Quantcast

3F or 4F black powder for ejection charge

The Rocketry Forum

Help Support The Rocketry Forum:

Ccolvin968

Well-Known Member
Joined
Oct 11, 2016
Messages
314
Reaction score
0
I have seen both 3F and 4F recommended for ejection charges.
What is the difference and how much would it effect my recovery deployment of a 28 inch parachute?
Just want to do some ground tests before letting her fly for my level 1 cert.
Thanks!
 

MCriscione

Well-Known Member
Joined
Jul 9, 2015
Messages
296
Reaction score
0
I've used 4F for my DD setups. The difference is essentially in size of the grains of powder. 4F is smaller, so it burns a bit faster. I don't think there is much difference in effect, especially in smaller airframes. However, because it burns faster, 4F may leave fewer burning particles to impact on your recovery gear, and therefore cause fewer holes in your chute. Not that holes are guaranteed with 3F or something like that. If you have good protection between charge and chute (nomex or lots of space/dog barf) then you'll probably be fine. I'd say use what's available, but lean towards 4F given a choice.
 

Ccolvin968

Well-Known Member
Joined
Oct 11, 2016
Messages
314
Reaction score
0
I just have a butt ton of 3f I've used for my no pistol that I no longer have. Guess I found a use for it. I'll pick up some 4f eventually. Thanks for the info!
 

Bat-mite

Rocketeer in MD
Joined
Dec 5, 2013
Messages
10,890
Reaction score
1,638
Location
Maryland
Just make sure you use whatever you ground test with. No guarantee 2 grams of 3F will produce the same volume of gas that 2 grams of 4F, and vice versa. If you use 3F, make sure it is packed very tightly. Shove in dog barf until you can't fit any more in, and then fit some more in. :wink:
 

Ccolvin968

Well-Known Member
Joined
Oct 11, 2016
Messages
314
Reaction score
0
Do motor ejection charges use 3 or 4f? I just want to get as close as possible.
 

manixFan

Not a rocket scientist
Joined
Feb 15, 2009
Messages
1,908
Reaction score
881
Location
TX
I just have a butt ton of 3f I've used for my no pistol that I no longer have. Guess I found a use for it. I'll pick up some 4f eventually. Thanks for the info!
You'll get the best results if you contain the BP in a cylindrical holder like a brass tube, empty .45 cartridge, or centrifuge tube. Think of it as making a very small barrel for the BP to burn in. At BALLS this year I used both .45 ACP and .45 Long Colt empty cartridges for ejection charge holders and they worked very well (up to 1.5 grams). I packed the empty space with Estes wadding and sealed them with black electrical tape - several wraps around top to bottom and then one around. The biggest concern with any metal container though is you have to make sure that you don't short the e-match leads against the metal.

Make sure the bottom of the ejection charge holder rests against the bulkhead so it doesn't move around. I tape mine to hold them in place during flight.


Tony
 

Handeman

Well-Known Member
TRF Supporter
Joined
Jan 18, 2009
Messages
7,736
Reaction score
336
Location
Stafford, VA
I've used both 3F and 4F. I've found that with 3F I had a few more holes burned in the nomex chute protector. I now use some dog barf in all recovery.
 

GregGleason

Well-Known Member
Joined
Nov 13, 2009
Messages
4,646
Reaction score
3
I used hobby brass tubing (13/32" OD) from K&S that I got at Ace Hardware for my charge holders.

Av.Bay.after.Switch.Band.Squared.Up.jpg

The reason why brass is used is that it is a non-sparking metal.

The difference between 3F and 4F is the grain size. The 4F has a smaller average size than 3F. The smaller surface area of 4F grains causes the BP to burn faster and therefore transfer the flame front more quickly, making the expansion of gas a shorter duration of time than 3F.

Ideally you want about a 1/4" or so of space remaining in the charge holder so you can pack in some "dog barf". Then you can place masking tape over the opening of the charge well to seal it up.

Greg
 

75Grandville

Well-Known Member
Joined
Feb 20, 2014
Messages
818
Reaction score
81
Location
Salt Lake City, Utah
I use 3F because it's all I could find locally. As others have said, just make sure you use the same thing in your ground tests and actual flight.
 

