That was about two years ago and Theo doesn't remember it at all. That was a new motor that used an existing aero shell that had to be extended a bit to fit the new motor. The whole process of designing and building a rocket is fun for me and actually getting out and flying it is the icing on the cake. Since Theo loves tinkering out in the garage as much as I do, we're going to design and build this from scratch. We don't plan on re purposing any existing pieces, other than maybe some of the electronics. While it may take a little more time with Theo's "help". Did I ever tell you about the time I thought he was cleaning up on the other side of the garage but was actually bungee cording my motorcycles together. Despite any setbacks we may encounter, I'm really looking forward to going through the whole process with him. I'll try and document the entire process here.
Theo's requirements are that the rocket be big and orange...maybe with some blue. With that in mind the motor is going to be based on this N-class motor that I designed, built, and tested a while back. You can see that motor by going here. The biggest difference is that the TR-1 motor will utilize EMT for the motor casing. As you may or may not know, EMT is one of my favorite motor casing materials. I'm not sure why, I think it's because of other peoples attitudes towards it. I discussed my feelings about EMT, or steel in general during the development of my last motor (the one pictured above), you can read that by clicking here if you're interested. The biggest advantage that I'll get from EMT for this motor is that I can use a standard four inch mailing tube for a casting tube. Four inch EMT actually has an OD of 4.5" and with a wall thickness of 0.083" the ID should be around 4.334". That should allow for a few wraps of rosin paper to be used as an insulator, like I did in the my other design. Though with EMT this isn't necessary for the casing, but will help cut down on the heat transferred to the aeroshell. My initial 4inch motor had and ID of four inches and I was rolling the casting tubes by hand, very time consuming and messy. Using Richard Nakka's "casing" spreadsheet I found that 4 inch EMT has a burst pressure of 2573psi. With a design pressure of 1050 PSI I end up with a design safety factor of 1.7 and a burst safety factor of 2.45, pretty conservative.
I did an initial SRM design, summarized here:
While my previous N-class motor was on the edge of the M/N class this new design ends up solidly in the middle of the N-class and should provide for an awesome experience.
More to come...