Endburner nozzle diameter

[mabuse00]

Hi guys,

 

here's a question for the endburner fans among us.

 

Nearly all information on the internet are pointing to a 1/4 id nozzle.

 

Facts are:

 

-when I made some tests last year, I used 1/5 nozzles, hand drilled, no de Laval shape of course. It was impossible for my to pop the motors even with my best BP, based on black alder, milled very long and riced with redgum. All Hand rammed, and using a rubber mallet, usually creating grains that are not compacted to well.

 

-I have a batch of the new 14mm id model rocket drivers from a german company. These are definitely based on whistle mix and also their thrust curves indicate that the core is (little) longer than it should be for constant thrust.

Their nozzles have a de Laval style shape, like i would expect the tools from firesmith to make (with that extra cone on the spindle).

Guess the nozzle diameters - they are only 1/5!

 

A 1/4 nozzle seems quite suboptimal to me, the smaller nozzle must be much more efficient!?

When I furthermore consider that I can always slow down the fuel if it becomes necessary my thoughts are to use 1/5 at most, rather something even smaller...

 

SO:

I'd like some real tooling now. What kind of nozzle would you choose?

 

 

 

I know Endburners are useless for most pyro applications but I like them anyway, lifting a small salute slowly to a great height is sooo cool

[Seymour]

Depends on the fuel. With 19mm ID end burners I've ranged from 2.5mm to 5.5mm. For whistle and BP + flash I use 4mm, with 3mm if I want it screaming. I've been surprised with how forgiving they are. 2.5mm was where they often blew up, but not always.

 

A short end burner can be made in only a few increments, thus quickly, and can be a good way to lob smallish effects in the air. Rockets with headers are pretty much obsolete in most shows, but they still have a place in our world. A good end burner can carry decent weight. Think 3/4" end burner lifting 3" shell.

 

I like a nozzle with an exit cone even if just for the looks.

[mabuse00]

Great information, thank you Seymour.

 

How far would you let the core protrude into the fuel?

 

Common values seem to be like 1/2id into the fuel and another 1/4id for the nozzle thickness at the throat.

 

 

That would mean a spindle for a 10mm tool would have to be like the cone's height + 7,5mm slim part.

Do you have an opinion on that? Is there some mistake in my thinking I don't see right now?

Edited September 3, 2014 by mabuse00

[Seymour]

I know a lot of people have a short core on 'end burners' but as a rule I don't. Ok, technically I do, but we're talking about less than one millimeter.

[ddewees]

Seymour,

 

I still haven't tried your bp+ flash in an endburner, but it's on my to do list.

[wildcherryxoxo]

I have an itch to produce some end burner tooling with 1/5ID nozzles, can always drill em out. I am with you seymour, if its more than a cats tit, I call it a core burner

[pyrokid]

Seymour,

 

I still haven't tried your bp+ flash in an endburner, but it's on my to do list.

 

ddewees, please give a few details about your experiences with flash rockets. I'm curious about how the flash presses. What comp did you use, and do you think straight hot flash would work?

 

I'm imagining that at some point, the pressure would be too great for even a nozzleless rocket, and failure would occur.

[dagabu]

Hi guys,

 

here's a question for the endburner fans among us.

 

Nearly all information on the internet are pointing to a 1/4 id nozzle.

 

Facts are:

 

-when I made some tests last year, I used 1/5 nozzles, hand drilled, no de Laval shape of course. It was impossible for my to pop the motors even with my best BP, based on black alder, milled very long and riced with redgum. All Hand rammed, and using a rubber mallet, usually creating grains that are not compacted to well.

 

-I have a batch of the new 14mm id model rocket drivers from a german company. These are definitely based on whistle mix and also their thrust curves indicate that the core is (little) longer than it should be for constant thrust.

Their nozzles have a de Laval style shape, like i would expect the tools from firesmith to make (with that extra cone on the spindle).

Guess the nozzle diameters - they are only 1/5!

 

A 1/4 nozzle seems quite suboptimal to me, the smaller nozzle must be much more efficient!?

When I furthermore consider that I can always slow down the fuel if it becomes necessary my thoughts are to use 1/5 at most, rather something even smaller...

 

SO:

I'd like some real tooling now. What kind of nozzle would you choose?

 

 

 

I know Endburners are useless for most pyro applications but I like them anyway, lifting a small salute slowly to a great height is sooo cool

 

I don't have a good answer as to why I use a 1/4 ID tit, perhaps it was the CATOs I got, maybe it was the first drawings I got for the end burner motors or perhaps it was the ESTES motors that I measured. Either way, there sure are a lot of fingers pointing to 1/4 ID but I will do a set with 1/5 ID and check it out, what the heck?

 

I do hate to disagree with the nomenclature discussion but the definition of an endburner has nothing to do with the tit, if the "end burn" portion of the fuel grain creates the thrust then it is a end burner, even a 1/5 ID nozzled rocket with a core all the way up (would likely CATO) is still a core burner since the thrust comes from the core burning. A hybrid can be 1/2 core, 1/2 end burning but not one or the other.

