Bananaphone69 Posted June 22, 2009 Posted June 22, 2009 I have been reading up on the construction of Farfalle (Italian for "butterfly") shells. It has been hard to come up with information on the shells, and I can't find a previous thread on this topic. This is what I've gathered:-The inserts should be around 4x as high as the width.-The inserts are filled with a BP mix that has 10&-20% Ti, Steel, or Ferrotitanium added.-The inserts have a hole drilled right above the plug on one end that has a nail inserted to keep a cavity through the powder during loading.-The nail is removed from the insert once the hole is drilled, and black match or some similar priming fuse is threaded through the hole.-The finished inserts are arranged around the outside of a canister shell.-The shell center is loaded with BP coated rice hulls, flash, and stars in a well mixed form to provide a strong break with a unpredictable scatter of center stars.-The shell is well spiked to provide sufficient break power even with flash booster. (it is the break that causes the spinning of the inserts, so a powerful break it is essential) Ok, so that is what I have gathered from many sites and posts on different forums brining together the ideas that seem to be the same with everyone. Often someone would contradict this list (drill the hole only threw one side, put the hole in the middle, etc.), but each person would contradict no more than one part, and the majority seemed to rule their position out. Because of the frequent contradiction, I put forward this list to make sure the information I have gathered is accurate. Also, very few people even put forward a hole size for the inserts so I have not included it in the list, but would like to know some of the generally accepted hole sizes. Finally, this post includes the word "flash" and I realize that this is only my second post. I have seen people get railed on their 100th post for flash, and I want to assure you that I have been working with pyro for some time, but often refrained from making posts on forums. I have made shells up to 4 inches for 3 years, and I want my first 5 inch to be a farfalle shell. Obviously, the flash does not need to be discussed past the point of whether or not it is necessary. However, I believe that it is necessary, because people often say they "got away" with using just whistle mix, so it seems somewhat important to boost the break. Having never made a Farfalle shell though, I put forward the chance of my error.
Mumbles Posted June 22, 2009 Posted June 22, 2009 Thats more or less correct in my opinion. I don't really contradict any of that, just do it slightly differently. I use a 1/8th or 3/32" or something along those lines for the vent. It can be placed in the center of tube, and still be somewhat traditional. It's done commercially on occasion. I think it may have the advantage of providing a denser "tail" without additional titanium, or in the commercial sense giving a denser tail with less Ti. I don't use the nail at all. I press in the bottom clay plug, drill the hole, and directly insert the blackmatch. The composition gets pressed right on top of the fuse, to anchor it down. No reason you couldn't do it either way. I use a slightly longer tube. 1/2" x ~2.5" They might be better shorter, but that's the size you get when you cut a traditional rocket tube in half. I'm still not convinced that a hard break is needed for proper performance. My first one didn't break extremely hard, and looked pretty good. The current class of younger builders seem to really be pushing larger, harder breaks, so it may have come from that. I think they've been watching too many Chinese shells. I just used a KP-like mix on puffed rice completely filling in the center, no stars, no flash. The KP like mix was designed for a larger shell, so it didn't break quite as hard as I like, but it still got the job done. I'd use a stronger mix next time. How do you think spinning contributes to the effect? I've heard this, an am always interested in how others think they work. Just from natural causes the insert does spin slightly, but it's not something that is really noticable, unless you blow out one endplug.
Pretty green flame Posted June 22, 2009 Posted June 22, 2009 I use a 1/8th or 3/32" or something along those lines for the vent. It can be placed in the center of tube, and still be somewhat traditional. It's done commercially on occasion. I think it may have the advantage of providing a denser "tail" without additional titanium, or in the commercial sense giving a denser tail with less Ti. Mumbles, is what you described basicly a heavily modified core burner rocket? That's what comes to mind.
Bananaphone69 Posted June 22, 2009 Author Posted June 22, 2009 Thanks for the feedback Mumbles! It has alway been my belief that the rapid spinning of the inserts was what caused the tail to be as thick as possible. It helps throw the sparks in all directions making a bushier tail...
Mumbles Posted June 22, 2009 Posted June 22, 2009 These things are hard to explain without pictures. The holes, and there must be 2, are placed on the side wall of the tube. They should not run parallel to the wall, as hummer vents are. They are placed through the center of the wall. There is no core in these inserts. There are inserts sometimes known as tourbillions, or whirlwinds, or spinners. The composition is capped with clay on both sides, and there is a single hole drilled just above one plug on one end. The farfalle just has the hole all the way through.
FrankRizzo Posted June 23, 2009 Posted June 23, 2009 The Maltese make theirs with the holes directly in the center of the tube (~180-degrees from each other). If you were to light one without being in a shell, the sparks would spray out in a shower left and right, then fall with gravity, forming the wings of the butterfly, and the tube would be the body of the butterfly.
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