September 1966: Pictured is the eight-place utility helicopter known as the H-31. Manufactured by Doman Helicopters Inc., Danbury, Connecticut, it featured a single Lycoming SO-580D of 400 hp. Rotor system consisted of a four-bladed main rotor and a three-bladed tail rotor; with all the blades made of wood. The rotor system was completely sealed, rigid and non-articulated. Commercial designation for the aircraft was LZ-5. The Army procured two H-31s in 1952 for purposes of evaluation.