OH 23 Hiller
The Hiller UH-12, derived from
the Model 360 two-seater of 1948 with a 180hp Franklin engine,
occupies an important place in the history of the American helicopter
industry in the fifties. Stanley Hiller Jr., who built the aircraft, was
something of a whiz kid, in that he designed and built his first helicopter,
the XH-44, in 1944 at the age of only 18. It was the first efficient
American helicopter with coaxial, contra-rotating rotors. The later
Hiller 360 leapt to fame in the summer of 1949 when it made the first
transcontinental commercial flight. 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
Its successor, the H-23B, powered by a 200-210hp
Franklin engine, was the first version used by the US Army as a trainer. A
considerable number were built: 216 were assigned to the Primary Flying
School at Fort Walters and another 237 were used for various tasks.
The UH-12B 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 a new variant, the UH-12C, appeared. It
retained the 200hp Franklin engine, but had all-metal rotor blades and a
"goldfish bowl" cockpit canopy. From 1956, 145 were delivered to the US Army
as the H-23C. A purely military version, the 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 The Franklin engine had been
replaced by the more powerful 320hp Lycoming VO-540, and the transmission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 of this sturdy little helicopter
was the UH-12E which had a more powerful engine. The US Army replaced
nearly all the OH-23Ds by Hiller 12Es, designated OH-23G.
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
The last civil variant, which appeared in 1963, was the
Hiller 12L-4 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; more than 300 were exported. Operators of the Hiller included
Argentina, Canada, Chile, Colombia, Great Britain, Guatemala, Japan,
Morocco, Mexico, the Netherlands, Peru and Uruguay.