motor mount tube

What are the design considerations for a LPR motor mount? What determines the length of the tube and placement of centering rings? I notice in kits the tube usually extends well past the thrust ring. Any reason for that? (I'm not talking about stuffer tubes, just an extra long motor tube.) Would...

Hello fellow rocketeers, hope you are doing well. As I kept designing my future rocket, one doubt came into my mind when looking at my BT and MMT. First of all, my BT is 1,968" OD and 1,85" ID; my MMT is 1,574" OD and 1,496" (38mm) ID. The thing is, there is only left 1 3/8 or 1,377" (3,5 mm)...