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Feature Article

Doman Helicopters: Unsung Innovations, Part 1

By Ken Collinge with contributions from Glidden S. Doman

One of the lesser-known pioneers of the helicopter world is Glidden S. Doman who developed new concepts in helicopters. Doman was born in 1921 and was a 1942 engineering graduate of the University of Michigan. As an employee of Sikorsky Aircraft, he formulated his own ideas about helicopter-rotor-head construction but because the company did not accept them, he decided to develop them independently. He established a small shop in a barn on the Sniffen family farm near the Chance Vought Division of the United Aircraft Corporation in Stratford, Connecticut. This is the current location of the Connecticut Air and Space Center on Sniffens Lane.

Doman founded the Doman Helicopter Company on August 31, 1945. He succeeded in interesting the government to the extent of obtaining a new Sikorsky R-6 helicopter on loan from the Army. With $30,000 of shareholder money, the aircraft was modified to accept his rotor system. It featured a hingeless, four-bladed, gimbal-mounted, semi-rigid rotor. In later versions, it was to have reduction gearing in the rotor head above the hub. This first Doman helicopter, designated LZ-1A, first flew in 1947. Strain gauge data taken on the first flights led to a $70,000 U. S. Air Force contract for highly instrumented flight tests and enabled the company to move to expandable quarters on the Danbury airport. The aircraft made many long-distance flights and demonstrations, including to Washington, DC, in efforts to raise financial capital. During one witnessed cross-country trip, it flew 40 minutes during which the pilot did not touch the cyclic pitch control. That was without servos or autopilot! This LZ-1A is now displayed in the New England Air Museum at Windsor Locks, Connecticut.

Designed and developed by Sikorsky and converted to this configuration by Doman Helicopters, Inc., this U.S. Air Corps R-6A is one of about 200 produced by Nash-Kelvinator just before the end of World War II. They were powered by 240 h.p. Franklin O-405-9 engines.

During 1948 and 1949 there were various proposals to license the use of the rotor on other helicopters then in development, usually where vibration was a problem. Then, Curtiss- Wright Corporation bought a limited-term patent license and, under an engineering service agreement, financed the construction of the LZ-4, a quickly built 400-horsepower prototype intended for research and development. In November 1950, the LZ-4 made its first flight and was re-designated the CW-40. The Army Signal Corps flew the CW-40 and proposed to purchase a cleaned up version under Civil Aeronautics Authority (CAA) certification, thus avoiding Air Force handbook engineering. However, Curtiss-Wright was then closing its Airplane Division and declined to make a proposal. Curtiss took the CW- 40 to New Jersey and, despite preservation efforts by the New England Air Museum, eventually scrapped it. Undeterred, Doman contracted to develop a successor, the LZ-5 / YH-31.

The prototype Doman LZ-5 / YH-31 was an eight-seat model powered by a Lycoming SO-580 supercharged, six-cylinder, horizontally opposed engine of 400 horsepower. The Army, in support of the YH- 31 program, also financed development of an improved, turbocharged, eight-cylinder, horizontally opposed engine, the THIO-720. More than 10 of these engines were built in anticipation of the Army plan to purchase 10 helicopters. The status of this engine program is not known, nor is it known if any engines of this model were installed.

Two YH-31-DM aircraft (S/N 52-5779 and 52-5780) were delivered to the US Army Aviation Test Board at Fort Rucker, Alabama. First flown in April 1953, the YH-31 had the unique Doman rotor with the final stage of reduction gearing above the hub. The 48-foot-diameter main rotor had four “plastic bonded” wooden rotor blades. The tail rotor was also hingeless and gimbaled.

Doman LZ-5/YH-31-DM (S/N 52-5780) in flight, Danbury, Connecticut. Source: Doman Helicopter, Inc., via Ken Collinge Archives

Although there was some long-lead-time component procurement for 10 helicopters, the Army had only funded 2 in the first year. Those two were under construction and headed for CAA certification when the Air Force intervened and blocked the follow-on activities. Looking for ways around that dilemma, perhaps through the commercial market, financial assistance was obtained through a Canadian joint venture, Doman Fleet Helicopters Limited. Tooling and parts were sent to Canada where an LZ-5 was constructed. One result was that the design was certificated simultaneously in Canada and the United States. There was a joint effort toward commercial sales, but Fleet dropped out when its production of F-86 wings was terminated. Doman Fleet Helicopters was dissolved and ownership of the helicopter passed to Doman where the craft had a long career through modifications and sales efforts.

With any prospect of quantity production canceled, the Army was reluctant to take delivery of its two helicopters. However, due to interest in the technology, it was persuaded to take them to Fort Rucker and fly them through the Board Six evaluation program. The resulting report stated, “[N]o requirement, needs a turbine engine, needs to be handbooked etc.” However, the Transportation Corps then took them, re-designated them VH-31, and flew them extensively until one was damaged by pilot error. The other aircraft was then purchased by the Navy and flown for a year or so at Patuxent River Test Center amid talk about applying the rotor concept to other Navy helicopters. That ship eventually was bought back by Doman and put in civilian paint. It is now on loan to the Hiller Aviation Museum at San Carlos, California, where it has been put back into the H-31 Army configuration. This action by the museum recognizes Hiller Aviation’s involvement with Doman as the Army’s planned production facility for the YH-31. (To be continued.)

Look for Doman Helicopters: Unsung Innovations Part 2 in the next NEAM news and on the NEAM Web site..

Glidden S. Doman contributed greatly to this article. He has retired from his helicopter career but continues to be active in the design and development of multi-megaWatt wind turbines. He lives in Granby, Connecticut.

Ken Collinge is gathering material for a history of the Stratford Lycoming gas turbine engines where he was an engineer for 37 years before retiring to Trumbull, Connecticut. He is a member of the New England Air Museum, the Connecticut Air & Space Center, the American Helicopter Society, and a Director of the National Helicopter Museum.