mabuse00 Posted October 26, 2011 Share Posted October 26, 2011 but the internal volume is decreasing meaning less pressure and lower thrust than when it took off,Can someone elaborate if this is physically correct? I would assume the pressure to stay constant as long as the nozzle does not erode and the burning surface stays constant too. I flew my 1lb coreburners up to 500g (complete rocket, dummy shell had 350g). But since I always lost the nozzles I expect them to carry at least 500g with some more fine tuning. Link to comment Share on other sites More sharing options...
dan999ification Posted October 26, 2011 Share Posted October 26, 2011 (edited) Can someone elaborate if this is physically correct? I would assume the pressure to stay constant as long as the nozzle does not erode and the burning surface stays constant too. I flew my 1lb coreburners up to 500g (complete rocket, dummy shell had 350g). But since I always lost the nozzles I expect them to carry at least 500g with some more fine tuning. the pressure output by the fuel is constant but the volume of the casing is not, the most thrust being produced by an endburner is at take off when the casing has max volume, as the fuel burns it decreases letting the gasses expand and lowering the pressure inside. casing burn through and nozzle erosion play a part.the fuel burning at a constant rate produces the same amount of gasses per sec, if you take a small volume case with this "constant delivery of gasses it will be at higher pressure than a larger case with the same delivery, gasses want to expand back to atmosphere the more space you give them the more they do it. dan. Edited October 26, 2011 by dan999ification Link to comment Share on other sites More sharing options...
dagabu Posted October 26, 2011 Share Posted October 26, 2011 the pressure output by the fuel is constant but the volume of the casing is not, the most thrust being produced by an endburner is at take off when the casing has max volume, as the fuel burns it decreases letting the gasses expand and lowering the pressure inside. casing burn through and nozzle erosion play a part.the fuel burning at a constant rate produces the same amount of gasses per sec, if you take a small volume case with this "constant delivery of gasses it will be at higher pressure than a larger case with the same delivery, gasses want to expand back to atmosphere the more space you give them the more they do it. dan. Dan, established thrust curves tell a different story. Endburners show a very flat thrust curve all the way across the thrust stage when proper nozzle material is used. If there is any thrust lost due to "chamber cooling" in an end burner, it is very small. This phenomena shows up more prominently in casings some 10x the fuel grain cross section size such as a 10" long casing in a 1" end burner. With the relatively short 4:1 endburners we use, the phenomena is hardly noticed. -dag Link to comment Share on other sites More sharing options...
dan999ification Posted October 26, 2011 Share Posted October 26, 2011 Dan, established thrust curves tell a different story. Endburners show a very flat thrust curve all the way across the thrust stage when proper nozzle material is used. If there is any thrust lost due to "chamber cooling" in an end burner, it is very small. This phenomena shows up more prominently in casings some 10x the fuel grain cross section size such as a 10" long casing in a 1" end burner. With the relatively short 4:1 endburners we use, the phenomena is hardly noticed. -dag i know the thrust curve is flat but it is a curve i feel that when i was testing the timing on my motors and rammed more id's than usual that they did run out of oomph around the time a normal sized fuel grain would have finished [ nozzles and casings were intact after ] i was just trying to say that they dont speed up and that ten id's is not optimal for an endburning rocket because of what you described so much better than me. dan. Link to comment Share on other sites More sharing options...
dagabu Posted October 27, 2011 Share Posted October 27, 2011 i know the thrust curve is flat but it is a curve i feel that when i was testing the timing on my motors and rammed more id's than usual that they did run out of oomph around the time a normal sized fuel grain would have finished [ nozzles and casings were intact after ] i was just trying to say that they dont speed up and that ten id's is not optimal for an endburning rocket because of what you described so much better than me. dan. In my "tests" on a postal scale, I found the end burners to have a very flat thrust curve all the way through the burn. The issue I am having right now is that i am making the fuel grain to long. A 4:1 fuel grain length would be great for lift but I want a 20 second burn time -dag Link to comment Share on other sites More sharing options...
