MWJ Posted January 30, 2014 Posted January 30, 2014 In the Turbo Pyro book it says to use commercial FFG for shell lift charge. I'm about to make my first mortar shell (plastic egg) and only have commercial FFFG BP. My question is, should I use my FFFG commercial B powder or should I use either my home made BP? I have milled (very fast) or un-milled (slower) BP. I live 60 miles from town and not a lot of money so if I can use something I already have it would be great. Thanks guys,Mike
Shadowcat1969 Posted January 30, 2014 Posted January 30, 2014 The FFFg would work, but so would your homemade BP (The faster variety prefferably for lift). It just will be a little more or a little less than the FFg. You should either do some Pyro Baseball testing or something similar. Make an inert shell (fill with sand or such and no fuse) and do some testing with what powders you have to determine what percentage of shell weight gives you a good lift.
MWJ Posted January 30, 2014 Author Posted January 30, 2014 Great! Thanks, I do have some already filled with sand that I use to get my chickens lay where I want them to. Great Advise!
nater Posted January 30, 2014 Posted January 30, 2014 Remember that FFFg will burn faster than FFg and will require less. I tried lifting a 3" ball shell with FFFg and had an impressive flowerpot. It is impossible to know if a softer lift would have worked or if there was another flaw in the shell. I haven't had issues using FFa which is the normally recommended mesh size. Do you know how your powder compares in speed to commercial powder?
Peret Posted January 30, 2014 Posted January 30, 2014 I used Goex FFFG for shells until I got confident enough in my own powder. It's certainly fine for the 1.75 inch shells described in Turbo Pyro. I never had any issues using 10% weight. Uh.. what am I doing writing about shells in this forum? I better run before the rocket guys get me.
nater Posted January 30, 2014 Posted January 30, 2014 Hah, I thought about saying to use a good motor to lift your shell instead of FFFg since this is the rocket forum, but I thought I should be nice instead.
Blackthumb Posted January 31, 2014 Posted January 31, 2014 Hey neighbor....fill an egg with sand or the like and send a few aloft with your homemade BP...
MWJ Posted January 31, 2014 Author Posted January 31, 2014 Sorry for posting in the wrong forum, I thought it fit. OOps. I just made my mortar and will launch tomorrow. I'm going to wear my fire gear (PPE) case. You guys make it look easy. I have two eggs with sand, the same weight as my egg "shell". I have 4g of my HM milled powder as the first test, then I'll test the FFFG powder. Thanks for having patients with me. Maybe I should have posted this in the newbee forum.
MWJ Posted January 31, 2014 Author Posted January 31, 2014 Ok, here's my test results so far: 4g Home made BP Ball milled: 25g egg - stayed in the tube4g FFFG Goex BP flight time 5 Sec. again with a 25g egg I don't know how high it went. Is there a calc. for that?
Shadowcat1969 Posted January 31, 2014 Posted January 31, 2014 If these are 1.75" or 2" eggs, I'd probably try to get about 1 more second of flight time in there, but 5 is probably do-able. 3" shells I look for around 7 seconds or a bit over (depending on what effect you have in it). There are some tables floating around with approximate flight times for many shell sizes, I'm not sure they go as low as 2". And I don't have one on tap at the moment to link to.
MWJ Posted January 31, 2014 Author Posted January 31, 2014 The eggs are 1 5/8 x 2 3/8. Dollar store eggs. Thanks for the input Shadowcat. I used 6g of FFFG and still got about 5 Sec. The tube is 2" x 18" ABS with a wood plug in the bottom. I'll try 8g next. I guess it can't hurt to try. Any idea why my BP didn't work? the mix is pn 75, ch 15, S-10 with home made pine charcoal. Then the mix was ball milled for 4 hours then granulated not corned. Seems to be very fast. I can go with the FFFG, I have 2 LBS of it, so now I can launch my egg shell tonight!
MWJ Posted January 31, 2014 Author Posted January 31, 2014 With 8 grams of FFFG I got 7 sec. I'll go with that for now. Thanks for you help and input.
Coulterbart Posted January 31, 2014 Posted January 31, 2014 MWJ, There is an article on SL I read a while back that can help you. The math is not exact but it is good enough for a close estimate. There are air resistance variables and things not taken into account but then again, we are not trying to dock to the space station or anything like that. Basically take drop time, ( 2/3 of total flight time ) let that be t 16 x t x t = height So if it fell for 5 seconds, it would be 16 x 5 x 5 = 400 ft Take it for what it is but it will get you close, it also has some more info about what you are working on. http://www.skylighter.com/fireworks/how-to-make/high-powered-black-powder.asp
MWJ Posted January 31, 2014 Author Posted January 31, 2014 Thanks Coulterbart, 400 ft is good!Peret: Do you corn your BP? How much do you use? My BP with 4g didn't lift at all. I would use a rocket motor but I don't have any rocket tools yet. I could use a Estes Rocket motor, I still have a "C-6" good for -4 oz. I think I would have to have to stabilize it with a stick attached to it. But Im not sure.Now I ready to have some fun and try out my first egg "SHELL" tonight!
