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EUROCOPTER OUTLINES RESEARCH STRATEGY

By Karl Schwarz

When companies carry out research, at the end of the day there is always one objective, to safeguard or enhance the position of the company amidst the competition world-wide. For Eurocopter this means specifically that the basic elements must be developed for new, powerful and competitive helicopters which accommodate customers' ever more demanding requirements and satisfy stringent environmental regulations. Despite all this, the purchase price of the helicopter and its operating costs must not rise if that is at all possible.

Quite a challenge for the engineers, who, moreover, have to manage with scarce resources. It is hence all the more important to concentrate on clear objectives and avoid duplication of work. At the most recent Paris Airshow, the German-French company therefore signed a far-reaching partnership agreement with the German Aerospace Research Establishment (DLR) and the Office National d´Etudes et de Recherches Aérospatiales (ONERA).

"It was not simple," recalls Michel Polychroniadis, Research Programme Director at Eurocopter, "but now we are the first in Europe to do something like this and thus a model for other areas." Nevertheless, the move from national research programmes to close binational co-ordination did not happen overnight, but was a process which has been advancing step by step ever since Eurocopter was established in 1992. Already in October 1998 DLR and ONERA had agreed to co-ordinate all future helicopter activities after they had previously carried out around one-fifth of the work together.

To harmonise the work, a list of Co-ordinated Action Programmes (CAP) was drawn up. This list contains the 12 most important research areas such as aerodynamics, noise, rotors, all-weather capability and crashworthiness, tailored to the wishes of civil and military helicopter operators.

These are asking, for example, for an extension of the operational mission capability, i.e. the helicopter should in future be able to fly for 50% longer than today. In this context, Eurocopter is working with its partners on an all-weather helicopter. The priority here is to develop novel visual systems which support the pilot. A range of technologies is being examined, from millimetre wave radar and lasers through to the use of three-dimensional terrain databases. No doubt a combination of several systems will be necessary.

The need to present additional data calls for new approaches in the design of the man-machine interface. In this area, larger liquid crystal displays using novel symbology are being investigated.

Other aspects of the all-weather capability are accurate navigation using digital maps and D-GPS (satellite navigation with improved accuracy through local transmitter) plus the development of a low-cost de-icing system. In addition there is an "intelligent" autopilot which relieves the pilot of some routine tasks. A converted BK 117 ("EC-Futura") and an EC 155 (Hélicoptère Tout Temps) are available for trials.

It is also important for the operational capability of the helicopter that it should gain acceptance among the local residents, and advances here depend on significant reductions in noise emissions. "We are already in the lead as regards noise reduction," says Research Director Polychroniadis. "The EC 120 and EC 135 are around six EPNdB below the ICAO limits. But in five years we intend to make this as much as ten decibels."

Considerable progress has already been made towards achieving this goal. An EC 155 equipped with DTV-4 rotor blades, optimised fenestron and noise-absorbing air inlets has already achieved a reduction of eight decibels, equivalent to halving the amount of noise generated. The next step is to use this to test an active engine control system.

Noise reduction is also the aim of the ERATO programme, which is examining new blades with swept back blade tips in the wind tunnel. These have been optimised for noise reduction on the especially critical descent and have produced acoustic gains of six decibels without any loss of performance in other aspects of flight. Other development programmes are to follow (Blade 2005, ATR III).

As well as these innovations in blade shape, the emphasis of the research is on technologies for the adaptive control of the rotor. For this purpose small servoflaps are to be installed on the trailing edges of the blades, towards the tips, in order to be able to operate with small deflections. Under the heading of AROSYS (adaptive rotor systems), preparatory work is under way on the use of piezoelectric actuators. These seem to be able to cope with the extreme requirements - 50Hz adjustment rate (one deflection every 1/50 sec) while at the same time acceleration forces of up to 1000g occur. Initial wind tunnel tests have shown that the adaptive rotor system works in principle. Flight trials are now under way.

"This could turn into a very significant step in helicopter technology, and, as well as the trailing-edge flaps, we could also change the leading edge," says Michel Polychroniadis confidently. "However, all the deflections need to be calculated in real-time, and that is difficult."