dan999ification Posted October 27, 2011 Share Posted October 27, 2011 In my "tests" on a postal scale, I found the end burners to have a very flat thrust curve all the way through the burn. The issue I am having right now is that i am making the fuel grain to long. A 4:1 fuel grain length would be great for lift but I want a 20 second burn time -dag i have never tested them on a scale just say what i seetwenty, and i thought twelve seconds was long i may have to try that fuel, does it have to be pressed? i assume the burn time is related to the density of the fuel grain. dan. Link to comment Share on other sites More sharing options...
dagabu Posted October 27, 2011 Share Posted October 27, 2011 i have never tested them on a scale just say what i seetwenty, and i thought twelve seconds was long i may have to try that fuel, does it have to be pressed? i assume the burn time is related to the density of the fuel grain. dan. Heck no, pound away on all BP compositions (without metal in them. -dag Link to comment Share on other sites More sharing options...
dan999ification Posted October 27, 2011 Share Posted October 27, 2011 Heck no, pound away on all BP compositions (without metal in them. -dag pressed hard, longer burn?rammed, shorter burn? dan. Link to comment Share on other sites More sharing options...
dagabu Posted October 27, 2011 Share Posted October 27, 2011 pressed hard, longer burn?rammed, shorter burn? dan. Thats about the gist of it. -dag Link to comment Share on other sites More sharing options...
ibizon Posted March 10, 2012 Share Posted March 10, 2012 On the topic of what the lifting capabilities of BP rockets are. I am looking at getting some smaller tooling to make smaller rockets that will carry 1.5-2" shells. More of a backyard rocket if that makes sense. Looking at Wolters BP tooling, what do you guys thing would be best between the 4 and 8oz sizes. I currently make 1lb rockets, so the 8oz isn't much smaller than what I currently use, but I don't want to go for the 4oz and have it not be able to lift my shells. Anyone here have experience with both and some info you can share on what each can handle? My 1lb tooling is the FireSmith 1lb universal tooling. I use a 75-15-10 fuel and most are nozzle less. Link to comment Share on other sites More sharing options...
JFeve81 Posted March 10, 2012 Share Posted March 10, 2012 On the topic of what the lifting capabilities of BP rockets are. I am looking at getting some smaller tooling to make smaller rockets that will carry 1.5-2" shells. More of a backyard rocket if that makes sense. Looking at Wolters BP tooling, what do you guys thing would be best between the 4 and 8oz sizes. I currently make 1lb rockets, so the 8oz isn't much smaller than what I currently use, but I don't want to go for the 4oz and have it not be able to lift my shells. Anyone here have experience with both and some info you can share on what each can handle? My 1lb tooling is the FireSmith 1lb universal tooling. I use a 75-15-10 fuel and most are nozzle less. There's an article on SkyLighter on making 1.75" canister shells to be used with 4 oz rockets. So you might be fine with the shell sizes you mentions. I don't have any experience in this so you might wait for one of the more experienced rocketeers to chime in. Here's the link to that article: http://www.skylighter.com/fireworks/Paper-Cylindrical-Shell-Rocket-Heading.aspThere is a video of a heading using red stars that might help you get an idea. Link to comment Share on other sites More sharing options...
allrocketspsl Posted March 12, 2012 Share Posted March 12, 2012 Hello everyone, i couldnt find any dedicated topic for how much can a BP rocket lift, so i decided to start one.My reason is to know how much can core/end burnning BP rockets can lift. Lets say,have anyone done any testings on 1" (25mm) end burning rockets,about how much can they lift?I have only tested my 16mm ID rockets,with 8mm choke,that are corer burners,and they did lift 70gr payload easily.Thanks in advance! you can make three inch shells with tt stars and the weight is nill compared to a magnalium say independend red star.The lifting capabilities are so different from one person to another.You will see on youtube people claiming they lift 500 grams with a rammed one pounder using 75/15/10.I have rammed bp one pounders for four years never got near that because it aint possible.The most I got using 57/34/9 was 223 grams.Thats because I like long tails.All in all find the comp of choice press it or ram it, find a tube ( I have nevr bought a tube yet),that will take pressure.add a shell(I always tested sand filled can shells of various weights to get an idea what will lift what)then fire one up.Good luck!! PS: nozzeless with lift more than cored lb for lb!! Link to comment Share on other sites More sharing options...
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