European Efforts Focus on Costs, Environment
European manufacturers are focusing their R&D efforts in the commercial helicopter field on a range of techological improvements ultimately intended to ensure better integration of rotary-wing aviation in the continent’s overall transport infrastructure.
Current efforts focus on fixing aspects of helicopter operations that draw most criticism from the general population, such as noise and perceived danger, and on rolling back the operational limitations due to the weather and to air-traffic management. In parallel, a variety of initiatives are intended to reduce direct operating costs, so making the helicopter more competitive as a mode of transport.
Many of these initiatives are sponsored and partially funded by the European Union under Framework Program 6, approved in 2002 and which runs until 2006. Several programs with a primary focus on fixed-wing transport aircraft (SILENCE(R); Tango, Awiator) also will benefit helicopter manufacturers in terms of noised reduction technologies; airframe materials and construction processes; engines with lower fuel consumption and lower emissions.
However, a specific European Union research program known as Friendcopter (see page 39) specifically focuses on reducing helicopter noise; the Friendcopter project team hopes to produce noise-absorbing engine inlets, methods to identify cabin noise leaks, and control technology to reduce rotor noise, vibration and fuel consumption.
Off its own bat, Eurocopter also is investigating ways to change its production processes to meet future anticipated environmental constraints, as well as other development areas that will allow better integration in the transport infrastructure
One area is that of composite materials, which make wide use of toxic solvents, resins and glues that may ultimately be banned as new regulations are enacted. The company’s goal is to find new production processes, for example thermo-formed plastics, that use fewer toxic substances and allow performance gains – or at least no performance loss – while reducing fabrication costs. Several new resins are now being evaluated, and could be integrated into the production process within four or five years, said Yves Flavennet, head of research and development at Eurocopter.
Also in the environmental field, the company is looking at ways to replace cadmium in aircraft batteries, and to find other anti-corrosion treatments based on less aggressive materials than the ones in use today.
Yet another research field is recyclability, as company officials believe that ultimately the requirements now being applied to the automobile industry will be extended to aerospace products. Here, investigations are focusing on how to amend production processes to allow recycling of airframe and other components.
Noise abatement and all-weather operations, however, are the areas on which Eurocopter is concentrating most of its R&D efforts.
Acoustics research focuses on reducing noise levels generated by the main and tail rotors by improving blade shape and controls, especially in the approach phase. At take-off, most noise is mainly generated by the engine, and so is the responsibility of the engine manufacturers, while in cruise flight the solution is simpler: reduce rotor rpms whenever performance is not required.
Thanks to past advances in acoustic signatures, an EC120 in cruise flight over an urban environment is barely audible, and is thus no longer a nuisance; Eurocopter now aims to achieve a similar noise signature with a larger helicopter, such as an EC155. The overall goal is to lower main rotor noise levels by 3 to 4 decibels, and in the long term to stay well under the progressively lower noise limits that will be mandated by ICAO. "The technology is available for next-generation helicopters, although it is increasingly difficult and expensive for each dB gained," said Frederic Balayn, Eurocopter’s deputy R&D chief.
For the longer term, Eurocopter believes that active rotor, in which blades are fitted with trailing-edge control surfaces with piezo-electric or electromagnetic actuators, offer the best potential for further noise reduction and for lower vibration, another goal of the Friendcopter program.
"We’ve demonstrated that this approach works on static blades, and we plan to make the first feasibility demonstration flight-tests in a few months," said Flavennet.
The problem in this case is to maintain flight safety if one of the blade control surfaces gets stuck. The solution is to have several control surfaces, instead of a single one, and to install a fail-safe mechanism that will return the surface to its default position in the event of actuator failure.
In cooperation with the German aerospace technology center (DZLR), Eurocopter has flight-tested an active rotor on a BO-105 flying test bed. This demonstrated a considerable reduction in the noise and vibration generated by blade-vortex interaction, a 50-percent reduction in audible noise on the ground, and a reduction of up to 90 percent of rotor hub charge factors, which practically canceled cabin vibrations. The next step is to flight-test a fully-equiped blade on a BK-117.
The main stumbling block here is, of course, cost, but Eurocopter believes that savings made possible by shifting rotor controls out to the blades will compensate for the higher cost of blade-mounted control surfaces. "If we re-think the entire dynamic chain, we should be able to maintain total costs at an acceptable level," said Flavennet.
Other, indirect benefits are also anticipated; for example, lower vibrations will allow for lighter airframes, generating additional savings that will allow manufacturers and operators to better amortize the cost of active main rotor blades.
Making helicopters more acceptable to society by lowering their noise levels is one thing; making them better able to carry out their missions is a second thrust of Eurocopter’s research. Here, the overall goal of this research, which comes under the Helicoptere Tous-Temps (all-weather helicopter, a.k.a. HTT) project, is to make it possible for rotary-winged aircraft to fly in low visibility, and as autonomously as possible from air traffic control.
Ultimately, Eurocopter hopes the HTT project will reduce weather-related mission aborts to less than 5 percent, which will substantially contribute to keeping northern European operators in business. Heli-France’s ill-fated helicopter shuttle between Paris’ Charles de Gaulle and Orly airports went broke after having to cancel about 50 percent of scheduled flights because of the weather, while for Heli-Air Monaco’s shuttle between Monaco and Nice airport, in southern France, cancellations due to weather are less than 2 percent.
