* The Bo 105 proving successful, MBB collaborated with Kawasaki of Japan to build an enlarged follow-on, which emerged as the "BK-117". As with the Bo 105, the BK-117 proved popular, leading in turn to the refined Eurocopter "EC145", now Airbus "H145". The same design concepts led to the Indian HAL "Dhruv" helicopter, and so it is discussed here as a footnote.
* In the mid-1970s, MBB was working on what amounted to a scaled-up and improved derivative of the Bo 105, the "Bo 107". In the meantime, Kawasaki of Japan was working on a helicopter with similar specifications, the "KH-7". The two companies got in touch and decided to collaborate, resulting in an agreement in early 1977 to develop a common "MBB-Kawasaki BK 117".
Four prototypes were built, with the initial flight of a German prototype on 13 June 1979 and of a Japanese prototype on 10 August 1979. A preproduction machine, made in Germany, performed its initial flight on 6 March 1981, with the first production machine, made in Japan, performing its initial flight on 24 December 1981. International certifications followed in late 1982 and early 1983, with deliveries of the initial "BK 117A-1" variant from both partners quickly following.
A "BK 117A-3" model -- there was no production BK 117A-2 -- was introduced in 1985, featuring maximum takeoff weight increased from 2,850 kilograms (6,285 pounds) to 3,200 kilograms (7,055 pounds), plus an updated tail rotor with greater diameter and twisted blades. Production then moved to the "BK 117A-4" in 1987, with minor improvements including a more robust power transmission, updated tail rotor head, and more fuel capacity.
* A general description of the BK 117 almost exactly matches that of the Bo 105. It had a conventional main-tail rotor configuration, with the main rotor system effectively borrowed from the Bo 105 but with larger blades (made of carbon composite instead of fiberglass), and a two-blade carbon composite tail rotor. The BK 117 had the same "pod and boom" configuration, with a somewhat more streamlined fuselage featuring skid landing gear and rear clamshell doors along with the side doors, plus twin swept fins on the tailboom. It was powered by twin engines, the powerplants being Avco Lycoming LTS 101-750B-1 turboshafts, each rated at 440 kW (590 SHP) for takeoff.
Like the Bo 105, few would have accused the BK 117 of being particularly sexy, though it had a certain clean utilitarian appearance. It was mostly made of aircraft aluminum, though it featured a few composite and titanium assemblies. Standard load was a pilot and seven passengers, with fewer passengers in executive versions. There was a forward-hinged door on either side of the cockpit and a rearward-sliding door on each side of the passenger compartment; the doors could be jettisoned in an emergency.
MBB-KAWASAKI BK 117A-4 _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ main rotor diameter 11 meters 36 feet 1 inch tail rotor diameter 1.96 meters 6 feet 5 inches fuselage length 9.91 meters 32 feet 6 inches footprint length 13 meters 42 feet 8 inches height (tail rotor) 3.85 meters 12 feet 8 inches height (rotor head) 3.36 meters 11 feet empty weight 1,705 kilograms 3,760 pounds max loaded weight 3,200 kilograms 7,055 pounds maximum cruise speed 255 KPH 160 MPH / 135 KT service ceiling 4,575 meters 15,000 feet range 585 kilometers 365 MI / 315 NMI _____________________ _________________ _______________________
Of course the BK 117 could be configured for air ambulance, SAR, cargo transport, and other duties. Optional kit included dual controls, a rescue winch, a belly cargo hook, weather radar in a nose pimple radome, searchlight, loudspeaker, inflatable flotation kit, skis, folding main rotor blades, and sand engine filters.
In 1985, MBB displayed a combat version of the BK 117A-3 designated the "BK 117A-3M" at the Paris Air Show. Kawasaki had nothing in particular to do with it: the Japanese constitution traditionally raised barriers to weapons export. The BK 117A-3M featured:
A wide range of alternate weapons fits was offered. There was polite interest, but nobody bought it.
In the late 1980s, MBB flew a BK 117 with a composite fuselage under a German government experimental program. In the early 1990s, Kawasaki also flew an advanced technology demonstrator, the "BK 117-P5", with a "fly by wire" flight control system. There were discussions with IPTN to assemble the BK 117 as the "NBK-117", but only three Indonesian machines were produced.
In 1987, production moved to the "BK 117B-1", with improved Avco Lycoming LTS 101-750B-1 engines and increased takeoff weights compared to the A-series. The follow-on "BK 117B-2" raised takeoff weight even more. The "BK 117C-1" series was introduced in 1992, featuring a modernized cockpit and twin Turbomeca Arriel IE turboshafts with 528 kW (708 SHP) each, replacing the Avco Lycoming powerplants.BACK_TO_TOP
* In 1997, work began on rethinking the BK 117 design, incorporating refinements derived from the EC135. Initial flight of the prototype was on 12 June 1999 in Germany, with a second prototype performing its initial flight in Japan on 15 March 2000; two more prototypes later joined the development program. Certifications of the "EC145", as the type was designated by Airbus, or the "BK 117C-2", as it was originally known and was designated in Japan, was in 2002, with production shipments beginning in that year.
