On a quick glance over the system, seems that you are adding three aditional points of failure:

The two extra critical linkages on the servo bridge and the posibility of one servo failing and going at one end of his travel arc.

As this is not resolving the problem of retaining the same amount of travel even in case of a optimal servo failure, the plane will probably turn incontrolable too... and having a dual rate switch to quickly overcame this will imply in having half the amount of the force applied on the surface on standard operation mode wich is a bad idea. Another built in disadvantage is the greater amount of slop on this system.

As far as I have seen, the best way to give safety redundancy on a single air surface is installing two brutally strong servos on it, wich in case of failure of one of them will still have enough torque to move the surface with all the flight loads and a dead servo thru the full travel.


Back in 1990, I had a giant scale Citabria using this.. but that was because there wasn´t strong servos available at the time!