BELL IS DEVELOPING a technique to reduce the fly-over noise of its Model 407 light single-turbine helicopter, to meet expected demand for quieter aircraft for use on sightseeing operations over US national parks, such as the Grand Canyon.

The company has demonstrated its Quiet Cruise concept to park officials. It has achieved fly-over noise levels equivalent to those of McDonnell Douglas NOTAR-equipped tail-rotorless helicopters, among the quietest aircraft used for Canyon tours, says Dale Cato, product manager, commercial development at Bell.

The concept uses the full-authority digital engine-control system on the 407's Rolls-Royce Allison 250-C47B turboshaft to reduce rotor RPM to 90% in the cruise. This lowers the helicopter's never-exceed speed to 110kt (205km/h), which "-fits the profile of tour operators", he says.

The Quiet Cruise concept is in development flight-testing at Bell's Canadian commercial-helicopter plant and is scheduled to be available by early July. Full rotor RPM is used for take-off and landing, but the pilot can flick a switch in the cruise and reduce rotor RPM to 90-93%. The exact reduction "-is still being fine-tuned", says Cato.

The US Federal Aviation Administration has proposed phasing out all but the quietest, "Category C", aircraft now used for sightseeing tours over the Canyon. The NOTAR-equipped MD520N and MD Explorer are the only Category C helicopters now in use.


Source: Flight International