Back Doman LZ-5 / YH-31, D-10B

Doman YH-31

The LZ-5 was similar to the LZ-4 but used a 400hp supercharged Lycoming 580-D engine, and had numerous detail changes. The first example was N13458 which flew on 27 April 1953. Doman gained a contract from the U.S. Army to supply two aircraft designated YH-31. These were evaluated following delivery in late 1953 but it was felt that the possible maintenance problems of the complex rotor system would cause problems with field maintenance. Consequently, the two aircraft were retired in 1958 following a period of use as executive transports. Doman also designed a small two-seat helicopter, the D-10, to an Army requirement. This would have been powered by an Allison 250 turbine but was not built.

Doman actually completed two more development machines in addition to the pair of YH-31s (N94561 and N812). The third aircraft was modified into a new variant - the D-10B - which had a turbocharged Lycoming HIO-720-A1A engine and minor changes and was the subject of a co-production agreement with Fleet in Canada. N812 became CF-IBG-X. A number of deals and production relationships were subsequently established by Doman in an effort to get the LZ.5 into production. Hiller were licenced to build the military version. Doman also entered into an arrangement with Ambrosini in Italy for them to market the D-10B and for production of 20 airframes to be carried out by Aeronautica Sicula at Palermo in Sicily with final assembly at Doman's factory in Danbury, Connecticut. A plan was also devised for Aeronautica Sicula to fit a D-10B with a Turbomeca Astazou turbine. The agreement with the Italians collapsed and a new company was subsequently established as Caribe Doman in Puerto Rico during 1966. Unfortunately, the LZ-5 was obsolete by this time as more modern turbine-powered helicopters flooded onto the market. A further company, Berlin-Doman was formed and a new project launched as the BD-19 but this was also stillborn and the Doman helicopters finally vanished into obscurity.

R.Simpson "Airlife's Helicopter and Rotorcraft", 1998

Doman LZ-5

The measurements and layout of this production model very closely resemble those of the hand-made LZ-4. The 8-cylinder supercharged engine is placed beneath the pilot's compartment; the crankshaft is inclined at an angle of 32 and drive engagement to the rotor is through a fluid coupling. The front cabin is big enough to take two pilots; the main cabin has room for six passengers with luggage, or four stretchers or cargo over an area of 3.7 square metres.

This helicopter has been supplied to the U.S. Army, where its official designation is YH-31. In order to speed up output for this outlet, Doman decided in 1953 to grant Hiller a licence to manu-facture the mechanical components of the military version, while Doman himself continues independently to produce the LZ-5 com-mercial version.

P.Lambermont "Helicopters and Autogyros of the World", 1958

Doman D-10B

In the spring of 1953 Doman Helicopters introduced their Model LZ-5 eight-place utility aircraft, the second of the firm's designs to incorporate a novel non-articulated, sealed rigid rotor system. The Army purchased two aircraft (serials 52-5779 and -5780) in late 1953 for service test and evaluation with the designation YH-31. The type'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. There was therefore no further YH-31 procurement, 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.

S.Harding "U.S.Army Aircraft since 1947", 1990

Doman LZ-5 / YH-31, D-10B

Technical data for LZ-5

Number of seats: 8, engine: 1 x Lycoming 580-D rated 400hp, rotor diameter: 14.64m, length: 11.57m, height: 3.12m, gross weight: 2363kg, empty weight: 1297kg, maximum speed: 169km/h, cruising speed: 138km/h, rate of climb: 396m/min, absolute ceiling: 5490m, range: 392km

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Anonymous, e-mail, 20.03.2021reply

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Steve doman, e-mail, 03.01.2011reply

Its always mind settleing to find other people, with your name, that has done great things! It doesnt matter if this man's dream did not come fully around to be reconized as a world mover in aero industries, he did something great!

Don, e-mail, 24.06.2010reply

Interesting design, looks kinda like either a leaf-eating aphid bug, or a flying school bus. It must have depended on repelling the earth by its shear ugliness, rather than depending on the underpowered Lycoming recip running most likely at full MP to barely remain in a HIGE hover, probably near sea level, with 7 clueless passengers who I'm sure thought that was the coolest thing they've ever rode in, as shown in the top photo. No engineer today could ever come close to matching such creepiness in design ettiquette. Poor guys had no turbine engine yet available to design a proper bird around. The 50's were a weirdly innovative time for sure.

jean, e-mail, 23.02.2010reply

I have 15 shares of common stock. Is it worth anythings?

Steve Doman, e-mail, 17.06.2009reply

In March of 2009, the last surviving Doman YH-31 /VH-31 was moved from the Classic Rotor museum in Romona, CA, to the New England Air Museum in Windsor Locks, CT and is on display there.

Steve Smith, e-mail, 25.01.2007reply

The last Doman YH-31VH-31 survives and is on display at the Classic Rotor museum located in Romona, CA

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