Shackman
Herc engines were electronically "synchrophased" ... synchronised first, to all run at exactly the same rpm, then "phased" so that the blades lead or trailed the "master" (either inboard could be chosen) by an exact amount of degrees. This ensured (or so the blurb said) that the noise levels / vibration levels were at a minimum throughout the airframe .. originally not done for crew/passenger comfort at all .. but as a way of reducing airframe fatigue !!
FE's were required to know how the system worked, but in reality it was "select a master on the switch, if it all works, leave it alone ". As the system was quite complex there were several more complicated procedures for restting/fault handling, but generally it was a pretty good system.
Hours of fun asking/answering complex questions during a ground cat!! (NOT !!)
