inonickname Posted July 14, 2009 Posted July 14, 2009 Well I've never seen a definitive test for the burn rate of black powder. Most people don't have an ultra-high speed camera so that route can be ignored. So, I'm assuming there isn't one before writing this; Do you believe there should be a test that is easy to perform and will give an accurate comparison of the speed of your black powder? What would be a good method to test this? A certain volume of black powder, poured into a jig of a certain length, width and height, then ignited electronically? Should black powder be judged on both energy density and speed? I've made mixes that are fast as hell, yet visually (and noticeably less thrust) much less powerful. Any thoughts on a standardized test of black powder? Of course there would be the average controls (for example, ignition.. blasting cord or detonating caps would be out of the question). I believe that a good black powder should be judged on speed and energy density. I can crank lots of sulfur into my BP and make it extremely fast, yet it will be weak as piss. How is that fair to the people who make a 'traditional' mixture that is actually useful?
qwezxc12 Posted July 14, 2009 Posted July 14, 2009 (edited) There is actually lots of anecdotal evidence that the relationship between speed & lifting power is fairly linear. Many, many, many discussions on Passfire among *knowledgeable* folks (both pros in the business and accomplished amateurs). If you haven't read Danny Creagan's charcoal testing blog, you should: http://www.creagan.net/fireworks/charcoal_tests.html... it's informative. He uses a standardized testing rig and tests a variety of charcoals (in std 75:15:10 formulation). I emulated his 30" burn trough and used video from my digital camera @ 30fps for timing when tuning my BP making process. I pretty much stopped tweaking when I arrived at successfully (and consistently) using 1/16 the shell's weight in BP for lift. Edited July 14, 2009 by qwezxc12
Pyrohawk Posted July 14, 2009 Posted July 14, 2009 Your BP is fast enough when your lift does what you need it to do without wasting a lot of chemicals. Thats just my opinion...personally I've never been that concerned on whether my BP is fast or not. Doesn't make any difference other than a personal pride in something that noone will ever know about. Now my shell breaks, color of my comps, symetry, thats the sort of stuff I stress about. I use 1/10 the weight of the shell in my lift. Its way more than what most people use. But thats fine with me, as long as it gets the job done and I'm not wasting a lot of it, its all good.
Swede Posted July 15, 2009 Posted July 15, 2009 Interesting - I just posted my homemade BP burn speed rig in this same section. It uses a quartz timer to measure the speed of a powder train in an aluminum angle. Without analysis of video, probably the easiest way is to launch tennis or golf balls with a given mass of powder, and use a handheld stop watch to time the flight. If you know the weight of the tennis ball, you can also do some physics and extrapolate the height of a shell.
dagabu Posted July 21, 2009 Posted July 21, 2009 (edited) Well I've never seen a definitive test for the burn rate of black powder. Most people don't have an ultra-high speed camera so that route can be ignored. So, I'm assuming there isn't one before writing this; Do you believe there should be a test that is easy to perform and will give an accurate comparison of the speed of your black powder? What would be a good method to test this? A certain volume of black powder, poured into a jig of a certain length, width and height, then ignited electronically? Should black powder be judged on both energy density and speed? I've made mixes that are fast as hell, yet visually (and noticeably less thrust) much less powerful. Any thoughts on a standardized test of black powder? Of course there would be the average controls (for example, ignition.. blasting cord or detonating caps would be out of the question). I believe that a good black powder should be judged on speed and energy density. I can crank lots of sulfur into my BP and make it extremely fast, yet it will be weak as piss. How is that fair to the people who make a 'traditional' mixture that is actually useful? I gotta say that I have found this article very informative, to test velocity, one only has to do as Swede has provided for in his rig. Another way is to measure the height or distance and the time a known object travels, I'm sure Swede can help with the math. http://www.skylighter.com/skylighter_info_...asp?Item=115#BP Edited July 21, 2009 by dagabu
NightHawkInLight Posted July 21, 2009 Posted July 21, 2009 Pressing to a standard density and burning a grain as you would in a spolette would be just about the only way to take out the most troubling variables. Then at least charcoals and the other components could be accurately compared for speed. Far to much can change the result of a trough test for it to be definitive, just a decent visual aid. It could define fairly well what is fastest, but cannot give out much else information accurately such as exactly what % faster it is than the rest. IMHO.
