1-2 years ago had a great helicopter 3d pilot crash close to the flight line and pieces of helicopter blades and parts flew and hit some people in the pit/observation area...and that prompted the president and owner of the field to push the flight line from 20 yards from the pit to 50yards. After that he was pretty vocal on how dangerous 3d helicopters can be and how he didn't really care for them. Especially when most operators fly the heli's right close to their face. Any r/c platform whether airplane or helicopter can fail and become a lawn dart. I don't mind them at all and like to see them fly, but I'll admit when they are flying when I'm flying I land and watch out!