Some jets fly quite nicely from grass. Obviously, the smoother, the better.

Having said that, some of the concrete runways I have flown off, are rougher than the grass field I regularly fly from (and it is rough). The advantage is that they are 1000's of feet longer.

The newer generation jets AV8R, Super Reaper, Facet, Reaction, etc are probably better suited to grass than the zippy sport models

A FOD guard is a must in my books. My turbine sucked a passing bug out of the air the other night, but the screen stopped it from going through the engine....