(Joe Bernard) built a solid propellant rocket motor and tried it out on a test stand, as you would in such a situation. The video below is not about testing, nor is it about the construction of the motor. Rather, this is a disassembly of the remains of the motor to better understand its design, and it’s quite interesting.
(Joe), also known as “BPS.Space” on YouTube, went from an avid model rocketeer to a full-fledged missile man along the way, and also seriously stepped up his motor game along the way. The knife in this video, the motor under the bandsaw, is Joe’s “Simplex V2,” a completely DIY build of his design. Considering the scale, the casing is constructed from a 6-inch (15 cm) diameter aluminum tube spanning a meter length with a machined aluminum forward closure and composite nozzle assembly. This is pretty serious engineering.
The closure and nozzle are the focus of the video, which makes sense since most of the action takes place there. To understand what happened during the test, (Joe) cut them off and cut them in half lengthwise. The nozzle throat, machined from graphite slug, performed very well during testing with only a small amount of slag buildup from the propellant, which combined powdered aluminum, ammonium perchlorate, and HTBP resin. The lower part of the nozzle, made from phenol-impregnated linen, also worked very well, building a pyrolytic layer that acts much like an ablative heat shield in a space capsule. The forward closure device, whose only job was to contain the hellfire and direct the exhaust somewhere other than up, rose to the challenge, although it took some beating. Of particular interest was the condition of the O-ring and how the igniter and closure were connected.
Post-mortems like this are valuable educational tools, and it would be heartbreaking to destroy something you’ve worked so hard to create, but you can’t improve what you can’t measure. Hats off to (Joe) for getting a glimpse into his world.