The EC145 retained the general configuration of early members of the BK 117 family, except for a revised fuselage that provided substantially more internal volume, partly obtained by removing the cabin center post and door supports. It also featured a new main rotor derived from the EC135, with composite blades and a titanium hub, as well as a "glass cockpit" with flat-panel color displays.
The EC145 scored a major win in mid-2006 when it was selected to fulfill the US Army's "Light Utility Helicopter (LUH)" requirement. The LUH program was focused on obtaining an off-the-shelf helicopter with minor military optimizations for non-combat roles, freeing up combat-fitted machines for frontline service. The EC145 was given the Army designation of "UH-72A Lakota", with initial deliveries in late 2006; Joe Red Cloud, a chief of the Lakota Indian nation, was a participant of the initial acceptance ceremony.
The US Army expects to obtain 411 Lakotas in all, with two thirds of them going into service with the National Guard. Production is at an Airbus USA facility in Columbus, Mississippi. 187 of them will actually be configured as dual-control trainers, the Army having decided to use the UH-72A to replace the Bell TH-67 Creek / Jetranger in the training role. There's been little mention of changing the designation of the training machines to "TH-72A", suggesting the trainers will be employed in utility roles as needed. The first trainer UH-72A was handed over in March 2015; some of the trainers will be built new, while some will be conversions.
At least five of the UH-72As were assigned to the desert warfare training complex at Fort Irwin in California to support field wargames, playing as transport, scout, or gunship helicopters as needed -- kitted up with a "laser tag" system to perform, and receive, "attacks". They have additional kit to support range operations control, and are painted in desert camouflage colors.
Airbus has more or less revived the unsuccessful BK 117A-3M with a proposal for an armed derivative of the UH-72A for the US Army's "Armed Aerial Scout (AAS)" competition, with three "AAS-72X" demonstrators being built by Airbus in collaboration with Lockheed Martin. The first flew in 2010. Illustrations of the machine show it to have an imaging / targeting turret under the nose, plus a stores rack on each side, each rack capable of handing two Hellfire anti-armor missiles, or two 70-millimeter rocket pods, or a rocket pod and a gun pod. The AAS competition was suspended, but the requirement remains outstanding, and so AAS is likely to be revived sooner or later.
Airbus is also offering a similar "EC645" for other military requirements, with options for twin stores pylons, an electro-optic targeting system, and helmet-mounted sight. It has since been redesignated "H145M".
In 2011, Airbus announced the "EC145 T2" -- now "H145" -- with uprated Arriel 2E engines and drivetrain, fenestron tail rotor, updated avionics, and other new features. Initial deliveries were in mid-2014. The firm also has a militarized version, the "H145M" -- previously "EC645 T2" -- on offer, with initial deliveries in 2015 to German Kommando Spezialkraefte (KSK) special-operations forces. In addition, the firm is working with the French Army on an "optionally piloted" configuration of the EC145 for robotic resupply, initial test flights taking place in the spring of 2013.BACK_TO_TOP
* The MBB family of helicopters includes an Indian relative. In 1984, Hindustan Aerospace Limited (HAL) of India signed a contract with MBB for development of what was then designated the "Advanced Light Helicopter (ALH)", leading to rollout of a nonflying test airframe in the spring of 1991, and initial flight of the first of five flying prototypes on 30 August 1992. The five prototypes included two engineering validation prototypes, plus one prototype each of army-air force, navy, and civil versions. The production machine was to be given the name of "Dhruv (Polaris / Pole Star)". Deliveries were delayed because of US objections to Indian nuclear tests that blocked delivery of LHTEC CTS800 turboshaft engines, but production machines were finally delivered to the Indian Army in 2002, with deliveries following to other users.
The resemblance of an army-air force Dhruv to the BK 117 is unmistakeable, though the Dhruv is a bigger machine, with an empty weight about 50% greater than that of the BK 117. Otherwise, the two rotorcraft are very similar, with the Dhruv featuring a pod-&-boom / main-tail rotor configuration, clamshell rear doors, skid landing gear, twin swept tailfins, and a four-blade main rotor. It does differ from the BK 117 in featuring a four-bladed tail rotor.
