Barry
It was originally devised for the steering of motorcars but I’ve found this site that explains the science behind the principle as applied to aircraft controls.
http://members.cox.net/bdfelice/Ackerman/ackerman.htm
Grahame
*** Grahame fascinating stuff,like the writer says I too have been introducing this into my control systems without even realising it in the past,also note how the Futaba rotary arms also allow for Ackerman in being pre marked as such ready for drilling,one important thing to remember is the introduction of standard differential to ailerons via cranking the horn forward is nothing to do with the Ackerman principle it only applies if a closed loop system is introduced,but what a useful system it really is.
Differential is a way whereby the upgoing aileron has more throw than the downgoing to avoid aileron reversal as the worst scenerio ( usually happens with aileron wings having some dihedral )
I only mention this to avoid confusion between the two.
The explanation & drawings on that page are first class and well worthy of study.