Since it was first introduced in the late 1970s, the S-76 has been a mainstay among corporate VIP helicopter operators, one of the most popular midsize executive rotary-wing transports. Sikorsky has now continued that tradition with introduction of the S-76D, the eighth rendition of the line that comprises the S-76A, A+, A++, B, C, C+ and C++.
First flown in March 1977 and with deliveries of the twin beginning two years later, the more than 800 S-76s put into service have collectively accumulated over 6.2 million hr. There are still more than 680 of the type operating in 42 countries around the world.
While the largest group of users, accounting for 430 aircraft, is the offshore oil industry, the second largest block of aircraft is devoted to executive transport and numbers more than 180 aircraft so far, logging in excess of 630,000 flight hours. Other markets primarily targeted by Sikorsky for the S-76 are emergency medical service (EMS) providers and search and rescue (SAR) units.
Those four groups are already welcoming the S-76D, with orders already placed by the Japan Coast Guard for SAR operations and the Chinese Ruili Jingcheng Group for aircraft configured for airline use. The Chinese company is expanding into the aviation sector through three aviation subsidiaries, including a helicopter operating company. Sikorsky also noted that along with the S-76D, Ruili Jingcheng ordered the larger S-92 for its airline.
A number of VIP executive transport aircraft have been ordered, and Sikorsky “is close to an EMS order,” according to Dan Hunter, Sikorsky's director of programs. There are also discussions with both Mexican and Chinese oil companies, he added, “and we're hoping for a U.S. fleet operator.”
Production of the S-76C++ ended in 2012, and first deliveries of the D model are scheduled for later this year. Sikorsky quotes a base price of around $12 million and up, depending on factors such as configuration, interiors, options and number purchased. This compares to $10.2 million to $10.4 million for a very, very new C++ and $8.5 million to $9 million for a midlife C++, according to Sharon Desfor, president of HeliValue$ Inc., the Blue Book of the helicopter industry.
The new model receivedcertification on Oct. 12, 2012, and is programmed to get Canadian Transport certification in April, followed by and Japanese certification in May. Brazilian certification is expected in the October/November time frame.
Airframe and Systems
The basic airframe remains the same as that of the legacy S-76. However, the new model is being offered with some significant improvements, which resulted from discussions with the owners, pilots and maintainers, Hunter said.
“They had a lot of input," he continued, "and we made a lot of changes based on their saying, 'This is really a pain, you did not think this out well.'” Discussions were held with users during 2005/2006, both in the U.S. and abroad, with “approximately 200 suggestions collected and used as input to the S-76D design,” according to Hunter.
The key areas addressed were reliability and maintenance, “with a number of items that were formerly options now included as baseline installations,” the executive said. “Most of the aircraft lighting has been upgraded to LED, and the remaining two non-LED lights are planned to be replaced as an in-line baseline change. LED lighting has increased reliability with lower power usage.”
Hunter also noted that a lot of the product improvements came from the S-92 program. “As they developed them, we stole them.”
Several changes have already been incorporated into the S-76D, while others are planned for the near future. The major upgrades include new engines, new rotor blades and a new all-glass cockpit designed to simplify single-pilot operations. Other changes now in the D model include a health usage monitoring system (HUMS), active vibration control and an improved autopilot. The HUMS had been available for the C++, but as an option. It is now standard on the D.
Improvements to come include a payload increase, SAR autopilot modes, improved crashworthiness of seats and floor as well as Type IV egress windows. A combined flight data recorder (FDR) and cockpit voice recorder (CVR) will be standard equipment on the aircraft, along with an integrated emergency flotation system. An automatic flotation deployment system will be available as an option.
One of the biggest changes involved replacing theArriel 2S2 engines on the S-76C++ with the Pratt & Whitney Canada PW210S, giving the D model not only more power, but greater fuel economy. (See “Power for a Gen-8 Helicopter” sidebar.)
The main rotor hub system is the same as that on the C++, but Sikorsky took the “Advanced Growth Blade” developed for the S-92 and newer versions of theBlack Hawk, and adapted it to the S-76D. These are all-composite blades as opposed to the metal blades on previous models and have a wider chord and reconfigured tips, although their length remains the same. The Advanced Growth Blade uses two geometric parameters — sweep and taper — to reduce main-rotor blade tip vortex. This gives the blade tip a swept-back angle, improving lift, while decreasing noise.
