Time to recurit some help

I am currently working on a Madcow Discovery and setting it up for Dual Deployment. This is the upper section, main parachute, test. The first test was with .5grams FFG Black Powder and the third test was with .75grams FFg black powder. My question is does FFg make that much of a difference? Below are two videos, one of each test. Should I switch to FFFF black poweder or keep upping the amount I am using. I do not want to go over 1.2 grams because that is the amount of 4F in Ceseroni's 29mm motors......thoughts. If need be I can and will switch to 4F, I just dont want to waste the FFG black powder I bought by not using it.

Test 1:
[video=youtube;8EcsV4XRdWk]https://www.youtube.com/watch?v=8EcsV4XRdWk[/video]

This a picture of how far out everything came.....



Test 3:
[video=youtube;2TO2EFQJHVo]https://www.youtube.com/watch?v=2TO2EFQJHVo[/video]

Thanks for taking a look at this and posting any suggestions.

~Chuck

I've seen FF used successfully before in rockets. I'd recommend containing it in something like surgical tubing to ensure a complete burn. The most important thing is to ground test exactly the way you are going to fly, then you should be set. I would suggest upping the charge, maybe to 1 gram. When I ground test I like to have the shock cord unravel - but not stretch tight.

More info: I put the BP and Q2G2 in the tip of a nitrle glove to keep it compact. This I put that into a PVC cap and cover it with a little dog barf. I tape everything down to keep
it tight. I dont want the shock cord to be tight but I want full extension so the chute can catch some wind.

Look at this for a compairison...

I have some ffffg black power that I got from Aerotech. I purchased several of the Electronic Forward Closure (EFC) : ECK-1 / Ejection Charge Kits - which are nothing more than 1.4 grams of ffffg black powder in a little tube.

I used 0.7g in a small plastic centrifuge tube for the test below.


[video=youtube;hZh8zxS19Vk]https://www.youtube.com/watch?v=hZh8zxS19Vk[/video]

scott
looks to me to be a little much bp...did you try .6g? will we get to see this bird at bong this year ?
rex

True blackpowder is rated in grain size (by sieve). FFg (2eff) has larger grains than FFFg(3eff), which has larger grains than FFFFg(4eff). 4F has much more surface area per weight volume than 2F, therefore, it burns up completely a lot faster than the larger grains, since gunpowder burns from the surface. This means that 2F produces less pressure than 4F in similar confinements, in an old pistol you will see a lot of 2F escaping the end of the muzzle whilst it is still burning , 4F could create enough pressure to blow the barrel.

All that said, if you used .75gram of 4F for that deployment test, try .9 and 1.2 of the same powder and see which of those suits you better, you dont have too much to worry about OVER pressurising with 2F.. the main problem you would see is that if it DIDNT push the pieces apart, you will have chunks of powder in the body tube that burns longer.

Rex R said:

scott
looks to me to be a little much bp...did you try .6g? will we get to see this bird at bong this year ?
rex

Click to expand...

Hoping to get more time for rocketry this year.
The one in the ground test video flew at Bong in 2011 (.5g) and failed to fire the ejection charge (no damage to the rocket)
I have a couple of DD projects I'm hoping to fly this year

In 2.6 diam rocket I use 1-1.25 of 4f BP.
Using 2F it should be more.
Are you using shear pins? If so you must also account for that.

What bearing does the amount used in motor play?

As Salvage-1 noted, the number of "F"'s corresponds to the particle size of the BP. We deal with "Sporting Grades" of black powder (type "G") rather than "Blasting Grades" (type "A", with a requisite BATF license to purchase). The following relates to the particle size of our "Sporting Grades" of BP:

1F = 1.68 - 1.19 mm
2F = 1.19 - 0.59 mm
3F = 0.84 - 0.29 mm
4F = 0.42 - 0.15 mm

The smaller the particle size, the faster the burn rate. There is no difference in the essential chemistry between the varying grades.

Greg

Ref: https://www.skylighter.com/fireworks/help/Black_Powder_Size_Charts.asp

I think if you are going to stick with the FFg, then you really need to up the amount and test with 1g to 1.5g. The amount you used for your test didn't even pull out the laundry.

Also, how tightly does that chute fit in the tube? Personally, I set things up so that everything slides in and out of the tube freely, with little to no binding.

