dangerousamateur Posted June 24, 2012 Share Posted June 24, 2012 Hi, why is it common to use such long engines? Almost every commercial available tooling sets use 10x internal diameter lenght. I think that this has a lot of disadvantages, mostly the time needed for ramming/pressing. If the motor was shorter and thicker, one could precess this thing with much less increments.Also shorter spindles do not bend so easily, and as most dealers that offer paper tubes here in europe focus more on groundsalute boomers, they are usually to short for the classic long engines. So how about using shorter tubes with shorter spindles and accordingly tighter nozzles? Does this have disadvantages I don't see? Link to comment Share on other sites More sharing options...
Potassiumchlorate Posted June 24, 2012 Share Posted June 24, 2012 A coreburner shorter than 10x its inner diameter will burn out in less than a second, at least if you use meal or corned BP. I have seen a guy who just milled the potassium nitrate and the sulfur and used larger grains of charcoal. His rockets burned relatively slow, with long beautiful spark tails. But as long as you use meal or corned BP, even the "weaker" 60:30:10, the rocket will burn so fast that 10x the inner diameter is necessary. Link to comment Share on other sites More sharing options...
ExplosiveCoek Posted June 24, 2012 Share Posted June 24, 2012 It's not about total burn time, that's what your delay comp is for, it's about maximum thrust. BP comps don't have as much thrust as whistle does, so they need longer rockets to deliver the same amount of power. Simple as that. Link to comment Share on other sites More sharing options...
dagabu Posted June 24, 2012 Share Posted June 24, 2012 (edited) Hi, why is it common to use such long engines? Almost every commercial available tooling sets use 10x internal diameter lenght. I think that this has a lot of disadvantages, mostly the time needed for ramming/pressing. If the motor was shorter and thicker, one could precess this thing with much less increments.Also shorter spindles do not bend so easily, and as most dealers that offer paper tubes here in europe focus more on groundsalute boomers, they are usually to short for the classic long engines. So how about using shorter tubes with shorter spindles and accordingly tighter nozzles? Does this have disadvantages I don't see? Great question. As has already been discussed, the long motor casing is used so that the total *impulse of the motor is great enough to lift objects. Because we use the potential "power" of the rocket motor to lift things like shells and whatnot, a shorter spindle with a smaller creates less impulse, thus less lift. In order to get a higher impulse then, a "hotter" fuel must be used. Hotter fuels make more gas in a shorter amount of time and therefore; more lift. there is no free lunch here, if you want the performance of a #3 BP motor, you have to trade something to get it. You are in fact in error about saying that almost all commercial tooling is X10 ID length for BP. The truth is that any tooling may be used for BP use but the X10 is an age old method at getting pretty darn close to the maximum thrust old fashion cases could handle, or at the point of diminishing returns where the casing weight becomes more of a hindrance then a help. I have several spindles just for 3# motors, all (except the traditional BP tooling) can be used nozzleless with hot whistle, coreless with mild to wild fuels and nozzled motors with lame fuels like red metallic fueled. The "shorter tubes with shorter spindles and accordingly tighter nozzles" are essentially what end burners are. They use a spindle just long enough to light the BP inside the tube and provide several seconds of thrust but at a very reduced rate. If one were to use an endburner spindle but increase the length to lets say, X5 the tube ID, the casing would CATO every time after a second of burn time or less. The pressures build as the fuel grain burns away exposing more and fuel causing higher and higher pressures. *http://upload.wikimedia.org/wikipedia/en/math/5/9/d/59de6573c7ec66dab41ed2c6cb3609df.pngWhere: F is the constant total net force applied,t is the time interval over which the force is applied,m is the constant mass of the object,v1 is the final velocity of the object at the end of the time interval, andv0 is the initial velocity of the object when the time interval begins. -dag Edited June 24, 2012 by dagabu Link to comment Share on other sites More sharing options...