To attain these goals, civil helicopters will benefit from advances made in military programs. One improvement is three-dimensional mapping, in which GPS-like systems such as Ignos and, ultimately, Europe’s Galileo network will be used to compute the helicopter’s position and display it within a computer-generated display of the terrain. Such a system would be particularly useful, for example, for dynamic flight planning, allowing pilots to update or change their mission profiles during a flight, and to automatically notify air traffic control authorities.
Such a system would offer other benefits. Eurocopter has already demonstrated the capability of an Ignos-based automatic landing system to fly the aircraft into the hover 50 ft. (15 m.) above its designated landing spot – the final landing phase is best left to the pilot because automating safe and efficient touch-down would be too expensive. This capability has been available to military helicopters, for example for Search and Rescue missions, for well over a decade, but the challenge here is to come up with a compact and affordable system for the civil market.
A second improvement is to equip civil helicopters with obstacle-detection sensors and possibly obstacle-avoidance systems. Eurocopter is evaluating laser, infra-red and radar devices, which each offer specific advantages: laser sensors, for example, are more accurate but their performance is degraded by rain, while the opposite is true for radar sensors. The probable solution, Eurocopter believes, is to fit a range of different sensors, and to merge their results so as to offer a simple, clear read-out to the pilot. However, this will add to costs, especially as such a composite solution will require considerable advances in man-machine interface.
More generally, improving the way flight information is displayed to the pilot is a major challenge for airrfame and avionics manufacturers alike, and it is made more difficult because all innovations must be affordable.
Thirdly, the company is looking at ways to improve the helicopter’s "hands-off" recovery by integrating automatic functions that will stabilize the aircraft in a safe flight position if the pilot lets go of the controls, for example in case of total loss of visibility. This entails adding new control laws into existing, analogue autopilots, since fly-by-wire controls do not appear economically feasible for small and medium civil helicopters.
In parallel, the company is also working on systems that will detect other aircraft flying in the vicinity, warn pilots of the risk they create, and possibly also suggest corrective or evasive action. Again, such systems imply a high degree of trust on the part of pilots, and this is not easy to achieve.
The major obstacle to implementing the capabilities being developed as part of the HTT project is that commercial pilots may not have sufficient confidence to trust their aircraft, and their lives, to electronics. "You need to have tremendous confidence in engineers, and in electronics in general, to fly into hilly terrain simply trusting three-dimensional positioning," said one pilot. "Anyone who has used a PC can understand why this would require a near-religious degree of faith."
Despite such misgivings, Eurocopter plans to have the capabilities developed under the HTT project available for initial retrofit to existing helicopters within three or four years. A complete system would be available for an EC155-sized aircraft within a decade, said Flavennet, depending on how regulators will react to such advances.
The French regulator, Direction Generale de l’Aviation Civile, is generally supportive of the new approaches being investigated by industry, and "is quite interested in ways to improve operations is areas that are under-equipped in terms of air-traffic management," said Balayn, but they will demand extensive evaluations and trials of new systems.
Regulatory and certification aspects, in fact, are very likely to constrain future development of rotorcraft technologies, said Flavennet. "If today we had to certificate the NH90’s fly-by-wire controls to civil standards, we wouldn’t make it," he said, and future technological advances are likely to be more difficult to certificate. At issue is the so-called "10-9" rule, which stipulates that safety-related innovations must demonstrate a failure rate of less than 10-9 per flight hour to cain certificatory approval.
This is one reason why the all-electric helicopter being considered for the future stands little chance of actually making it into revenue service. This would see electric actuators replacing all of the hydraulic actuators, and the extensive hydraulic circuits they require, thereby allowing a very substantial reduction in costs. "Today, hydraulic actuators on the main rotor are not redundant," said Balayn. "But if we were to replace them with an electrical system, we would have to demonstrate a failure risk of less than 10-9 per flight hour, which is practically impossible."
"We also have other technological solutions that we believe are certifiable, such as electro-mechanical actuators, but again we must prove their reliability before introducing them into operational service," he adds.
Now that technology is running up against the physical limitations of helicopters, Eurocopter is also mulling a major change in how it views helicopters. Until now, its products were designed as multi-purpose aircraft, able to carry out a broad range of different missions and thus designed as a compromise between competing technical specifications. Now, the company is willing to think of future helicopters as having a basic core consisting of common systems, from which it would be able to derive variants tailored to specific missions. By optimizing a modular design, a specific configuration and a corresponding equipment fit for a single niche mission instead of striving for multipurpose capabilities, Eurocopter believes it would be able to develop a helicopter with better mission performance and lower costs. The flip side of the coin, however, is that this would require operators to either specialize in a given mission, or to operate a fleet of very different, but complementary, aircraft. And this, obviously, would add to an operator’s total costs, and obviate the savings made possible by "niche" helicopters.
The scope of ongoing R&D efforts, however, is limited because helicopter technology is already approaching the technical limits inherent to rotary-wing design. Thus, any further improvements in performance or operating costs will, perforce, be limited despite development costs that will continue to increase according to the last of diminishing returns. As is often the case in aviation, the last few percentage points of performance gain can end up costing as much to develop as the previous 95 percent.
Eurocopter is obviously conscious of these inherent limitations to its R&T work. "Our challenge is to be sufficiently modular in our approach so that the cost of future improvements is not prohibitive," said Flavennet.
This is one block to the alternative solutions to working around physical limitations. Another is that helicopter designs are already so advanced that any future improvement risks being too costly and too complex to make economic sense. This is where R&T development efforts may run into the law of diminishing returns as into a brick wall.