April 2014

2014 AprilDoman LZ-5

The Doman LZ-5 was a utility helicopter developed in the United States in the early 1950s by Doman Helicopters Inc. of Danbury, Connecticut. The LZ-5 utilized an unorthodox gimbaled rotor head system which featured the elimination of rotor hinges and dampers and included blades of soft-in-plane dynamic design. The servo control system was entirely contained within the rotor head, with no external oil tanks or plumbing. The tail rotor was also hingeless and free floating to eliminate stresses during rapid tail rotor turns. The cockpit located the pilot and co-pilot over the engine with a six-passenger compartment located directly behind. The engine was cooled by exhaust ejectors, producing an energy saving that increased payload by approximately 800 pounds. The aircraft featured a four wheeled undercarriage.

The first prototype flew on 27 April 1953. The Army purchased two aircraft in late 1953 for service test and evaluation with the designation YH-31. Eventually, the Army concluded that they had no requirement for an additional piston-powered helicopter model in this size category, and no further orders were placed.

The Doman’s unique rotor system was found to provide only a slight increase in performance over that of other, more conventional systems, and was also judged to be more difficult to maintain under field conditions. Consequently, no further YH-31 procurement occurred and the two service test machines were ultimately converted into VH-31 VIP transports and used in the Washington, DC area until their 1958 withdrawal from the Army inventory. The LZ-5 never entered production.

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