dangerousamateur Posted June 19, 2017 Share Posted June 19, 2017 Just imagine a typical 1lb tube with 1/8" walls. What is in your opinion the maximum length of the fuel that can be used until the tubes fail? Unfortunately my own 1lb tool is very short, only 4" in length.I like to fit them with small salutes and let them rise to high altitude. I wonder if a 7.5" long tool makes sense...? Link to comment Share on other sites More sharing options...
NeighborJ Posted June 19, 2017 Share Posted June 19, 2017 7.5" is perfectly reasonable for NEPT tubes. I've made a few 1# endburners 10" long in an attempt to answer that same question but it never burned thru. I have a theory that once the grain burns beyond a certain distance up the wall it will stop or at least slow the wall erosion down near the nozzle. The most significant wall erosion only seems to happen at the flame front. Further attempts to lengthen the motor were inconclusive because the motors simply went too high, the 15g salutes they were fitted with were almost completely inaudible. I wasn't able to recover the motors for examination beyond 10" length and bigger salutes were becoming too heavy for it to lift safely with the added fuel weight. Jason Link to comment Share on other sites More sharing options...
lloyd Posted June 19, 2017 Share Posted June 19, 2017 With NEPT virgin kraft tubes (NOT the pulp-paper type), we got 20-second burns on our 20' gerbs with nary a sign even of impending burn-through. Our 20x20 silver and gold gerbs were a 'catalog item', and never failed to please. Lloyd Link to comment Share on other sites More sharing options...
usapyro Posted June 19, 2017 Share Posted June 19, 2017 I have done 8" endburners without issue on dry-rolled tubes with normal 20# copy paper, lol... You should try double-stage rockets. They are fun! You just need to attach the stick to the top stage, and connect each stage with a paper sleeve. Link to comment Share on other sites More sharing options...
dangerousamateur Posted June 19, 2017 Author Share Posted June 19, 2017 So burnthrough is no problem. I better get some longer rammers then Most people do not seem to do this, because at some point they come back I love these long burning rockets. The sound and gentle movement WRRRRRSH... Link to comment Share on other sites More sharing options...
NeighborJ Posted June 19, 2017 Share Posted June 19, 2017 Nah, lots of people do this but they call them drivers and they strap'em to a girandola or wheel. Well... At least the girandola builders do it. Link to comment Share on other sites More sharing options...
Mumbles Posted June 20, 2017 Share Posted June 20, 2017 Nozzle burn through is largely a function of the nozzle itself. Using a good tool that forms nozzles with convergent and divergent sections is very helpful. Lesser quality tooling that makes flat nozzles will make the burn through problem worse. I don't really have much to add in terms of workable length unfortunately. Normal end burners are made approximately 7x the ID long. 1lb end burner rockets generally use 5" or 5.25" long tubes, though I know a few people who make them with normal core burner lengths (7.5"). Link to comment Share on other sites More sharing options...
usapyro Posted June 20, 2017 Share Posted June 20, 2017 So burnthrough is no problem. I love these long burning rockets. The sound and gentle movement WRRRRRSH... Gentle movement? I dialed my end burner nozzles down tight with my new high-PSI hand rolled tubes... Things take off like a flash and perform like my old BP core burners of years ago. They ignite, and they are GONE! Link to comment Share on other sites More sharing options...
dangerousamateur Posted June 20, 2017 Author Share Posted June 20, 2017 Yes but you've got much more to watch as with a coreburner. Nozzle burn through is largely a function of the nozzle itself. Using a good tool that forms nozzles with convergent and divergent sections is very helpful. Lesser quality tooling that makes flat nozzles will make the burn through problem worse.Is a simple convergent/divergent 30°/30° nozzle like the Rocket Tool Scetcher proposes be sufficient? Because some toolmakers offer different angles, like Ben Smiths Endburner tool, wich has a less steep exit cone. Link to comment Share on other sites More sharing options...
Mumbles Posted June 20, 2017 Share Posted June 20, 2017 Hopefully someone more versed will answer that. The steeper angle on the exit side is supposed to simulate a DeLaval nozzle. I've used both at some point, but am not accomplished or experienced enough to really say if it makes a huge difference in performance. The biggest thing with preventing burn through is the angled rammer on the inside of the rocket. This helps to guide the hot exhaust gasses out to the nozzle. Without it, the gasses can hit the flat nozzle, generating a more turbulent flow, and causing increased erosion and burnthrough at the point/corner where the nozzle and tube meet. The same concept is also helpful for gerbs with microstars to help guide them out of the aperture instead of burning up inside the body. Link to comment Share on other sites More sharing options...
lloyd Posted June 20, 2017 Share Posted June 20, 2017 Mumb,I've not seen a lot of difference in initial thrust with a DeLaval style, as opposed to 'just a hole'. But what I have seen is a lesser-tendency for the nozzles to erode and enlarge when the proper DeLaval profile is employed. We made ALL of our gerbs that way, so that they would sustain the same column height throughout the (sometimes long) burn. LLoyd Link to comment Share on other sites More sharing options...
dagabu Posted June 21, 2017 Share Posted June 21, 2017 That is my experience as well, the more of a "cup" in the convergence, the more likely none of the paper is consumed while the end burner is firing. Even the sets with the rammer with a step at the end can exacerbate the burn through phenomena causing the biggest problems with the pulpy tubes. Link to comment Share on other sites More sharing options...
dangerousamateur Posted June 21, 2017 Author Share Posted June 21, 2017 Thanks. Ill get a new set of rammers. I found that whistlemix also makes a powerfull endburner fuel. I also had one blown up. The flame should be more erosive also.Did you ever use whistlemix for endburners?Who cares about hybrid mixes if pure whistle works so well... Link to comment Share on other sites More sharing options...
dagabu Posted June 21, 2017 Share Posted June 21, 2017 Thanks. Ill get a new set of rammers. I found that whistlemix also makes a powerfull endburner fuel. I also had one blown up. The flame should be more erosive also.Did you ever use whistlemix for endburners?Who cares about hybrid mixes if pure whistle works so well... Yes, many, many times but I haven't had one CATO on me yet. Hybrid is cheaper if by hybrid you mean whistle and BP? I like to use hybrid fuel to economize the cost and still get a lot of "OOMPH!" Interestingly, the erosive nature is not apparent in a well designed motor, the pressure will exacerbate the issue if there is a flat spot where the gasses are allowed to push against the casing instead of pouring out the nozzle. Link to comment Share on other sites More sharing options...
Mumbles Posted June 21, 2017 Share Posted June 21, 2017 Hybrid fuel still gives a tail. Whistles of any type aren't very visually pleasing, and whistle end burners don't make much noise other than maybe a chirp at take off. They're just high thrust, boring motors. It's the same reason sugar rockets aren't used all that much in pyro. If all you care about is performance and cost isn't a factor, by all means use straight whistle end burners. Link to comment Share on other sites More sharing options...
Recommended Posts