Originally Posted by
MurphyWasRight
Thanks, that is roughly what I guessed from the diagram, works by balancing the control input and servo output to a "zero'' at the pilot valve, in electronics same as an op-amp.
So Is this roughly correct?
If the control path disconnects the system could be rigged to settle on the 'aerodynamic neutral' mentioned above.
If the feedback path fails then the servo will likely continue to be driven to a stop since there is no (or at least incorrect) input at the pilot valve.
I believe you are correct though I'm not entirely sure about the 169 TR Servo. Often the servos are made so that the pilot valve is spring loaded (for want of a better term) to neutral. That doesn't mean the servo goes to neutral. It means the servo stops moving, wherever it may be at the time.
If the feedback path fails, as I see it on the diagrams, then there is nothing to tell the pilot valve to stop porting fluid to the servo. So it would, in theory at least, go full one way. What I don't know is if manipulation of the pedals could still operate (albeit very roughly) the pilot valve, thereby controlling the servo to a certain extent. You'd have to try that on a 169 with a hydraulic cart hooked up. I also don't know if the servo will self-center if the feedback loop is disconnected.
In other words, if the lever is no longer connected to the servo through the feedback attachment, is any self centering force on the pilot valve enough to overcome the weight of the lever? If yes, then the servo should stop where it is. If no, then it may be possible for it to keep on moving to full extension.
I do not however know the answer to that.