MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
The rough edges in the picture are from a poorly printed raft and not the exhaust of the engine.
Recommend that you use a strip or two of electricians tape (or even masking tape) to add a little friction to the rocket engine and prevent it from sliding out.
I was able to launch successfully three times using Estes A8-3 engines. I would not use anything more powerful because the rocket is light and prone to angling off in the sky.