The HSS-1 and later the H-34 had an Automatic Stabilization System (ASE) that was based on the Lear auto pilot that was originally installed in the North American F-86. On the Navy version it had Barometric hold in that it would maintain a fixed altitude. For SONAR dipping it had hydrostatic sensor in the SONAR ball that would maintain a fixed depth for the SONAR ball. In heavy waves as the water pressure changed the helicopter would ride up and down with the waves. It also had a directional hold and it had the capability of maintaining a fixed attitude, which was in reference to a fixed cyclic position. It also had sensors that detected movement of the SONAR cable due to moving water current. These sensors would send a signal to the ASE and it in turn would move the servos to make the helicopter move with the current keeping the SONAR below the helicopter. In essence it was an autopilot but it had no SAS/SCAS capabilities. If as Nick said it had auto hover capability I don’t know, as this inclusion would have been made long after I left the program.
On the Apache the normal control inputs by the pilot into the servos was by mechanical push-pull tubes into the mixing unit and then into a servo pilot valve that moved in relation to a fixed servo valve spool. If the pilot moved his controls too quickly LVDTs attached to his controls would send a signal monitored by the control section of the air data computer. If the control movement were sufficient enough to cause heavy stresses in the airframe this signal would be processed and sent to the SCAS servo, which in actuality is the spool on the servo. The spool would move in relation to the pilot valve and in effect moderate the pilots input so the end effect was a smooth input and not causing overstress of the airframe.
If for any reason any control lane became jammed the pilot would force the control until he broke a shear pin. In doing this, two micro switches would be enabled causing the mechanical input to the effected servo to be locked out. Then, any movement of the controls would send a corresponding signal from the LVDTs through the air data computer and then to the SCAS servo valve moving the spool in relation to the fixed pilot valve resulting in the correct movement of the servo. This is a SCAS. Many commercial and military aircraft have similar control systems. I believe the concept was developed by Bertea.
I do not believe the other systems described are the same.
