People have. There are all kinds of videos on YouTube, but none of them really show much of anything. Someone needs to do this experiment with a radio controlled jetliner on a conveyor system a-la Mythbusters.....Hopefully they'll reply to the email sent to them...

I just don't understand how it is so difficult for people to understand the forces being acted upon and the forces at work here....I've said it many many times.....

The conveyor belt puts a force on the wheels, NOT the engines. The engines are completely indepentant of the conveyor. The conveyor WILL NOT provide any resistance to the engines and the engines will continue to pull the airplane forward, thus creating lift, thus allowing the plane to take off. What's so difficult about that?!?