Background

A Hughes 500C (Model 369HS)

A Hughes 500D

The Hughes 500/MD 500 series can be traced back to the early 1960s and the issuing of a requirement for a Light Observation Helicopter (LOH) for the United States Army.^[3] Following a competitive tendering process, Hughes' Model 369 was selected as the winning bid, triumphing over rival submission from the helicopter manufacturers Bell and Hiller. On 27 February 1963, under the service designation of OH-6 Cayuse, the maiden flight of the type was performed.^[4][5]

The MD 500 series 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.^[6] 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, which gives it an agile control response and also makes it less susceptible to weather-cocking. It had a distinctive atypical teardrop-shaped fuselage, a feature that sometimes led to personnel referring to it as the "flying egg".^[4][7]

Hughes had allegedly succeeded in the LOH contest with its OH-6 helicopter by submitting a very low and aggressive price per airframe (without an engine), to the point where the company allegedly lost money .^[8][9] Due to price escalations for both the OH-6 and spare components, the U.S. Army opted to reopen bids for the programme in 1967.^[10] Seeking to profitably produce the type, Hughes offered the machine at a more realistic unit price of $56,550, however, this bid was undercut by the redesigned Bell OH-58 Kiowa, a militarised version of the JetRanger series.^[8][9] Despite this, some OH-6 helicopters were still ordered by the U.S. Army, though at a much reduced number.

Hughes/MD 500

Even prior to the first flight of the OH-6, Hughes had announced that it was working on a civilian version of the rotorcraft, which would be marketed as the Hughes 500.^[5] It was available in basic five- and seven-seat configurations.^[3] A utility version with a more powerful engine was offered as the 500U (later called the 500C).

During 1976, the improved Hughes 500D became the primary model. It with outfitted with a more powerful engine, a T-tail, and a new five-blade main rotor; furthermore, a four-blade tail rotor could be optionally installed.^[3][11] The 500D was replaced by the 500E from 1982 with a pointed nose and various interior improvements, such as greater head- and legroom.^[12] The 530F was a more powerful version of the 500E optimized for hot and high work, being furnished with an enlarged main rotor and more powerful Allison 250-C30 engine, capable of producing up to 425 hp.^[13]

During January 1984, Hughes Helicopters, the original manufacturer of the 500 series, was acquired by the American aircraft manufacturer McDonnell Douglas. Accordingly, starting in August 1985, the 500E and 530F were rebranded as the MD 500E and MD 530F Lifter respectively.^[3] Following the merger between Boeing and McDonnell Douglas, the division was briefly owned by the new entity; Boeing opted to quickly sell the former MD civil helicopter lines to the newly-created MD Helicopters in early 1999.^{[14][15][16][17]} Military variants are marketed under the MD 500 Defender name.

MD 520N

A NOTAR MD 520N

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.^[3] Exhaust from a fan is directed through slots in the tailboom, using the Coandă effect to counteract the torque of the main rotor, and a controllable thruster at the end of the tailboom is used for yaw control. Because the fan is enclosed in the tailboom, tail rotor noise—the major source of noise from most conventional helicopters—was significantly reduced.^[18] 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 manoeuvring 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 changes to the diffuser and fan rigging, also increased range.

Civilian

The MD 500 series had proven to be popular with civilian operators, with which the type has seen use for a diverse range of purposes. According to Flying magazine, it has been particularly popular in circumstances where the primary passenger and pilot are both in the front seats, as can be typical in aerial observation, utility, and law enforcement work.^[19] A minority have been used for executive transportation, for which suitable rear seating is typically provisioned; it is more common to see it used as a private/personal helicopter instead.^[20]

While numerous operators have opted to procure MD 500s with the newer Rolls-Royce 250-C20 engine, which provides greater reliability and power output than older counterparts, some operators have reportedly chosen to remove these engines and substitute them with Vietnam-era surplus engines which are available even into the twenty-first century at a considerably lower purchase cost.^[21]

El Salvador

At the start of the Salvadoran Civil War, the Salvadoran Air Force operated a total of six MD 500D helicopters purchased from civilian sources. Amid the conflict, these were supplemented by a further nine MD 500Es that were supplied by the United States in 1984. The type was typically operated in the gunship role, having been armed with both XM27 7.62 mm Minigun subsystems and unguided 70mm rocket pods; additional mission roles included aerial reconnaissance and liaison duties. By the end of the conflict, only two MD 500D and seven MD 500Es were reportedly in an operational condition. By 2012 Salvadoran Air Force received three brand new MD 500Es from MD Helicopters to be used for the United Nations mission in Mali, Africa. In 2022 the United States donated four MD 530Fs which were previously owned by the Department Of State Air Wing (DOSAW) which will also be used for United Nations missions. El Salvadoran Air Force as of 2023 currently operates six MD 500Es and four MD 530Fs.

