ADVANCED TECHNOLOGIES FOR HIGH PERFORMANCE NH90 BLADES

Significant improvements have been made during the 70’s with the replacement of the former metallic blades by composite ones. Composite technology has been and will continue to be improved and a new generation of composite blades is in progress. In order to provide EUROCOPTER with all the necessary experience and state-of-the-art technologies, a very intensive research effort has been made for all activities and technologies related to blades which have been launched over the last years. NATO Helicopter NH90 main rotor blades are confronted to a very challenging specification : a very large flight envelope, low production and maintenance costs, de-icing and automatic folding capabilities and damage-tolerant design according to the latest certification standards. Blade aerodynamics has taken advantage of the availability of the new airfoil generation with advanced blade planform, all of this being supported by 3D numerical computation methods developed in co-operation with ONERA/DLR. Controlling vibration is of a great importance for such heavy helicopters and a modern numerical code has been used to predict dynamic behaviour of the blade in accordance with the anti-vibration suspension and the composite airframe. Controlling production costs and reducing operating costs are a very important concern for helicopter manufacturers, especially for blades which are a key component in helicopters. The parts which were expensive to manufacture in the past, are now available with improved and well controlled costs for the customers thanks to CAD/CAM tools allowing more robust manufacturing processes, new composite materials with less variants, automatic processes and manufacture reengineering. A specific blade root concept has been designed to reduce the overall cost of folding function. A unique experience has been obtained with blades flying in several countries under various environmental conditions : all in-service feedback information help to improve constantly their reliability and to reduce operating costs. The new blades are incorporating the last improvements in terms of erosion and impact behaviour, lightning strike protection, de-icing capability. For example, all the blades have been equipped with full built-in de-icing. Thanks to carbon fibre technology de-icing service life has been increased. In order to improve the damage-tolerance of new blades which is especially demanding for military applications, a multibox structure concept has been introduced in these new generation blades with multiple load paths. The main objectives of the development phase have now been reached : full flight envelop demonstration, flight in icing conditions, fatigue and endurance testing, successful folding demonstration. NH90 blades have reached their technical maturity and they are now entering into the industrialisation step.