|Object Name:||Pitch Relais Jack Sensor|
|Year of Manufacture:||circa 1967|
|Location:||Archive Object Store|
Unit: Relais Jack Sensor - Pitch
Ser No. 06
The position transmitters on the flying control hydraulic booster jack are known as ‘Relais’ jack sensors. These produce two-wire synchro information on stick position for the autostabiliser and autopilot.
There is a separate unit for each axis of flying control movement i.e. pitch, roll and yaw.
Each unit carries the necessary synchros for channels 1 and 2and command and monitor computing. The units therefore incorporate design techniques aimed at minimising the common failure probability.
The units are mounted on the auxiliary hydraulic servo unit earth point and auxiliary servo extension is transmitted via a trailing link to the sensor input arm.
Each Relay Jack is a twin-ram, electro-hydraulic actuator. Each ram's displacement in speed and
direction is controlled by a spool valve. Each spool valve is monitored for jamming by a detector,
linked to the BLUE jam light (if the corresponding ram is supplied by the Blue hydraulic system), or the GREEN jam light (if the ram is supplied by the Green hydraulic system).
The detection of a jammed condition automatically signals the relevant Relay Jack hydraulic
selector to shut, thus removing hydraulic power (normal or standby) from the jammed side of the
relay jack. This automatic shut-off ensures that a flight control axis cannot be frozen by this single
Each Relay Jack is also used as an Auto-Pilot input point.