Work on the rotor not only serves to reduce the external noise, but greater passenger comfort is also an important goal. The long-term aim is to reduce the noise level in the cabin to below 70dB and to also cut the vibration level significantly.

In this connection ground experiments in active noise suppression are being conducted in a Dauphin using loudspeakers, which introduce additional noise phase shifted by 180º (anti-noise). Such systems already exist for turboprops, however the suppression of high frequencies is considerably more difficult and requires special algorithms.

Another technology is currently undergoing flight trials on a BK 117. Once again this entails the generation of anti-noise fields through piezoceramic coating of the transmission struts, this time however with the aim of suppressing the passing to the transmission struts of structure-born sound originating from the transmission. Similar tests are being carried out in the area of vibration.

"This technology is already pretty mature, but we will probably not start to use it in larger helicopters first for a few years yet," says Michel Polychroniadis.

Another requirement is to increase safety in the event of an accident. Here the issue is to optimise the crash behaviour of the airframe and to examine new safety equipment such as airbags.

Active measures to increase safety are being tested on a converted EC 135 under the ACT/FHS fly-by-light demonstrator programme that the German Ministry of Defence is funding. Here, the control signals of the pilot are transmitted via fibre optics to the actuating cylinders of the main and tail rotors.

In order to be able to offer all these advances at the lowest cost possible, Eurocopter plans to significantly reduce development effort and time. A new model should not take more than three years to reach the production stage, and a new version should be feasible in one year. These ambitious goals are to be implemented with the aid of the "virtual helicopter".

The first and most important element here is the Complete Helicopter Advanced Computational Environment (CHANCE) programme, in which integrated teams from ONERA and DLR are taking part. A first step, in which the performance of a rotor in the hover was calculated and the accuracy of predictions relating to changes in the blade geometry was reviewed, was recently successfully completed. Similar work on the fuselage is currently under review. The calculations here are very much more complex since, due to the compact form, the irregularities and all the various attached items, a number of different flow breakdowns occur.

"By 2005 we want to be in a position to define the entire air flow around a helicopter in a single calculation based on Navier-Stokes equations," says Michel Polychroniadis, outlining the ambitious goal. Hitherto the engineers have been forced, due to lack of suitable computational tools, to work on the different zones of the helicopter (rotor, air inlets, fuselage etc) separately.

All the technologies mentioned so far are intended mainly for the civil markets, but most of them are also relevant to military helicopters. Specifically for this area there is also a separate Coordinated Action Programme. Under the catchword, "Stealthy Helicopter", the primary consideration is to reduce detectability by radar and infra-red sensors. Amongst other things, work is being carried out together with ONERA on new concepts for the suppression of hot engine exhaust gases.

As well as continuous improvements in conventional helicopters, Eurocopter is also interested in the long-term in a "second generation tiltrotor". "This research requires a high outlay, so here we are collaborating with AgustaWestland," explains Michel Polychroniadis.

After some problems in agreeing on a joint concept, there were also difficulties over raising funds. Some projects on critical technologies are now to be implemented under the 5th Framework Programme for Research and Technology of the EU. These include the following:

• DART: an optimised rotor head, expected to produce significant cost savings.
• ADYN: a study of the dynamic behaviour of tiltrotors in forward flight. The aim here is optimisation of wings and blades, and a series of wind tunnel tests (with DNW and in Modane) are planned. AgustaWestland is leading this research.
• TRISYD: studies on propulsion system and swivelling mechanism, headed by AgustaWestland.
• TILTAERO: AgustaWestland is leading studies on the aerodynamic interaction between rotor and wings.
• ACT-TILT: primarily at Eurocopter, system studies on control systems are taking place. Simulations are planned with pilots in the loop, the main interest here being safety.
• RHILP: this study is concerned with predictions of handling and loading in flight. Once again, Eurocopter is planning to run simulations with pilots.

According to Polychroniadis, all the contracts should be finalised by the beginning of 2002. The EU is providing Euro 20 million and the companies have to then contribute an equal amount themselves. What is not feasible now, for example a ground testrig for integration work, will be proposed for inclusion in the 6th Framework Programme.

From page 94 of FLUG REVUE 2/2002