GRAHAM WARWICK / WASHINGTON
Medium twin-turbine will have uprated engine, quiet tail rotor and de-icing system
Sikorsky plans to introduce an improved S-76 medium twin-turbine helicopter in the second quarter of 2004. Upgrades will include an uprated engine, quiet tail rotor and de-icing system. Evaluation of an integrated cockpit and cabin comfort enhancements continue, says Tommy Thomason, vice-president, civil programmes.
Engines will be upgraded to the Turbomeca Arriel 2S2, offering 6% more power than the current 2S1 and featuring dual full authority digital engine control. Thomason says the extra power will be used not only for performance enhancement but to ensure the engine reaches its scheduled overhaul interval - an issue with the Arriel 2S1 after its introduction on the current S-76C+.
Already test-flown on the S-76, the quiet tail rotor has an improved aerofoil with swept tip and flush fasteners. This allows rotational speed to be slowed, reducing tip speed and annoyance level, and brings S-76 noise "well within the range" of competing helicopters, says Thomason.
The uprated engine and quiet tail rotor will be standard on the improved S-76. The electric-mat main and tail rotor de-icing system will be optional. All three upgrades are expected to be retrofittable to at least some of the S-76s in service. "The uprated engine will be retrofittable to the C+, and possibly the C, while the de-iced rotor may be limited to the C," says Thomason.
A decision on a new cockpit with flat-panel displays and digital databus architecture is expected early next year. Honeywell's Pirmus Epic and Rockwell Collins' Pro Line 21 are candidate systems. Goodrich's health and usage monitoring system will be an integral feature of the new design, and differential-GPS satellite navigation with automatic approach to hover will be an option.
Sikorsky is evaluating options to enhance cabin comfort, including active noise control (ANC), active vibration control (AVC) and a low-noise main transmission. AVC has been developed for the S-92 and a production-standard ANC system will be test flown this year. A low-noise transmission would use gear designs from the Boeing Sikorsky RAH-66 Comanche.
The upgrades are intended to maintain the S-76's competitiveness against the slightly smaller Eurocopter EC155, now entering service, and the slightly larger BellAgustaAB139 now in development. All three manufacturers are eyeing the potential market to replace some 250 S-76As now in service, mainly with the offshore oil and gas industry.
Sikorsky has increased investment in the S-76 after securing a deal with Aero Vodochody in the Czech Republic which will reduce production costs for the helicopter. The transfer of airframe manufacture to Prague-based Aero has entered its third and final phase, with the Czech company beginning fabrication of the structure from raw material. In the previous two phases, Aero first completed then assembled airframes produced by Sikorsky.
Airframes manufactured by Aero are shipped to Sikorsky in Stratford, Connecticut, for final assembly, flight acceptance and airworthiness certification. Green aircraft are then flown to Keystone Helicopter in West Chester, Pennsylvania, for interior completion. The first S-76s fully manufactured by Aero will be delivered early next year.
Source: Flight International
