Txmustangflyer

And going minimum distance isn't neccesarily always a good idea. Probably can get closer with aluminum vs carbon fiber. I'd have put it at close to max distance, myself. ..I tend to be conservative onnthose types of things until I see how it acts later. Just seems to me that if you have any object that purposely generates flame and heat that more is better at first...

Can always move it closer later, hard to move it closer if the plane went up in smoke..

The OP wants to blame CARF because he thinks a designer is going to design something that works for every single application. Its like saying a Chevrolet car should be able to use a ford engine direct bolt in without requiring modification. It don't work that way.

I'm betting, with a bit of exploration, we'd probably find a set of specs for that bell that states max temp, and I'm betting at 22 mm his turbine exceeds that threshold by a ton. The exhaist gas temp starts to really shed temp when it exits the turbine, but the closer to that nozzle you are, the hotter it is. During his bench run, might have been a goid idea to check it to figure out how to mount to keep the bell from melting.

Boils down to wrong application and lack of knowledge maybe? Or just in a rush to fly...