In 1945, Glidden S. Doman formed Doman Helicopters Inc. in order to develop various helicopter engineering concepts. These included a new hub system which was essentially similar to the mechanism used on a variable pitch propeller. The rotor system also incorporated a gimbal mounting to provide the necessary tilting of the rotor disc. Doman's theories were tested initially by installing an experimental system on a USAF Sikorsky R-6. This helicopter was known as the Doman LZ-1A and it started flight tests in early 1950 with remarkably good results. It was followed by the larger LZ-2A Pelican.
Doman's system was then designed into a larger helicopter that was seen as a viable commercial production machine. The LZ-4A had a capacious fuselage with three rows of double seats in the main cabin and a two-crew flight deck in front. Large folding doors provided access for loading bulky cargo into the main compartment. The tail boom was conventional with a cranked-up rear section mounting a tail rotor, and the LZ-4A sat on a four-leg undercarriage with trailing link dampers. A 400hp Lycoming SO-590-B engine was positioned in the lower nose, driving the four-blade rotor via a flexible transmission. Following its first flight in November 1950, and subsequent testing, Doman moved on to the improved LZ-5 and transferred the LZ-4A (N74147) to Curtiss Wright as a test vehicle.
R.Simpson "Airlife's Helicopter and Rotorcraft", 1998
The LZ-4 is the engineer-produced and hand-built prototype of the LZ-5. Built specifically for research purposes, it was taken over by Curtiss Wright, where it was given the designation of CW-40. The LZ-4's maiden flight took place in November 1950.
P.Lambermont "Helicopters and Autogyros of the World", 1958
Technical data for LZ-4
Number of seats: 8, engine: 1 x Lycoming SO-590-B rated 400hp, rotor diameter: 14.64m, length: 11.7m, height: 3.41m, gross weight: 2165kg, empty weight: 1343kg, cruising speed: 125km/h, rate of climb: 244m/min, absolute ceiling: 4880m, range: 336km