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.
won that election. With the notable exceptions being the model's Pro Line nav/com radios and '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.”
In its instructions to Thales to develop a totally pilot-friendly avionics suite, Sikorsky said that it wanted virtually all of the commands from the pilot to require no more than two pushes of a button, significantly reducing pilot workload.
“We did not meet that [two-push criteria] everywhere,” Hunter said. “There are some places that require more than two button presses because there is no way around it. But if they didn't design the software with that in mind, they had to come to me and ask permission to do it another way.”
The Thales system is fully coupled to the helicopter's flight control system so that by punching the appropriate button, most flight commands are automatically recognized and initiated at the appropriate time, such as flying to an ILS localizer and coupling with the ILS to fly the approach to touchdown.
The overall system is designed to provide everything the pilot needs in a single-pilot operation, requiring the absolute minimum amount of effort. It basically does everything but brew coffee, something to consider for a future E model, perhaps. (See “Avionics Suite as Computer” sidebar.)
Also new to the S-76D is aVigor HUMS as baseline equipage. The system provides the operator with a detailed analysis of the health of the aircraft, feeding the information to the operator and, at the request of the user, allowing that information to be fed to Sikorsky's Fleet Management Operations Center (FMOC) where it is monitored on a 24/7 basis and analyzed for trends in the aircraft's maintenance and usage. The FMOC personnel look for and evaluate any inconsistencies in performance against fleet trends to alert operators to potential maintenance problems.
The use of HUMS also allows the FMOC to recommend changes in maintenance programs. Hunter noted that the S-76D HUMS comes from the S-92 program, and those being used on that aircraft allowed operators to go from 4,700-hr. TBO to 9,400 hr. on the swash plate alone.
Hunter said that at this time the HUMS data are accessed through a USB port in the baggage compartment. However, several formats that operators can use are in the planning stage, including a card in the cockpit to allow the pilots to access the information, as well as eventual options for remote wireless access.
The D model is also equipped with a Moog active vibration suppression system, using force generators that measure the vibration frequencies and produce exact opposite frequencies to counter them. Operators can order up to six of these force generators, although each one adds weight and cost. While each operator will determine how much vibration is acceptable to the mission, Hunter said Sikorsky expects three to four to be the average.
The anti-vibration system is one of only three systems using AC power, although Sikorsky is looking at a program that may change the anti-vibration system to DC.
Sikorsky went with a totally redesigned electrical system for the S-76D “to address some customer issues and to maximize compliance with the FAA regulations,” Hunter said. He noted that the systems in the legacy aircraft were not satisfying D model requirements, such as providing additional torque to start the PW210S engine, requiring an increase from the legacy 200-amp rated generator to a 300-amp unit. The redesign put all the systems except anti-vibration, windshield heat and RIPS on a 28-volt DC electrical system newly developed by Sikorsky just for the S-76D.
Two AC generators were installed on the aircraft for the RIPS, with each capable of powering the whole system. These generators were put on the engines rather than the gearbox since the Pratts are able to produce plenty of power during cold weather when RIPS is needed, Hunter said. “All it does is raise the temperature of an engine a little bit. It doesn't rob torque out of the box. In the winter we have boatloads of power, boatloads of ITT margin. I want to use that torque that is going to the main gearbox to fly the aircraft, not to power the RIPS.”
The aircraft has also been designed to carry more fuel, which, combined with the more efficient engines, should result in greater range. However, the added components, such as HUMS and vibration control units, add weight which, in turn, threaten such gains, “and you never, ever want to deliver an aircraft with less range than its predecessor,” Hunter said. So to counter that, Hunter says Sikorsky plans to increase the maximum gross weight from 11,700 lb. this summer to 11,875 lb. and "essentially will get us back on parity with the C++ across the spectrum.” He further notes that the weight increase will actually increase the range over the C++ since most operators of that aircraft have already added optional equipment, such as HUMS, which is standard on the D.
The new model has a total fuel capacity of 296 gal. contained in two fuel tanks with gravity fuel fillers. These are supported by two independent suction fuel systems with cross-feed capability.
Flying the S-76D
Sikorsky offered BCA an opportunity to fly the new S-76D at its West Palm Beach, Fla., facility in late November 2012. While conditions on the appointed day were perfect for flying — winds light, about 17 kt., temperature a balmy 78F (26C), MSL a mere 20 ft. — they were terrible for an evaluation flight. And the aircraft weighed in at 9,494 lb., well below its 11,700-lb. max takeoff weight.