North Korea

During the 1980s, North Korea managed to circumvent US export restrictions and covertly purchase a total of 87 civilian-type Hughes MD 500s through a legitimate West German export firm before the US government learned of the illegal action by North Korea and acted to prevent any further deliveries to the country.^[22] Once they had arrived in North Korea, efforts continued to be made to conceal their existence, and are believed to have been flown only sparingly at least for a large portion of their service life.^[22] There have been allegations that at least sixty of the helicopters delivered to North Korea have been modified to serve as helicopter gunships. As South Korea produces the MD 500 domestically (under license) for use by its own armed forces, the modified helicopters operated by North Korea were deemed useful in conducting covert or deceptive operations against South Korea (such as incursions past the border).^[22]

The modified MD 500 helicopters were finally revealed by North Korea in an obviously visible manner, even to international observers, during the country’s annual Victory Parade held in Pyongyang on 27 July 2013, which commemorated the 60th anniversary of the end of the Korean War in 1953. According to analysists, it is visible that the North Korea's fleet of MD 500s have been modified significantly so that they can function as light attack helicopters. Amongst these changes was mounting points and interfacing apparatus to allow them to fire Soviet-designed AT-3 Sagger anti-tank wire-guided missiles.^[23]

Military

For military variants, see McDonnell Douglas MD 500 Defender and Hughes OH-6 Cayuse.

MD 530F

Data from MD500E Performance Specifications,^[53] The International Directory of Civil Aircraft^[3]

General characteristics

• Crew: 2
• Capacity: 3 passengers
• Length: 32 ft 7 in (9.93 m)
• Height: 8 ft 9 in (2.67 m)
• Empty weight: 1,591 lb (722 kg)
• Max takeoff weight: 3,550 lb (1,610 kg)
• Powerplant: 1 × Allison 250-C30 turboshaft engine, 650 shp (480 kW)
• Main rotor diameter: 27 ft 4 in (8.33 m)
• Main rotor area: 587.5 sq ft (54.58 m²) * Blade section: - NACA 0012^[54]

Performance

• Maximum speed: 152 kn (175 mph, 282 km/h)
• Cruise speed: 135 kn (155 mph, 250 km/h)
• Range: 232 nmi (267 mi, 430 km)
• Service ceiling: 18,700 ft (5,700 m)
• Rate of climb: 2,070 ft/min (10.5 m/s)

MD 500C

Data from ^[55]

General characteristics

• Crew: 2
• Capacity: 2
• Length: 30 ft 3.75 in (9.2393 m)
• Height: 8 ft 1.5 in (2.477 m)
• Empty weight: 1,229 lb (557 kg)
• Max takeoff weight: 2,700 lb (1,225 kg)
• Fuel capacity: 61.5 US gal (51 imp gal; 233 L) in two 50% self-sealing bladder tanks under rear cabin floor
• Powerplant: 1 × Allison T63-A-5A turboshaft engine, 317 shp (236 kW)
• Main rotor diameter: 26 ft 4 in (8.03 m)
• Main rotor area: 544.63 sq ft (50.598 m²) * Blade section: - NACA 0012^[54]

Performance

• Maximum speed: 130 kn (150 mph, 240 km/h)
• Cruise speed: 130 kn (150 mph, 240 km/h)
• Range: 330 nmi (380 mi, 610 km) at 5,000 ft (1,524 m)
• Ferry range: 1,354 nmi (1,558 mi, 2,508 km) with 1,300 lb (590 kg) of fuel
• Service ceiling: 15,800 ft (4,800 m) * Hover ceiling OGE: 7,300 ft (2,225 m)
• Hover ceiling IGE: 11,800 ft (3,597 m)
• Rate of climb: 2,070 ft/min (10.5 m/s)

Citations

Bibliography

• Cefaratt, Gil (2002). Lockheed: The People Behind the Story. Turner Publishing Company. ISBN 978-1-56311-847-0.
• Elliot, Bryn (March–April 1997). "Bears in the Air: The US Air Police Perspective". Air Enthusiast. No. 68. pp. 46–51. ISSN 0143-5450.
• Frawley, Gerard (2003). The International Directory of Civil Aircraft, 2003-2004. Aerospace Publications Pty Ltd. ISBN 1-875671-58-7.
• "MD 500: Peak Performance". Flying. Vol. 116, no. 6. June 1989. pp. 44–52. ISSN 0015-4806.}
• McGowen, Stanley S. (2005). Helicopters: An Illustrated History of Their Impact. ABC-CLIO. ISBN 978-1-85109-468-4.
• Rivas, Santiago (October 2015). "Fighting d Drug War". Air International. Vol. 89, no. 4. pp. 118–121. ISSN 0306-5634.