Bell Canada: composites not a grey area

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Colour is a giveaway as to the technology difference between Bell Helicopter's new Bell 429 medium-light twin helicopter and its more traditional brother, the Bell 412, on the final assembly line at the company's Mirabel plant near Montreal.

Michel Legault, director of business development for Bell Helicopter Canada, explains the difference - grey parts are made of composite, yellow parts are metal. "The 412 has a lot of yellow; the 429 has a lot of gray," he says of the helicopters' pre-paint livery.

The trend is set to continue as grey further becomes the new green for the Canadian arm of Bell Helicopter, the location responsible for the fuselage, integration and assembly of all of Bell's civil helicopters, including the 429.

Originally intended as an instrument flight rules version of the Bell 427 twin, the 429 started instead as a larger clean-sheet design in 2004, taking advantage of a C$230 million ($209 million) Technology Partnerships Canada loan that covered about one-third of the cost of its development. The resulting Modular Affordable Product Line (MAPL) initiative was responsible for key new technology items on the 429 from the Canadian side.

studio yves beaulieu
  © Studio Yves Beaulieu
The Bell 429 is the helicopter manufacturer's first clean sheet design since the V-22 Osprey

Legault says the 429 frame, which is being built by Aerospace Industrial Development Corporation in Taiwan, is "mostly" composite on the outside, although inside it is roughly half metal and half composite. The two-piece drive shaft connecting the two Pratt & Whitney Canada PW207D engines to the X-shaped tail rotor is also composite, allowing for fewer bearings along its length compared with the four-piece metal shaft on legacy models, reducing friction and increasing life.

Along with an all-graphite tail boom, built with a flat bottom for easy placement of antennas, the 429's horizontal stabiliser is also composite.Composites are not always lighter and cheaper than traditional metals parts for items like the tail boom, at least not initially. The big gain for Bell has been in the reduction of rivets and the associated fatigue that occurs at the joints due to a helicopter's rotating elements.

With the technology proven on the 429, cost savings because of simplified construction of the structures should start to accrue. Operators will see longer life of composite elements, not only through having fewer rivets, but because composite parts like the tail boom can be repaired after a ding whereas monocoque aluminium versions have to be replaced if dented, says Neil Marshall, Bell programme director for the 429 and MAPL programme.

Once the 429 certification is complete this month, Legault says Bell may investigate a single-engine version certificated under Part 27 - below 3,180kg (7,000lb), which the current 429 model is being certificated under - and an enhanced twin-engined model certificated under Part 29. All-new helicopters that employ and expand the MAPL technologies are also in discussion, says Legault.

Novel research, described as "pre-competitive", will push the composite state of the art for helicopters coming later in the next decade and beyond. Legault says Bell is "working with another Canadian company" on how to develop an all-composite fuselage for future helicopters using technologies that not only reduce the cost of fabrication, but also allow the composites to be used for more complex types of parts. Such technologies, says Legault, will make current composite construction techniques seem antiquated.