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This is a rocket that I have been working on for Balls 2003. Since I got my lathe...(and no Woody I don't feel bad)..I have really enjoyed being able to take my pencil drawing and then go out and make it on the lathe. I also learned how to anodize things..which is also fairly easy to do. I wanted to see how high and or how fast I could make a 3" rocket go. The entire rocket is based around the motor which is 40" long... 40" is how long I'm able to do on my lathe right now... It also seems to be about optimal length for 3" motors and still maintain some...(I forget the term but at some point the core size is so big that the amount of propellant left is not very much)..atleast for APCP motors.
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A wood nose cone was turned from a block of Mahogony ..thanks Steve!..on my lathe. I was trying for a 5 to 1 conical but it came out about an inch short at 14" long. The "plug" was then covered with about 5 layers of 6 oz glass and polyester resin. I then glassed some wood supports to it. The mold was cut in half with a skill saw into two halves. The wood plug was popped out. I then waxed the mold and used 6 oz cloth and polyester resin. There is about 5 layers of glass in the nose cone.
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The nose cone is also the electronics bay. I then glassed some of the 2.5" "gas pipe" inside the nose cone to act as the electronics bay. You can see the electronics board and the cover along with the shock cord mount.
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The coupler was made from some solid 3" stock and bolts to the forward closure after the motor is put together. The bolt also acts as the other shock cord anchor point. It pinches the snap ring in place and rides on edge of the motor case. The two o-ring grooves are for friction fit and they can be thightened up if needed or I could also add some shear pins too.
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This left the fin can. I was going to weld one up but changed my mind. I really don't like the looks of welded fin cans and figured I could make one out of composites that would hold up. I peeled down a 3" ID card board tube leaving just a bit of card board. I needed and wanted some cardboard to act as insulation and to act as a form for the glassing process. I did 4 layers of 6 oz glass with System Three T-88 epoxy. That would give me a good base for the fin can. The fins are .125 G-10. Airfoils were sanded into the G-10 and then they were roughed up with 50 grit and then scratched up with a sawzal blade. They were tacked in place with 5 min epoxy. A filet of T-88 and carbon fiber pulp was applied, then strips of 6 oz glass over the filets. Then some 5 oz carbon fiber and then another layer of 6 oz almost tip to tip.This was all done in one step so that there would be no "cold joints" between layers. Once all three bays were done it took maybe an hour with some 50 grit to knock the edges off.
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The motor tube is 40" long and takes 32" of propellant plus about 2" of tracking smoke. With just unde 9 pounds of propellant the motor ready to go is 15 pounds 9 ounces. The numbers I have for the motor right now work out to about an M2400 with just over a 3 sec burn time. This leaves me with room for a 3" long nozzle. The case was left at a true 3" OD and the snap ring grooves are a bit deeper then normal.
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I weighed all of the rocket parts electronics batteries chute shock cord etc.. and it comes to about 7 pounds for the rocket parts. The motor ready to go os 15 pounds 9 ounces..with just under 9 pounds of propellant...So it looks like it will weigh under 23 pounds ready to go..
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I also needed to come up with a fool proof ejection method...so I borrowed Tom Rouse's CO2 ejection concept. I went with some un-threaded 12 gram CO2 cartridges becasue they are much cehaper then the threaded ones. It still uses BP as the charges but it is in a sealed area and should not be affected by the extreme altitude. An e-match fires the BP that ounctures the CO2 cartridge
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