BP fuel adjustment

[kpknd]

What is the right way to adjust the BP fuel? If too stong, reduce PN or, add more charcoal? if too slow, add more PN or, reduce charcoal? Keep the sulfer the same?

Edited April 28, 2014 by kpknd

[Blackthumb]

I regulate and "stretch" mine with fine sawdust...cheap and easy...adds some "tail"

[bob]

That is interesting BlackThumb.

What is a good starting amount of the sawdust, 8%?

Perhaps you could mention this in your "No Frills Rocket Tutorial"

bob

[Mumbles]

There are obviously going to be more than one way to go about this. From looking at a couple of standard default formulas, it seems that sulfur is kept about the same. You can make it hotter or more tame by adjusting the KNO3:C ratio. You can also get fancier and add in coarse charcoal and stuff too. In normal BP, the ratio is 5:1. In the sort of standard core burner formula, it's 2:1. I know several people who get the formula closer to 2.5 or even 3.5:1 for hotter core burners if their methods, tools, and tubes will allow it

 

 

Hot "standard" BP

KNO3 - 75

C - 15

S - 10

 

Core Burner

KNO3 - 60

C - 30

S - 10

 

It will get a little harder if you're trying to adjust a pre-made composition. I can help with that. Generally speaking as long as you're in the realm of formulas above, adding charcoal will slow it down and adding KNO3 will speed it up. Too much KNO3 will slow it down again and increase the amount of slag. Keep careful notes so you can keep track of what the overall formula is so you can replicate it in the future.

[nater]

I prefer to add more charcoal to slow fuel down since you get the benefit of more charcoal in the tail. To speed existing fuel up, I would add whistle if you own a press. If ramming is the only option, I would follow Mumbles' advice.

[kpknd]

Thanks for the advice. I plan on making just more than enugh fuel for one rocket at a time so I do'nt waste any thing, and note it down.

[nater]

Are you ramming or pressing? I like to make several rockets with a given fuel to note consistency and to be sure that there is not another factor effecting the performance. Cracks in the grain, pressing / ramming forces, nozzle erosion, etc... can all change the performance. One motor does not allow you to note these things as much, three or four would give you a better picture.

 

This is why I had a 1/2" set made to the same specs as my larger tools. Rockets don't scale up in a linear fashion, but a 1/2" motor should give a decent idea how your fuel will perform. Just keep in mind that fuel that is on the redline in a smaller motor will likely CATO a larger one.

 

Do you have a thrust stand to help you dial in your motors, or are you just making observations on the ground and in flight?

 

Edit to add: there is no need to waste any fuel. If it is too slow to fly, add 10% - 20% metal to it and call it a gerb comp.

Edited April 29, 2014 by nater

[kpknd]

I am ramming the fuel and both observing on the ground and flight. I have actualy taken junk BP and added titanium to it for fountains.

[markx]

I have usually tuned the speed of BP fuel with just the amount of KNO3 and always left the C/S ratio equal to 3/1. So 9/3/1, 8/3/1, 7/3/1 and 6/3/1 by mass are my standard compositions beginning from the fastest. And yes, the formulations do not add up to 100% the way I display them (at least 3 of them for sure), a habit from the time when I had no proper scales and comparison of masses was easier this way. It is quite easy to convert to a format that adds up to 100% if someone finds it more convenient...anyways, it's the ratios that count.

I also find it is easier to get consistant results with slower fuels, so 7/3/1 is about as fast as I go these days (depending on case dimensions, the bigger, the slower the filling). With slower fuel all the little inconsistancies like variation in grain density, deformation of casing, a stray crack from drying or removing of the spindle or dropping the motor, humidity content, etc have less leverage on creating a cato. One can tune into the sweet spot of the slower fuel with channel depth and nozzle diameter and still have a safe band to work around little fluctuations without bursting the case. With a faster fuel this seemed a hard task and catos were easy to happen if everything was not perfect at all times.

[FlaMtnBkr]

Are you able to make hot BP? Really hot BP? That is the neat thing about nozzleless rockets, is that you use the hottest BP you can make and they work great and can lift a good amount.

 

They might not have the best tail but it can be good with the right delay. You can also add some atomized aluminum to help the tail and not slow it down much.

[kpknd]

markx, Are you ball milling your powder, if so how long? I want to try the 7/3/1

[dagabu]

I prefer to add more charcoal to slow fuel down since you get the benefit of more charcoal in the tail. To speed existing fuel up, I would add whistle if you own a press. If ramming is the only option, I would follow Mumbles' advice.

 

Yup, that was my method as well.

[Maserface]

What sort of tooling are you working with?

[dagabu]

Who? Me?

[Maserface]

Op

[nater]

What sort of tooling are you working with?

I have assortment of tooling now. Most of mine is based on the Hybrid Universal spindle which is more forgiving to dial in a hotter fuel.