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BP advice needed


Jsweimer

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I seem to have a consistent problem with my attempts at BP rockets, in that they simply explode rather than fly.

 

Some research brought me this-

 

Core depth to be approx. seven times the inside diameter.

Core diameter to be 33% of inside diameter.

 

That said- if I had a body that was .75 i.d. x 7.5" in length, my core would be .250" X 5.25".

 

Cannot figure out why I am making big firecrackers rather than rocket motors.

 

Any help would be greatly appreciated!

 

Jeff

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Those dimensions sound right. We can't give much more help if you don't provide more information. Type of tube, formula, how you're ramming/pressing, what sort of tooling, etc.

 

I'm going to take a total stab in the dark, and say it's probably the propellant you're using. You can't use full strength BP in nozzled core burning rockets. If you made them without a clay nozzle they'd probably fly fine. 60:30:10 nitrate:charcoal:sulfur is probably the most common core burner fuel.

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You could try nozzleless rockets. Use hot milled BP in small increments and make sure it is well rammed or pressed. I always rub the rammers and spike with a candle. This helps to lubricate things a little.

 

This process will get some good motors flying. In the meantime you can experiment with nozzled rockets.

 

I suggest this as it can be very frustrating if you can't get ANYTHING to fly properly at all.

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I've quit putting nozzles in my rockets I use for lifting headers altogether and just use nozzleless using the hottest BP I can make. With my nozzled core burners I'd still get the occasional CATO even with weaker fuel and I got tired of premature erockulation taking out a header I'd spent hours building. My core burners are standalone devices that give a pretty tail and a salute at the end.
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I seem to have a consistent problem with my attempts at BP rockets, in that they simply explode rather than fly.

 

Some research brought me this-

 

Core depth to be approx. seven times the inside diameter.

Core diameter to be 33% of inside diameter.

 

That said- if I had a body that was .75 i.d. x 7.5" in length, my core would be .250" X 5.25".

 

Cannot figure out why I am making big firecrackers rather than rocket motors.

 

Any help would be greatly appreciated!

 

Jeff

 

 

I am not surprised that you are gettin catos with those tooling dimensions, a more traditional design would use a 50% nozzle opening, that is, 0.375" opening in a 0.75" ID rocket.

 

The difference between a 0.375" nozzle and a 0.25" nozzle is actually pretty huge, as far as performance goes.

 

you could reduce the length on the taper to 2.25" for a more reliable rocket :)

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