Endburner too weak?

[PyroCube]

Hi all

 

Lately I built a 24mm endburner rocket with quite hot BP. (6mm nozzle diameter)

I thought about lifting a 3" Ballshell (120g weight) with it but it emerged that my

endburner was too weak, it didn`t fly as high as I was expecting, the shell bursted

a few meters over ground.

 

Are endburners always so weak or am I doing something wrong?

Whith a 15mm Endburner I`m managing to lift 30g payload, is my fuel too weak?

Normally my nozzle is about 1/4 of inner diameter.

 

I wonder how Estes gets that much thrust out of their quite small motors?

 

Greets

Edited February 6, 2013 by PyroCube

[AlexPyro66]

Your fuel was normal bp or something else?And the tube was hand rolled?

[PyroCube]

Yes it was 75/15/10 hot BP Ballmilled. I normally use this stuff for lifting my shells.

It`s not the hottest BP but for lifting Shells its good enough.

My tube wasn`t hand rolled, it has quite thick walls, surely enough for an endburner.

 

Greets

[dan999ification]

my 10mm endburner lifts 30g, nozzle 2mm. I find the hotter the better for fuel in endburners.

You could try a smaller nozzle for more power if the tube can take it, ive seen 1'' endburners lift 3'' ballshells but its not very common, the motor will have to be at its redline.

Are you using tooling?

 

Dan.

[PyroCube]

Hi

 

If your 10mm endburner lifts 30g my 24mm motor should be able to lift 120g with ease.

I`m using a simple selfmade toling.

Maybe my fuel is just not hot enough.

 

But how can a endburner with 14mm ID lift over 100g without problems? (Estes C6)

 

 

Greets

[AlexPyro66]

I am not sure If they will but a well made 24mm one will definetly lift 100g

[AlexPyro66]

In rocket competition there is a video of 24mm endburners lifting 3'' canister shells

[dan999ification]

it all depends on the design/dimensions and fuel, the hottest fuel combined with the smallest nozzle without cato and a longer than usual nipple will all help.

It takes time to dial in motors to optimum performance, i cato'd many finding the sweet spot.

Imho the normal dimensions for endburners are not about max power but functioning reliably without catos, estes motors are made to high standards with equipment we will never have so expectedly will outperform most hobby rockets.

Since you use tooling and cant really adjust nozzle dia and nipple length hotter bp is the way to go.

 

Dan.

 

[Mumbles]

it all depends on the design/dimensions and fuel, the hottest fuel combined with the smallest nozzle without cato and a longer than usual nipple will all help.

It takes time to dial in motors to optimum performance, i cato'd many finding the sweet spot.

Imho the normal dimensions for endburners are not about max power but functioning reliably without catos, estes motors are made to high standards with equipment we will never have so expectedly will outperform most hobby rockets.

Since you use tooling and cant really adjust nozzle dia and nipple length hotter bp is the way to go.

 

Dan.

 

What special equipment might this be?

[dan999ification]

who said anything about special, the equipment used.... We will never have.

 

You did say you stopped reading my posts

 

Dan.

[Col]

According to the info floating about, estes use KNO3 71.79, C 13.81, S 13.45, Dextrin 0.9, pressed to 15,000psi. You`d need a solid support sleeve and 4.78 metric tonnes of weight on a 24mm rammer

[AirCowPeacock]

Which is pretty close to stoichiometric for a typical charcoal (which is not pure carbon, guys.)

[Seymour]

I've been told that they use 75/15/10 and that formula was produced by combining the quantity of smoke grain and propellant grain and averaging the percentages for the device as a whole. The delay/smoke grain is high in sulfur and contains dextrin, and this skews the percentages this way.

 

 

I have nothing to back this statement up with, though it does make sense to me, because why would you have such a high sulfur content in them? From a rocketry perspective that does not make sense to me. The world of commercial pyrotechnics seems to be full of people playing such silly tricks.

 

Whith a 15mm Endburner I`m managing to lift 30g payload, is my fuel too weak?

 

Are endburners always so weak or am I doing something wrong?

 

Yup

 

Normally my nozzle is about 1/4 of inner diameter.

 

That is what you are doing wrong.

 

The rule of thumb I've often seen floating around, and what i consider o be a good starting point for end burners, is that the constriction of the nozzle should be one fifth the tubes ID. In practice this can be considerably smaller. For my 19mm ID rockets I have been able to push the hole as small as 2.5mm using flash boosted Paulownia BP end burner fuel and not have them all explode. With that same fuel, and whistle I comfortably fly them with a 3mm hole. My rule of thumb would suggest 3.8mm is a good size for plain black powder, so I'm really able to 'crank things up' a lot, and reap the benefits.

 

For a 24mm ID end burner my rule of thumb, or more accurately, my suggested starting point, is 4.8mm. This is assuming you have quite fast BP, definitely over 10mm/sec, ideally in the 12-15mm/sec range (burning atmospheric pressure). You have 6mm, which is a quite big step in the other direction. Ideally I would advise drastically reducing the nozzle opening size.

 

In reality you have this set of tooling. One way to still use it would be to drill a small core, no more than a couple of centimeters in to the BP, the depth of which you'll have to tweak with trial and error. That way you have a initial burst of really high thrust to get things in the air, and then the lower thrust purely end burning phase helps is coast upwards. To a limited extent almost all end burners have this small core, and this is just an exaggeration of it. Such rockets are quite effective at carrying firework type payloads, where you need the high thrust to carry the weight, but you want it to go off quite low, as opposed to the traditional end burner that goes nearly out of sight. However, true core burners are even better at carrying shells for all the reasons I just described, only more so.

 

Also, if you are drilling out small cores, you really may as well ram/press a solid plug and drill out a nozzle of a more appropriate size.

 

Imho the normal dimensions for endburners are not about max power but functioning reliably without catos

 

IMHO they are about max power or visual effect AND functioning reliably.

[PyroCube]

That was a helpful answer, thank`s a lot Seymour!

I recently tried an 24mm Endburner with a 5mm nozzle and

a little core, about 1/2 inch long.

It was a CATO, the top bentonite plug was blown out.

Maybe ramming a 24mm rocket isn`t a good idea, I`m looking for a

low cost hydraulical press, but I havent found one so far.

 

Greets

[Mumbles]

If you're blowing the top out of an end burner, I'd definitely say there is either something wrong with your compaction technique or your tubes.

[PyroCube]

I thought that too, but my coreburners and nozzleless rockets work great.

I use a steel hammer in standart size, I ram it with quite great force.

[CrossOut]

for those who were at the most recent DO-IT event, those large rocket motors that people purchased from the flying phoenix there were 1" ID (3lb) end burner rockets. they were lifting 4" TI salutes no problem. that said ive heard of people using a 3lb rockets for lifting 6" shells as well but those may be core burners or whistle.

 

as for the press, if you live in the US, try looking at harbor freight or garage sales or craigslist. i know harbor freight has a nice one for about 70 when on sale.

[PyroCube]

Here in switzerland are nice hydraulical presses available, a 6 ton presse

is about 80 dollars.

But on these cheap things arent any gauges attached so I cant see with how much pressure

I`m treating my rockets.

Has anyone a cheap and easy method to measure the pressure?

 

Greets

[Col]

You can make a pressure-to-force guage using a short bodied ram and a pressure gauge.

http://www.wichitabu.../ptof/ptof.html

Edited February 9, 2013 by Col