A heavily modified, ultra-quiet version of the Sikorsky S-55, dubbed the Whisper Jet, has been unveiled by its Washington-based developer following certification by the US Federal Aviation Administration.

Conceived and developed by Whisper Jet in conjunction with Florida-based Vertical Aviation Technologies, the initial version of the helicopter is entering service with Papillon Grand Canyon Helicopters on sightseeing tours of the noise-sensitive canyon area.

The six-year, $10 million project is the brainchild of Whisper Jet and Papillon president Elling Halvorson, who has struggled to overcome the increasing pressure from environmentalists to stop or curtail air tour operations around the Grand Canyon.

Key modifications include a switch to a five-blade main rotor system in place of the three-blade configuration and re-engining with a Honeywell TPE331-10 turbine fitted with an acoustically treated inlet plenum and a noise treated exhaust.

"The goal was to reduce noise by half," says Halvorson, adding that the more powerful engine also provides significant performance improvements.

Measured at a flyover altitude of 500ft (150m) and a gross weight of 3,500kg (7,700lb), the Whisper Jet has a sound exposure level of around 81dB, compared to roughly 82dB for the MD Helicopters' MD900. Planned enhancements are expected to reduce this to around 78dB at weights over 3,630kg, says the company.

The new rotor and bigger engine allow the rotor tip speed to be reduced, while increasing overall performance capability. Engine RPM is cut back to 92% for operations, further reducing noise.

Source: Flight International