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DMN Q&A: Sikorsky VP for Research and Engineering Mark Miller

The X-2, the S-97 Raider, and the future of helicopter technology

Sikorsky Aircraft, the first to mass produce both military and civilian helicopters and creator of the basic design on which all helicopters have been built for nearly a century, recently pushed the rotorcraft envelope to a new level – super speed.

The Sikorsky X-2 set a world record of 250 knots in level flight in September 2010, a few weeks before Eurocopter revealed its own contender – the X-3 – which reportedly achieved a few minutes of level flight at 232 knots in May 2011. Both mark nearly twice the cruising speed of most other helicopters in use today.

But according to Mark Miller, Sikorsky’s vice president for research and engineering and a former Lockheed Martin Skunk Works executive, speed is only part of the equation. Miller recently discussed the X-2, the follow-on S-97 Raider and the future of helicopter technology with Defense Media Network senior writer J.R. Wilson.

J.R. Wilson:  How has your Skunk Works background influenced the direction you are taking in Sikorsky R&D?

Mark Miller: Technically, the challenges we have here are similar. Of all the vehicles I worked on, from fixed-wing to spaceships to missiles, the helicopter presents some unique technology challenges. The technical expertise already existed at Sikorsky, but the kind of innovative culture is something I brought with me.

In a time of tight budgets and new program cancellations or delays, why did Sikorsky decide to self-fund R&D on the X-2 technology demonstrator?

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. We also thought we would learn a lot along the journey to accomplishing that.

So when we set the program up, we set up other goals, as well – to see if we could do rapid prototyping faster at a lower cost, for example. Then we could leverage a lot of the resulting technologies into current products to make them more relevant, create new products and new markets, conceivably, and take the skills of faster development and apply them to other programs, both DoD and commercial.

The X-2 represents a number of technology and performance advances; how important was it to bring all of those together in the same test aircraft?

It was very important. We talk a lot about X-2 in the context of speed, but it was more than that.

Sikorsky X-2 in flight

The pioneering, record-breaking Sikorsky X-2 in flight. Photo courtesy of Sikorsky

We also chose low vibration and reduced pilot workload because, in the 1970s, when Sikorsky looked at coaxial technology to go fast, there were technical hurdles they could not leap, including vibration and how complex it was to fly. So we looked at the X-2 as a demonstration to show the speed element, but it also was very much a technology readiness demonstration for the practicality of doing this process.

As an OEM [original equipment manufacturer], Sikorsky is, first and foremost, a system integrator, so bringing out the best of individual technologies and putting them together in a system is what we are all about.

What were the key technology enablers for those systems and capabilities?

A lot of it was advanced control laws, fly-by-wire, active vibration control – those were some of the key technologies we brought to bear on the program. Fly-by-wire is a foundational element for us now. Comanche was fly-by-wire, the X-2 is fly-by-wire, our Canadian maritime helicopter program [a derivative of the S-92] is fly-by-wire and we have a variant of the Black Hawk completing its test program that is fly-by-wire.

What is the advantage of fly-by-wire and how does its implementation in the X-2 differ from traditional helicopter control systems and from other fly-by-wire systems?

The X-2 is fundamentally more complex because it has two rotors and two swashplates and servos. There are flight control laws resident in the flight control computer and the prop pitches are operated by a separate server. But the implementation of that in the X-2 is unique largely due to the counter-rotating dual rotor system.

To what extent and how well did the X-2 achieve its key performance parameters, such as:


  • high speed

The team fully believes, based on all the margins available and handling qualities, we definitely had some more speed left in the aircraft, but when we hit that KPP of 250 knots in September, that essentially was the end of the program. So you claim success and move on.


  • low noise

The acoustic signature is roughly half that of a conventional helicopter at lower speeds or we were able to achieve levels at the full 250 knots at some of the best-of-class of conventional helicopters.
One of the main signature characteristics of a helicopter is the noise emanating from the tail rotor. There are other phenomena relating to the main blade, but taking out the tail rotor on the X-2 made a significant difference. In addition, the variable rotor RPM, where we can slow the main rotor down, also allows us to reduce the acoustic signature.
And, finally, at low speed the prop would be declutched and not turning, removing any signature from it. So without commenting on specific levels, I would say those aspects of the X-2 give you some unique acoustic capabilities and industry-best levels.


  • low vibration

The levels we achieved were best-in-class for a conventional helicopter. We also looked at some variable tuning so we can optimize them at different frequencies, but again it was taking a technology developed for a conventional helicopter, modifying to meet our needs and integrating into the whole system.


