Paraffin Vs Dextrin in a BP propellant mix.

[Bourbon]

I conversed with the late Ed Brown who worked at Estes Industries for over 30 years, where he designed and tested their BP engines.

 

Based upon his experience and several reports that I personally researched, more than 2% water results in

substantially slower burn rates.

This was typical fast 75/15/10

This BP was pressed to about 1.9 g/cm3

But, 1-2% was still used, just not over? Just want to make sure I understood this correctly. Thanks!

[shockie]

But, 1-2% was still used, just not over? Just want to make sure I understood this correctly. Thanks!

Correct. When you go above 1-2% water content it slows the burn rate . And Yes to your question, don't go over 1-2% water max

 

Tests have been done on BP at room temperature up to say 150 F.....at elevated temperatures the burn rate of the BP increases ....so in essence you can "heat cure" BP to alter its burn rate properties

Tests have also been done with BP vs Humidity..these tests have shown that BP exposed to high humidity levels results in lower burn rates .

Pressing can also effect burn rates. Typically using a mallet will get you a max of about 1.2-1.3 g/cm3 whereas using hydraulic press can get you to 1.5-2.0.... the higher pressed BP has a slower burning rate.

But there is a limit to pressing, where more will get you nothing.

 

So basically you have a number of items that you can control to get the burning rate you want

 

The majority of Estes engines if not all , are small cored end burner, while most BP pyrotechnic engines are fully cored.

 

Traditionally for the cored BP pyrotechnic engine ,used a slow 60/30/10. Why? With a fully cored BP engine the chamber pressures rises rapidly.... so you use a slow BP to control the burn rate and chamber pressure .....in Estes cored end burners they can use a fast 75/15/10 as the chamber pressure is much less... in fact Estes model rocket engines have a thrust spike for approx. 0.2 sec where the chamber pressure is maximized then it settles down into a lower chamber pressure.

Typically the high chamber pressure is in the ballpark of 200-300 psi while the lower sustaining thrust is say 100-125 psi

 

On pyrotechnic BP engines the chamber pressure is much greater maybe as much as 2-4x but it's for a much smaller time period.

 

Back in the day from 1959-1966 Estes had a cored model rocket engine called a B14 ....and they used much thicker paper tubes to contain the higher chamber pressures.

They would press a typical cored end burner engine then use a slow drill to drill out the rest of the core.

circa 66-70 they switched from the thicker fireworks tubes to a thinner tube, and they dropped the B14 because it was too dangerous to drill the core even though they had a developed a semi-automatic means plus the thin wall just couldn't contain the chamber pressure

 

Later Estes-Centuri created a C5 motor that had a pressed formed mid-range core somewhere between the typical cored end burner and the fuller core b14.....

Edited November 26, 2020 by shockie

[shockie]

A few points:

 

1) Dextrin is activated with water, so I don't think it serves much purpose in your formulation.

2) Black powder is known to burn faster when it contains a small fraction of water, like from ambient humidity. I'm not sure if your dehydrator treatment will yield the best results.

3) Dextrin bound granules can make consolidation of the fuel grain challenging. In some cases, the grains are too resilient, and voids are left in the fuel grain.

4) Rocket motors subjected to multiple environmental fluctuations are known to lose reliability. Treatment in a drier makes me nervous.

5) You may want to research the process of "tube waxing," where a thin coating of wax is applied to the inner surface of the rocket tube before pressing. I've never tried it, but proponents of the method claim that it makes the motor more tolerant of variations in process and storage parameters.

 

1, Agree....BP doesn't need dextrin as a binder if it is pressed enough

2. Agree...Not needed

3. Agree...Not Needed

4. Agree...

5. No experience with this...yet..... I may do a research study on this: waxed vs non-waxed all pressed at the same pressure and using the same BP then do some thrust-time tests to see if there are any major variations

 

 

[shockie]

It's always surprised me that people have got to either ball mill all the ingredients to powder or use alcohol and dextrin etc. For rockets, you DO NOT want the granules to be hard, you don't want paths for fire to travel, a simple mix of milled KNO3, sulfur and airfloat charcoal, mixed together in a ziplock bag and screened a few times with 1/2 a percentage of water finely misted over it will de-dust it an allow for a minimum of an airborne cloud of charcoal.

 

Spending money of mineral oil, paraffin, alcohol and dextrin etc is a huge waste.

 

I tend to agree....All these additives just complicate things..KISS......and it's no longer BP IMHO//YMMV

[justvisiting]

Shockie, I also had the privilege of communicating with Ed Brown. He sent me the papers that show in detail much of what you are saying here. It was Ed Brown that suggested I compact 75-15-10 with 2% additional water when pressing an end burner. When I did that, my grain density went from about 1.4 to about 1.8- quite a difference! When I cut away the tube, my grains looked EXACTLY like Estes end burner grains. I use 3% water in my 60-30-10 nozzled, long-cored BP motors, to good effect.

 

The current manager of Estes has written two lengthy books on black powder. Neither of those books gives step by step instructions for making good black powder. When I suggested single component milling as a safer way to make good black powder than 3 component milling, the author dismissed the idea as common knowledge, and had pity that I thought I had an original idea! A careful combing through of both of his books was unable to find mention of this 'common knowledge'.

 

Waxing the tubes is not really done to increase thrust. It's done to prevent CATO that can arise from fire sneaking up between the grain and the inner tube wall, mainly. It does give better consolidation, but not by a whole lot. Another advantage is that the tube is not squashed during pressing, and so does not rebound later, causing voids in the grain. It was Shimizu that originally suggested lubricating the inner tube wall for pressed items, in his book F.A.S.T. I just followed his instructions when it became obvious to me that HIS idea was a good one. I've written a couple of articles on it, and I probably posted them somewhere here, I can't remember.

 

The problem with suggesting the use of water is that we are up against decades of admonitions against ANY moisture being used. The guy that wrote books on rocket making using water has been basically dismissed by the more popular rocket maker guru that advocates dry pressing.

[Bourbon]

Was the increase to 3% water for your 60-30-10 do to the increase of charcoal?

[justvisiting]

Bourbon, yes I figured all that extra charcoal might try to lure some of the water away from doing its job, so I added a 'sploosh' extra