Building a High Speed Helicopter
An Interview with Jean-Michel Billig
12/21/2010 – In early October 2010, Second Line of Defense had a chance to talk with Eurocopter about its new high-speed test helicopter, X Cubed. Jean-Michel Billig is Executive Vice President of Eurocopter for Research and Development. The slide show and the accompanying video below show the X3 during the test flight on September 6th.
Credit : Eurocopter, October 2010
The X3 helo demonstration project began its flight tests on September 6 at the Istres test facility in southern France. The helicopter combines conventional rotary blades with forward positioned turbo prop blades. The X3 is a blend of the Dauphin fuselage, the EC155 main rotor, the EC175 gearbox, NH 90 engines, and features a twin fin tail instead of the tail rotor. It also features two forward facing five-bladed props mounted on stub wing sponsors on the upper fuselage, which are driven by shafts from the main gearbox.
The helicopter is designed to provide a low cost high-speed operating form factor while ensuring the versatility and functionalities of an helicopter, such as VTOL, hovering, autorotation. It is aimed at customers who use rotorcraft for various missions where speed or mission duration is of the essence and therefore who could use higher speed to provide better solutions to their core missions.
And it aims at “affordable” high speed, by which Eurocopter sees mission costs reduced by the rotorcraft using both rotor blades and turbo props to gain efficiencies. And by building from a technical architecture extremely simple and close to classic helicopter platforms, Eurocopter is very confident it can provide limited increase of the production costs of the product.
The X3 can change the speed of its main rotor in flight, avoiding drag divergence on the advancing blade and increasing the stall speed of the retreating blade, while also reducing noise. The small stub wings unload the main rotor at speed, thus allowing for the reduced main rotor rpm.
SLD: The hybrid concept of the helicopter is really interesting. How do you put together the rotor blades with the turbo propellers?
Jean-Michel Billig: We have built the test platform around mature and affordable technologies. We have been involved in high-speed research for a long time and have been breaking some high-speed record for some 20 years ago. But we have been searching for high speed within a very simple, mature, architecture.
What do we mean by this? We do not want to offer high speed at any cost; we want affordable solutions. Therefore, we have modified main gearbox, which instead of having one drive shaft, will have two drive shafts, one on each side to the propellers. That means that actually for the dynamic system, it is exactly of the same complexity or maturity as regular helicopters.
SLD: Could you describe how this is done?
Jean-Michel Billig: In hover, we control the rotorcraft like any other helicopter. The main rotor is fully dedicated to lift the helicopter and we control the yaw axis with the two propellers. The differential pitch of the propellers is controlled with the pedals like the pitch of a tail rotor. For the forward flight at high speed, the pitch of the 2 propellers is controlled via a trim on the collective stick while the attitude of the helicopter is kept at zero. So, we have the rotor, which keeps it main functionality to ensure the lift and at high speed we reduce the lift of the rotor by reducing the rotation speed of the rotor, and the wings are taking over up to 40% of the lift and this allows us to go to high speed because, as you know, the limitation for high speed is high rotor rotation with the tip of advancing blade, which shall not be supersonic.
SLD: I think the trick there, as you are describing it, is that you lift with the rotor blades, but then you are going to shift to the propeller blades for your higher speed and lower mission cost.
Jean-Michel Billig: We do not shift; we combine both. We have the main rotor fully dedicated to lift at any time. When we reach high speed in forward flight, we just reduce rotation speed of the main rotor and we take advantage of the lift of the wings.
SLD: Do the rotor blades shift forward, is that what you are saying, or do they stay in the same position?
Jean-Michel Billig: The main rotor stays into the same position. Its architecture is exactly the one from the helicopter. But the hydraulic system has been modified to cope with two propellers.
SLD: Your expectation is that this is a fairly robust solution, then?
Jean-Michel Billig: Technologically speaking, it is extremely robust; it is exactly the principle of a helicopter.
SLD: And you were emphasizing that building an evolutionary approach is at the heart of the objective to provide for cost-effective high-speed solutions?
Jean-Michel Billig: We are not aiming at demonstrating high speed, as such, we are aiming at creating cost effective high speed. We believe that for those missions where speed is important, we want to demonstrate that we can lower the mission costs for those missions. So, this is all about the concept of our X3.
We are not aiming at demonstrating high speed, as such, we are aiming at creating cost effective high speed. We believe that for those missions where speed is important, we want to demonstrate that we can lower the mission costs for those missions. So, this is all about the concept of our X3.
SLD: Your point is that the target here is to be more cost effective than a helicopter, but to add to an increase in factor of time in executing the missions?
Jean-Michel Billig: Yes. I will give you an example. Oil and gas, where the platforms are very far away, we believe that the time to get to the platform is taking longer and longer and it means time and money for the companies. They want to shorten this time. Similarly, for search and rescue missions, where time is of the essence, we believe there is a market. Special Forces applications come to mind as well. We can lower the cost for these missions providing high speed, and our target is to lower the cost of this mission by 10 to 20% compared to the same size helicopter without the high-speed capability of X Cube.
SLD: Two points that derive from this. One is that I note that in the video that I watched that the various systems on the helicopter that were derived or taken, literally, from other Eurocopter systems, so that obviously, you’re not going to have supply chain difficulties with this thing. It’s already embedded in the extant Eurocopter supply chain.
Jean-Michel Billig: Yes, we do not expect challenges in the manufacturing. Of course, every time we have a new development, there are challenges. But having said this, we do not anticipate manufacturing difficulties to reproduce these concepts.
SLD: I’m going back to those mission set issues and I’d like to look at a couple of them. One is this deep-water drilling issue, which was not highlighted by the Gulf crisis. The issue is getting out there quickly to sustain the operations, to get people off the platform, to deal with crisis, to deal with resupply. It is a long way out. So, there’s clearly a need for this kind of helicopter, for that kind of mission.
Jean-Michel Billig: Absolutely, yes. The layout of the final product is under investigation. Today the demonstrator is exclusively to demonstrate the high-speed capabilities. How the final product would look, this is something we are investigating.
SLD: So, your point is that how it gets customized, how it actually gets manufactured, will be linked very much to the missions and the kind of what the customer needs would be?
Jean-Michel Billig: Very much so.
SLD: So, the point is, on the one hand, you’ve got the technology demonstrator; you’re looking at how you could manufacture this capability. On the other hand, you’re looking at the potential form factors within which you can insert this technology, dependent on mission requirements and customer demand. Is that a fair way to summarize it?
Jean-Michel Billig: This is so. On the one hand, we have the demonstrator, and we are validating the cost effective high-speed concepts, and on the other hand, we are capturing the various mission requirements, be they commercial or military, in order to ensure we understand commercial requirements for cost effective high speed.
On the one hand, we have the demonstrator, and we are validating the cost effective high-speed concepts, and on the other hand, we are capturing the various mission requirements, be they commercial or military, in order to ensure we understand commercial requirements for cost effective high speed.
Credit : Eurocopter, October 2010