PARIS AIR SHOW: Bell: certification imminent for Bell 429 rotor rocket

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Bell Helicopter is confident its new medium-light Bell 429 helicopter, here at Paris for customer demonstrations, will be a game-changer once it achieves certification this month. From its all-graphite tail boom and X-shaped tail rotor to its high cruise speed and Bell-engineered single-pilot instrument flight rules integrated cockpit, this PWC 207D-powered twin smacks of modern, courtesy of a technology push by both Bell's US engineering team and the company's Canadian arm in Mirabel.

While aircraft's speed was outstanding - it has a high speed cruise of 150kt (277km/h) with skids, 153kt with retractable gear, just under its 155kt red line power-on speed - perhaps more impressive was the amount of "grey matter" I saw on our tour of the production line here. Grey matter, in this case, refers to composite materials. On the 429, the gray components (the colour of the composites before final painting) represent a large portion on the helicopter's outer frame compared with earlier helicopter models like the Bell 412, also produced at Mirabel.

studio yves beaulieu 
 © Studio Yves Beaulieu

Michel Legault, director of business development for Bell Helicopter Canada, says the 429 frame is "mostly" composite on the outside, although on the inside it is roughly half metal and half composite. Korea Aerospace Industries had initially been selected to produce the frames, but Bell says the company "opted out" of the production, delivering instead subassemblies and/or parts for the first 25-35 aircraft. "Their scope has since been transferred to another supplier, Aerospace Industrial Development Corporation of Taiwan, a proven supplier of Bell Helicopter on existing products," Bell says.

The 429's two-piece composite drive shaft connecting the helicopter's two Pratt & Whitney Canada PW207D engines and 1,100shp (820kW) transmission to the tail rotor is also composite for the first time, allowing for fewer bearings along its length compared with the multi-section metal shafts of legacy models, a change that means reduced friction (hence noise) 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.

Despite popular notions, composites are not always lighter and cheaper than traditional metals parts for items like the tail boom, at least not initially, says Legault. The 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 proved out on the 429, cost savings due to simplified construction of the structures should start to accrue.

Operators will see longer life of composite elements, not only because of having fewer rivets, but because composite parts like the tail boom can be repaired after a ding whereas previously used monococque aluminium versions have to be replaced if dented, says Neil Marshall, Bell's programme director for the 429 and MAPL programmes. MAPL (modular affordable product line) is a technology development program Bell initiated in 2004, funded in part by C$230 million ($208 million) from the Canadian government.

The 429 is the first of a new line of Bell helicopters that will be beneficiaries of the programme. Bell Canada is responsible for the fuselage, integration and assembly of all of Bell's civil helicopters, including the 429.

On the flight line, a technology developed by Bell in the USA, providers of the dynamic components of the company's civil line of helicopters makes for a more neighbour friendly aircraft. "Something is missing," says Lagault of the "bold" sound the 429 makes when operating due to the slower speed of the four-bladed tail rotor. Legault says engineers considered a variety of counter-torque systems, including the fenestrom design, but ultimately chose an "X" configuration of two conventional tail rotors offset on a drive shaft, a solution that provide superior performance while eliminating problematic resonances typical with equally spaced four-blade tail rotor systems. Bell is evaluating a lightweight, low-cost tail rotor guard system that is says will be available in the first quarter next year.

Bell expects the 429 to be a tough competitor for similar Eurocopter and Agusta models. Marshall says the 429 features the cabin size and performance of the EC145 but at a price - $4.865 million in 2007 dollars per the letters of interest signed by customers - much closer to the EC135. The 429's price will increase once certificated, although Bell has not yet published the new "firm" price, says Marshall.

Bell is reporting 301 orders for the 429, which represents production up to 2013, says Marshall. The percentage of customers that will covert their letters of interest to firm orders, typically around 95%, remains unclear. "I'm not sure we'll get [95%]", says Marshall. Bell expects to produce a "handful" of aircraft this year, says Marshall, ramping up to 40 plus or minus 5 in 2010; 80 in 2011 and 96 in 2012. Maximum production capacity in Mirabel is 115 a year. "We'll get to 96 and see how the market is responding," says Marshall.

Within the 301 orders are 159 for corporate users or those who have not determined the configuration, 71 for emergency medical services, 17 for law enforcement, 49 for utility or offshore work and five "other". The largest percentage of the helicopters will go to North American (40%), with Europe, Africa and the Middle East coming in at 25%, Asia Pacific at 20% and Latin America at 16%.

Although Bell has met its plan to limit maximum weight of the 429 to 3,180kg (7,000lb), the upper limit of a Part 27 certification rather than the more rigorous Part 29 transport category, the aircraft has gained weight, reducing useful load from the planned 1,225kg to 1,175kg, a cut of 2.6%, says Marshall.

Production aircraft will initially come with skids, although Bell says a retractable landing gear, available in 2011, will increase maximum cruising speed to 153kt. Expected direct operating costs for the helicopter will be $664 an hour initially.

Bell Helicopter test pilot Leo Meslin, flying ship number 57002 for our demonstration flight, noted that the 429 with skids has an endurance of 2.25h flying at 150kt and 94% power, a value that is easy to read on power situation indicator page of the centre console flight display, one of two Rogerson Kratos displays that come with the standard package. Three displays are available as an option. At near gross weight, Meslin established at 60kt airspeed at 98% torque that resulted in a 2,600ft/min (13.2m/s) climb. Upon simulating an engine failure, an easy feat with the Bell-designed software for the integrated avionics, Meslin cruised at 94kt and was able to climb at 1,200ft/min with a forward speed of 60kt. Autorotation for the 429 is similar to that of the Bell 206B, he noted, with 2,000ft/min descent rate 60kt airspeed.

The 429's dual automatic flight control system (AFCS), which features both systems running simultaneously for hot back-up, includes a stability augmentation system that damps motion in turbulence, slows the aircraft's reaction to pilot inputs and provides for a more co-ordinated and more comfortable ride for passengers. "It makes a bad pilot look good," jokes Meslin. With the system turned off, the 429 is "slightly" more unstable in yaw and quicker responding, but there are no operational limits such as reduced speeds that kick in as a result, he says

Once the 429 certification is complete, Legault says Bell will investigate a single-engine version certificated under Part 27 (under 3,180kg), which the current 429 model is being certificated under, and an enhanced twin-engine model certificated under Part 29. "As soon as the Bell 429 is certified, we will flight test to see how much more 'juice' is in the aircraft," he says. All-new helicopters that employ and expand the MAPL technologies are also in discussion. Legault says: "We're working hard to decide the what, when and if on other models of the MAPL line."