Sikorsky Aircraft Co., a division of United Technologies, was the first to mass-produce military helicopters. A leader in vertical flight technology since founder Igor Sikorsky immigrated to the United States from Russia in 1919, it became increasingly challenged throughout the 20th century by both domestic competitors – such as Bell, Boeing (nee McDonnell Douglas, nee Hughes), and Kaman – as well as foreign – including Eurocopter, Mil, and AgustaWestland.
In recent years, however, the helicopter industry as a whole has been accused of failing to innovate, failing to push the envelope the way fixed-wing aircraft have, from military fighters to commercial airliners to private and business platforms. The last major innovation, insofar as many observers are concerned, was NOTAR (no tail rotor), introduced on production helicopters by McDonnell Douglas in 1990.
No matter the manufacturer or mission, helicopters in 2011 are built on the same primary design that made Sikorsky the first successful rotorcraft nearly a century earlier. Some analysts blame a limited market with no tolerance for risky – and expensive – new designs. Aside from improvements in materials, engines, rotors, flight controls, and, even more modestly, speed, range, and payload capacity, the remaining manufacturers, while highly competitive, have not been encouraged to push the envelope.
Which makes the nearly simultaneous decisions by Sikorsky and Eurocopter to self-fund a radical improvement to a long-standing rotor-wing limitation – speed – all the more interesting. Sikorsky got there first with its X2 TechnologyTM Demonstrator, which set an official level flight record of 250 knots on Sept. 15, 2010. Eurocopter’s X3 joined the exclusive new superfast helicopter club a few weeks later at 180 knots, then reported achieving 232 knots at level flight for a few minutes on May 12, 2011.
A month later, Sikorsky Vice President for Research and Engineering Mark Miller spoke with Defense senior writer J.R. Wilson about the X2, which won the prestigious National Aeronautics Association Collier Trophy for 2011, the 100th anniversary of its creation. Miller, a former Lockheed Martin Skunk Works executive, emphasized anyone hoping to sell a superfast helicopter first must demonstrate it also exceeds existing aircraft in a wide range of key performance parameters (KPPs).
J.R. Wilson: How has your Skunk Works background influenced the direction you are taking Sikorsky R&D?
Mark Miller: Skunk Works was a culture of innovation, taking small, empowered teams – early in big programs, throughout the life cycle of smaller efforts – giving them a very tough operational problem to solve and the resources to do that. So thinking out of the box, making a paradigm change in certain mission parameters that could make a real difference to the customer, is something I brought here from Skunk Works.
In a time of tight budgets and new program cancellations or delays, why did Sikorsky decide to self-fund R&D on the X2 Technology Demonstrator?
We have been operating in this industry very much in an age of incrementalism. If you look at how a helicopter flies and its characteristics, it really hasn’t changed much in the last 50-plus years. So we could have waited for a challenge and funding from the U.S. military or continued on the path of incremental improvements to conventional designs.
But we felt it was time to lean forward and do something creatively that would change the game in how helicopters are viewed and how they operate. The challenge was to take everything great about a helicopter – low-speed handling qualities, maneuverability, low down operations – then add a dimension – in this case, speed. So it is not an airplane that can hover, but a helicopter that adds the dimension of speed.
The X2 represents a number of technology and performance advances. How important was it to bring all of those together in the same test aircraft?
Sometimes when you innovate, you do go along a certain dimension. With the X2, we used anything we could that already existed and wasn’t pertinent to the innovations we wanted. But there also was innovation beyond just speed.
The key performance factors included speed – 250 knots – but also low vibration, low pilot workload, and low acoustic signature. So we brought together fly-by-wire flight controls, coaxial, pusher-prop, interactive vibration control, etc., and integrated those in the X2 to achieve all those elements.
If we had just done speed and not demonstrated the others, you would always be answering the question: Would these things be issues in a production program? I think we fundamentally proved not only the physics of going fast, but doing it in an environment that was quiet, easy to fly, low vibration, and everything a helicopter can do well.
