MD Helicopters traces its roots back more than 50 years to when Hughes Tool Company, Aircraft Division first started to develop “light helicopters” in 1955. After years of successfully manufacturing such models as the Hughes 269, 300, 500 and 530F for civil use and TH-55 Osage, OH-6 Cayuse and highly successful AH 64-Apache, Hughes sold its helicopter business to McDonnell Douglas in 1984. For the most part, McDonnell Douglas stayed true to the original Hughes designs and nomenclatures.
In 1997, McDonnell Douglas merged with Boeing to become the Boeing Company.
In 1999, Boeing sold the former MD commercial helicopter lines to MD Helicopter Holdings, Inc., an indirect subsidiary of the Dutch company, RDM Holding Inc. Included in the sale were the MD 500E and MD 530F single-engine helicopters, with conventional tail rotors; the MD 520N and MD 600N single-engine helicopters, with the Boeing-exclusive NOTAR® no tail rotor system for anti-torque and directional control; and the MD Explorer series of twin-engine, eight-place helicopters.
Boeing maintained the AH-64 line of helicopters, and rights to the NOTAR system.
MD Helicopters Holdings, Inc., was acquired in July, 2005, by Patriarch Partners, LLC, an investment fund. The company was recapitalized as an independent company, MD Helicopters, Inc.
MD Helicopters is based in Mesa, AZ, and the current product line includes the MD 500E, MD 530F, MD 520N, MD 600N and the MD Explorer.
In 1960, the U.S. Army issued a specification for a four- or five-seat light single-engine turbine observation helicopter. Hughes (now MD Helicopters) won the competition with the Model 369 and received an order from the Army for 1,000 aircraft. Full-scale production of the commercial model, called the Hughes 500, started in 1968. Three major improvements to this popular helicopter (the 500C, 500D and 500E) focused on improving performance, increasing the takeoff gross weight and improving passenger comfort.
In 1981, the company flew a prototype of a new type of directional control, the NOTAR, on a U.S. Army OH-6 test bed. The NOTAR uses cool, low-pressure air emerging through two Coanda slots on the side of the tail boom, as well as through steering louvers, to obtain directional control. The air blown through the Coanda slots counters the main rotor torque. The steering slots at the end of the tail boom provide the directional control and movable fins mounted on the horizontal stabilizer also assist. An engine-driven variable pitch fan at the head of the large hollow tail boom supplies the low-pressure air. This method of directional control has two significant advantages: first, it eliminates the tail rotor; and second, it is much quieter. The Army test program was successfully concluded in 1986. A commercial application of the NOTAR technology, the MD 520N, was announced in 1998.
The MD 520N is a light single-engine turbine helicopter. It uses the same five-bladed, fully articulated rotor with medal blades and main transmission as the 530F. The engine used is the Rolls-Royce 250-C20R. A NOTAR system provides directional control and the fuselage has conventional aluminum construction, except for the NOTAR tail boom, which is made of composites. The cabin has three seats in front and two seats in the rear. The engine and transmission are mounted on a diagonal behind and below the main rotor head. This yields a very narrow “doghouse” on top of the cabin and makes for excellent maintenance accessibility. It also results in a characteristic bulge that separates the left and right rear seats. A skid landing gear is used for the sake of simplicity
Development of the 520N was launched in 1988 and certification was obtained in 1991. Deliveries started the same year and the 520N is currently in production.