The S-56 (also known as the Sikorsky CH-37 Mojave), was born in the 1950's and was one of the large piston engines ever made. It was retired about 10 years later and gave way to helicopters such as the CH-53 Sea Stallion.
This is a companion discussion topic for the original entry at https://www.helisimmer.com/video/video-s-56-blade-bending-in-flight/