Sikorsky chose to scrap the mix of Rockwell Collins and Honeywell avionics in the S-76C++ and start fresh by partnering with Thales, a French company that also supplies avionics systems to helicopter makers Eurocopter and AgustaWestland. Dominating the S-76D's instrument panel are four large-format, flat-panel displays measuring 6 by 8 inches each, two integrated flight management systems, an electronic standby instrument and two beefy cursor-control devices mounted between the pilots on the center pedestal.
Unlike the various soft keys you might be used to in Garmin's G1000 or Avidyne's Entegra cockpits, the Thales TopDeck cockpit instead incorporates trackball controls that pilots use to access most any cockpit function, from setting the radios to calling up Nexrad weather images. Simplified drop-down menus ensure the pilots can access needed information as quickly as they can open a file on their PC.
TopDeck components take up less physical space in the cockpit, allowing Sikorsky designers to streamline the instrument panel and provide more legroom and better visibility, both of which should be welcomed improvements for pilots who complained they'd bang their knees in earlier S-76 models or they had trouble seeing over the glareshield. Ergonomic improvements aside, the ease of use and tremendous capability of the Thales suite should have pilots falling in love, designers say.
"The technology Thales has developed in the airline world for Airbus and the advanced integration of its avionics were really the two factors that led to our decision to go with the TopDeck cockpit," said Tim Fox, Sikorsky S-76D program manager. "Thales was able to offer features our customers said they wanted, such as advanced digital maps, integrated flight management systems and an architecture designed to keep the pilots' heads up and to present information so that typically they're no more than two mouse clicks away from any given function."
The Thales dual-channel digital autopilot in the S-76D will incorporate operating modes similar to those in the C++, in addition to a number of search-and-rescue modes offered as an option. One such mode, based on GPS input, lets the pilot press a button on the cyclic when directly over a rescue scene, such as a boat in trouble, and command the helicopter to fly a descent pattern putting it directly over that location in a hover at 50 feet — without the pilot ever having to touch the controls. This capability, Sikorsky stressed, will be included in a future TopDeck software load, probably about a year after initial certification, as will functionality more familiar to general aviation pilots such as GPS RNAV WAAS LPV approaches, XM satellite datalink weather and automatic dependent surveillance-broadcast (ADS-B).
Equally as important as what's being added in the cockpit are the improvements on the outside, and nowhere are the changes more apparent than atop the helicopter. The S-76D incorporates all-new composite main rotor blades with a wider chord and swept tips, enabling the use of less power to yield the same performance. The S-76D's introduction will also mark a switch to Pratt & Whitney Canada power after a 15-year hiatus, during which S-76 models have rolled off the production line with Turbomeca Arriel-series engines. The new main rotor blades enable the S-76D to lift about 500 pounds more than the C++ model does, though Sikorsky has decided against increasing the helicopter's maximum takeoff weight, currently 11,700 pounds, choosing instead to focus on performance improvements in challenging operating environments.
"Our customers told us they wanted more power to be able to operate higher and hotter, so rather than increasing the max gross weight, we went after the ability to operate the helicopter in a wider range of environments," Fox said. "The S-76D has more power than the S-76B and better fuel efficiency than the S-76C, so the engine change is bringing extra power to the helicopter in a very economical platform."
For pilots concerned about the structural integrity of the composite rotor blades, Sikorsky describes them as being "flaw tolerant," meaning that if cracks begin to form, they do so in a controlled way — in other words, when the rotor blades start to fail, they shouldn't tear apart in flight with potentially catastrophic consequences. Don't worry, though: The chance of the rotor blades developing cracks in the first place is said to be between slim and none.
The improved rotor design substantially reduces noise, to the point that Sikorsky has set a goal of marketing the S-76D as the quietest helicopter in its weight class. More flight-testing is needed before Sikorsky can make that claim, but designers promise the S-76D will exceed the Grand Canyon National Park standard — the world's strictest noise rule. Indeed, when the S-76C+ chase aircraft is heard flying overhead followed by an S-76D test helicopter, the difference is obvious. The S-76D's main rotor actually operates with lower lift, while the tail rotor, thanks to a number of design changes that allow it to rotate more slowly, essentially has disappeared from the noise signature.
The S-76D also incorporates rotor icing-protection technology borrowed from the larger S-92. The system uses electric heater mats embedded within the main rotor blades to shed ice automatically without pilot input — something you'd probably love to have on the wing and tail surfaces of your airplane. Sikorsky expects the S-76D to gain certification for flight into known icing after the full regimen of winter flight-testing is completed in early 2013.
Another improvement to the S-76D is the introduction of an automatic dual-rpm main rotor that switches from high to low speed based on a set of predetermined airspeed and altitude criteria. You can think of it sort of like the single-lever power in a Cirrus that adjusts throttle and propeller rpm simultaneously. The S-76D rotor operates in high-speed mode during takeoff and automatically transitions to low-speed mode when crossing certain altitude and airspeed thresholds, squeezing more range and reducing noise in cruise flight. The opposite happens when transitioning from cruise to approach and landing. Pilots and passengers — as well as people on the ground — can tell when the change occurs by the difference in sound, but there is no obvious performance difference, Fox noted.