In 1994, McDonnell Douglas announced a stretched, 8 place version of the popular MD 520N. This model, originally referred to as the MD 630N, was named the MD 600N when the project received production go-ahead. The new helicopter had several notable features, in addition to the fuselage stretch. The most important was that it would get directional control from a NOTAR tail.
In 1981, the company flew a prototype the NOTAR, a new type of directional control, 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. The first two commercial applications of the NOTAR technology were the MD 520N and the MD 900, both, was announced in 1998. The MD 620N was to be the third application.
The MD 600N is a light single-engine turbine helicopter. It uses a six-bladed, fully articulated rotor with medal blades and an up-rated main transmission. The engine used is the Rolls-Royce 250-C47 with FADEC. A NOTAR system provides directional control. The fuselage has conventional aluminum construction, except for the NOTAR tail boom, which is made of composites. Inserting a 30-inch plug just aft of the cockpit and cabin bulkhead of the MD 520N has stretched the cabin. In addition, the MD 600N has a 28-inch plug in the tail boom. The stretched cabin provides three seats in the cockpit, three seats in the front part of the cabin, and the standard two seats in the rear of the cabin. The engine and transmission mounting has not changed significantly, so the two back seats continue to be separated by the characteristic bulge. Alternatively, the cabin has ample room for one or two stretchers and one or two medical attendants. The cabin has a flat floor to assist with loading cargo. A skid landing gear is used for the sake of simplicity.
The first flight of the 600N took place in 1994 and certification was received in 1997. Deliveries started the same year and the 600N is currently in production.