Production 500N with tailplane and twin fins. Prot. N520NT FF 1 May 1990.

R.Simpson "Airlife's Helicopter and Rotorcraft", 1998

TYPE: Light utility helicopter.

PROGRAMME: First flight OH-6A NOTAR (no tail rotor) testbed 17 December 1981; extensive modifications during 1985 with second blowing slot, new fan, 250-C20B engine and MD 500E nose; flight testing resumed 12 March 1986 and completed in June; retired to US Army Aviation Museum, Fort Rucker, Alabama, October 1990. Commercial MD 520N and uprated (485 kW Rolls Royce 250-C30) MD 530N NOTAR helicopters announced February 1988 and officially launched January 1989; first flight of MD 530N (N530NT) 29 December 1989, but this variant not pursued; first flight 520N (N520NT) 1 May 1990 and first production 520N 28 June 1991; 520N certified 12 September 1991 on MD500 type certificate; first production 520N (N521FB) delivered to Phoenix Police Department 31 October 1991. MD 520N set new Paris to London speed record in September 1992, at 1 hour 22 minutes 29 seconds. Now certified in 21 countries.

CURRENT VERSIONS: MD 520N: NOTAR version of MD500, offering more power, higher operating altitude and greater maximum T-O weight than MD 500E. Engineering designation is MD 500N.

Description applies to 520N.

MD 600N: Stretched version, described separately.

MD 520N Defender: Military variant, being developed.

CUSTOMERS: Total of 99 registered by mid-2002. Four delivered in 2000, two in 2001 and four in 2002. Law enforcement agencies flying MD 520Ns include Phoenix, Arizona (first operator; two more delivered in early 2002); Burbank, Glendale, Huntington Beach, Los Angeles, Ontario and San Jose, California; Hernando County, Florida; Orange County, Florida; Jefferson County, Kentucky, which took delivery of one in March 2002; Prince George County, Clinton, Maryland, which took delivery of two on 4 October 2000; Hamilton County, Ohio, which has seven 520Ns; El Salvador, whose Policia Nacional Civil took delivery of two in 1996; San Juan, Puerto Rico; Honolulu, Hawaii; and Calgary, Alberta, Canada. Other operators include the Tata Group of Mumbai, India, Weetabix Ltd, UK, and Belgian Gendarmerie (two).

COSTS: US$980,000 (2002). Direct operating cost US$224.71 per hour (2002).

DESIGN FEATURES: NOTAR system provides anti-torque and steering control without an external tail rotor, thus eliminating the danger of tail strikes; air emerging through Coanda slots and steering louvres is cool and at low velocity. Believed to be currently the quietest turbine helicopter, based on FAA certification test noise figures. Main rotor rpm 477; main rotor tip speed 208m/s; NOTAR system fan rpm 5,388. Emergency floats among options. Redesigned diffuser in NOTAR tailboom and revised fan rigging introduced from early 2000 and available for retrofit; combined with uprated Rolls-Royce 250-C20R+ engine; these improvements increase the aircraft's payload capability,

FLYING CONTROLS: Unboosted mechanical, as in earlier versions. Rotor downwash over tailboom deflected to port by two Coanda-type slots fed with low-pressure air from engine-driven variable-pitch fan in root of tailboom; this counters normal rotor torque; some fan air is also vented at tail through variable-aperture louvres controlled by pilot's foot pedals, giving steering control in hover and forward flight. Port moving fin on tailplane connected to foot pedals, primarily to increase directional control during autorotation and allow touchdown at under 37km/h; starboard fin operated independently by yaw damper.

STRUCTURE: Same as for MD 500E/530F, except graphite composites tailboom; metal tailplane and fins; new high-efficiency fan with composites blades fitted in production aircraft. NOTAR system components now have twice the lifespan of conventional tail rotor system assemblies. During 1993, NOTAR system components' warranty increased from two to three years. Thicker fuselage skins, to reduce surface rippling, will be introduced during 2001.

POWER PLANT: One Rolls-Royce 250-C20R turboshaft, derated to 317kW for T-O (5 minutes) and 280kW maximum continuous. Improved, heavy-duty transmission, rating 447kW, derated to 317kW for T-O, 280kW maximum continuous, on production aircraft from June 1995. Rolls-Royce 250-C20R+ engine, providing improved hot weather performance and 3 to 5% more power, introduced from early 2000. Fuel capacity 235 litres.

SYSTEMS: Electrical system includes 87Ah starter-generator. Aero Aire air conditioning system optional.

EQUIPMENT: Phoenix Police Department pioneered use of MD 520Ns for firefighting, using 341 litre "Bambi" buckets to drop 151,416 litres of water on fires in remote desert and mountain areas.

Jane's All the World's Aircraft, 2004-2005

- In 1991 the Arizona Police Department, based in Phoenix, became the first operator of the MD 520N.

- This fine helicopter draws its basic design from the Vietnam-era Hughes OH-6.

- In September 1993, an MD 520N set a new Paris to London record of 1 hr 22 min.

- The NOTAR, or 'no tail rotor' concept is also used on the larger MD 630N and MD 900 Explorer helicopters.

- An MD 520N rescued four climbers from an 1800m mountain in Hawaii.

- Over 1,000 hours of testing was done before the MD 520N became operational.

- In September 1993, an MD 520N flew the 215km trip from Paris to London in a class record of 1 hour 22 minutes and 29 seconds.