The Gyroflex Rotor employed special balance weights fitted to the roots of the rotor blades instead of flapping or lead-lad hinges. The Filper Helicopter had fore and aft rotor pylons and the pilot sitting stride a central beam which served as a load bearing beam.
An Allison light 250 C 18 powered the aircraft.
Filper moved to Reno, Nevada and then later closed down. No FAA certification was ever achieved despite the fact that there were dozens of prototypes built. It flew in 1966. In 1969, Filper closed.