Bölkow Bo 105

The Messerschmitt-Bölkow-Blohm Bo 105 is a light, twin-engine, multi-purpose helicopter developed by Bölkow of Ottobrunn, West Germany. It was the first light twin-engine helicopter in the world, and the first rotorcraft that could perform aerobatic maneuvers such as inverted loops.Moll 1991, p. 96. The Bo 105 features a hingeless rotor system, a pioneering innovation in helicopters when it was introduced into service in 1970. Production of the Bo 105 began at the then-recently merged Messerschmitt-Bölkow-Blohm (MBB).

The main production facilities for producing the Bo 105 were located in Germany and Canada; due to the level of export sales encountered, additional manufacturing lines were set up in Spain, Indonesia, and the Philippines. MBB, acquired by DASA in 1989, merged its helicopter division with that of France's Aérospatiale to form Eurocopter in 1992 (rebranded Airbus Helicopters since). The latter continued production of the type until 2001. The Bo 105 was formally replaced in Eurocopter's product range by the newer Eurocopter EC135. By the close of production, over 1400 had been produced in Germany, and with license production 1640 had been produced in total.

Development

In 1964, development work began at Bölkow upon the helicopter that would become the Bo 105, although work on the hingeless rotor it would use had begun earlier.Rieck, Joan M
"Bölkow's Bo105."
''Flight International'', 18 May 1967, p. 794. On 16 February 1967, the second Bo 105A prototype conducted its maiden flight at Ottobrunn in Germany; the first public demonstration was held in May 1967. The test program was broken down into stages as the Bo 105 comprised a new airframe, new rotor system, and a new engine; thus the flying Bo 105 prototype was initially equipped with a main rotor from Westland Helicopter's Scout rotorcraft and a pair of Allison Model 250 turboshaft engines instead of their production counterparts. Sud Aviation worked with Bölkow on developing the rotorcraft; an Alouette II helicopter was modified with the Bo 105's rotor and used to test its performance envelope. The third Bo 105 prototype was equipped with the initial production standard MAN Turbo 6022 turboshaft engines; six pre-production Bo 105s were constructed for testing.

On 13 October 1970, the German Civil Aviation Authority certified the Bo 105; initial deliveries for the first customers, ADAC Air Rescue and the Bavarian State Police, took place shortly thereafter. In 1972, further type certification was granted by the Federal Aviation Administration (FAA) and the Civil Aviation Authority (CAA), enabling export orders from the United States and Britain respectively, which soon followed. In 1972, an improved version of the rotorcraft with more powerful engines, the Bo 105C, was developed; this model quickly superseded the Bo 105A. On 25 September 1973, the prototype Bo 106 performed its first flight;Taylor 1976, p. 73. the Bo 106 shared many similarities to the Bo 105, the principal difference being a widened cabin area, capable of seating three abreast in the front row and four abreast in the rear of the cabin. However, nothing further came of the Bo 106 project.''Air International'' May 1976, p. 246.

In 1976, the Bo 105CB, equipped with more powerful Allison 250-C20B engines, was introduced. The Bo 105C was further developed to become the Bo 105CBS, the primary change being a fuselage stretch of 10 inches to meet American demand for emergency medical service (EMS) operations; this version was often referred to as the Bo 105 Twin Jet in the United States. US aerospace firm Boeing-Vertol served as a partner in the type's production and further development, and marketed the BO 105 in the US.Weeghman 1975, p. 54. The Bo 105 CB and the Bo 105 CBS variants were also subject to license manufacturing agreements, leading to them being produced by the Philippine Aerospace Development Corporation in the Philippines which produced 44 units from 1977-1997, Indonesian Aerospace (IPTN) in Indonesia, and Construcciones Aeronáuticas SA (CASA) in Spain in addition to the main production line in Germany.

