The tail rotor also received a tapered blade tip and its chord was increased by “about an inch,” Hunter said, adding, “This allows us to slow the tail-rotor tip speeds down through changing the gear ratio in the intermediate gearbox. This gives us the same performance because it's an increased efficiency rotor [while] substantially lowering the acoustics of the aircraft.”
Sikorsky rates the external noise levels of the D model at 86 dBA and internal at 83 dBA, compared to 92 dBA and 87 dBA, respectively, for the C series.
Both the main- and tail-rotor blades are built with heating mats in them for the rotor ice protection system (RIPS), whether a new owner wants RIPS installed or not. RIPS has not yet been certified, but all the provisions for the system can be optionally built into the aircraft. Certification is expected in the 2014/15 time frame, at which point the system boxes can be added. The hardwiring put into the airframe weighs about 100 lb., while the boxes weigh around 200 lb. However, the operator can take the boxes out during the summer months to save that weight.
Perhaps the most significant product improvement to the D model, at least as far as pilots are concerned, is the fully digital glass cockpit.
The very earliest S-76s had virtually no digital instruments, while the C++ had a limited glass cockpit provided by Parker-Gull of Long Island, N.Y.
“For the avionics suite, we started with about eight vendors who responded to the RFP. Then we down selected to three and scheduled a customer's conference, with all three presenting their systems to the customers. Then the customers voted on it,” Hunter explained.
Thales won that election. With the notable exceptions being the model's Rockwell Collins Pro Line nav/com radios and Honeywell's Mark XXII EGPWS, all of the avionics are from Thales' TopDeck avionics suite, powered by the DC generator. Thales offered a com radio with its system, but the customers clearly preferred the Pro Line unit.
Thales also developed the four-axis autopilot, of which the S-76D has two. That way, if one fails, the other automatically takes over with no pilot input, although the pilot is alerted to the fact.
Thales says the TopDeck integrated modular avionics suite represents the company's “most advanced avionics suite for rotor-wing aircraft.” For the S-76D, Thales specifically created a new program that uses a “click to fly” concept. The Toulouse, France-based company says that the new concept is based on “functionalities that improve intuitivity, interactivity, integration and safety,” or “Icube-S.”