I remember seeing the S-69 ABC do a fly over at the family day air show sometime in the 70’s. I also have or had pictures of the S-67 Blackhawk doing a loop over Long Island sound. Really cool aircraft.
I was up at the Sikorsky factory back in the 70’s on a visit pertaining to the CH-53D. While there, they gave me the Grand Tour of the ABC.
It had THREE swashplates! One for each rotorhead and a third on the BOTTOM of the transmission to vary the relationship between the two main swashplates to give the helo YAW control!
Wild!