In 1984, the Bo 105LS was developed with the enlarged fuselage of the Bo 105CBS combined with uprated Allison 250-C28C engines to increase the maximum take-off weight as well as hot-and-high flight performance; the Bo 105 LS was manufactured under a cooperative arrangement with Eurocopter Canada. Improvements and modifications to the Bo 105 LS continued until 1995.

Production of the Bo 105 by Eurocopter formally ended in 2001, principally due to the type having been superseded by the more modern Eurocopter EC135, itself a direct development from the Bo 105. By the end of production, 1,406 rotorcraft had been manufactured and delivered to operators in 55 nations worldwide.Gotzhein, Christina
"Eurocopter Celebrates the 40th Anniversary of the Maiden Flight of the BO105, the World's First Light Twin-Turbine Production Helicopter."
''Eurocopter'', 15 February 2007. Including the license production in Canada, Indonesia, Philippines and Spain the total is about 1640; of that 1404 were made in Germany.

Design

The Bo 105 has a reputation for having high levels of maneuverability; certain variants have been designed for aerobatic maneuvers and used for promotional purposes by operators, one such operator in this capacity being professional pilot Aaron Fitzgerald, flying for Red Bull. During the 1970s, the Bo 105 was known for having a great useful load capacity and higher cruise speed than the majority of its competitors.Weeghman 1975, pp. 54–56. While not being considered a visually attractive helicopter by some pilots, the Bo 105 was known for possessing steady, responsive controls and a good flight attitude.Moll 1991, p. 105. Most models could perform steep dives, rolls, loops, turnovers, and various aerobatic maneuvers; according to MBB the Bo 105 is cleared for up to 3.5 positive G force and one negative. One benefit of the Bo 105's handling and control style is superior takeoff performance, including significant resistance to catastrophic dynamic rollover; a combination of light weight and the twin-engined configuration enables a rapid ascent in a performance takeoff.

Perhaps the most significant feature of the Bo 105 is its rotor blades and rotor head. The rotor system is entirely hingeless, the rotor head consisting of a solid titanium block to which the four blades are bolted; the flexibility of the rotor blades works to absorb movements typically requiring hinges in most helicopter rotor designs.Moll 1991, p. 101. The rotor blades are made from reinforced-plastic glass-fiber composite material; the flexibility of the main rotor allows for active elements other than rotor pitch changes to be removed, greatly simplifying maintenance and extending blade lifespan.Weeghman 1975, p. 56. The reliability of the advanced rotor system is such that, in over six million operating hours across the fleet, there was a total of zero failures (as of 1991). The rigid rotor design adopted on the Bo 105 has been partially responsible for the type's agility and responsiveness; it remained an uncommon feature on competing helicopters throughout the Bo 105's production life.Moll 1991, p. 103.

Military operators would commonly operate the type at a very low altitude to minimise visibility to enemies, the Bo 105 being well matched to such operations, as the helicopter's flight qualities effectively removed or greatly minimised several of the hazards such a flight profile could pose to pilots. When outfitted with optional auxiliary fuel tanks, a basic model Bo 105 had a flight endurance of roughly five hours under load.Moll 1991, p. 104. In the event of a single engine failure, the Bo 105 could typically continue its flight, albeit with a reduction in cruise speed and range. Besides the two pilots, the cabin can be configured to accommodate up to three passengers on a single rear bench, which can be removed to make room for cargo or a stretcher, which can be loaded and unloaded via the large clamshell doors located at the rear of the fuselage.Weeghman 1975, p. 57. In a maritime context, the BO 105 can be equipped with auxiliary fuel tanks, emergency flotation equipment, an inflatable life raft, folding rotor blades and high skid landing gear.

