Some internet guff by GT about it all (excerpts about Unified Control Law by John Farley are available)....
Test Flying The Joint Strike Fighter 17 Jun
2011 Graham Tomlinson
Test Flying The Joint Strike Fighter
"The STOVL mode control system is derived from ‘Unified’ developed by the ‘RAE’ on the VAAC Harrier. The throttle commands acceleration and deceleration (or thrust on the ground and in the STO mode, and in all conventional modes); in the hover the stick moved backwards/forwards commands upwards/ downwards vertical velocity (or pitch rate elsewhere); in the hover the stick moved from side to side commands bank angle (or roll rate elsewhere) and if released returns the aircraft to wings level; in the hover the pedals command yaw rate (or sideslip elsewhere).
Future development will clear full envelope autopilot/auto throttle, automatic deceleration to a spot, and TRC (translational rate command) which in the hover allows the pilot to make small positional corrections easily, and will then bring the aircraft to a standstill if the pilot releases the controls. A pilot’s helmet mounted display (HMD) is fitted instead of a HUD.
In the Harrier the pilot must obey the rules. The F-35B flyby-wire system gives angle-of-attack and sideslip control, and departure protection. Further pilot workload reduction is given by performance deficit protection, conversion speed window protection and FOD protection warning; and flight test has a watching brief on the requirement for possible tail strike protection during slow landings (currently not considered necessary [2011]). Pilot cognitive errors (of trying to control thrust with the throttle) have been mitigated in the design...."
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History of Unified Control Law development (and alternatives) here:
A V/STOL FLIGHT CONTROL JOURNEY ENABLED BY RAE SCIENTISTS by John Farley
2006
http://www.rafmuseum.org.uk.nyud.net...rier-Story.pdf (25Mb)
“...UNIFIED. Unified was the most radical mode. Here the pilot pulls back on the stick to go up and pushes to go down, regardless of airspeed. At all speeds above 40 kt ground speed the stick commands flight path rate and so relaxing it to the centre position when the aircraft is flying level maintains height. If the aircraft is in a climb or a dive, relaxing the stick maintains the existing climb or dive flight path angle. As the aircraft decelerates through 40 kt the stick response blends to become a height rate control by 30 kt ground speed so, in the hover, with stick centre commanding zero height rate, it appears to the pilot as a height hold.
When flying up and away lateral stick commands roll rate. This blends between 130 and 100 kt to become a closed loop roll attitude control, so that relaxing the stick to centre below 100 kt commands wings level. Above 40 kt ground speed the rudder pedals command sideslip. Decelerating below this speed the pedals blend to a yaw rate command by 30 kt, providing a heading hold in the hover with feet central.
A throttle-type left hand inceptor, incorporating two detents, commands longitudinal acceleration.
Putting the inceptor in the centre detent holds the current speed. Acceleration or deceleration is selected by moving the lever forward or aft of the detent, with full travel demanding maximum available performance. Decelerating through 35 kt ground speed starts a blend and below 25 kt the aft detent commands zero ground speed. Either side of the aft detent gives the pilot a closed loop control of ground speed up to 30 kt forwards or backwards.
In summary, if the pilot centres both the stick and throttle when flying on the wings, the aircraft holds the existing speed, bank attitude and climb or dive angle. In the hover, centralising everything maintains the existing hover height, position and heading. Such hover characteristics are the stuff of dreams for every Harrier pilot at the start of their conversion...”