  • high-altitude hover

Fundamentally, the technology has very good hot/high performance. We have a follow-on program we are targeting at specific missions and that aircraft will have very good hot/high performance characteristics – hover altitude at 10,000 feet on a 95 degree Fahrenheit day.
Looking at an OH-58D [Kiowa Warrior] operating in Afghanistan today, where you have lots of hot/high conditions, the kinds of coverage you can get with this type of vehicle are tremendously expanded. So we demonstrated the physics and all the KPPs with the X-2 and now we are onto an operational variant.

How did you resolve problems related to incorporating multiple flight controls into the small space available?

Sometimes when you do things smaller it introduces other challenges. The X-2 package was extremely tight. It’s one thing to look at it in a 3D design, but it’s another thing in practice.

Artist's conception of the S-97 Raider

Artist’s conception of the S-97 Raider, the follow-on to the X-2, employing its technologies in a production aircraft for the military. Image courtesy of Sikorsky

It was optimized to the point where we had no problems with temperature controls; the temperatures in the body were sufficient that we did not have any reliability issues. We don’t have an ECS [Environmental Control System] in the cockpit, so we limited the amount of time the pilot spent in the aircraft and did not want to go out on too extremely hot days. But we didn’t have any excess electronic sources of heat that caused any problems with our components or the overall reliability of the system.

To what extent were simulators used in the X-2 program – and how did they affect its development?

Simulation was a significant part of the X-2 and has become a major element in all of our programs today. We were able, with a very quick tempo, to take what we had learned [during actual flight] into the simulator – whether stability augmentation or control laws or interaction of the rotors and fuselage and how that translates into flyability and handling qualities.

If you look back at how long flight testing historically takes, we’re seeing orders of magnitude reduction by doing a lot of that in a simulator. And that translates into significant dollar savings and the earlier learning up front also saves time and dollars.

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?

To do a flight test on an all-new helicopter, employing all-new technologies, in 50 hours [the time allotted by Sikorsky] was a very aggressive program – yet all the major KPPs were met in the first 17 hours of flight, which I consider a very impressive and unprecedented number. I credit all the tools we have honed over the years on commercial and military helicopters; better simulator tools and modeling got us off on a very strong start and enabled very rapid turn time in incorporating changes.

So our philosophy now is simulator – fly – simulator update – fly.

How about payload?

You have a cruise speed of at least 220 knots, with weapons, six armed troops, 2.7 hour endurance – even when loaded, it is a very effective aircraft. And that is a 40 percent payload increase over the OH-58D, plus 100 percent endurance increase.

A lot of attention is given these days to fifth generation fighters – high-speed cruise, stealth, range and payload advantages. How would you rank the X-2 – and other rotorcraft – in those terms?

There is a niche place for a high-speed fighter, but helicopter missions prove day-in and day-out the utility of the machine and its usefulness. I think we’ve just enhanced that considerably with the X-2.

Whether the mission is SAR or armed scout, this particular package, including speed, is a game-changer. Helicopters are extremely useful, both in war and disaster relief, but when you bring to that the capabilities of the X-2, it becomes even more relevant.

What response have you had from potential customers to the X-2?

We just had the X-2 and a Raider mockup at the Pentagon a few weeks ago, with both military and civilians coming down to look at them. And as people really began to understand what this machine can do, it opened a lot of eyes.

The customers are excited about all the new capabilities, that we have reduced the risk and that we were willing to do this kind of innovation on our own dime. And that we didn’t just limit it to speed, but combined it with improvements in all those other areas.

Other than the Raider, what applications does Sikorsky see for X-2 technology in other future helicopters?

Vibration, flight controls and drag reduction are probably the primary spin-offs, but also advanced manufacturing techniques. We already have adapted a number of these things on our other programs.

How important was winning the Collier Trophy to Sikorsky?

We were very honored to receive what I consider to be the number one American award in aviation.

The X-2 is talked about a lot with respect to speed, but it also highlighted Sikorsky’s systems level capabilities, taking all the attributes of a helicopter then adding not only much higher speed but also making it lowest vibration, lowest acoustic signature, lowest pilot workload, etc.

What has the X-2 brought to Sikorsky in terms of future developments?

An architecture with fly-by-wire at the foundation and incorporating all the control work we have done, but making it platform agnostic, so we can go into any platform and enable it to fly remotely piloted or with one or two crew, depending on mission needs.

We’re definitely not done with X-2 and continue to invest aggressively in three technology pillars – actualization for a self-aware and adaptive helicopter, the optionally piloted helicopter and the dimension of speed. Those are just three of the areas in which Sikorsky is making significant investments and advancements for the future.

An expanded version of this interview appears in the Defense: Fall 2011 Edition.


J.R. Wilson has been a full-time freelance writer, focusing primarily on aerospace, defense and high...