BK117 – a Versatile High Performer
The medium sized BK117 utility helicopter boasts a rich design history. Two industry greats combined their aeronautical know-how and industry experience to produce a tough and robust design.
Since its introduction in 1983 almost 400 BK117s have rolled off the production line. Many of them have proven themselves in the highlands of Papua New Guinea and other remote regions of the world, to performing as fire fighters in less remote but, nonetheless, forbidding environments elsewhere.
The BK117 is capable of carrying a maximum of nine passengers in a high density seating configuration and it can carry up to four stretcher patients and two attendants in its role as an air ambulance if required. However, whether it is performing as a VIP charter helicopter or in an emergency services capacity, the BK117 is renowned for its reliability and strength – comforting factors in helicopter operations.
Many Emergency Medical Services (EMS) providers and Search and Rescue (SAR) outfits around the world recognise the helicopter’s structural robustness and durability and several examples are operated in Australia for precisely that reason.
One such operator at Essendon Airport in Melbourne, uses a BK117 B-2 for operations ranging in diversity from tourist and VIP charter flights to fire-fighting and air ambulance contract work.
The Helicopter Service Australia’s Chief Pilot Mitch Vernon, who has nearly 1,000 hours on the BK117 and 6,200 helicopter flying hours in total, said the helicopter had proven itself as a tough and dependable workhorse in the 11 years it had been with the company.
“The BK117 is built like a truck and we’ve used it for a whole range of diverse tasks since we started operating it. What’s more, it’s proven itself as a reliable and dependable platform: both bonuses in today’s operating environment.”
Despite the fact the company operates a number of helicopters, ranging in size and complexity from the Robinson R44 and Bell 206 JetRanger, to the Eurocopter AS350 Squirrel, the BK117 provided the company with larger carrying capacity clout with the larger charter operations.
While the Robinson R44 can carry a maximum of three passengers, the Bell 206 JetRanger four and the A350 Squirrel five, the BK117 can carry nine passengers if required.
“It’s got a respectable carrying capacity of 1,200kgs, which the other helicopters in our fleet can’t match. It’s powerful and it’s relatively straight forward to fly,” Vernon said.
The design history of the BK117 can best be described as the successful marriage of two engineering greats – German consortium Messerschmitt-Bolkow-Blohm (MBB) and Kawasaki Heavy Industries of Japan. Both companies had extensive experience in rotary-wing aircraft design, and the BK117 was the next logical step in the construction of a, “multi-mission medium-weight class, twin-engine civil helicopter” – the agreement for which the two companies signed in 1977.
In fact, the BK117’s predecessor, the smaller German designed Messerschmitt-Bolkow-Blohm MBB-105 utility helicopter possessed many of the features, such as the company’s rigid rotor system design, which would later be incorporated in the BK117; both helicopters share the same rotor head, despite their difference in size.
The two companies divided the design and labour of the main and tail rotors, tail boom, hydraulic systems and flight controls, empennage, transmission, landing gear and fuselage between them and prototypes for their combined efforts were unveiled in 1979. Since then, close to four hundred of the helicopters have been built and continue to fly today.
Despite having gone through a series of modifications/upgrades since then, such as gross weight increases and the addition of more powerful powerplants, the BK117 is still considered an exemplary design that was conceived in the ‘70s.
The fact it is still flying today – and probably will for some time yet – is testimony to the design’s success. The BK117 is powered by two Honeywell LTS101 turboshaft engines, which are rated up to 750shp depending on the series. Each successive series of the helicopter is denoted by the letters A, B or C which immediately follow the BK117 designation. The numbers immediately following the letter indicate further refinements/modifications, specific to that particular series.
The various series differ from each other primarily by their Maximum Take-off Weight (MTOW) and the maximum power output of their engines. The Helicopter Service Australia’s BK117 B-2 is equipped with the latest generation Honeywell engines and is capable of ‘hot and high’ operations; a performance characteristic which provides the company chief pilot with a degree of comfort, especially when operating in demanding conditions.
“The BK117 is quite a high performing helicopter. It can take quite a pounding and it’s not unlike a Ute in that you can basically load it up with items ranging from stretchers to skis and then just take off.”
“It is only 13 metres long, which is only 400mm longer than the Eurocopter AS350. However, it’s able to land in the same area as the AS350 because it has the same rotor diameter of 11 metres, yet it’s able to carry a 30 percent larger payload.”
Incidentally, the helicopter’s main rigid rotor assembly is the defining characteristic of the BK117 design. It consists of a titanium hub with attached reinforced fibreglass blades – which contrast with the standard semi-rigid rotor system of the Bell 206 JetRanger and the fully articulated rotor system of the AS350.
The strength derived from this assembly is sufficient enough for the BK117 to fly aerobatically – a feature not commonly associated with helicopters possessing the standard rotor mast assemblies.
Although Vernon insists the company’s BK117 does not perform such daunting manoeuvres during the course of its work, it does provide a degree of comfort and reassurance to fly such a structurally strong machine.
“Although it’s a fully endorsed aerobatic machine, we certainly don’t push the envelope there but it does have an extensive flying capability: it’s manoeuvrable and flies relatively well.”
According to the chief pilot though, the BK117’s rigid rotor system is both a blessing and a curse. He observed that the structural strength inherent in the design provided for a ‘harsher’ ride compared to other helicopter main rotor assemblies.
“Because the system is so ‘rigid’, as its name implies, the control response is fast but twitchy and the ride is not as smooth compared to other helicopters that don’t have this type of rotor system. But it’s built like a truck and it was designed as a utility helicopter first and foremost, so there is a trade off there.”
In addition to its unique main rotor design, the BK117 also includes two rear outward opening clamshell doors, which permit rear access to the cabin.
The helicopter is an effective stretcher patient transport, by virtue of its relatively roomy cabin dimensions and straight-forward access.
The BK117 has a maximum cabin height and width of 1.280 metres and 1.490 metres respectively, while the cabin length can be increased to 3.3 metres, depending on internal seating arrangements. Air Ambulance operators around the world have capitalised on this design feature of the BK117s, which explains their popularity as EMS platforms around the world.
The Helicopter Service Australia’s BK117 has served as an air ambulance for Victorian emergency services in the past – a capacity which was exploited during Victoria’s recent devastating bushfires. Although Vernon insists all helicopters in the company’s fleet perform well, it was the BK117’s versatility in being able to perform many roles that set it apart from the rest.
“We used it recently as an air ambulance, but we’ve also used it for fire-fighting and aerial crane lifting work too. And for the past 11 years we’ve used it for our ‘heli-link’ shuttle service to Mount Hotham and Falls Creek, during the ski season. In short, it provides quite a degree of versatility for our business.”
Despite a design that goes back to the ‘70s, the BK117 has proven itself as a very capable and durable twin-engine, multi-role helicopter. The helicopter has established its staying power credentials in an industry that is quick to sideline poor performers. It also goes to show that when rival companies put aside their differences and collaborate, their joint designs can be high-performing winners.