Think BEagle's spelling is correct, JD. As you've picked up on this one, can I offer part of a piece I wrote a few days ago, but decided not to post in case it might be old-hat?
I'm deleting the VC10 bit, which you've just nicely covered. Here goes:
Imagine a wagon drawn by two horses, side-by-side. The idea is to ensure that they share the load equally. How do you make the lazier one do his share of the work? The solution is to attach their harnesses to either side of a transverse bar, which is pivoted vertically on the hitch of the wagon, and free to rotate. As the keener horse pulls ahead, the bar comes forward on his side, but pushes aft on the other side, increasing the load on the lazier horse.
This assembly is known as a whiffle-tree. If the angle of the bar reaches a set limit, as in the event of a failure of one feel-unit, a microswitch will activate a warning.
The BAC 1-11 also uses a whiffle-tree system for its rudder PCU (the only one on the A/C, if memory serves), supplied by 2 hydraulic systems. In the event of one hydraulic system failing, the other continues seamlessly to do the work, and a W/L illuminates. You are then invited to close a "kill lever" (can't remember what its proper name is) to isolate the rudder PCU from the failed (or failing) hydraulic system.