View Single Post
Old 03-05-2006, 09:43 PM
David Simmons David Simmons is offline
Charter Member
Join Date: Nov 2001
Posts: 12,684
Originally Posted by zut
But remember that the conveyor responds to engine thrust with a change in acceleration, not just a change in velocity. For example, you calculated a nominal required acceleration in your linked post, based on some mass and thrust assumptions.

If we ignore physical limitations for a second, then what would happen in a perfect system would be that the plane's engines would light off, the treadmill would respond with the constant acceleration that you calculated, all the forces would balance, and the plane wouldn't move. Right?

In a less-than-perfect control system, there would be some lag in the response. So the plane's engines would light off and the plane would surge forward slightly before the treadmill had a chance to respond. The control system would register the increased wheel speed, and respond with a larger treadmill acceleration than the steady-state acceleration you calculated. The increased acceleration would transmit more force to the plane, slowing it down, until plane speed = 0. Then wheel speed = conveyor speed (even though both are still accelerating!) and everyone's happy.
I would like to see a computation. I think you are describing a Type 1 velocity system that will track a constant velocity with zero error and I'm not sure that this setup fits that description.