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#1 Deano 1

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Posted 12 July 2013 - 08:59 PM

As some of you may know, I acquired  an Estes rocket kit from my local car boot. It's great fun and I'm trying to copy the motors for my own use and I have hit a wall.

 

The thrust comp is no problem as that is the comp I use in my own rockets, then there is a smoke delay to make it visible which is no problem, it's just a nitrate rich comp.

 

But then there is the ejection charge, it has to be substantial to pop the nose cone off 10 inches away with recovery wadding.

 

The charge is about 2mm thick, black as charcoal and pressed, with a thin layer of clay pressed on top.

 

I have made the tooling and cracked the tube rolling, I just need the ejection comp.

 

Any Ideas?

 

Dean


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#2 pyromaniac303

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Posted 13 July 2013 - 11:15 AM

I always assumed it was something like H3, but I don't advise you to make this of course as it uses chlorate. It need not be too much more powerful than the propellant, it only needs to break through the thin clay plug at the top.

 

If you want to stay true to the original design then you'll have to be really accurate with the thickness of the top clay plug and ejection charge. I would be tempted to drill down into the smoke comp through the clay plug in the same way as a normal rocket motor, and add a gram or so of finely granulated BP, then a cardboard plug or tissue wadding to hold it in place. That way you'll have less testing to do.


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#3 Arthur Brown

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Posted 13 July 2013 - 11:35 AM

What altitude do you expect your rocket to reach? BP does NOT work at high DIY rocket altitude.


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#4 Deano 1

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Posted 13 July 2013 - 07:28 PM

What altitude do you expect your rocket to reach? BP does NOT work at high DIY rocket altitude.

It's only a baby Roger, 600 to 700 feet max


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#5 Deano 1

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Posted 13 July 2013 - 07:34 PM

I always assumed it was something like H3, but I don't advise you to make this of course as it uses chlorate. It need not be too much more powerful than the propellant, it only needs to break through the thin clay plug at the top.

 

If you want to stay true to the original design then you'll have to be really accurate with the thickness of the top clay plug and ejection charge. I would be tempted to drill down into the smoke comp through the clay plug in the same way as a normal rocket motor, and add a gram or so of finely granulated BP, then a cardboard plug or tissue wadding to hold it in place. That way you'll have less testing to do.

I'm not bothered about staying true to design and I did think about your suggested method. I might even do away with the recovery wadding and replace it with a piston made  from a paper tube.


Our saviours : In the ninth century, a team of Chinese alchemists trying to synthesize an "elixir of immortality" from saltpeter, sulfur, realgar, and dried honey instead invented gunpowder.

#6 Sparky

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Posted 14 July 2013 - 04:55 PM

What altitude do you expect your rocket to reach? BP does NOT work at high DIY rocket altitude.

 

Arthur, why doesn't it work?

 

Deano - I think it is a layer of pressed commercial BP and the clay is really just a thin layer to cover it. I think once it ignites this last fastest BP layer then it is enough to pop the shoot out. The clay offers very little resistance and the final BP layer is fairly weak.


Edited by Sparky, 14 July 2013 - 04:56 PM.


#7 whoof

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Posted 15 July 2013 - 01:35 PM

Just loosely packed bp.
Some amateurs use a capsule on a timer with about 1g powder.
Bp does not burn at altitude.

#8 cooperman435

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Posted 15 July 2013 - 05:31 PM

Am I missing something regarding the altitude issue?

 

Im aware BP wont burn in a vacuum as there is insufficient heat transfer to sustain the combustion but from memory its fine in even close to vacuum conditions.



#9 Arthur Brown

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Posted 15 July 2013 - 06:00 PM

The burn rate of BP is very pressure dependant. Burn in the open it's feet per second confined as in QM it's hundreds of metres per second. Take the air pressure away and it tends to zero unless confined.

 

Past 5000 feet the phut will fail to deploy the chute unless it's an enclosed charge like a  half inch shell.

 

Exactly what altitude BP starts to fail I don't know.


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#10 Karl Mitchell-Shead

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Posted 15 July 2013 - 06:31 PM

http://projects.fit....rd_chamber.html

 

Makes for some very interesting reading, not something I have ever considered Arthur!


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#11 Arthur Brown

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Posted 15 July 2013 - 06:40 PM

Fireworks wise anything above 1000ft is in the clouds in November, but High Power Rocketry wise 20 -75000 feet is a reasonable target lots of things happen differently up there.


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#12 pyromaniac303

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Posted 16 July 2013 - 11:18 AM

I would have thought (possibly wrongly) that the hot gasses through the passfire would be sufficient to pressurise the ejection charge and possibly the rest of the parachute chamber, as the volume of the rocket that you have is only small. Would be an interesting test to carry out.


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#13 whoof

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Posted 16 July 2013 - 04:21 PM

If someone brings a genny I could bring my vacuum tank to the do and have a go.




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