I think the key phrase is conventional wisdom.  There's no doubt that dirt and such will eventually wear out an engine, all evidence suggests that it's going to take a long time to do that on a rotary in our application.  As you likely know, Tracy has never had a filter, and flies off a grass strip.   I can't think of anyone who's verified damage from anything that came from outside the engine, though it can certainly happen.   

 

Rusty, And Group,

 I don't know of a aircraft example, but I can tell you my old racing partner ran his brand new Yamaha TZ 250 on a just swept race track and had a guy crash in front of him.  There was enough rocks and dirt kicked up that he ruined both cylinders. After wasting that $1000 he never ran without a trash screen again. It CAN happen to you even on a relatively clean strip. Run at least the Mooney system.

Bill Jepson