Thanks for the link.

3 Re: Circular motion in vertical plane  from ahmedelshfie ( [url=http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1887.0]http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1887.0[/url] ) is a good one to start with.

Most simulations I can view without problem.
Some stay black The mentioned one is playing now. I hope it will stay like this.
Thanks again