What were the key technology enablers for those systems and capabilities?
Fly-by-wire enabled us to automate some things, so that is a foundational element for us now. Active vibration control is a technology on our S-92 platform, where you have a distributed active system tuned to reduce vibrations at certain frequencies. That was tailored for the X2, [combining] an active vibration control system, the ability to vary rotor speed, and having the prop and main rotor interactively controlled.
What is the advantage of fly-by-wire and how does its implementation in the X2 differ from traditional helicopter control systems and from other fly-by-wire systems?
Fly-by-wire enables advanced control laws. You think along the lines of automation, especially if you get into unpiloted modes, and helicopter control laws that allow you to auto-hover and land and continually fly in a challenging environment. The control laws we incorporated address all that, plus the expanded speed envelope, the dual-rotor system, and its interaction with the pusher-prop.
The X2 is really a system and needs to be viewed as a system. We’ve done most of these technologies on other programs, but how we integrated on the X2 is truly unique and a real differentiator.
To what extent and how well did the X2 achieve its key performance parameters, such as:
- High speed?
KPPs are the few vital performance attributes that, if you find at any point you won’t meet, it will stop the program. The speed KPP was 250 knots, which was achieved in September 2010 in level flight. We actually got above 260 in a bit of a dive.
It’s interesting with development programs; we said when we met all program goals, that would be the end of this demonstration program and we would then look at whether to launch any derivatives of it. And that’s what we’ve done.
- Low pilot workload?
Simply put, easy to fly, single-pilot operations. Back in the ’70s, when we had another go at this, it was very much a dual-pilot workload and a very challenging aircraft to fly. This time, it took us 17 flights to do the full envelope expansion of the aircraft and the KPPs, so the handling qualities were conducive to a low pilot workload and single-pilot operation.
- Low noise?
There are two ways to look at it: You could fly almost double the speed of a typical helicopter today with the same noise signature or at lower speeds with almost a 50 percent reduced signature.
Another attribute is you can declutch the prop, so the helicopter can fly with just the counter-rotating rotors. In urban environments, for example, you can take out the tail rotor signature completely, which is a major part of the overall helicopter signature.
Of all the attributes of the helicopter, I think that is a very operationally compelling feature for commercial, but also certainly for military applications.
- Low vibration?
Without going into specific numbers, we used an active vibration control system, with software subsystems mounted in specific locations on various parts of the aircraft to counter vibration from the moving components, such as we also use on the S-92 and the Blackhawk UH-60M. For the X2, we optimized where these would be employed; it was less distributed throughout the aircraft and more attacking vibration at the source to achieve conventional helicopter best-in-class levels.
- High-altitude hover?
We didn’t do a lot of that with this particular aircraft. We met the performance attributes of the X2 without predetermining a mission.
We were developing a suite of technologies, proving the fundamental physics, showing the package addressed any technical challenges we had seen earlier and, having met all KPPs, seeing how to apply it. We have since launched the S-97 RaiderTM, basically targeted at the armed aerial scout requirement. We will have two prototypes pushing maneuverability and the “g” envelope, along with hot/high performance.
- Increased maneuverability?
The X2’s maneuverability is a very sporty capability because of the prop accel/decel. We will push out to 3 g on the S-97 because maneuverability was not a major KPP for the X2, but will be fully demonstrated on the Raider.
How did you resolve the need to incorporate multiple flight controls into the small space available?
The computational challenges weren’t really an issue on the X2, but packaging all the components, systems, and subsystems was a testament to our design tools and digital design environment. Having seen what others in the industry are doing, I think those tools allow for the tolerancing and fit and precision assembly that were really necessary to package this system together. So it was not so much just miniaturization – space and weight also were considerations.
To what extent were simulators used in the X2 program – and how did they affect its development?
Between each flight, we took what we learned and the pilot would get into the simulator and basically fly the mission again. It was a bit of a wind-tunnel-in-the-sky approach, where we learned things as we flew, then incorporated those into the simulator to adjust the control laws as necessary before we went back out to fly again.