Potassiumchlorate Posted June 24, 2012 Share Posted June 24, 2012 Well, I'm still an idiot what rockets concerns. I still don't get how to properly ignite the payload without having a CATO, for instance. Link to comment Share on other sites More sharing options...
dagabu Posted June 24, 2012 Share Posted June 24, 2012 Well, I'm still an idiot what rockets concerns. I still don't get how to properly ignite the payload without having a CATO, for instance. If your rockets fly without a heading then you are good to go, just use strands of black match to pipe the fire to the shell from the top of the delay. I don't know where all the use of clay bulkheads came from but it has been years since I used them, I just use fast burning comps on top of the spindle and a nice metal rich delay for the tail. -dag Link to comment Share on other sites More sharing options...
Potassiumchlorate Posted June 24, 2012 Share Posted June 24, 2012 I like when people are optimists like you, dag. I'm often too pessimistic myself. They take off good. A 1" ID coreburner will fly some 200 meters at least. I just have to stabilize them properly and make proper headers. Link to comment Share on other sites More sharing options...
nater Posted June 24, 2012 Share Posted June 24, 2012 A 1" ID coreburning motor will fly 800-900 meters with a light salute heading fairly easily. Link to comment Share on other sites More sharing options...
Blackthumb Posted June 24, 2012 Share Posted June 24, 2012 I get my 5/8" x 3" tubes to an estimated 500-600' without any problem. If I want a slower rising rocket, I gut the BP with cedar sawdust and add some flake AL and Ti for tails....quite the display.With a little effort, I create what I call a hovering waterfall effect...rocket rises slowly and seems to hover at 30-50'. Link to comment Share on other sites More sharing options...
dagabu Posted June 24, 2012 Share Posted June 24, 2012 I get my 5/8" x 3" tubes to an estimated 500-600' without any problem. If I want a slower rising rocket, I gut the BP with cedar sawdust and add some flake AL and Ti for tails....quite the display.With a little effort, I create what I call a hovering waterfall effect...rocket rises slowly and seems to hover at 30-50'. I LOVE your rockets BT, I wish I could get mine to work like yours do. I do get beautiful orange waterfalls though. -dag Link to comment Share on other sites More sharing options...
Potassiumchlorate Posted June 24, 2012 Share Posted June 24, 2012 A 1" ID coreburning motor will fly 800-900 meters with a light salute heading fairly easily. Maybe my estimation was wrong. They don't go 800-900 meters for me, though. Link to comment Share on other sites More sharing options...
nater Posted June 24, 2012 Share Posted June 24, 2012 A simple way to estimate distance, is to count the delay from when you see the flash of a salute until you hear the boom. Sound waves travel about one mile (1600 meters) in 5 seconds. Using imperial measurement this is actually easier, for each second of delay the rocket is about 1000 ft away. - The last rocket in this video is a 3/4" core burner that using a medium speed BP fuel, far from the red line. If you watch closely, when the puff of smoke from the heading first forms to the report, it is about one second. A 1" BP core burner with hotter fuel will get much more height. I use H/U spindles, which are shorter than standard BP tooling, but I still cut my tubes at 10x ID. After the delay grain, this leaves enough space to add a binary mixed report, and end cap, and shake it up. The next rockets I build will use this as a color to report heading as discussed in the PGI Anthology. You could not use this technique with short tubes. Link to comment Share on other sites More sharing options...
Potassiumchlorate Posted June 24, 2012 Share Posted June 24, 2012 OK, this is a ½" that I shot 2 years ago. Maybe this went 200 meters? In that case my 1" went much more than 200 meters. I'm simply not good at estimating things with my eyesight. https://www.youtube.com/watch?v=0PkVYY-6S8U Link to comment Share on other sites More sharing options...
nater Posted June 24, 2012 Share Posted June 24, 2012 It is hard to tell how high that went. I can't judge height very well without a report or something nearby of a known height to compare it to. I saw some 1/2" nozzleless rockets made by a master builder that went quite high. Link to comment Share on other sites More sharing options...