Kevin O

Thanks for all of the replies. I think that I will get some 4F use that.

Nessalco, the shock cord and chute/chute protector are not so tight that it is hard to insert or remove them. I cut off the bottom of the Nose Cone and placed a bulkhead inside to allow more room for the recovery gear.

~Chuck

blackjack2564 said:

In 2.6 diam rocket I use 1-1.25 of 4f BP.
Using 2F it should be more.
Are you using shear pins? If so you must also account for that.

What bearing does the amount used in motor play?

Click to expand...

Excellent question by Crazy Jim about shear pins. My question also. Not only do you have to test to see if the charge will blow the shear pins and nose cone, but you have to test that your drogue charge will separate the booster section without blowing the shear pins. You probably already know this. But once you blow the main high up at apogee by mistake, and chase your rocket all over the place, you will test these well.

Chris

GregGleason said:

As Salvage-1 noted, the number of "F"'s corresponds to the particle size of the BP. We deal with "Sporting Grades" of black powder (type "G") rather than "Blasting Grades" (type "A", with a requisite BATF license to purchase). The following relates to the particle size of our "Sporting Grades" of BP:

1F = 1.68 - 1.19 mm
2F = 1.19 - 0.59 mm
3F = 0.84 - 0.29 mm
4F = 0.42 - 0.15 mm

The smaller the particle size, the faster the burn rate. There is no difference in the essential chemistry between the varying grades.

Greg

Ref: https://www.skylighter.com/fireworks/help/Black_Powder_Size_Charts.asp

Click to expand...

I believe the grain size ranges listed there are a bit off based on the screens used to do the sorting. I developed a spreadsheet to determine the relative surface areas for the various powders and determined the relative burn rates based on grains per gram, surface area and radius at atmospehric pressure.

For the same weight, all powder sizes will generate the same amount of gas, but the burn rate wll be different. If you consider 4FG as the 100% rocketry standard, 3FG generates gas at 62% of the standard rate, 2FG generates gas at 31% of the standard rate, and FG generates gas at 18% of the standard rate.

Without confinement, you need 3 time the amount of 2FG than 4FG to get the same weight of gas generation if the BP is unconfined. (A latex glove is not significant confinement.) However you will generate 3 times the final pressure which might damage the airframe and cause thermal damage.

The rate differences go away with pressure, so confining the charge in a centrifuge tube wrapped with tape will mostly minimize the size effects and shoud allow you to use the same weight independent of size, however 4FG is always preferred for parachute deployments.

Bob

bobkrech said:

The rate differences go away with pressure, so confining the charge in a centrifuge tube wrapped with tape will mostly minimize the size effects and shoud allow you to use the same weight independent of size, however 4FG is always preferred for parachute deployments.

Bob

Click to expand...

Bob, I would have to disagree with this last statement. If it were the case, then I could load my 44-40 cartridges with 2F or 4F without a difference in muzzle velocity. That isn't the case. It is all about how fast that pressure is released.

Take an analogy of a simple balloon. When it is inflated, it has a limited amount of pressure inside. If you open the hole big to let it out, all the air comes out at once. If you open the hole just a tiny bit, the pressure leaks out slowly. This is what we are looking at with the different grades of powder. A slowly leaking balloon doesnt provide the oooomph that we need to push the nosecone, etc out.

4F will generate its gas pressure far more quickly than 2F will if the same amount of powder is used.

I made a mistake of previously mentioning that you measure BP by weight. YOU SHOULD NEVER DO THIS. Black Powder should be measured in VOLUME. That is why the best measure is a 'cup' or 'dip'. When we say 1gram, we are/should be referring to the volume not the weight. This mistake has been made by quite a few 'primitive' shooters, including me, and it is a mistake I would push people not to make themselves.

If we were loading cartridges I would agree with you: 2FG is not interchangable with 4FG because 4FG will pressurize the cartridge faster than 2FG, and indeed if you look at my second paragraph, I actually presented the differences in the rate of pressure rise for each grade of BP.

But we are not loading cartridges. We are loading a canister that will burst at maybe 150 psi or so, not the 10-25 kpsi that you have in a BP cartridge that we don't want to rupture. What we have to do is to insure each BP grain will ignite before the canister bursts so that we utilize all the BP to generate gas.