Is this the first time simulation has been used to this extent – during the actual flight tests – on a program of this size and complexity?
The sophistication of our modeling is now very good, as is the ability to simulate the flight characteristics of the vehicle. So we start a program with better knowledge of how the aircraft will fly and behave than we’ve had before. Then when we do a flight and find some control law needs fine tuning, we can go back into the simulator, quickly make adjustments, prove their effectiveness, incorporate them into the aircraft control laws and software, and get back into flight very quickly. On the X2, that proved to be very effective.
So our philosophy now is simulator-fly-simulator update-fly.
Your test pilot said the X2 flies like a jet more than a traditional helicopter. What does that mean, in operational terms as well as mission performance?
This aircraft has very stiff rotor blades, fly-by-wire controls, and the pusher-prop instead of the usual helicopter tail rotor. That ensures it can cruise efficiently and smoothly at 250 knots without the pilot having to manipulate the controls every second. That lower pilot workload, plus minimal fatigue from lower vibrations and achieving speed and level acceleration/deceleration with the prop, makes it more like flying a fighter in the high-speed flight regime.
How important is the X2’s ability to maintain level attitude rather than dipping the nose down to gain forward momentum? Was that a design intent or was it just serendipitous?
Yes. That ability is a characteristic of this technology, so it was envisioned we would be able to do it. And it has operational benefits. Basically, changing the pitch of the blades on the pusher prop allows the pilot to do a quick stop, hold a precision hover while pivoting, and maintain weapons on target without having to keep an eye on nose attitude. So it changes how a pilot would use the helicopter in certain mission scenarios and that is a very useful feature in certain missions.
How does the X2 compare to other rotor and short takeoff/vertical landing (STOVL) aircraft in terms of the ability to hover at multiple altitudes and pitches other helicopters or even other STOVL aircraft might not be able to attain?
The dimensions of that are fairly unlimited. The variable pitch on the prop gives you another dimension of operating ability in a given envelope. That really opens some doors to greater creativity in using the helicopter. In addition, the X2 has the low downwash characteristics of a helicopter, so it can hover over a building roof to do a rescue.
What about such factors as pivoting without sliding backward, range, speed?
If we look at an operational situation, with all the characteristics of a helicopter – lower speed, improved handling, downwash – then arm it, it will do 225 knots, significantly more than double an OH-58D. So you have speed to the fight, then maneuverability and agility and other capabilities when you get there. And that 100 percent speed increase is what is important.
We’re looking at dash speeds of 275 knots, so it isn’t as fast as an MV-22, but it is a helicopter and brings the attributes of a helicopter the [tilt-rotor] Osprey does not, which is significant to many missions.
How about operating altitude and payload?
It will hover out of ground effect at 6,000 feet in 95 degree F temps with six passengers [with full combat gear] and has the capability to operate at over 10,000 feet. If you look at an OH-58D in Afghanistan, where you get maybe 40 percent coverage of the country, we’re projecting more than 90 percent coverage with the S-97 Raider. So you can get places and do things you can’t do with the asset they have out there today.
How will the Raider differ from the X2?
With the Raider, we will have two aircraft, about one-third bigger than the X2 at 10,000-plus [pounds] gross weight. The first aircraft will do all the structure envelope expansion and demonstrations. The second will do actual mission demos, carrying a range of weaponry and external as well as internal stores. We’ll have the customer work with us on missionizing that aircraft with weapons and sensors and demonstrating mission features.
And a major concern in the field – logistics and maintenance tail?
Direct operating cost numbers are certainly below current aircraft – tremendously lower, targeting at $1,300 to $1,400 per flight hour. It is very helicopter-like in reliability and maintainability. We’re not reinventing any new systems with inherent lower life components. We’re taking everything we’ve learned from our fleet management center and rolling the best of that into this helicopter.
A lot of attention is given these days to fifth-generation fighters – high-speed cruise, stealth, range, and payload advantages. What designation would you give the X2/S-92?