[dagabu]

 

ddewees, please give a few details about your experiences with flash rockets. I'm curious about how the flash presses. What comp did you use, and do you think straight hot flash would work?

 

I'm imagining that at some point, the pressure would be too great for even a nozzleless rocket, and failure would occur.

 

I think most of us "loaf heads" that have made and pressed lots of motors have done the flash rocket. Mine was a nozzleless #1 and I used red gum to bind the mix with alcohol to keep the dust down and allow the mix to become a grain. it was frightening and I was glad when it was over. the funny thing is that it flew slower than my Sali whistle rockets...

[ddewees]

ddewees, please give a few details about your experiences with flash rockets. I'm curious about how the flash presses. What comp did you use, and do you think straight hot flash would work?

 

I'm imagining that at some point, the pressure would be too great for even a nozzleless rocket, and failure would occur.

I've never pressed straight flash, but I've heard of people who have.

 

The formulas I've used are mostly bp based, containing up to 30% flash +/- with a few other ingredients. They are a sight to see, and move like nothing I've ever seen before.

 

They are my favorite motors to build (currently), followed by the AP fuels seymour shared in another thread.

 

If you plan on going to Gillette next year, I'll be happy to show you what I mean.

Edited September 4, 2014 by ddewees

[Seymour]

I definitely think whistle beats my boosted BP + flash + MgAl mixes by quite a margin when it comes to power. My aim is really for it to look bigger than it is (flame) and be kind of cheap.

 

Maybe I shouldn't have used quotation marks in my earlier post. I definitely do understand why short cores are used on many end burners and just as Dag said, so long as most of the motor is end burning, I'm pretty happy to call it an end burner.

 

I've never pressed straight hot flash. I'm quite happy that in my rockets the 70/30 content is capped at 30% and there is always wax added, and of course, very much pressing only.

Edited September 4, 2014 by Seymour

[mabuse00]

I think there is some misunderstanding here.

 

I do NOT mean a core to give an extra boost on takeoff, but rather a core to compensate for the small burning area at ignition.

That seems to be the purpose of the small core like it is proposed by the RTS scetcher.

 

 

I know a lot of people have a short core on 'end burners' but as a rule I don't. Ok, technically I do, but we're talking about less than one millimeter.

I would assume this rocket to burn a short time on the launch pad. If we assume the burning area of the endburner as a disk, or maybe a slight cone, in the moment of ignition you only have a small part of that lit and trust would increase until the fire reaches the tubes walls.

The short core must be a compensation for that fact. It does not increase thrust at startup but rather compensates for not having the whole disk area burning right away.

 

Is that correct?

 

And can anybody comment on my assumption here

 

Common values seem to be like 1/2id into the fuel and another 1/4id for the nozzle thickness at the throat.

 

 

That would mean a spindle for a 10mm tool would have to be like the cone's height + 7,5mm slim part.

I dont mean to copy anything, but if you have a tool from Mr. Wolter or Mr. Smith handy - do they use that proportions?

[Seymour]

I usually just accept that initial buildup phase. I find that they are generally flying well before reaching the plateau, and what graceful takeoff you get (not all end burners take off slowly) I appreciate.

 

However I definitely see a place for that short kick start 'core'. It's really just a matter of preference at the time, and making something work for you.

Edited September 4, 2014 by Seymour

[dagabu]

I think there is some misunderstanding here.

 

I do NOT mean a core to give an extra boost on takeoff, but rather a core to compensate for the small burning area at ignition.

That seems to be the purpose of the small core like it is proposed by the RTS scetcher...

 

Forgive my ignorance but what is the difference?

[kpknd]

My favorite endburn motor for now is a 5/8" I.D. tube motor, it uses a 3/32" nozzle. Details can be found further back on this if you go back a few pages to the posted topic "Good end burn motor" posted 10 Oct 2013. There is a video of one of these motors being used in a model rocket. The statement made in the description says to use a 1/4" deep core, I found that to be too deep later on, it caused a few CATO's, 1/8" is good enugh.

[mabuse00]

 

Forgive my ignorance but what is the difference?

IMHO it makes a difference if you create a constant thrust from the beginning or a short burst of extra thrust, which is greater than the "normal" coreless thrust.

 

Thanks kpknd.

 

Well, the core is to deep, one can always put more betonite in there to shorten it.

[dagabu]

Got it! Constant v.s. Burst.

[Bobosan]

Ya butt,

 

Constant = good rocket

Burst = CATO baaaad rocket.

 

How about high initial impulse.

[Maserface]

As long as the fuel lights, I'm happy. I get real sour when my fuel doesn't ignite

[ddewees]

Lol... Yeah you do. Need to bring extra fuse down with you next time.

[Maserface]

gotta dip my visco in nc/flash powder, get them puppies going!