With the twin PW210S FADEC-controlled engines producing 1,077 shp each, pushing the aircraft to its limits was unlikely. But what I really wanted to see was just how much the pilot's workload was reduced by the new Thales TopDeck system. And as it turned out, an hour's flight with Greg Barnes, project pilot for the S-76D program, more than satisfied my curiosity.
The initial part of the demonstration flight was fairly standard, with me sitting in the right seat and Barnes in the left. The aircraft, N767J, was being used as an experimental/test aircraft, configured for flight tests, so no passenger accommodations were installed in the cabin.
Start-up was simplicity itself. Start-up power is supplied by a lead-acid battery capable of providing up to three starts. Power is controlled by two overhead “T”-shaped throttles, each having a start button at the end of one arm of the “T.” Push the button and the engine starts. If the engine senses anything amiss, it will automatically shut down. A hot start will cause the fuel flow to stop, but the engines continue to motor in order to cool down.
Push the throttle forward and you've got full power. The power can be applied slowly, in stages or in one quick thrust — pilot's choice. It's probably ill-advised to make it one quick thrust on an icy helipad.
Taxiing from the helipad to the runway was similar to the experience with most wheeled helicopters — pull in a little power, push the cyclic forward a bit to get it rolling, then steer with the pedals while giving just a bit of cyclic during a turn to keep it level. We taxied out to the active runway, where Barnes started by showing me that the aircraft can do a 360-deg. turn around its own axis.
He then picked it up to a hover while I checked power levels. Like most of today's glass cockpits, the Thales system uses a power limit (PL) indicator to monitor torque, inter-stage turbine temperature (ITT) and gas generator (Ng), displaying the one closest to the limit. In the S-76D, the gauges are based on 100%. In the event of an engine out, however, the remaining engine power can go up to 140% for 30 sec.
Rotor rpm is rated at 107%. It was originally set at 100% but was later increased to 107% of the original rpm, so that's where the limit rests.
If the aircraft enters a non-standard situation, such as operating 30 sec. with one engine inoperative, the scale moves the green line to the percentage limit for that condition with the time limit shown in amber.
As expected, at no time during our hovering exercise did the PL get close to 100%. The aircraft automatically computes its own weight, and at 9,494 lb., a stable hover showed 62% torque. The aircraft is limited to 35-kt. sideward and rearward flight, which required only 79-80% torque for each. There was no problem with authority with the tail rotor stuck into the wind since the wind was minimal. There was a slight increase in vibration, but that was it.
I found the aircraft to be a bit tight on the controls during a standard hover, and Barnes recommended using the force trim release buttons to loosen it up. That helped a lot — although it then seemed to be a bit too sensitive. But like pilots, every helicopter has its idiosyncrasies. A pilot simply gets used to each aircraft's, and it didn't take long to figure out how to handle this one.
The aircraft has force trim on both the cyclic and collective, so the pilot can adapt either or both controls to his own “pilot technique” feel for flying the aircraft. All hovering can, however, be done by simply “beeping” it where you want it to be by engaging the autopilot's velocity hold (VHLD). There is also a beeper trim button to move the aircraft up or down.
Placing a green circle at a point on the map display of the runway with zero airspeed dialed in puts the aircraft in a stable, hands-off hover. Repositioning the green circle repositions the aircraft. Changing the heading while maintaining zero airspeed turns the nose of the aircraft without changing its position. To change position, the pilot simply dials in where he wants to go. If it's a stable hover and the wind blows it off its hold point, it will recalculate and return to the original position.
Takeoffs, both normal and max performance, were without drama. Climb-out for a normal takeoff was at 75 kt., 750 fpm at 59/60% torque. The aircraft can monitor OAT and aircraft weight to determine best rate of climb, for both normal and OEI climb-outs, and indicate that rate by a little white triangle on the airspeed indicator.
Vibration level was moderate — acceptable but not great — although Barnes pointed out that the test aircraft only had one vibration suppression unit, whereas standard S-76Ds would likely have three or four, reducing vibration levels much further.
We climbed to 2,000 ft. holding 100 kt. in the climb, then accelerated to 130 kt. and engaged VNAV and RNAV (airspeed and area) to hold us on a steady course and altitude.
