European helicopter experts are working within the framework of the Friendcopter programme to reduce helicopter noise emissions. Defining low noise flight procedures is a promising line of research that Eurocopter is actively pursuing.

In developing a more environmentally friendly helicopter, Eurocopter has for many years been focusing on the fight against noise as a key issue. The design offices of the companies that would later form Eurocopter were already looking into noise reduction in the 1970s. Their unstinting work resulted in three generations of the Fenestron tail rotor, each quieter than the last. With noise levels way below the regulatory requirements, Eurocopter now possesses the quietest range of helicopters in the world. Nevertheless, environmental pressure necessitates that the hard work be continued.

Exceptional testing
Unlike the Clean Sky programme, which also aims to make aircraft more environmentally friendly, the European Friendcopter programme involves a more advanced level of technology and is entirely dedicated to helicopters. Noise is central to this project, on which Eurocopter is working with some thirty partners, including several research centres. “An important aspect of Friendcopter relates to low noise procedures, and this is defined in three ambitious goals,” explains Marc Gervais, who is in charge of this Eurocopter work group. “In the first place, we wanted to propose a European methodology for acquiring and analysing the necessary data for the definition of low noise procedures. We then needed to create a reliable tool to calculate the noise footprint on the ground and, ultimately, to perfect these procedures.” A flight test campaign, one of the most exhaustive carried out in this field to date, was performed with an EC130. Every possible manoeuvre was tested in order to acquire a comprehensive database, including stabilised flight procedures (takeoffs, approaches and overflights) and non-stabilized flight procedures (acceleration, turns and decelerating steep approaches). As many as 36 microphones were set up over an area of approximately 45 hectares (780 m x 580 m). “This is a truly exceptional test procedure,” insists Marc Gervais. “By way of comparison, the certification of helicopters is normally performed using only three microphones on the ground. But, during these tests, we employed the same method that was used for the certification of the Airbus A380.” And even though they are still being analysed, the results promise a wealth of information. An indication of this potential is the fact that the Eurocopter team won an award for the initial report that it presented at the latest European Rotorcraft Forum (see inset).

For the benefit of everyone
“At the same time, we have also developed HELENA (HELicopter Environmental Noise Analysis), a tool that predicts noise footprints,” continues Marc Gervais. “HELENA will allow us to measure the environmental impact of helicopters more accurately. It is a tool that is very well adapted to rotary wing aircraft because it not only takes into account noise levels on the ground, but also the very particular characteristics of noise directivity, including the question of advancing and retreating blades, which makes helicopter noise studies more complex than those for airplanes. HELENA will be ready by the time the Friendcopter project draws to a conclusion, and we will then use it to assess the modifications made to helicopters as part of the Clean Sky programme.” Two versions of HELENA have been developed: the first for manufacturers and research centres, and the second for public users such as operators, and the airport and aviation authorities - all of whom are potentially interested in a precise assessment of the noise impact of helicopters.

Compatibility
“Beyond noise reduction procedures, Friendcopter also covers other noise-related subjects,” adds Marc Gervais, who cites engine noise reduction as an example. But engine manufacturers are not the only companies affected by this issue: engine integration, and the shape, position and design of tail pipes and air intakes are the helicopter manufacturer’s responsibility. Finally, mention should also be made of work being carried out on active noise control systems for main rotors. Friendcopter is investigating this field as part of its overall objectives to reduce noise, and Eurocopter is also conducting its own research programme on this subject. The next step for this research will be to apply the Friendcopter results within an actual regulatory framework. This will assess whether helicopters using the new procedures will be compatible with other air traffic.