NightHawkInLight Posted June 25, 2012 Share Posted June 25, 2012 I wondered this also for quite a while. Dag is right about the reasons that rockets are made as long as they are in the States, as it seems to be the most efficient ratio of length to diameter. A number of old timers have told me that in most of Europe and Asia they do use shorter rocket bodies as the standard. Who knows why. Maybe because it's all it takes to lift the salute headers they use so why waste more time ramming. I have made my own 1lb tooling designed for a much shorter rocket body than typical with pretty good results. If I remember right the grain length is about 4 1/2" rather than the 7 1/2" or whatever is typical for a 1lb. I chose the smaller size mostly because it required much less precision when making the spindle, but also because I knew I could lift all I needed with that size engine. I wouldn't lift 4" or larger shells with them, but anything smaller works just fine: http://www.youtube.com/watch?v=zE1UwqD9W6g Link to comment Share on other sites More sharing options...
Potassiumchlorate Posted June 25, 2012 Share Posted June 25, 2012 Well, I have European BP coreburner tooling from two different sources, one being Pyro-Stuff. Both are made for 10x the ID. Link to comment Share on other sites More sharing options...
spitfire Posted June 25, 2012 Share Posted June 25, 2012 Very neat idea NightHawkInLight, extracting the spindle with the bolts! Haven't thought of that myself. Thanks for the great video! Link to comment Share on other sites More sharing options...
Potassiumchlorate Posted June 25, 2012 Share Posted June 25, 2012 When I first saw his videos on YT, before I was a member here, I thought he was much older, because everything he did was very smart. But still, I think that it is the commercial rockets in Europe and Asia that they make shorter. Link to comment Share on other sites More sharing options...
nater Posted June 25, 2012 Share Posted June 25, 2012 The commercial rockets here in the U.S. are shorter than most people build to. Most of the consumer rockets here have crappy motors compared to the hobbiests as well. Link to comment Share on other sites More sharing options...
dagabu Posted June 25, 2012 Share Posted June 25, 2012 The commercial rockets here in the U.S. are shorter than most people build to. Most of the consumer rockets here have crappy motors compared to the hobbiests as well. I have yet to see any commercial motor over 8oz here in the states, the only motors that are bigger are ESTES motors for models. I would love to know if there are larger 1.3 rockets available but all the lists and catalogs show 8 oz max. -dag Link to comment Share on other sites More sharing options...
nater Posted June 25, 2012 Share Posted June 25, 2012 I have yet to see any commercial motor over 8oz here in the states, the only motors that are bigger are ESTES motors for models. I would love to know if there are larger 1.3 rockets available but all the lists and catalogs show 8 oz max. -dag Most of the 1.3 rockets I have seen were 4oz or 8oz and I don't think 1.4 rockets can exceed 4oz, still they are usually shorter than 5 inches. Link to comment Share on other sites More sharing options...
dagabu Posted June 25, 2012 Share Posted June 25, 2012 Most of the 1.3 rockets I have seen were 4oz or 8oz and I don't think 1.4 rockets can exceed 4oz, still they are usually shorter than 5 inches. Thats what I was thinking, 8 oz is the limit on commercial rockets. I have never looked in the OB to see if there was a limit on 1.4 rockets but I would agree with the 4 oz size. -dag Link to comment Share on other sites More sharing options...
Blackthumb Posted June 26, 2012 Share Posted June 26, 2012 http://www.aerotech-rocketry.com/products.aspx Link to comment Share on other sites More sharing options...
dagabu Posted June 26, 2012 Share Posted June 26, 2012 (edited) No, BT, those are not pyrotechnic rockets, they are model rockets and are not in the same realm. That was pretty snappy wasn't it? I must have been really tired, sorry BT. -dag Edited June 26, 2012 by dagabu Link to comment Share on other sites More sharing options...
Blackthumb Posted June 26, 2012 Share Posted June 26, 2012 missed the fine print... Link to comment Share on other sites More sharing options...
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