FrankRizzo Posted July 21, 2009 Posted July 21, 2009 (edited) To test my powder, I make spolettes by ramming a 1.125" - 1.25" column of powder in a 1/4" ID tube, then using a drill bit turned by hand, drilling back the powder until I have exactly a 1" column. I set up my camera in video mode and time how many frames it takes from igniting one end until flame spits out the other. I consider the powder "lift worthy" if the 1" column burns in 2 seconds or less. As Nighthawk said, there are too many variables that come into play when using an open burn test. Simple conditions that can change day-by-day if not hour-to-hr such as atmospheric pressure and relative humidity weigh heavily on burn rate. Edited July 21, 2009 by FrankRizzo
Swede Posted July 21, 2009 Posted July 21, 2009 I agree with Frank. The rig I made does one thing - burn speed. It does not measure gas volume, or how the BP behaves under pressure. All BP burns accelerate under pressure, but I'm sure there may be some variation based upon granulation, pressing, composition, charcoal, etc. We want BP to do WORK, moving a mass a given distance. I've always liked lobbing baseballs, tennis balls, etc, because you are measuring work, and it can be done with a handheld stopwatch. I suppose a rig could be set up with an extremely strong combustion chamber that moves a heavy mass along an inclined rail a short distance, something like that, but now you're moving towards expensive lab-type equipment. Or, you could scale up one of the old powder testers that use a little flintlock pistol to move a disk. Picture a heavy pendulum that is blown from its resting position along an arc. Measure the height of the mass along a scale in the background - it'd probably be an effective tool.
dagabu Posted July 21, 2009 Posted July 21, 2009 To test my powder, I make spolettes by ramming a 1.125" - 1.25" column of powder in a 1/4" ID tube, then using a drill bit turned by hand, drilling back the powder until I have exactly a 1" column. I set up my camera in video mode and time how many frames it takes from igniting one end until flame spits out the other. I consider the powder "lift worthy" if the 1" column burns in 2 seconds or less. As Nighthawk said, there are too many variables that come into play when using an open burn test. Simple conditions that can change day-by-day if not hour-to-hr such as atmospheric pressure and relative humidity weigh heavily on burn rate. I like baseballs in a 3" mortar, I look for 300' timed to apogee and total time to landing. Though not the most scientific, it answers a lot of questions about initial lift (the thump) and total energy spent. BTW, Federal Ammunition tests smokeless (I know, not the same thing) in a pressure vessel that fires a known amount of powder that drives a cone into a brass sphere. The width of the dent is measured and the energy is mathematically interpolated.
NightHawkInLight Posted July 21, 2009 Posted July 21, 2009 I like baseballs in a 3" mortar, I look for 300' timed to apogee and total time to landing. Though not the most scientific, it answers a lot of questions about initial lift (the thump) and total energy spent. BTW, Federal Ammunition tests smokeless (I know, not the same thing) in a pressure vessel that fires a known amount of powder that drives a cone into a brass sphere. The width of the dent is measured and the energy is mathematically interpolated.Yes, for pure performance (which is all anyone really cares about right?) the good old golf ball test, or baseball test is all that is really needed. If the same weight of BP as another sample can keep a ball in the air 25% longer, it is obviously 'better'. For most uses in fireworks anyhow. That's all the information I really need to know. Whether it's faster, or just generates higher gas volume can be decided later. I don't know. Maybe there's just no way around using a variety of tests to really understand the 'why' behind certain BPs performance compared to another.
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