Difference between 3f and 4f ... ?

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DAllen

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Tried doing a search on the forum but couldn't find anything - and am probably not using the right search terms - in terms of deployment charges is there a significant difference between 4f and 3f? If I go from 4f to 3f do I have to add/reduce powder to the charge?

-Dave
 

blackbrandt

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4f burns quicker than 3f. You will need to ground test to determine how much you need. One thing I have seen is that containment is a bigger issue with 3F, because the particles take longer to burn.
 

Incongruent

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For searching, go to google and use 'site:rocketryforum.com' after your search term, which in this case would probably be "3F" 4F" (the quotes limit results to only those with the exact phrase)

The forum search doesn't count words three letters long or less.

FOOM and FWoooosh; the more Fs, the worse my report card... wait, no. Wrong context. The more Fs, the smaller the particle size. In a gun, you don't want the black powder to burn as fast in larger guns since the projectile has inertia and if there's too much energy released in a given time, it can't speed up fast enough and the barrel gives first and you have a firecracker. Or so I hear. So the 4F burns faster and pops whereas the 3F burns slower and still pops, but slower.

EDIT: So put together the search term would be: "3f" "4f" site:rocketryforum.com
 

DAllen

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So is there anyone here that actually uses 3f?
 

Bat-mite

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There are! They will show up sooner or later. From what I gather, if you use it, make sure you pack it tightly. If you can, minimize the surface area of the charge (i.e., longer, narrower wells). Ground test, see if you are burning it all or leaving some in the well. You might need to move your match around to find the best ignition point.
 

DAllen

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There are! They will show up sooner or later. From what I gather, if you use it, make sure you pack it tightly. If you can, minimize the surface area of the charge (i.e., longer, narrower wells). Ground test, see if you are burning it all or leaving some in the well. You might need to move your match around to find the best ignition point.
Interesting...I already do those sorts of things with 4f. Pack it in a 18mm used estes motor glued to the bulkhead and essentially bury the ematch in the powder using the finger-tip rubber glove method and then pack it in to the casing nice and tight with some dog barf.
 

Bat-mite

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The question to get answered is where to put the e-match. If it is buried, as you say, or at the bottom, it might blow out some of the top powder when the bottom powder lights, but I'm not sure. That is where you will need an experienced mentor.

Of course, you could always put two e-matches in series, one at each end. :wink:

You will still want to ground test as the volume of gas produced may not be the same.
 

Bat-mite

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jimzcatz, 75Grandville, and Handeman are three people who have used 3F. Might be worth a PM.
 

Handeman

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Yes, I've used 3F, but quite a while back. I didn't contain it. I just laid the ematch on a 3" to 4" long piece of duct tape, creased it, pored the powder over the ematch and squeezed the tape together to seal it.

I did not see a significant difference in the power/gas pressure from the ejection. Now I never did comparative ground tests, and I suspect I had sufficiently large charges of both types that ejection was good with either.

What I did notice is that my nomex chute protectors had a lot more small burn holes in them when using 3F then when using 4F.

I've also found that putting the powder in a holder, I use copper pipe caps, and holding everything in with dog barf and masking tape makes for a noticeably stronger ejection.

Hope this helps.
 

Incongruent

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Yes, I've used 3F, but quite a while back. I didn't contain it. I just laid the ematch on a 3" to 4" long piece of duct tape, creased it, pored the powder over the ematch and squeezed the tape together to seal it.

I did not see a significant difference in the power/gas pressure from the ejection. Now I never did comparative ground tests, and I suspect I had sufficiently large charges of both types that ejection was good with either.

What I did notice is that my nomex chute protectors had a lot more small burn holes in them when using 3F then when using 4F.

I've also found that putting the powder in a holder, I use copper pipe caps, and holding everything in with dog barf and masking tape makes for a noticeably stronger ejection.

Hope this helps.
The holes are from the still burning particles of black powder that are carried with the deflagration, the 3F burns longer and hence more still burning particles reach the chute protector.

The stronger ejection result from the black powder's property of increasing burn rate under pressure. In the open, black powder burns fairly slowly, but enclosed, such as in a firecracker, (or the slug of a rocket (engine/motor)) the burn rate increases dramatically. The faster burn releases gas faster, and the larger volume created over the same time pushes out the laundry faster and more energetically.

In theory. Theory as in this is what fits all the data, so it's our best guess as to what's happening and predicting what will happen.
 

Buckeye

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So is there anyone here that actually uses 3f?
Yes, me. 3F was all the gun shop carried when I bought a can almost 20 years ago. I pack it tight in a centrifuge vial. Can't tell the difference. Works just fine with eyeball gram measurements.
 

jcamhale

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So is there anyone here that actually uses 3f?
I use 3F for all of my charges. It's all that the local sporting goods stores stock. I haven't had any problems with it. I use dog barf and masking tape to contain the charge in the well. My nomex chute protectors are quite dirty but don't show any signs of holes in them.
 

Cl(VII)

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So is there anyone here that actually uses 3f?
I do exclusively. Never had a problem, but I do all my ground testing with it too. I typically make sure it is tightly confined by packing the well with dog barf and putting 4-5 layers of masking tape over the end of the well. I will probably change to 4F for a planned flight to about 20k'. The FFF has worked for me at the ground tested amount up to 14k'.
 

MikeyDSlagle

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So is there anyone here that actually uses 3f?
I use 3F as I have several cans from my black powder days. I put my match in first facing out, pour in charge, add dog barf and tape over the top. Then do a wrap around the well because sometime the take doesn't stick that great. Always say I am going to use foil and a zip tie but never do. I use an old blowgun to make my charge wells so something like .625" x 2.5" long. About to go to spent rifle/pistol casings though. Every high power flight I've made has had electronic deployment, either at apogee or DD. No issues so far and my gear just gets dirty, I haven't noticed any burn holes. I haven't had al that many flights though.

4F has smaller grains so it burns more aggressively so you get more energy from 4F than you would from a 3F charge of the same size.

Mikey D
 

Lowpuller

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3F no problem, I add about 10% over what the calculators figure, works fine for me.
 
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