On YORF, Solomoriah reports a surprise when building a new Semroc Blue Bird One:
The engine tube is supposed to be a BT-50J, 2.75″ long, but the one in the kit is much longer. I forgot to measure it, but it’s either a 9″ piece or the 7″ (or so) main tube for an Alpha.
This is an issue because the kit does not include a thrust ring installation tool (i.e. fake engine casing) to push the ring into place. The instructions are still the original Semroc materials, and so do not explain what to do… Either the instructions should be changed AND the installation tool included, or the correct tube should have been in the bag.
I bought a Blue Bird Zero at eRockets in February, but hadn’t opened it before seeing this thread. Now I have opened it, and indeed mine too has the 9″ (I measured) BT-50:
So it’s not an isolated case of someone grabbing the wrong tube.
Solomoriah went on to say he’d done a simulation and concluded the Blue Bird Zero should fly well on an E9-6, so why not have a longer motor tube — but he’s right, the instructions should be updated and the installation tube should be provided for those who don’t have spent casings lying around.
Rich's Rockets 