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What I have been doing (Novice endeavours with rockets)


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#61 Baldor

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Posted 16 April 2018 - 06:31 AM

It's the same BP that worked with the 15mm motors. I asked in the discord chat, and 1/3ID for nozzleless is OK with fast fuel. The problem is with the method, and maybe the sleeve. I'm out of black match, so there will be a few days until the next test, still raining, but seems this is the last day.



#62 stix

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Posted 16 April 2018 - 07:00 AM

Well 1/3ID "seems" absolutely ok, but it importantly depends on the length too. Your core length is way too long for your fast bp fuel to give nothing but cato.

 

The 15mm version was also able to be compacted more easily and therefore it will have the effect of slowing down the burn rate (with bp).

 

Scaling up a design takes a bit of thought. In melted sugar motors, the fuel can be made more consistent in density when poured into grains and therefore has the overall affect in that the burn rate "slows down" the bigger you go. In a PB pressed motor, the bigger you go, it's always going to be harder to press it to the same density and there will also be issues with "crimpling" of the sides, Therefore with BP motors, when you go bigger, the burn rate will generally increase because it's harder to compact the fuel to the same density.

 

This is my basic philosophy of "Scale Up" theory. Take it, or leave it.

 

It may be worthwhile doing some measurements to determine the density of your fuel (not hard to do), ie. 15mmID compared to the 19mm version. Density of the fuel is often overlooked, but is a big contributing factor to the burn rate.

 

And btw. if you asked about it in the discord chat, then why wasn't fuel/core length, density, Kn ratios etc. discussed?


Edited by stix, 16 April 2018 - 07:23 AM.

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I just start the conversation - someone else has to question them.


#63 Baldor

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Posted 16 April 2018 - 08:36 AM

Well, shorting an spindle is easy, lengthening it not so. So first I will solve the other problems, and if it still cato, will be time to shorten it. :-)

 

All the other wasn´t disused because it seemed to big increments was the primary suspect.


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#64 justvisiting

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Posted 16 April 2018 - 11:09 AM

Baldor, you should be able to make excellent nozzleless BP rockets with that tooling. The click click click that you can hear and feel is the propellant grain sliding on the spindle as it rebounds from the pressing force. I use wax in the propellant or on the tube to have zero CATO. For long term storage, I may do both. Some folks mill the BP with mineral oil, but I prefer wax.  I use 2% of the propellant weight, dissolved in naphtha (camp fuel). The propellant is then granulated through a screen. Using straight mill dust is the worst way to make black powder rockets, IMHO. Granulating your propellant with wax will give you reliability and allow you to use 1 ID increments.

 

EDIT: you can also rub some candle wax on the spindle to help with the clicking.


Edited by justvisiting, 16 April 2018 - 11:15 AM.

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#65 Baldor

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Posted 16 April 2018 - 01:11 PM

I will wax the tubes. I waxed some tubes with my nozzled 15mm core burners, and noticed no difference, but with 19mm could be diferent.

 

I don't exactly use green BP from the mill. I wet it with a little bit of water, and granulate it trough a screen. Would pressing pucks (without binder), corning and screening give better results?

 

Took some time away of the rockets. I'm out of black match, just started raining when I wanted to make an small batch. Seems today is the last day of rain, so I'm making a pocket sized version of Calebs black match machine. Tomorrow should be finished.



#66 justvisiting

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Posted 16 April 2018 - 02:32 PM

I think pucking, corning, and screening is unnecessary and may be detrimental. Using wax helps with CATOs. But if the rocket was not going to CATO anyway- it still won't ;) You didn't have a CATO though. You had a blowthrough. You can just use your milled propellant instead of clay for a bulkhead, for 25mm above the spindle. This will give maybe 2-3 second delay after the main burn. 



#67 Mumbles

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Posted 19 April 2018 - 07:21 AM

Maybe I missed it, but what material are you using for the bulkheads?  I know some people add a coarse, hard material to their clay mixtures to make it bite into the tube harder.  Have you ever tried to cut into a dummy tube or spent tube to see how well the bulkhead is grabbing the wall?


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#68 ollie366

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Posted 19 April 2018 - 09:56 AM

Not hijack the OP thread, but I'm not clear on why granulated BP performs better than milled BP when pressed.  It would seem the packing density for pressed milled would be higher (slightly) than for pressed granulated due to the smaller particle size and less interstitial air.  I've seen the comment many times that the best performance is achieved using granulated but don't quite get why.  Can someone please enlighten me?  



#69 Baldor

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Posted 19 April 2018 - 10:21 AM

Plain bentonite, Mumbles. I had no problem with the 15mm tubes, and my plan is to use only delay as the bulkhead in "production". I'm using the bentonite to protect the test stand. I think that the bulkhead was too thin. The bulkhead in spent 15mm tubes has been always intact.

 

Olie, if you use a press, i think the density will be the same. The usual fuel for rockets is milled, a little water added, and screened, no need to puck and corn. If you not use a press and just ram, and use hard grains, you have the risk of the grains not consolidating enough.



#70 Baldor

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Posted 20 April 2018 - 12:31 PM

Made 60m of black match with 150g of BP.  A breeze with a pocket replica of Calebs machine.

 

The machine likes bigger batches, when more than half the capacity have been emptied, it will like a replenish.

 

Test in 24h. If it burns well, i think I have BM for this year.



#71 Baldor

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Posted 22 April 2018 - 05:06 AM

Seems I put a little too much CMC in the BP. The leftovers take forever to dry. BM seems to work fine, but I will try a larger batch with less MCM.

 

Finished a little tooling for waxing tubes brush style, and waxed a dozen of tubes in a moment. I previously tried the cone tool and didn't like the spillovers. 

 

Grinded some charcoal of unknown origin for testing the pressing method. It doesn't consolidate well, so will try with bentonite.

 

Made an apprentice mistake and bent the 19mm tooling spindle. Still, seems the acordioning is under control. (Used a wood riser and all went wrong)






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