Ccolvin968

Well-Known Member
Joined
Oct 11, 2016
Messages
314
Reaction score
0
I'm just trying to simulate the motor ejection charge is all. So it will be 4F from the motor. 3F with the tests. For some reason I'm nervous the 1.2g in the 28mm will not have enough oomph to push off the nosecone. 38mm have 1.3g of bp from what I have been informed on my other posts... Probably not a warranted fear, but it's still there.
 

MikeyDSlagle

Well-Known Member
Joined
Dec 17, 2013
Messages
2,306
Reaction score
285
Maybe I shouldn't mention it, but you can mill 3f down to 4f. Spark proof mortar and pestle probably the cheapest route. A rock tumbler may be another.

I once knew of a guy that supposedly used a cheap blender - he would set it a good ways off behind a tree and plug it in...not an option I would use or recommend though.

Oh, and for ejection canisters, I chopped up an old blow gun I had. A #10 nut is a nice tight fit. A little JB Weld and all thread and I got some ejection canisters.
 
Last edited:

Ccolvin968

Well-Known Member
Joined
Oct 11, 2016
Messages
314
Reaction score
0
Mikey, good to know! I'll blend it up with firecrackers!
Kidding... But the mortar and pestle sounds like a good idea.
Thanks!
 

Nessalco

Well-Known Member
Joined
Nov 9, 2012
Messages
281
Reaction score
0
Just make sure you use whatever you ground test with. No guarantee 2 grams of 3F will produce the same volume of gas that 2 grams of 4F, and vice versa.
Actually, yes there is. The same weight of the same BP will produce equal amount of gaseous product, no matter the form. The difference is how quickly it burns - and there is very little difference between speed of FFFG and FFFFG. There is significant difference between brands, however.

KO
 

OverTheTop

Well-Known Member
TRF Supporter
Joined
Jul 10, 2007
Messages
4,374
Reaction score
1,604
Location
Melbourne Australia
I use only FFFG and have not had any problems. I usually pack the extra space in the canister with a short length of party streamer (crepe tape stuff) to soak up the gap. Make sure you get the streamers from reputable party suppliers so it has fire retardant in it. Some of the cheap and cheerful discount shops (supplied from China) have streamers without the fire retardant :(
 

Buckeye

Well-Known Member
TRF Supporter
Joined
Sep 6, 2009
Messages
2,513
Reaction score
361
Maybe I shouldn't mention it, but you can mill 3f down to 4f. Spark proof mortar and pestle probably the cheapest route. A rock tumbler may be another.

I once knew of a guy that supposedly used a cheap blender - he would set it a good ways off behind a tree and plug it in...not an option I would use or recommend though.

Oh, and for ejection canisters, I chopped up an old blow gun I had. A #10 nut is a nice tight fit. A little JB Weld and all thread and I got some ejection canisters.
I think you guys are really making too much of this. 3G and 4G work equally well for rocketry recovery. I have used both in equal volumes for ground testing and real flights. No difference, at least through 2g charges. My BP mass measurement error is easily +/- 0.2g, and still no problems. Pack dog barf into any unused space - this is just good practice regardless of the type of powder.

Use the 3G you already have with no worries. Please don't put it in a blender.
 

NateLowrie

Well-Known Member
Joined
Jun 28, 2016
Messages
667
Reaction score
4
Maybe I shouldn't mention it, but you can mill 3f down to 4f. Spark proof mortar and pestle probably the cheapest route. A rock tumbler may be another.

I once knew of a guy that supposedly used a cheap blender - he would set it a good ways off behind a tree and plug it in...not an option I would use or recommend though.

Oh, and for ejection canisters, I chopped up an old blow gun I had. A #10 nut is a nice tight fit. A little JB Weld and all thread and I got some ejection canisters.
Make sure you know what your doing if you attempt to mill it down. I highly recommend not going this route unless you are highly familiar with ball miling and understand the dangers. Regarding using an electrical operated device: It is a major safety hazard to ball mill black powder, oxidizers, and even fine metals on a device where the electrical shaft extends into the milling chamber. You are garuanteed to leak around the shaft seal at some point which can easily lead to combustion if it gets in the motor..

If you want 4F, go buy 4F. It's only $20 for 1 lb at the gun store and it'll last you a while.

That said, regarding the original question, 3f needs to be contained a little longer for full combustion. Tony's suggestions on cartridges are spot on. For larger gram loads, 1/2" copper piping with end caps is cheap and easy. I use a 4" length and I get full combustion every time, even with Pyrodex.
 
Top