Operational history

In 1975, the German Army decided to procure a specialist anti-tank version armed with up to six Euromissile HOT missiles, designated as the Bo 105 PAH-1 (Panzerabwehrhubschrauber: antiarmor helicopter). A total of 212 Bo 105 PAH-1s were delivered between 1979 and 1984. German Army leaders saw the PAH-1 as a temporary measure only, having originally sought a more capable anti-tank helicopter; they were particularly dissatisfied with the PAH-1's inability to perform nighttime combat missions and its self-protection capabilities; ultimately, the Eurocopter Tiger was developed as a replacement. In 1977, the German Ministry of Defence selected the Bo 105C for its light observation helicopter (VBH) program, leading to the procurement of another 100 rotorcraft. The helicopter was retired from German Army service on 13 December 2016, the occasion was marked by an 18-aircraft formation flyby from their base in Celle. The Bohicans, as their pilots were called, had clocked over 1.38 million flying hours.Last Of The Bohicans
- Aviationweek.com, 23 December 2016

During the 1970s, MBB issued a license to produce the Bo 105 to Indonesian Aerospace (IPTN) as part of a wider agreement to help develop Indonesia's aviation industry. Within ten years, manufacture of the Bo 105 had been entirely localised within IPTN's own facilities. The Bo 105 has been used by various branches of the Indonesian National Armed Forces; military-operated Bo 105s have been reportedly used during the 1999 East Timorese crisis and the Papua conflict. Indonesian Bo 105s have also participated in several large-scale joint exercises.

The Mexican Navy operated a number of armed Bo 105s to perform maritime reconnaissance duties; during the early 1980s, Mexico procured a number of a Uribe-class patrol vessels which were equipped to handle the Bo 105 for off-shore operations. In 2005, work was completed on a series of upgrades to 11 of the Mexican Navy's Bo 105s, having received Forward looking infrared (FLIR) sensors, Global Positioning System (GPS) receivers, search radars, new rotor blades, armament pylons, and other changes. In November 2014, Jet Rescue Air Ambulance inaugurated Mexico's first dedicated civil air ambulance rotorcraft using a Bo 105.

During the late 1990s, the Republic of Korea Army aviation procured a number of Bo 105s as part of an ongoing drive to improve the force's reconnaissance and surveillance capabilities; these were manufactured under a co-production arrangement between Eurocopter and the newly formed Korea Aerospace Industries (KAI), receiving the designation ''Korean Light Helicopter'' (KLH), KAI also promoted the type to export customers.

The Bo 105 gained widespread use by emergency medical service (EMS) / medevac operators; in 1998, Flying Magazine reported that between the Bo 105 and the MBB/Kawasaki BK 117 (a newer rotorcraft derived from the Bo 105), MBB held 35% of the EMS market share. The first EMS-orientated Bo 105 in Scotland entered service in 1989; in November 2015, the last Bo 105 air ambulance operated in Britain was retired, the type having typically been replaced by the newer Eurocopter EC135. In 2009, the last Bo 105 to be produced was purchased by Canadian EMS specialist Dam Helicopters.

In May 2014, Airbus Helicopter reported that, worldwide, the Bo 105 had accumulated 8 million flight hours, and that approximately 700 Bo 105s remained in service.

Variants

The variants used by the German Army are the Bo 105P and Bo 105M.
;Bo 105A:First production model primarily for civil use and equipped with two Allison 250-C18 turbine engines.
;Bo 105ATH:HOT-armed anti-tank version for the Spanish Army. Local designation HA.15.Donald and Lake 1996, p. 162
;Bo 105C:Initial version. Developed in 1972 and equipped with two Allison 250-C20 turbines engines.
;Bo 105CB: Main production version from 1975, powered by two Allison 250-C20B engines.Taylor 1988, p. 93