We don’t use X-Gen titles [for rotorcraft], but I think people are seeing this will enable missions done today to be done more efficiently, plus helicopters doing things they could not do before. Let’s continue a comparison with the OH-58D – where the X2 has twice the range, twice the speed, twice the endurance, twice the payload, and 150 percent hover altitude increase and better acoustics. These are not incremental improvements, they are game-changers when you think about how it will operate.
What response have you had from potential customers to the X2?
I think we have created a bit of a buzz, not only with innovation in the helicopter industry, which has not seen a lot of innovation in recent memory, but also that we did it in a fraction of the time it has taken others to do a lot more incremental changes.
When DoD [Department of Defense] looks at budgets and overruns, a lot of that is driven by technical risk. We have essentially taken a lot of the risk out of the X2 by demonstrating it ourselves and will do more of that with the S-97. So if there is a request for a new armed scout, we would deliver an actual aircraft as our proposal.
How does funding and development of the follow-on S-97 Raider differ from the X2?
Program costs for a larger aircraft will make it a multiple of the $50 million investment the company made on the X2, which opened a lot of eyes itself in an era of billion-dollar programs. The Raider will be a multiple of that and we have asked partners to invest with us on the S-97. And I’m happy to say we have had significant response to that. We have about 20 or so partners lined up and almost the same number making some investment on their own.
What advantages would an X2-based Raider have over the Kiowa Warrior armed reconnaissance helicopter it is being designed to replace?
All of the numbers we’ve already discussed. Speed is 100 percent [improved], as is endurance, payload about a 40 percent increase, hover altitude about 150 percent higher, maneuverability – including a 50 percent reduction in turn radius – the acoustic signature about 50 percent lower. And because of the compact nature of the design, allowing smaller rotors for the lift it provides, it is almost a 15 percent reduction in size, which can be important in an urban environment.
Will the Raider incorporate all of the technologies demonstrated in the X2?
It is about one-third bigger, with a higher maximum gross weight and side-by-side pilots. We will do more mission demonstrations and push the high altitude and 3 g capability and maneuverability at the edge of the envelope. This will really push the helicopter to all the extremes and show its operational capability across the full bandwidth.
Do you plan to add any new advances to the Raider?
Again, it will be a more missionized aircraft and will take anything that was not specifically demonstrated on the X2, including how we package the total system. It will be more “productionized,” mission-tailored, and closer to a production aircraft.
Other than the Raider, what applications does Sikorsky see for X2 technology in other future helicopters?
Besides military applications, you have missions such as SAR [search and rescue] and its “golden hour.” The ability to get there and back quickly also is important to the offshore oil market as we push platforms farther out; faster transit speeds will reduce fatigue and increase sorties per day.
Other X2 technologies we plan to spin off, to single- as well as dual-rotor aircraft, include low drag reduction and vibration reduction techniques. In addition, some of the control laws can go into added functionality features on our other products.
How important was winning the Collier Trophy?
We were extremely proud to receive the 100th anniversary Collier. It also was a real shot in the arm for the helicopter industry, which for many years has been criticized for lack of innovation. We sort of placed a bet on the X2 and that was an endorsement that we not only took a bold step, but had significant accomplishments.
For us, I think it was as much about process innovation as anything else. We took what has been learned here across many years and used it to bring about an exceptional advance in technology in record short time and very low cost.
You do have at least one potential competitor in the Eurocopter X3. Any thoughts on that?
I’ll just say I like being in a position where others are reacting to you and I think the X3, just from the name alone, was a reaction to the X2. We’re very comfortable with the approach we took and the results speak for themselves.
Looking to the future, we have set up a group called Sikorsky Innovations that is sort of our Skunk Works. Their challenge is to solve the toughest problems in vertical flight. The dimensions they are working on include speed, actualization – a set of technologies where the helicopter is aware of its surroundings and is able to adapt to its external environment, mission, and health – and what we call “optionally piloted,” the ability to have two-crew, one-crew, no crew, depending on the mission.
This article was first published in Defense: Summer 2011 Edition.