Im pretty certain this is an old subject but I'm looking for ideas on what causes mostly higher speed aircraft such as jets to begin porpoising (rotating up and down) in climb and decent while in Autopilot mode. It stops as soon as the A/P is disconnected. Its happening with any including default Lear, etc. The higher the speed, the more violent it gets.

Weight and Balance is off and the autpilot cannot make timely corrections. I forgot what I did but it had to do with some minor modifications to the autopilot response in the aircraft.cfg file. Or of course change your fuel and payload to better balance the aircraft. Hope that helps a little--

I had this problem with the NGX and while Jim might have had a weight and balance issue, mine was fixed after a FSX reinstall. :huh: