BELL HOPES TO emulate the success of the 407 with its new light twin-turbine helicopter, the Model 427. At just under $2 million, the price goal is even more challenging than that for the 407, because the 427 is essentially an all-new aircraft. The 427 will be certificated simultaneously to the latest US and European FAR/JAR 27 aviation rules, requiring the helicopter to meet crashworthiness requirements Bell avoided on the 407 by amending the existing 206 type certificate, says commercial product manager Michael Blondino.

The result is an entirely new fuselage, which has been stretched 330mm compared to that of the 407 to enable the fuel cells to be moved out from under the passenger seats. The forward cell has moved to behind the crew seats and made taller, as has the aft cell, which is located behind the rear passenger seats. This allows the installation of energy-attenuating seats for all occupants.

The stretch has also enabled Bell to install six forward-facing seats in the cabin, instead of the two aft-facing and three forward-facing seats in the 407. The roof beam which reduces headroom for the middle occupant on the 407's rear bench has been relocated on the 427 to above the roof. The cabin floor has also been "cleared out", Blondino says, to make it easier to carry cargo.

The stretched fuselage is long enough to allow a litter to be carried in the cabin while there are two crewmembers in the cockpit, "...which is difficult for a light helicopter," he says. For single-pilot operation, the left forward fuel-cell can be removed and the litter pushed forward into the cockpit, enabling the attendant to sit at the patient's head.

The fuselage is composite and will be produced in four pieces - two side panels, floor and roof - and the longer nose, which is modelled on that of the Bell 430, to provide more room. The tailboom is metal, which is both lighter and cheaper, Blondino says. Eventually South Korea's Samsung Aerospace will produce fuselages and tailbooms for all 427s.

The rotor system is based on that of the 407, but strengthened and with 305mm longer blades. The 427 is powered by a pair of Pratt & Whitney Canada PW206D turboshafts capable of producing 910kW (1,220shp) take-off power, but limited to 595kW by the transmission, which provides good hover and hot-and-high performance, Blondino says.

The new "flat-pack" transmission is simple, with only four gear meshes compared with ten in the 407. There is no combining gearbox, as used in the 206LT light twin, and the engines drive directly into the transmission, reducing weight. A liquid-inertial transmission-mounting system, like that on the 430, is used to reduce vibration.

Other planned design features include a machined I-beam skid landing gear which is dynamically tuned to avoid ground resonance. This design offers "tremendous" weight and cost benefits, he says, and may be fitted to the 407.

The 427 will have a 2,720kg maximum take-off weight, 1,140kg useful load, 136kt (250km/h) maximum cruise, 653km (353nm) range and 10,500ft (3,200m) out-of-ground-effect hover ceiling - figures which Blondino says are "very competitive" for this class of helicopter.

Bell has begun assembly of the first 427 prototype at its Canadian commercial-helicopter plant at Mirabel, near Montreal, and the aircraft is scheduled to be flown in December 1997, with certification following in December 1998.

Source: Flight International