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Why did my rocket blow up


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#1 Pretty green flames

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Posted 31 December 2004 - 03:04 PM

well, made my first "real" rocket with the nozzle and everything.
When testing day came, i nicely put the rockets in the launch tube, ignite the visco fuse, whooooshh half a second late BANG

The same happened to the next rocket......WHY

Some technical data:

ID: 16mm
Nozzle: 3 mm
Lenght: 75mm

the BP propelant was rammed in the tube with a mallet
what could've gone wrong


Any ideas


Thnx

#2 RegimentalPyro

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Posted 31 December 2004 - 03:29 PM

Was it an end burner or a core burner? If core burner what was the dimensions of the core?

From the sounds of it your nozzle is a little small for a rocket of that size [1lb?].

#3 Pretty green flames

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Posted 31 December 2004 - 04:07 PM

Was it an end burner or a core burner? If core burner what was the dimensions of the core?


It was a core burner. The dimensions of the core are as follows
Lenght 55mm (1cm for each end plug)
ID 16mm (same as ID of tube)
The nozzle was drilled to about the half of the core

From the sounds of it your nozzle is a little small for a rocket of that size [1lb?].

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What nozzle dimensions are we talking about here, maybe 5 or 6mm

#4 alany

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Posted 31 December 2004 - 04:36 PM

What was the propellant composition?

15:3:2 BP in a core-burner is generally asking for a cato.

#5 Pretty green flames

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Posted 31 December 2004 - 04:46 PM

it was 6:2:2
KNO3:S:C

#6 Yugen-biki

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Posted 31 December 2004 - 05:19 PM

Try adding coal in small proportions untill it works ;)

If this does not work the CATO is due to cracks in the fuel or the fuel is not solid enough.

#7 alany

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Posted 31 December 2004 - 07:47 PM

Was it milled, or just screened?

For a 5/8" rocket you'd expect a nozzle throat of about 5-6 mm ID (rule of thirds) and a core about 100-120 mm deep (the case being about 150 mm long). But yours is quite a bit shorter than that, so you'll need to tune the nozzle carefully to make it work efficiently.

The problem with "short" core-burning grains is the internal pressure changes quite a lot during the burn, which is hard to engineer around if you want an efficient motor. The case has to survive the peak pressure, but the nozzle has to be narrow to make use of the small initial surface area. Your thrust curve ends up very steep.

3:1:1 is very slow, that is probably why it managed to survive for a moment until the internal surface area increased to an unsustainable point. Enlarge the nozzle and see if its efficiency is good enough for you. If not, make it longer as well.

#8 Andrew

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Posted 21 March 2005 - 03:01 PM

Why did my rocket blow up?

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Because it was trying to "blow down" too hard. :lol:

Sorry, couldn't resist.
Not very helpful I know.

#9 seymour

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Posted 22 March 2005 - 08:25 PM

My endburner cato'd last night. It just poped the clay nossle out and shot up aout 40m still burning. mind you I was using 75:15:10 Bp with fast burning willow charcoal so I was asking for trouble. Its just my ground tests indicated that end burners with that Bp would not survive, I taped them to a stick and used them as upside down fountains. my ground tests for core burners though showed that they make good Bp bangers! :D My end burner must have had qa crack in the fuel or something.
The monkey leaped off it's sunny perch and flew off into the night sky.




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