressive sound at ignition.

I don't know much more about end-burners except that they are used in Estes motors for model rocketry.

Either design (core or end) requires you to dial-in the fuel for performace and reliability.

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

I suspect that end-burners are being used in consumer pyrotechnic rockets because faster powders are utilized and therefore smaller engine size gets the rocket up to the lame 250-300 feet. Those skyrocket motors are not very big. But if you were to build a BIGGER end-burner than what is seen on consumer fireworks, you will have some serious performance.

Core-burners are a very old design, end-burners came into play with modern rocketry and faster burning fuels that include BP and others fuels.

[Seymour]

It all depends on what you want to do with it.

When you want to lift a nice four inch shell, A good coreburner, with its high but short period of thrust is ideal. You don't want the shell too high. Additionally, that great orange tail is stunning.

In rocketry, lifting shells is not the aim, and nor is leaving a pretty tail. For black powder type fuels, there is no benefit of having 30% Charcoal for a coreburners (all that potential fuel is just dumped out the back!), so something close to regular BP is used, which requires an end burner to work.

For slower fuels like Potassium nitrate and sugars, a core burning, or other high surface area grain type motor is best for rocketry uses.

I'm in endburners to, always have been. I compare it with a drag race, a big powerful motor against a regular motor. The powerful motor is the fastest but it burns all his fuel in 100 meters but the regular motor can do hundreds of kilometers.

You have a good point, but you are exaggerating a bit! All the solid fuel motors I've heard of that have made it several hundred kilometres have been core burners, and their fuel lasts more than a hundred metres!

[Pyropow3r]

[quote name='Eric70' date='Sep 5 2009, 09:41 AM' post='53603']
I have only done core-burners because you are not required to ball mill the BP.

You do not have to ball mill your black powder to produce a quality end burner because i dont.

As long as you have some quality charcoal (like willow) some potassium nitrate also some sulfur and coffee grinder plus some screens 100 mesh and 20 mesh your in business.

Grind the Kno3 then grind the charcoal and sulfur together. mix and screen the tree components screen through 100 mesh screen several times. dampen with water until it can hold its own weight.

press through 20 mesh screen to granulate it leave it out to dry. Once dry press granules through 100 mesh screen then dampen again and granulate it again do this 3 times.

Now you will have some high quality black powder that it more than adequate for end burners.

[Eric70]

You do not have to ball mill your black powder to produce a quality end burner because i dont.

That is good to know, thanks.

I still prefer core-burners because I am strictly concerned with pyrotechnics and having the orange tail is part of the visual satisfaction for me.

On the other hand, I grew up with Estes rockets, had a range of models rockets from the mini-engined Mosquito to the 6-foot long, D-engined Mean Machine. I can see myself building end-burners someday for model rockets but that may be a while.

[PyroMan16]

I have only done core-burners because you are not required to ball mill the BP.

You do not have to ball mill your black powder to produce a quality end burner because i dont.

As long as you have some quality charcoal (like willow) some potassium nitrate also some sulfur and coffee grinder plus some screens 100 mesh and 20 mesh your in business.

Grind the Kno3 then grind the charcoal and sulfur together. mix and screen the tree components screen through 100 mesh screen several times. dampen with water until it can hold its own weight.

press through 20 mesh screen to granulate it leave it out to dry. Once dry press granules through 100 mesh screen then dampen again and granulate it again do this 3 times.

Now you will have some high quality black powder that it more than adequate for end burners.

You don't even have to do that. I just grind my KN03, then grind the sulfur with charcoal(hardwood) and shake it in a bag. Then I granulate it once and its good to go.

Edited by PyroMan16, 22 September 2009 - 07:03 PM.

[skyisthelimitinc]

Well, i have only made endburners bp rockets, but as stated here, it needs a very fast fuel, i pretty much make 20mm ID engines with the 4mm nozzle hole and about 50mm grain, they are very powerful and ive lifted a total weight of over 250 gram, and its very easy to make 2 stage engines this way aswell, but i think a coreburner with a slower fuel as delay are more push in, but i have yet to try one, i also think its easier to fail with a core engine.

