successful Hughes 500/MD 500 series began life in response to a US Army
requirement for a light observation helicopter. Hughes' Model 369 won
the contest against competition from Bell and Hiller. The OH-6 Cayuse
first flew in February 1963.
The 500 series design features
shock-absorbing landing skid struts, a turboshaft engine mounted at a
45-degree angle toward the rear of the cabin pod, a fuel tank cell under
the floor and the battery in the nose. The engine exhaust port is
located at the end of the cabin pod underneath the tailboom. It has a
short-diameter main rotor system and a short tail, giving it an agile
control response and is less susceptible to weather-cocking.
won the US Army's LOH contest with its OH-6 helicopter by submitting a
very low and aggressive price per airframe (without an engine). Due to
rising prices, the US Army later re-opened the contest, where Hughes
offered the machine at a more realistic price, but was undercut by the
redesigned Bell OH-58 Kiowa (military JetRanger). OH-6 helicopters were
still ordered by the US Army, though at a much reduced number.
to the OH-6's first flight, Hughes announced it was developing a civil
version, to be marketed as the Hughes 500, available in basic five and
seven seat configurations. A utility version with a more powerful engine
was offered as the 500U (later called the 500C).
Hughes 500D became the primary model in 1976, with a more powerful
engine, a T-tail, and new five-blade main rotor; a four-blade tail rotor
was optional. The 500D was replaced by the 500E from 1982 with a
pointed nose and various interior improvements such as greater head and
leg room. The 530F was a more powerful version of the 500E optimized for
hot and high work.
McDonnell Douglas acquired Hughes Helicopters
in January 1984, and from August 1985 the 500E and 530F were built as
the MD 500E and MD 530F Lifter. Following the 1997 Boeing/McDonnell
Douglas merger, Boeing sold the former MD civil helicopter lines to MD
Helicopters in early 1999.
Military variants are marketed under the MD 500 Defender name.
MD 520N introduced a revolutionary advance in helicopter design being
dispensed with a conventional anti-torque tail rotor in favor of the
Hughes/McDonnell Douglas developed NOTAR system. Exhaust from a fan is
directed through slots in the tail boom, using the Coanda effect to
counteract the torque of the main rotor, and a controllable thruster at
the end of the tail boom is used for yaw control.
Douglas originally intended to develop the standard MD 520N alongside
the more powerful hot and high optimized MD 530N (both were launched in
January 1989 and were based on the conventional MD 500E). The MD 530N
was the first to fly, on December 29, 1989, the MD 520N first flew on
May 1, 1990. Development of the MD 530N was suspended when McDonnell
Douglas decided that the MD 520N met most customer requirements for the
530N. Certification for the MD 520N was awarded on September 13, 1991,
and the first was delivered on December 31 that year.
In 2000, MD
Helicopters announced enhancements to the MD 520N including an improved
RR 250-C20R+ engine with 3-5% more power for better performance on warm
days, and, with changes to the diffuser and fan rigging, increased