New Bell presages MAPL technologies

Paris Air Show » 2005
December 12, 2006, 12:12 PM

Bell’s 429 IFR light twin caused quite a stir at its February 2005 launch during the Helicopter Association International show in Anaheim, California. Not only did it replace a machine with a shelf-life of only 11 months–the 427 IFR–but it embodied many features of what the manufacturer has hailed as a new approach to rotorcraft design.

Bill Stromberg, Bell’s executive director for commercial programs, is responsible for breathing life into both the 429 and the wider MAPL (modular affordable product line) concept. He told Aviation International News that while the 429 (priced at just under $4 million) may look like the 427 (priced at $3 million plus) and shares some of its characteristics, the new helicopter will require a separate pilot type rating.

“It has the same Pratt & Whitney 207D engines, but with better OEI [one-engine inoperable] performance, and a slightly modified transmission,” Stromberg explained. “It has a larger cabin [built by Korea Aerospace Industries], a new tailboom and new rotor blades. The blades are built using a new fabrication technique and have better aerodynamics that give the aircraft full capability up to 20,000 feet.”

Cabin volume is significantly increased–200 cubic feet compared with 130 in the 427. “Externally it’s slightly wider and longer,” said Stromberg. “We gained internal space by eliminating the fuel tanks from underneath the cabin bench seats to below the floor.”

The floor is now flat, which offers a great deal of flexibility; especially in the emergency medical services role. It will take two litter patients, loaded either via the twin sliding doors or the optional rear clam-shells, and two attendants. Extra space was gained by relocating the flight control runs from inside the bulky “broom closet” between the seats–something of a Bell trademark–to behind the seats.

Significantly, the 429 employs 10 of the 13 “critical technologies” that form the basis of the MAPL philosophy.

Current plans call for early MAPL aircraft to be roughly the same size: the single-engine entry-level Model 351 will employ the 429 cabin. However, Bell is able to plug or de-plug sections to suit, for example, a FAR 29-compliant twin, and it will be at this point where the concept of common type-ratings–much like Airbus–come into play.

Bell is now about halfway through detailed design and anticipates completion of that phase by year-end. “We have already begun flight testing components,” reported Stromberg. “We took the engines, in a 427 testbed, up to 20,000 feet and they performed flawlessly. We are now mapping temperature interaction within the cowlings and onto the composite tail boom, to help us map cooling systems and exhaust patterns.

“We have also flight tested new cable directional controls that run up the center-post of the windscreen,” he continued. “We’ve found absolutely no problem with either engine or control cables, up to 20,000 feet and, in an environmental chamber, down to -40 degrees C [-40 degrees F]. We are starting to build the new rotor blades, with a view to flight testing them around the end of the year.”

A month ago, partner KAI released its first drawings of the cabin. Assembly of prototypes is to start late this year and of production aircraft late next year. FAA/Transport Canada certification and first deliveries will start in 2007.

New Paths to Improvement


The New Bell 429 employs 10 of the 13 so-called “critical technologies” that form the basis for the manufacturer’s modular affordable product line (MAPL) market initiative.

• Rotor blade fabrication technique
• Blade tip shape
• Autopilot
• Aircraft data interface unit
• Cockpit
• Dual hydraulics
• Cabin
• Tail rotor drive-shaft
• Skids or retractable landing gear
• Avionics suite

The three others–which Bell is still working on–are an advanced technology engine with low running costs, a quiet anti-torque device and a main rotor system to enable higher speeds and center of gravity variations.

What Was Wrong with the 427i?

Customers who were quick to sign up for the Bell 427 IFR model have swallowed the premium associated with upgrading to the bigger 429. But why did Bell ditch the 427i?

Bill Stromberg, Bell’s executive director for commercial programs, said customer reaction prompted the move. “We have a [liaison] process that, among other things, helps us design new products. Initial team inputs were incorporated into the design of the 427i; in particular, calls to grow its cabin. As we developed the design, however, it became clear to everyone that just modifying it would not provide the space, features and comfort required to fulfill their expectations.

“At the same time, teams were exploring ways to accelerate the availability of the MAPL product line. In September 2004, we decided to develop a totally new cabin for the 429 as a MAPL technology.”

And it turns out the 427 still lives, at least for now. “Demand for the 427 VFR is excellent,” claimed Stromberg. “It is a reliable, low-cost light twin and we expect to continue selling it for many years.

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