Coulterbart Posted January 31, 2014 Posted January 31, 2014 How long did you wait after you granulated you BP to test it. It has to dry, the outside might feel dry but if it isn't completely dry, it will act WEAK. I have to use about 12% lift (to shell weight) but I know my powder is a little weak. That is why you have to dial it in. I have some C6 Estes and even think the B6 would work for smaller shells. Look up some big rockets that use the C6 motor and check out their weights it their specs. that should give you a range of what you can lift.
MWJ Posted February 1, 2014 Author Posted February 1, 2014 (edited) After I wet and screened my BP I spread it out (8oz at a time) in a clean cat litter box then use a big comb (turbo pyro book) to get more surface area to dry and put it in my lab room 70+ degrees F. and let it dry for at least 18 hours. It looked very fine and fluffy grey in color. I did look up the C-6 motor and it said it will work for 4 oz and under payload. If I figured it right, 12% of 25 gram egg, it would be 3 grams of BP. I tried 4 grams (turbo pyro use's 3.5 grams). I could try to use more bp like maybe 8 grams. I'll try that tomorrow. I would really like it if I can use my own BP because of the cost. Instead of buying BP I can buy some Kno3 from "Lambentveteran". I can always use more, right? Edited February 1, 2014 by MWJ
nater Posted February 1, 2014 Posted February 1, 2014 I think 400 ft would be too high for an easter egg shell. I would aim for 150-200 ft to display such a small shell closer to your audience.
Shadowcat1969 Posted February 1, 2014 Posted February 1, 2014 Yeah, 400 is a bit high for a shell that size. I kinda use a rule of thumb of about 100' per inch of diameter (for smaller shells). Depends on what effect you have inside, how long the stars burn and the like, but I find that works ok as a starting point. With a baseball, which is fairly equivalent to a 3" shell in both diameter and weight (I find them actually a little heavier than most of my shells), a 7-8 second flight time equates to about 300' which is pretty much ideal for most 3" shells. That is where I "baseline" for my flight times. As far as your own powder, I would suggest to go ahead and dry it longer than 18 hours. It quite likely isn't fully dry, especially if you are using water granulation. Are you using a binder, like Dextrin? I personally do not, but some folks do, and that can affect drying time. I granulate with alcohol (when I granulate instead of pressing and corning), rather than water. The grains dry much more quickly and, in general give a faster and more physically robust grain. If your BP is "very fine", that too will play a part. You probably want some grains that will be more along the line of FFg in size, or even slightly larger. So if your BP is finer than the FFFg that you have, then you will want to re-granulate it through a larger mesh screen. It can also take a bit of work to get your own BP working well. It took me a little over a year from my first, poor batch, until I got it figured out well enough to make some good fast BP for lift. For me the key was to actually buy a couple of kinds of charcoal, that way I had more of a "known quantity" that others had used successfully. Now I can use that as a comparison for other charcoals, whether I make them myself or not. So don't get discouraged, just keep working on it!
Dean411 Posted February 1, 2014 Posted February 1, 2014 On your milled powder did you granulate it? Even if you milled it if it is still in powdered form it cannot be used for lifting shells or mines.
Peret Posted February 1, 2014 Posted February 1, 2014 MWJ, I damp my mill dust with water, consolidate it with hand pressure and push it through a 10 mesh screen. I use no binder. When it's dry I screen it again into >20, 20-30 and fines. It's mostly >20. The fines I return to mix with the next batch. I did try consolidating with much higher pressure and breaking it after it was dry, but that was a lot more work and made no difference to the performance, though the same weight of compressed powder took up a lot less space than the simple screened. Newton's laws of motion let you calculate the height if you know the time. Typically a shell falls slower than it ascends (because of air resistance). It never falls faster than it ascends, so of the total flight time, between 1/2 and 2/3 is the falling time. Newton's Law states that the distance traveled equals the starting speed times the time, plus half the acceleration times the time squared. In the more familiar form that you surely remember from high school, S = Ut + 1/2 f t^2 If we start from the highest point, initial falling velocity U is zero, and it gathers speed as it falls with the acceleration due to gravity, 32 ft/sec^2. So if the total flight time is 5 seconds, let's say 2 seconds is rising and 3 seconds falling. So S (distance fallen) = 1/2 * 32 * 3 * 3 = 144 feet In your second case, 7 sec flight, height would be 256 feet if it rose for 3 and fell for 4. These heights are typical in my experience and are probably close.
MWJ Posted February 2, 2014 Author Posted February 2, 2014 Wow! Thanks, that's sounds more accurate. The first test to me looked about 100 ft or so. So your calc. are probably correct. Thanks! I like smart people! That's why I really like THIS forum and all of you!
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