An assortment of charts is available to the pilot on the digital map (DMAP) display, to include Jeppesen approach charts and Thales multifunction moving maps. Barnes pulled up a vector chart to demonstrate the aircraft's flight path control. He simulated a large storm cell directly between our points A and B, then used the cursor control to mark a point to the right of the storm cell. The aircraft automatically turned toward that mark. He then remarked the original Point B, noting that when the aircraft reached the new point in space, it would automatically track to Point B, avoiding the storm. This was all done using the trackball and pushing a single button.
Sikorsky initially installed the Honeywell Primus 440 weather radar on its S-76s but discovered customers were replacing that with the 660 system. So, the Primus 660 is now the standard weather radar for the S-76D. The Thales system also offers XM Weather for on-screen satellite weather service as an option. Also available as an option is ADS-B and GPS precision approach capabilities.
To test basic flight characteristics, we took the aircraft up to its 155 kt. Vne, pulling only 50%. Barnes noted that while Vne is 155 kt., because of the efficiency of the Pratt & Whitney engines, maximum cruise speed for best range is 154 kt. He also noted that Sikorsky already has the data to expand the 155 kt. Vne limit “down the road.”
For steep turns, Barnes “beeped” the aircraft over into a 30-deg. angle of bank and put it on automatic hold. The aircraft held steady at 110 kt., pulling only 40% torque. The 30-deg. angle of bank is the maximum for automatic hold. That can be manually overridden to allow up to a 60-deg. bank — with a warning voice letting you know when you are reaching power limits.
Virtually all aspects of the flight can be done using the push-button controls on the autopilot control panel (APCP) located directly behind the trackball housing on the center console.
Barnes programed a flight plan for the approach back to Sikorsky's field and then coupled in the heading, airspeed and altitude using the push buttons on the APCP. The aircraft flew itself to the ILS and then automatically transitioned to ILS mode. The navigation, glideslope and deceleration commands are coupled to the primary commands in the autopilot, allowing the aircraft to fly hands-off down to the runway.
Repair work was being performed on the approach end of the runway, so we had to take over and land manually. However, by engaging VHLD and plunging the trim switch, you can program the system so that the aircraft descends to a specific altitude and comes to a hover over a specific spot, still hands off.
The aircraft also automatically decelerates. Once below 130 kt., the gear can be dropped and the aircraft settles on to the ground. The green line on the PL indicator automatically drops to 130 kt. when the gear goes down, one of the results of pilot input during the initial planning stages for the new D model.
Once on the runway, I taxied back to the pad with no trouble.
For shutdown, the book says that no cooldown time is needed for the PW210S engines. However, Barnes said he always cools them down for 1 min. Old habits die hard. I would have waited two.
The flight lasted 70 min., with a fuel burn right at 650 lb. Sikorsky shows a fuel burn of 578 pph in its charts, so our 557 lb. was very close. A lot of factors affect fuel burn, but the figures came out about right.
As for transitioning into the D model, Barnes said that a new guy could be using the aircraft “within a few hours,” and that after one or two flights, “the guys are doing things on their own.” I can see why. It's just a matter of learning which buttons to push. BCA
|2 Pratt & Whitney PW210S|
|Dual Channel FADEC|
|OEI (30. sec.)||1,241 shp|
|Continuous OEI||1,077 shp|
|Max Takeoff||1,050 shp 5 min.|
|Max Continuous||1,077 shp|
|Max. Gross Weight||11,700 lb.|
|Max. Cruise Speed||155 kt,|
|Max. Cruise Speed Vbr||154 kt.|
|Max. Range No Res.||441 nm|
|HIGE Ceiling||9,700 ft.|
|HOGE Ceiling||5,000 ft.|
|OEI Service Ceiling||7,550 ft.|
|CAT A — 100 ft. Deck||11,700 lb.|
|Cabin Length||7.92 ft.|
|Cabin Width||6.25 ft.|
|Cabin Height||4.42 ft.|
|Cabin Volume||204 cu. ft.|
|Baggage Volume||38 cu. ft.|
|Exec. Seating||2 + 6/13|
|External Noise||92 dBA||86 dbA|
|Internal Noise||87 dBA||83 dbA|
|CAT A, 100ft. Elev. Deck|
|Fuel Burn||94 gph||94 gph|
|Rig Approach Upgrade||N/A||✔|