Robert DeHate made a rocket out of a spent Aerotech G80 motor casing. I thought it was so funny that I made one myself. ConstructionI had to wait awhile to find someone with a G80 and a rocket they'd launch on it. Drew Ortiz, a regular at the Zia Spacemodelers launches launched his Astrobee on one in September, 2003, and let me have the casing when he was finished.The first thing I did was coat the exterior surface of the motor tube in masking tape to protect it from damage. Then I used a Dremel cutting wheel to shear off the nozzle. This was a relatively quick and painless operation. I had to experiment with various Dremel bits to find the right one for boring out the forward and aft closures. The best one I found was the "high speed cutter" bit that looks like a <1cm thick cylindar with cutting ridges running down the sides. Even with this, the aft closure ate two bits before I could ream out a large enough hole for the BT20 motor tube to fit through. The forward closure was somewhat soft, and after working out the first centimeter or so the rest proved to not be attached to the casing walls and just fell out. The aft closure/nozzle was much harder on the bits and took significantly longer to remove. I removed all of the aft closure out to the inner diameter of the casing tube down to a depth of about 4mm to make a "moat" around the motor mount tube for epoxy. Then I borred through the remaining material to open up a hole for the motor mount tube. I cut a section of BT20 tubing a little shorter than a motor and stuck it through the aft end of the motor mount hole. I left about 5mm of tubing extending beyond the end of the body tube (about 1 cm beyond the bottom of the moat). Then I mixed up some 30-minute clear epoxy and filled in the moat. I made the epoxy flush with the body tube on the outside and gave it a nice fillet where it meets the motor mount tube. In this way, it matches the basic shape of the aft end of the original Aerotech motor. When the epoxy dried I took a sharpie and colored the epoxy and motor mount tube black. It looked just like the nozzle extension on a real motor, except a bit wider and a bit shorter. Next up was the nosecone. A BT50 nosecone is too small; the shoulder fits inside the motor casing. A BT55 nosecone is too large. Robert used some special nosecone from an out-of-production model for his that fits just right, but he had to buy it on Ebay. I just took a BT55 and modified it. First I stuck the nosecone point-first into the body tube and made a mark with my sharpee around the nosecone slightly above where it become as wide as the inner case diameter. I cut nosecone to this length with my bandsaw. The diameter of the cone more or less matched the diameter of the body tube, but there was no shoulder. I took a 1" length of BT50 (24mm) body tube and wrapped one layer of masking tape around it. This made the tube fit nicely into the body tube with a small amount of friction. I put thick CA around one end of the outside of this tube and jammed it up into the truncated nosecone, making sure to keep it centered and axially aligned. When this dried I had a nosecone with shoulder that fit the body tube perfectly. Because the nosecone was truncated by almost 50%, the nosecone meets the body tube with a small angle, rather than with a continuous line. But I still think it looks good. Next up: the fins. I made up a fin template on card stock that I thought looked well-proportioned and then cut three fins out of a sheet of 0.062" thick G-10 that I bought from Giant Leap Rocketry. I made sure the fins had a sweet such that the rocket would sit on the fin tips rather than on the "nozzle." I chose a single caliber span and only slightly longer root chord. In retrospect, the fins are perhaps a bit undersized. Robert's fins are much larger. I hope the stability of this rocket is OK, we'll see when I test fly it. I removed the masking tape from the body from the aft up to slightly above where the forward end of the fins would be. I figured out where the fins would go such that they didn't interfere with the interesting parts of the yellow printing on the body tube. I masked off everything except for the footprint of the fins and then sanded the exposed areas to make them more bond-friendly for epoxy. I removed the masking again and applied each fin with thick CA. When the fins were attached, I masked off everything except the area that would be covered by the fin fillets. I used the head of a big nail to shape the fillets. I chose not to roughen the body tube beneath the fillet because it whitens the material enough to make it look bad. I hope the fillets will grip the smooth body tube reasonably. The last step was the recovery system. I used Kevlar thread which I epoxied to the outside of the motor mount tube inside the rocket, and then to the inside of the tip of the nosecone. A simple 12" plastic parachute was attached to the shock cord about 3" below the end of the nosecone. I didn't have any Nomex laying about, so I'll just use wadding. Parts1 spent G80 motor 3 0.062" thick G10 fins 1 Estes BT55 nosecone 1 Estes BT20 (18mm) motor mount tube 1 Estes 12" plastic parachute Kevlar shock cord | ||||||||||||||||||||||||||||||||||||||||
