Bell 429 showcases MAPL technology

 - October 16, 2006, 9:07 AM

Bell’s 429 IFR light twin caused quite a stir at its February launch. Not only did it replace a machine that lasted a mere 11 months–the 427 IFR–but it embodied many features of what the manufacturer proclaims to be a new approach to rotorcraft design.

Bill Stromberg, Bell’s executive director for commercial programs, is responsible for breath- ing life into both the 429 and the wider MAPL (modular affordable product line) concept. He said that while the 429 may look like the 427 and share some of its characteristics, it is a new aircraft that will require a separate pilot type rating.

“It has the same PW207D engines but better OEI performance, and a slightly modified transmission. It has a larger cabin (built by Korea Aerospace Industries, KAI), 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 increased significantly–220 cubic feet compared with 130 in the 427. “Externally it’s slightly wider and longer,” continued 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 EMS role.”

EMS Operations

The 429 has room for two litter patients, loaded either via the twin sliding doors or the optional rear clamshell doors, and two attendants sitting at their heads. Extra space was gained by relocating the flying control runs from inside the bulky “broom cupboard” between the seats– something of a Bell hallmark–to run behind the seats themselves.

Significantly, the 429 employs 10 of the 13 “critical technologies” that form the basis of the MAPL philosophy. Those technologies are: 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; and avionics suite.

The three others–which Bell is still working on–are an advanced-technology engine with lower running costs, a quiet anti-torque device and a main rotor system that enables higher speeds and c.g. variations.

Current plans call for first MAPL aircraft to be roughly the same size as the 429; in fact, the single-engine entry-level 351 will have the same cabin as the 429. However, Bell is able to “plug or unplug” sections to suit, say, an FAR 29-compliant twin, and it will be at this point that the idea of common type ratings comes into play.

Flight Tests

Stromberg said Bell is about halfway through detailed design and anticipates completion of that phase by year-end. “We have already begun flight testing components. 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 tailboom, 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 windshield. That’s not a Bell first or a MAPL technology, but it does enable us to design an open cabin by eliminating the control column behind the cockpit. We modified a 427 and have been flight testing it for more than a month without any problems. We have also been running the cables to temperatures as low as -40 degrees C without any observed problems.

“We have a vendor for these cables and expect to certify the design through the windshield center post as discussed. We are starting to build the new rotor blades, with a view to flight-testing them at around the end of the year,” Stromberg added.

A month ago, partner KAI released its first drawings of the cabin. Assembly of prototypes starts late this year, followed by assembly of production aircraft late next year. FAA and Transport Canada certification and first deliveries are expected in 2007.