On TRF Les had an unstable Quinstar flight with a D12-0 engine.
Some thought maybe it got hung up on the launch rod, starting to spin on the way up.
For anybody interested in a 24mm conversion,
Here's my TRF response -
I've launched my Quinstar with both C6 and D12 engines. My flights were stable.
I've attached a picture showing a D12 engine installed and how far it extends, 1/4" out the back.
Also shown is the 18mm adapter. The upper end slips inside the 20/50 centering ring used as an engine block.
With the 18mm adapter the casing extends 3/8" out.
To see the entire Quinstar build conversion from finish to the start: CLICK HERE