nitratedhotdog Posted February 1 Posted February 1 I ve built a tapered spindle measuring 150mm in length, a diameter of 7.64mm at the base and a diameter of 6.05mm at the top. I want to make nozzled coreburner bp rockets. I know the general rule is the motor ID has to be a tenth of the motor lenght and judging by the spindle lenght i think 15mm ID rockets are a little small for what i imagined, can i not respect this rule? is this rule mixture specific? what are other rules i should know? and how important is the diverging/converging nozzle thing? Also i want to use screen mixed bp 70-20-10 in this kind of rockets.
Darkonez Posted February 1 Posted February 1 Do a search for a book called “Easy PVC Rockets “ by Jason smiley! if you can’t find a copy I have one! It’s a great read and I believe will answer all your rocket questions and more.
Mumbles Posted February 3 Posted February 3 I don't know if I'd call it a rule per say. That just some standardized dimensions from a long time ago people made rockets to, and thus many tool makers also follow. Nothing is set in stone and there is plenty of margin for error. There are also a few caveats and deviations when looking at the full spectrum of common rocket sizes. Usually you just tweak the formula to match the tooling if it's not performing right or to your liking. A "standard" BP core burning rocket uses a tube that is 10x the ID of the rocket. It has a spindle that is 7x the ID. The spindle starts at 1/3 the ID and tapers to 1/4 the ID. Core burner in the standard sense doesn't necessarily mean cored entirely through the rocket. I prefer a converging/diverging nozzle, but it's not a deal breaker. It reportedly adds a small to moderate amount of performance improvement, ~10%. I find it to be more important in end burners as it helps prevent the tube from burning through at the nozzle. The spindle you have is appropriate for a ~21.5mm ID rocket.
BengalFlair Posted February 5 Posted February 5 I just only differ in a point that the spindle usually starts at I/2 the ID and then tapers for a bp core burner.
Mumbles Posted February 5 Posted February 5 You're right, I think I got core burners and end burners mixed up in my head. Most tooling commercially available will be 1/2 the ID in nozzle diameter. Below is an example of dimensions for 3/4" ID (1lb) rockets. https://www.truetex.com/bp_rocket.pdf
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