dagabu Posted June 28, 2012 Posted June 28, 2012 Dag tell me more about the PVC cato's you have had, how close you were to the rocket etc. The reason why I ask is that when I first started playing with pvc sugar rockets I cato'd a few of them myself, and the pvc DID shatter into hundreds of little pieces of shrapnel. One thing I noticed is that the PVC didn't carry its energy very far not many pieces flew more than 30 feet even though some of them were able to punch through Masonite that was only a few feet from the motor. Once I got the hang of it I have made hundreds of motors with no catos. In fact I have even made reusable motors with pvc and one of them has been fired more than 30 times. I think PVC is kind of a paradox. It can make good rocket motors but it should only be done by people that have adequate experience, similar to flash powder. The thing is by the time most people acquire enough experience they usually have already bought reusable aluminum hardware that will outperform PVC in every way. At the minimum you should deliberately keep your operating pressure low and have a minimum stand off distance of 100 feet with electric ignition. Back on the topic; I need to know more about your motor design before I might be able to help. You say the top grain is not cored so I am assuming this is a bates grain motor? First are these sugar motors? The tracking grain has a tendency to go out with sugar propellants especially if it is recrystalized propellant. If this is the problem try adding some red iron oxide or coarse charcoal only to the propellant in the smoke grain. Fantastic questions! I really don't know exactly how far I was away, I posted this a while ago and my memory was much better at that time about my placement but as I recall now, I was several meters away, thinking I was at a safe distance when it blew. The piece that hit me was about 1/4 of the 3/4"x6" casing and it stuck into me like a throwing dart, straight in. It missed all the important stuff and left me with wet shorts. Yes, I understand the paradox with PVC and for model rocketry with safe distances, it is even less dangerous then the Aerotech motors inside aluminum casings. The issue is that there a lot of people that come by here and peek in for a look see and read about PVC and cement then think, "What a great idea!". Not knowing that this may be a model rocket motor specifically but is posted in a general thread under the "Pyrotechnics" heading. BTW- My motor was a static test, it just blew up, no burn time at all. -dag
dan999ification Posted June 29, 2012 Posted June 29, 2012 Thanks guys for the correction, don't know why I have that in my mind... Pressed them without a sleeve? That is one stout tube! -dag i use similar if not the same for 3" mortars very strong even though spiral wound with 1" walls, 50 shots no damage yet.someone on another forum calculated the burst pressure to be a little over 500 psi, surely 3" whistles produce at least that? and it suprises me that thay would stand up to unsupported pressing.i may be responsible for the pvc fetish after i compared pressure rated pipe to card tubes a year or so ago i was merely answering the question, "why did it not cato and mine do" sorry if this is the case, roll or buy paper/card tubes, even though i found it extremely difficult at first with maybe one usable tube from ten rolled i now have the nack after many late nights and swearing and can make better tubes with free paper than i can buy,it has took nearly a year but hey, as said they can and will be better than comercial if you put the time in after all how do they do it? dan.
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