You know, we must have a telepathic connection :-) I was thinking after I did the post .. I just updated to the latest firmware on the 18MZ (since they fixed the british units zero bug on the airspeed) .. "I wonder if it was not originally there and appeared after an update". That way I get feel better about not having a lousy memory. But way too much trouble to go reload old firmware to check!
I kind of got the impression that with the larger channel count on the 18mz that Futaba was moving away from multiprop but maybe not. I always amazes me how how fast jets (especially scale jets with speed brakes, operating canopies, tail hooks, parachutes ... etc etc) can eat up channels and the MPDX-1 is such a nice solution to trading update speed for add'l proportional channels for non-flight-critical functions.
Thanks for the pointer to the writeup. I have a theory of how it probably works, I'll go check it against your writeup .. nothing like real data and real analysis!
And of course I am +always+ interested in what you have cooking if you are willing to tell about it...
Dave