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Hiller UH-12 / H-23 / HTE-1

 

 

Stanley Hiller Jr designed the Model 360 which has enjoyed considerable commercial success since its first flight in 1948. It was derived from the UH-5 which had proved very unstable during trials and had subsequently been fitted with a new stability system patented as the Hiller 'Rotormatic'. It entailed fitting the two-blade rotor with two small paddles which acted as a control rotor and were also connected to a hanging stick. This servo 'paddle control' system tilts the rotor head and actuates the cyclic pitch control.

The Hiller 360 received its FAA (Federal Aviation Administration) approval in October 1948 and a year later a production model designated Model 12 made the first transcontinental helicopter flight across the USA. At that time it still had an open cockpit, and the 178hp Franklin 6V4-178-B33 was in an open engine bay.

 

Known as the Hiller UH-12 as Hiller had become part of United Helicopters, the Hiller UH-12, incorporating a two-bladed main rotor and a two-bladed tail rotor on an upswept boom. The UH-12 had a framed 'bubble'-type cabin, no fuselage structure around the engine, skid undercarriage and a 175hp Franklin 6V4-178-B33 engine. Maximum takeoff weight was 1015kg.

 

In 1963 the US Army was buying 137 more Hiller OH-23 observation helicopters to meet its requirements until a five-way competition for a light helicopter was decided at Ft. Rucker, Alabama. In 1963 the British navy was adding seven UH-12E to the 14 bought in 1962. The Royal Navy used its 12E’s to train fleet pilots at Culdrose Naval Air Station in Cornwall. They were fitted for instrument flying. 12E were also in use with Canada’s army and air force, known as CH-112.

The UH-12A Raven production two-seat UH-12 with collective pitch ballast system and wooden rotor blades for civil and military customers had a takeoff gross weight of 1082kg. With an uprated engine and new UH-12A rotor blades, it was purchased by the US Army and Navy for battlefield evacuation and observation tasks, with the designation H-23 Raven, whilst the Navy ordered the same basic model as the HTE-1 for training.

The commercial UH-12A to UH-12D became the OH-23A to OH-23D Raven respectively for service with the US Army, and the US Navy acquired UH-12As as HTE-1 and HTE-2. 

 

HTE-2

The UH-12A successor, the H-23B, powered by a 200-210hp Franklin engine, was the first version used by the US Army as a trainer. 216 were assigned to the Primary Flying School at Fort Walters and another 237 were used for various tasks. The Hiller UH-12 was the US Army's primary trainer until 1965.

The UH-12B (and as the HT Mk.1 for the Royal Navy) normally had skid or flotation gear, but a wheeled undercarriage was fitted to a batch ordered by the US Navy (the HTE-2).

In 1955 the UH-12C, was basically a UH-1B. It retained the 200hp Franklin engine, but had all-metal rotor blades and a "goldfish bowl" cockpit canopy and three seats. From 1956, 145 were delivered to the US Army as the H-23C.

 

 

A purely military version, the UH-12D / OH-12D, flew on 3 April 1956 and 483 went to the US Army. The Franklin engine had been replaced by the more powerful 320hp Lycoming VO-540, and the transmission had also been changed to increase the service life of the helicopter.

The commonest version was the UH-12E which had a more powerful 305hp Textron Lycoming VO-540-A1A engine. The US Army replaced nearly all the OH-23Ds by Hiller 12Es, designated OH-23G 3-seat dual control trainer. In 1960 the Model E4 was developed from the Hiller 12E, with a longer cabin to seat four and an anhedral stabilizer on the tail boom. Twenty-two of these were acquired by the US Army as the OH-23F, for geodetic research.

 

 

The UH-12EL was a UH-12E retro-fitted with Ham-Standard rotor stability augmentation system, stainless steel rotor blades and 1400kg TOGW.

UH-12E3 was the revised designation for Hiller Aircraft Corp production UH-12E with 3 seats, and UH-12E3T the Hiller Aircraft Corp UH-12ET.

The UH-12E4 featured inverted rear tail planes and lengthened cabin to accommodate pilot plus rear bench seat for 3 pax. All new helicopters now have these features and they can be retrofitted on Model 12Es. Designated UH-12E4T when fitted with Soloy conversion to 400shp Allison 250-C20B turboshaft. This engine conversion was jointly developed with Soloy Conversions of Chehalis, Washington who began work on it in 1976.

The UH-12ET was the UH-12E fitted with Soloy conversion to 400shp Allison 250-C20B turboshaft.
UH-12E5 was the UH-12E4 fitted with five seats and 340hp Textron Lycoming VO-540 piston engine. A prototype was flown but no further development was undertaken.
The Korean War gave an added impetus to improvements and when the Hiller 12E appeared in 1959 it came either as the L3 with a 305hp Lycoming VO-540-C2A or as the SL3 with a supercharged 315hp TIVO-540-A2A engine.
The UH-12SL was the UH-12E with supercharged Textron Lycoming TIVO-540 engine and 'L' series rotor head with gyro-controlled stability augmentation system.
UH-12L was UH-12SL with unsupercharged VO-540 engine.

Civil versions with uprated powerplant included the UH-12E variants suffixed L3, L4, SL3 and SL4. The last civil variant, which appeared in 1963, was the Hiller 12L4 which was also used as a test-bed for a PT6 turbine, but the project was taken no further.
Total sales of the Hiller 12E family exceeded 2000. Over 1,600 UH-12s went to the US Army and were used in Korea and Vietnam.
At the height of UH-12/OH-23 production Hiller was taken over by the Fairchild Corporation, but in 1973 a new company, Hiller Aviation, acquired design rights and production tooling for the UH-12E, and for some years provided support for the world-wide fleet of UH-12 variants.
UH-12E5T was a proposed turbine-powered UH-12E5 with Allison 250-C20B. Not built.
UH-12J-3 was an unofficial designation for Soloy-converted UH-12E.
UH-12SL4 was the UH-12L with the E4 four-seat cabin.

The Canadian army acquired OH-23Gs which it operated with the designation CH-112 Nomad, and the Royal Navy used a number of ex-US Navy HTE-2s under the designation Hiller HT.Mk 2.
In April 1984 Hiller became a subsidiary of Rogerson Aircraft of Port Angeles, Washington. Renamed Hiller Helicopters and later Rogerson Helicopters, the company, now known as Rogerson Hiller, relaunched the piston-engined UH-12E in 1991 as the Hauler, and a number have been exported. The company is also proposing the Allison turbine-powered UH-12ET development for the US Army's NHT (New Training Helicopter) requirement.
The Model 12 has the usual equipment for helicopter safety and civil work, but can also be fitted with a night-lighting kit, a 454kg capacity cargo hook, twin heavy duty cargo racks, and auxiliary fuel tanks. Equipped with extra tanks the 12E has a maximum range of 676km. Production of both the 12E and 12E-4 is ran at about five a month.

A number were fitted with an Allison 250-C20 turbine as Soloy UH12E-SCL conversions. The 400shp Allison (derated to 305 shp) is mounted slanting backwards from the adaptor gearbox, leaving a large uncluttered area where the previous engine was.

 

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