The four blade tail rotor on the 500 dates as far back as 1969 with the early testing for the OH-6A “Quiet One “ experimental helicopter. I think they started testing the 500D 4-blade tr in 1977 with the first customer delivery in 1979. If you have ever heard the difference in noise output from the 2- and 4-blade tr, it is significant!
This new blade system on the 564 is not a low noise system but runs at standard rpm, according to Ryan Weeks. Will still be interesting to see if it is a bit quieter than the 530F tr. The 4-blade tr on the A/MH-6M is different again from the 564 tr.