After receiving a layoff from Sikorsky Aircraft, I had the opportunity to work for Glidden Doman in 1959 - 1962.
He had originally worked as an engineer for Sikorsky Helicopter and had proposed a new transmission/rotorhead design which was not readily accepted by the engineering department of Sikorsky Aircraft. He had faith in the theory of his new design and soon left Sikorsky to find his own company. All of the dozen or so of us working at Doman Helicopters had faith in the design which was remarkable. Most helicopters of the time had a massive gear reduction at the reciprocating engine and power was transmitted to the transmission/rotorhead as low speed/high torque via a hollow shaft of 5 to 6 inches in diameter.
The Doman design had engine gearing that sped up the output RPM to transmit power via a solid shaft of about 1 and a half inches diameter at a high revolution. The force being transmitted was low torque/high speed.
The rotorhead transmission was completely enclosed. All mechanical linkages were housed within the transmission body which gave the appearance of having the rotor blades project from the large transmission "can" which sat above the fuselage. The efficiency of the design allowed the Doman helicopter to carry a much higher payload and it was much more efficient at altitude. It was the only helicopter of the period which had the ability to cross the Andes Mountains carrying a payload. Many of the records then set remain unbroken.
Test pilots reported the absence of high vibration and ease of control. Due to it's stability, the craft could be flown without having a death grip on both yoke and cyclic sticks.
War is the father of all great developments, and if Doman could have survived into the Vietnam War era we would see the Doman design as the standard of today's helicopter.
The system was patented and information may be attained through the U. S. Patent Office. As these patents have now expired it may be time for someone to resurrect the design.
