description
Blew the rear closure thru the 54mm to 38mm adaptor. I believe the liner was too long. The forward closure was seated fully. The rear closure would only thread 3.5 full turns. It spread the end of the Dr. Rocket 38/420 case, sent the rear closure, nozzle, and adaptor thru the threaded slimline motor retainer, bending it into a cone shape. The recovery harness was attached to the forward closure with a JB welded eyebolt. The altimeter ejected the main chute and recovered the forward section and av-bay. The fin can fell from approx. 1000 feet, bounced about 5' in the air, and laid still. The adaptor, rear closure, and grain casting tubes shot onto a access road. The phenolic liner split, and broke into pieces upon impact. The forward seal disc, and a portion of the 54mm to 38mm adapter (the washer) were not found after a thorough search. I had just flown the exact same motor in the exact same case the weekend previous. I felt like the phenolic liner was too long. I followed the instructions to fully seat the forward closure. I believe I should of loosened the forward closure and make the threaded area even on both closures, or I should of contacted Aerotech for a new liner. I also considered sanding the liner on my bench mount belt sander, but felt like it would be ok. It was not ok, If you have a liner that seems to long contact the manufacturer, and measure it with a micrometer.
Comments
According to the blueraven it burned for .4 of second, and experienced 397.3 G. I expect that is the upper motor case and eyebolt hitting the bottom of the av bay, while the bottom closure and adaptor were shooting out the bottom of the rocket. The rocket masses 5.5 lbs. empty, and that number of G of acceleration is not possible from a normal launch. I hope this helps someone avoid the failure I experienced.