These 2 videos are 20mm endburners, the first one is a 2stage rocket and get a very good height, the second rocket is a singel stage and it weighs 250 gram and the 5% Ti sponge added to the fuel, makes a very nice spark show, but i think it seems the additional metal added, slows the engine down a bit



the second video is two stk 2stage rockets and one singel engine, the singel engine weight is close to 300gram and the engine is pushed to the limit


-skyisthelimitinc-

[dagabu]

I have been doing HP rocketry since the 1980s but I have to say, I have never made en end burner! Sugar, RC-Candy, AP, BP, all core burners. I launched a bunch of 3# two stage rockets at PGI this year and I have one 3#er lift a 5" ball to 300'. It broke well and all the stars went out before landing. It was a prefab shell but it did work.

I am having pianomistro make me a set so I can see what all the fuss is about end burners.

Dave

[cawley333]

My personal favourite would be the core burner. The core burner has more of a surface area to burn, therefore I don't have to ball mill my black powder in order to get the adequate thrust I need. Since the end burner has a small surface area it needs more than just meal to get it flying.

[Yafmot]

A simple hole down the middle of the grain doen't begin to demonstrate how superior a core burner is for acceleration, especially those first few critical feet. Check out how any of the big boys do it (Thiokol, ATK, Aerojet, Raytheon etc). The port is usually shaped like a multipointed star or a spline socket. Otherwise, you've got the least amount of surface area burning at the initial phase, with the gas generation & temperature, and hence thrust, at its max toward the end of the burn.

But with the "star" or "spline" configuration, the area ratio is nearly the same initially as it is right before burnout. You do lose a little bit in duration and total impulse (impetus), but for something like a multistage booster, where you have to accelerate a lot of weight from a dead stop, or a man-portable munition (think RPG) that doesn't weigh much, but has to get a move on quickly, you've got to enhance the burn rate somehow.

There is another way to do this without giving up any propellant mass. That is to build your grain in layers, with a faster fuel toward the center, and a slower one farther out for sustaining positive thrust through the rest of the (now-lengthened) burn. If you run a good test stand with a datalogger, you can tweak it for a nice, long, flat thrust curve. Flat, that is, except for a big spike at the start, just short of a CATO.



You must also be sure of the mechanical integrity of the grain. The big guys have a problem with "slivering," where even a little sliver of propellant breaking loose can cause a pressure spike when it passes through the nozzle throat, and it's autoignition time (BOOM). Therefore, you've really got to pay attention to process control when consolidating the grain.

The trick is to either use a large plug that leaves a gap between itself and the wall of the size needed for the slower portion of the grain. Once you've poured and set the outer section, you pull out the plug (you DID remember mold release, didn't you?), and slightly rough up the inner surface of the charge. then just pour your faster stuff into the center, either with a nail or something in the middle to leave a port, or just solid and drill it later.

The propellant? Depends on what you've got to work with. For BP, one of the ideas I've been kicking around is to soup it up with varying percentages of yellow powder, where you use Potassium Carbonate in place of charcoal. It supposedly burns three times as fast as BP, and according to a letter on p. 31 of COPAE, can be made to burn 8 times faster by adjusting the proportions. Seems like it might be worthwhile to bark up that tree and see what flushes out.

More on this subject later. (There's probably already a thread on it.)

Edited by Yafmot, 07 November 2009 - 07:48 PM.

[dagabu]

Oh heck yea I could be wrong!

The issue is pressure and if you have a core burner with several inches of surface burning at once, there is nothing that black powder could do when placed on top that would create more pressure then the core burning unless you did one of the following:
1. You didn't give a FULL increment of the core fuel above the spindle. Lets say you use a 60:25:15 fuel (don't laugh, I have seen it in big bores) for the core section and use a Balsa charcoal 75:15:10 mix right on top of the spindle, the sucker would blow due to a pressure spike as the fast BP took flame.
2. You didn't use enough pressure when pressing/ramming the motor. A grain can crack from humidity, pressure release, drilling the core, pulling the spindle or just dropping the motor. It's not likely but it happens. Too much pressure is just as bad since an accordion motor casing will straighten out and cause the grain to crack too.
3. The motor casing is not good for end burners since this is what you create when you add increments of hot BP on top of your core burning fuel. You can use a spiral wound tube for core burners (in most cases) if your fuel is dialed in and the core is short enough. If the fuel burns off in one second, the casing will not burn since it doesn't get hot enough but add a bunch of fuel on top of the spindle and you are now an end burner causing a lot more heat on the casing walls that can burn through and pop the casing.

