Which is why a picture always helps at the start...
The
following paper gives some detail.
As I recall, the original idea passed into the flying game via DAC and, because it turned out not to be patentable, has found a reasonably general application.
Further (if my recollection is correct - I'd left the organisation some years prior so I don't have any detail) the first Nomad fatal mishap (Avalon) in the late 70s (in which Dave and Stuart were killed and Patrick severely injured) involved the use of a similar modification in an attempt to work a fix for the flap 20 long stab problem on that aircraft .. so the idea goes back a ways. The suggestion was that the lack of research data probably didn't help the fix attempt .. If
djpil sees this thread, he may be able to add some details.