The Dhruv is powered by twin Turbomeca TM333-2B turboshafts, each rated at 788 kW (1,057 SHP). The ultimate goal is to fit the locally-built Ardiden 1H / Shakti turboshaft, built by HAL with Turbomeca assistance, providing 895 kW (1,200 SHP) each for enhanced "hot & high" operation -- an important consideration for the Indian Army and Air Force, since operations are often conducted in the mountainous northern regions of the country. Composite materials make up a large proportion of the rotorcraft's structure. Fuel tanks are bullet-resistant, crashworthy, and self-sealing.
Two flight crew are normal, with 12 seats for passengers or 14 seats in a high-density configuration. In the medical role, the Dhruv can fit four stretchers and two medical attendants. Along with the clamshell rear doors, there is a hinged cockpit door and sliding passenger door on each side.
HAL DHRUV (ARMY-AIR FORCE VARIANT): _____________________ _________________ _______________________ spec metric english _____________________ _________________ _______________________ main rotor diameter 13.2 meters 43 feet 4 inches tail rotor diameter 2.55 meters 8 feet 4 inches fuselage length 13.43 meters 44 feet 1 inch footprint length 15.87 meters 52 feet 1 inch height (tail rotor) 4.98 meters 16 feet 4 inches height (rotor head) 3.93 meters 12 feet 11 inches empty weight 2,550 kilograms 5,622 pounds max loaded weight 4,500 kilograms 9,920 pounds maximum cruise speed 265 KPH 165 MPH / 145 KT service ceiling 6,500 meters 21,320 feet range, 10 passengers 220 kilometers 135 MI / 120 NMI _____________________ _________________ _______________________
The Dhruv can be configured as a gunship, with sensor turret on top of the nose; an undernose turret carrying a 20-millimeter cannon; and stores pylons for unguided rockets pods, anti-armor missiles, or air-to-air missiles. It is also possible to mount a light machine gun on a pintle in one or both doors; a defensive countermeasures system can be fitted as well.
The naval / coast guard version of the Dhruv differs from the army-air force version in having wheeled retractable tricycle landing gear -- skid landing gear is inconvenient for shipboard operations -- with the main gear assemblies retracting into sponsons. The naval version also includes a deck harpoon capture fixture; a sonar system; a stores attachment on each side of the fuselage for a torpedo or other munition; and a nose radar. A roof-mounted infrared imager is an option. HAL is working with Israeli Aircraft Industries to develop a drone version of the naval Dhruv.
The civil version uses the same wheeled landing gear scheme, but it differs from other versions in being fitted with hinged passenger doors. Civil Dhruves have been exported to Ecuador, Mauritius, Maldives, and Nepal. HAL has worked with Israel Aircraft Industries (IAI) on a military export version of the Dhruv, with a full "glass cockpit", a sensor system, a defensive countermeasures system, and an expanded range of offensive stores.
* The Dhruv is being used as the basis for a two-seat helicopter gunship, the "Light Combat Helicopter (LCH)". It is a direct descendant of the Dhruv, essentially taking a Dhruv in gunship configuration -- with undernose 20-millimeter cannon turret, day-night sight on top of the nose, and stores outriggers -- and replacing the normal forward fuselage with a stepped tandem seat fuselage. It features nonretractable wheeled tricycle landing gear. Initial flight of the first prototype was in March 2010. The Indian Air Force and the Indian Army expect to obtain 30 LCH gunship each, with the high power ratings of the engines making them particularly suitable for combat use under "hot and high" conditions.BACK_TO_TOP
* The primary sources for this document was a set of JANE'S ALL THE WORLD'S AIRCRAFT from my local library. Miscellaneous items were also obtained off the internet, particularly writeups from "aerospace-technology.com". Gorka Martinez, a fine source on things that fly over Spain, was kindly enough to field some questions on the Spanish Bo 105s on request.
I was actually intrigued to see both Bo 105s and BK 117s operating in the colors of a medical service in my original hometown of Spokane, Washington. There was a time when it was unusual to see foreign-built flying machines in the USA, but it is much less unusual than it was. Incidentally, the Red Bull brewing company, which has pumped a fair amount of money into flashy airshow flight demonstrations, operates a Bo 105 -- maybe more than one -- in airshow aerobatic demonstrations. I managed to finally see it in action at Marine Corps Air Station Miramar in California in 2012.
* As concerns copyrights and permissions for this document, all illustrations and images credited to me are public domain. I reserve all rights to my writings. However, if anyone does want to make use of my writings, just contact me, and we can chat about it. I'm lenient in giving permissions, usually on the basis of being properly credited.
* Revision history:
v1.0.0 / 01 jul 09 v1.0.1 / 01 apr 10 / Review & polish. v1.0.2 / 01 mar 12 / Review & polish. v1.0.3 / 01 feb 14 / Eurocopter became Airbus Helicopter. v1.0.4 / 01 jan 16 / Antitank Bo105s retired. v2.0.0 / 01 dec 17 / Broke into two chapters for ease of maintenance.BACK_TO_TOP