Originally Posted by M2dude
Concorde had triple-axis auto stabilisation, where pilot demands were routed via an AUTOSTAB COMPUTER and summed with any stabilisation demands.
Allow me to nitpick a moment.....
Pilot demands in manual flight produced electrical signals corresponding to the control position, which were sent to the 'servo control amplifiers' (eight in all, one per control surface) which in turn commanded the PFCUs (power flying control units) that hydraulically moved the control surfaces.
Autopilot demands directly moved the pilot's controls (stick and rudder) via hydraulic cylinders (the 'relay jacks') so that the same signals as in manual flight then went to the servo control amplifiers.
The purpose of the autostab was to provide proper dynamic stability over the full flight envelope. The aircraft could be flown without autostab, but over some of the speed range it was only marginally stable.
The electrical signals from the autostab computing were fed directly into the servo control amplifiers, so there was no feedback to the pilot's controls, unlike the autopilot demands.
There was occasional confusion about exactly what did what and how and where.... because the servo control amplifiers - although a function independent of the autostab as such - were housed... in the autostab computers.
To complete the tale, this is what those servo control amplifiers look like.
The one of the left is from prototype 002, the one on the right from a production aircraft. To give them scale, the one on the right is about the size of a box of large kitchen/fireplace matches.
CJ