;Bo 105CBS:Utility transport version, with the fuselage stretched by and an extra window.
;EC-Super Five:High performance version of the Bo 105CBS.
;Bo 105CBS-5:Also known as Superfive, with increased lifting capabilities similar to the LS A3 Superlifter
;Bo 105D:UK certified offshore version.
;Bo 105GSH:Armed scout version for the Spanish Army. Local designation HR.15.
;Bo 105HGH:A high speed research variant with aerodynamic refinements, such as a rotor head fairing, rear fuselage fairing, small individual skids and long fixed auxiliary wings.
;Bo 105 KLH:license-produced combat version of CBS-5 custom-fitted with Korean mission equipment package including communication, navigation, electronic warfare and target acquisition system, to meet Republic of Korea Army's operational requirements. KLH also has greatly improved rotor blade and transmission system. 12 are in service.
;Bo 105LOH:Observation version for the Spanish Army. Local designation HR.15.
;Bo 105LS A1:Developed in 1984 with stretched fuselage and two Allison 250-C28C turbine engines.
;Bo 105LS A3:Developed in 1986 with maximum take-off weight increased to 2,600 kg.
;Bo 105LS A3 "Superlifter":Developed in 1995 with maximum mission weight increased to 2,850 kg.
;Bo 105M: Light transport and surveillance helicopter for West German Army. German Army designation VBH (Verbindungshubschrauber; 'liaison helicopter').Michell 1994, p. 84 They were phased out and replaced by disarmed and modified PAH1.
;Bo 105MSS:Maritime version, fitted a search radar.
;Bo 105P/BSH: Proposed modification of PAH-1s into escort version for the German Army, armed with Stinger air-to-air missiles. Cancelled 1993.

;Bo 105P/PAH-1: Anti-tank helicopter armed with wire-guided HOT ATGMs for West German Army. German Army designation "PAH-1" (PAH=Panzerabwehrhubschrauber; 'Anti-tank helicopter'). Following the arrival of the Eurocopter Tiger attack helicopter, some were retired while others disarmed and downgraded to the VBH version for continued service.
;Bo 105P/PAH-1A1:Upgrade of PAH-1 anti-tank version for the German Army.Michell 1994, p. 85
;Bo 105P/PAH-1 Phase 2: Planned further upgraded version of PAH-1 with infra-red roof mounted sight for HOT-2 missiles giving a night attack capability. Programme cancelled 1993.
;Bo 105S:Search and rescue version.
;Bo 105/Ophelia:Test and trials aircraft fitted with a mast-mounted sight.
;NBO-105:Were Manufactured by IPTN under license from MBB (now Airbus Helicopters) 1976–2011; only rotors and transmission now supplied by Germany; originally NBO-105 CB, but stretched NBO-105 CBS available from 101st aircraft onwards. 122 were produced, Dirgantara Indonesia stopped production in 2008.
;NBO-105S:Stretched version.
;Bo 105 Executaire: Boeing Vertol and Carson Helicopters manufactured a 24.5 cm stretched version of the Bo 105 under license as the ''Executaire'' in an attempt to break into the U.S. light helicopter market, but sales were dismal.
;Bo 105E-4:12 German Army Bo 105P upgraded and overhauled for a 10 million euro contract and donated to Albania first batch delivered in 2006, the helicopters have better performance and avionics. The conversion of other Bo 105 helicopters from the German Armed Forces is also under consideration with a view to future sales.
;Bo 106:Widened cabin to seat 7 instead of 5. First flight was on 26 September 1973. A single helicopter of that variant has been made (registration D-HDCI, serial no. 84). The Bo 106 was also equipped with more powerful Allison 250 C 20B engines. In 1981, the German air rescue organization Deutsche Rettungsflugwacht/DRF Luftrettung bought that prototype and had it rebuilt into a 105 CB-2 with a standard cabin. It flew for DRF until November 1993 under the registration D-HCCC, but in 1994 it was put aside to gain spare parts for another DRF helicopter (Bo 105 CBS-S, registration D-HNNN, serial number 662).
;Philippine Aerospace Development CorporationHummingbird: An unlicensed development of the Bo 105C with revised cockpit structure.

Operators

Military

;
* Albanian Air Force –4 units.
;
* Royal Bahraini Air Force – 4 units.
* Royal Bahrain Naval Force

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