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The MD Helicopters MD 500 series is an American family of light utility civilian and military helicopters. The MD 500 was developed from the Hughes 500, a civilian version of the US Army's OH-6A Cayuse/Loach. The series currently includes the MD 500E, MD 520N, and MD 530F.
The successful Hughes 500/MD 500 series began life in response to a U.S. 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 tail boom. 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.
Hughes won the U.S. 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 U.S. 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 U.S. Army, though at a much reduced number.
Prior 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).
The improved 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.
The MD 520N introduced a revolutionary advance in helicopter design, dispensing 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 Coandă 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. Because the fan is enclosed in the tail boom, tail rotor noise — the major source of noise from most conventional helicopters — was significantly reduced. It also eliminated the vulnerable exposed tail rotor blades, eliminating the possibility of persons being injured or killed on the ground and the cause for many confined area maneuvering accidents.
McDonnell 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, and 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 Rolls-Royce 250-C20R+ engine with 3% to 5% more power for better performance on warm days, and, with changes to the diffuser and fan rigging, increased range.
The original OH-6 Cayuse helicopter proved its worth during the Vietnam War in the light helicopter role. The designers at Hughes realized there was a market for a light multi-mission helicopter with an improved equipment fit than the OH-6 and Model 500M. The resulting design was the Model 500MD Defender which first flew in 1976. It was tailored for specific roles including unarmed observation and an armed scout helicopter equipped with TOW anti-tank missiles. An anti-submarine version was developed with a search radar, magnetic anomaly detector and the capability to carry lightweight aerial torpedoes.
The helicopter was popular with customers like Kenya who could buy a capable anti-armor helicopter for less than half the cost of a gunship such as the AH-1 Cobra or the AH-64 Apache. Israel used the Defender extensively during the conflicts of the late 1970s and 1980s against Syrian armored forces.
The Defender was later built as an improved version as the MD530MG, with increased engine power, handling, avionics, and a redesigned forward fuselage. Later developments included a mast mounted sight (MMS).
In December 2012, Boeing demonstrated their Unmanned Little Bird to the South Korean Army. The pilotless aircraft flew autonomously for 25 minutes. The purpose of the demonstration was to show unmanned capabilities technologies, such as enhanced ISR and resupply, in the system that could be integrated into Army MD 500 helicopters.
MD Helicopters had submitted a version called the MD 540F in the U.S. Army's Armed Aerial Scout program. This caused Boeing to try and block MD Helicopters from participating, citing agreements the companies struck in 2005 to offer the Mission Enhanced Little Bird in the Armed Reconnaissance Helicopter program. As part of the venture, MD Helicopters sold intellectual property related to the aircraft's design. The two companies lost the bid and the program was ultimately cancelled. When MD Helicopters disclosed plans to offer the MD 540F in the AAS program in April 2012, Boeing claimed that they could not sell any “similarly configured” aircraft to any U.S. or foreign military organization. Boeing offered their AH-6 Little Bird in the competition. MD Helicopters said Boeing did not object to previous sales to armed forces and governments in Japan, Jordan, and Italy, as well as to U.S. special operations, and local U.S. police forces. Restrictions on selling aircraft similar to the Little Bird, domestically or to foreign users, would have put the company out of business. In July 2013, a federal court ruled that MD Helicopters could not be blocked from offering their aircraft. The Army ended the AAS program in late 2013.
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