I was browsing through some pictures of tandem helicopters and some of the older pictures of Piasecki tandem helos appear to not have gearbox synched rotors as seen in most the later Piasecki tandems and of course Boeings follow on tandem of the chinook and sea knight where the rotor blades pass in between one another. So this would leave me to believ that Frank Piasecki's early tandem helos had just enough clearance between the blde tip path plane so as not to require gear synching.
I went to the Piasecki Aircraft page and thumbed through their history and found this statement regarding the "XHRP-X":
An autorotation was done by having the "interconnecting shaft between rotors disengaged as well as disengaging the engine." So, if the blades had been synched (with the blades passing in between one another), disengaging the interconnecting shaft could allow the blades to eventually strike one another as the rotor RPMs would be different between each rotor disc given the changes in relative wind passing up through both discs.
This leads me to believe that the rotor systems were not synched in the earlier platforms. Just some random thing that I noticed. Further comments from anyone?
Από κάθε γενιά μεταξύ κάθε έθνος ανθρώπων, να θυμάστε νεκρών στρατιωτών μας.”
The Platt-LePage XR-1 and XR-1A lateral tandems were not synched, and was part of the problematic early control system.