The timescales for ejection charge burning is much longer than a cartridge in a rifle or pistol. The muzzle velocity of most BP rifles will be between 1200-1800 fps with 2F or 3F powders. A 43" long barrrel shootiing 0.50 cal ball with 3FG powder at a muzzle velocity of 1800 fps has a ~0.004 second acceleration time, so in the ideal work, all the powder will burn out in 0.004 seconds. The linear burn rate of BP at 1 atmosphere is ~0.8 cm/s and at 10 atm ~2.4 cm/s, at 100 atm ~3.3 cm/s and at 1000 atm ~5 cm/s. 3FG grains range in size from 0.035 cm and 0.07 cm diameter and will burnout in 0.0035 to 0.007 seconds @ 15 kpsi, that's reasonable for the rifle example above. 4FG grains range in size from 0.025 cm and 0.035 cm diameter and will burnout in 0.0025 to 0.0035 seconds @ 15 kpsi, which is indeed faster than the transit time and would probably overpressurize the barrel.

A nosecone muzzle velocity could be around 15-30 fps and for this example might have a 3" shoulder resulting in a 0.033 to 0.017 seconds. At 1 atm, the burntime of 4FG ranges from 0.016 to 0.022 seconds which is great for the example, 3 FG ranges from 0.022 to 0.044 seconds which is marginal, and 2FG ranges from 0.044 to 0.088 seconds which is way too long. If we confine the BP in a canister that bursts at 150 psi (10 atm), the burnrate increases by a factor of 3, so even the biggest 2FG grain burns out in 0.030 seconds.


View attachment 121758 Charts from BP reference above.

Bob

Bob, you wouldn't be very fun at a cocktail party

Depends on the number of drinks...........uke:

Salvage-1 said:

YOU SHOULD NEVER DO THIS[/B]. Black Powder should be measured in VOLUME. That is why the best measure is a 'cup' or 'dip'. When we say 1gram, we are/should be referring to the volume not the weight. This mistake has been made by quite a few 'primitive' shooters, including me, and it is a mistake I would push people not to make themselves.

Click to expand...

Sorry to have to disagree. While you can measure BP by volume and get repeatable results, any ejection calculator I've seen refers to BP by weight. I do a lot of pyro as well, and we never use volume measurements in compositions. There is often BP in various compositions, and it is always weighed. Also, a "scoop" of 4F will not weigh the same as a "scoop" of 3F, 2F, etc.

For what it's worth, I mostly use 2FA these days.

Kevin O

Below are the latest test results. To prepare the ejection charge I took 1g of FFG and put it into a nitrle glove finger and ground down the BP until it was a very fine powder. After that I inserted a Q2G2 and sealed the open end. Following this, I placed the charge into the charge holder on the end of my av-bay. Then I put a little bit of dog barf on top of it and taped it down.



Here is the video of the test:

[video=youtube;xlGtt7YTgZ4]https://www.youtube.com/watch?v=xlGtt7YTgZ4[/video]

Pictures of the results:



My question:

Is this good enough? Should I step up to 1.2grams?

Thanks for the input and replys.

~Chuck

Chuck,

Your first test was a bit anemic, but I believe that you have fixed it with the test posted above, DD Test #3. I would keep your main parachute charge at that amount, then if you have do a backup that is set to go off either by altitude or time (my preference, 3-5 seconds) that is twice that amount. If your parachute is out in open air, then the charge does nothing but dirty the tube a bit and make a pop. If something is stuck it can clear it, sometimes damaging the airframe in the process. I prefer to damage the airframe and deploy the chute in that situation than have something come in with no recovery system activated.

Edward

bobkrech said:

If we were loading cartridges I would agree with you: 2FG is not interchangable with 4FG because 4FG will pressurize the cartridge faster than 2FG, and indeed if you look at my second paragraph, I actually presented the differences in the rate of pressure rise for each grade of BP.

etc..
Bob

Click to expand...

Damn good points there Bob.. I step back and bow my cap. I am so used to using BP with muzzleloaders over the last dumdedum years that I have always worked on the same principles for the safe use of BP for rockets.
We are not experiencing the same confinement and pressurization that we would find in a rifle, etc. If anything, after looking at your data, we are more akin to a cannon!!