I think it all comes down to this, your mileage may vary. I have tubes that I have been using (I have a buddy that works for a tape manufacture and get tape cores for free) for 10 years that work great with a 3" spindle and a 75:15:10 hard wood charcoal BP but they burn for only 3/4 of a second before passing fire to the header.

I now have tooling from SDK, SLD, Pinaomeistro (just got it today) that blow the casings up every time no matter how much charcoal I add. I have to use my NEPT tubes for all of thier tooling due to the power boost that comes with a longer spindle. I have to keep core burners down to 5" or less even in these tubes due to the heat and burn through.

To close, the issue as I understand it was that the rockets were round tripping and not igniting the headers until too late. A lighter header, hotter fuel, smaller delay increment, whistle fuel, shorter lighter stick, smaller nozzle etc. could be used to help. There are just to many variables to make a quick fix.

I do agree though,

Just my two cents, fact or friction, you decide, my videos on Pyrobin will attest to the validity of my claims.

D

[FREAKYDUTCHMEN]

dagabu, longer spindles will not mean that you have more power immediately, (so you don't need the strongest tubes like those from NEPT or ours) For longer spindles you will need slower fuell, it's just that simple. And there are more ways to decrease the power of your fuell, not only the type of charcoal of course.

Just test them and see how much they can carry without blowing up. Then you'll know how strong your tube is compared with the payload weight it can carry. Stronger tubes means you can add more weight on top of your rocket, OR (without any payload or not that heavy) they fly higher.
And I don't think you'll need less strong tubes for endburners, they seem to need strong tubes as well, cause they create almost the same trust as coreburners when they are proper made.

[dagabu]

dagabu, longer spindles will not mean that you have more power immediately, (so you don't need the strongest tubes like those from NEPT or ours) For longer spindles you will need slower fuell, it's just that simple. And there are more ways to decrease the power of your fuell, not only the type of charcoal of course.

Just test them and see how much they can carry without blowing up. Then you'll know how strong your tube is compared with the payload weight it can carry. Stronger tubes means you can add more weight on top of your rocket, OR (without any payload or not that heavy) they fly higher.
And I don't think you'll need less strong tubes for endburners, they seem to need strong tubes as well, cause they create almost the same trust as coreburners when they are proper made.

If you use the same powder it surely will. Make one with a longer spindle if your fuel is on the edge, you will see.

True, stronger tubes can withstand more pressure but with end burners, the tube has to contain not only pressure but must be able to handle the duration of the burn. This is where a proper convergence becomes so important. With a poorly designed convergence, the pressure (flame) will burn through at the nozzle edge and CATO the motor.

No need to argue about this, go build a motor and you will see immediately that it is true. Don't launch it though, you want to keep the casing for inspection afterward.

D

Edited by dagabu, 10 November 2009 - 12:39 PM.

[FREAKYDUTCHMEN]

Hehe of course it surely will with the same powder, but coreburners and endburners ask for different powders. For coreburners it should be something like 60:30:10 and endburners something like 75:15:10.
The tools and tubes should been seen like the standard you don't play with. Adapt your fuel is the easiest thing to do.

[dagabu]

Hehe of course it surely will with the same powder, but coreburners and endburners ask for different powders. For coreburners it should be something like 60:30:10 and endburners something like 75:15:10.
The tools and tubes should been seen like the standard you don't play with. Adapt your fuel is the easiest thing to do.

Like he said

[firetech]

How do you guys mix your bp coreburner rocket fuel? And what fuel do you use?

[dagabu]

How do you guys mix your bp coreburner rocket fuel? And what fuel do you use?

I have only fired core burners on a test stand so far but I have stayed with hard wood charcoal in the traditional 75:15:10 ratio.

D