Introduction of New Infusion Manufacturing Processes for Main Rotor Blades: Opportunities, Drawbacks and a common Endeavor to make it a Success

Abstract:
The succession of the BK117 D-2 main rotor concept from the semi-rigid rotor to the BK117 D-3 bearingless main rotor (BMR) system, derived from the H135, held many new and innovative additional benefits in its wake. Although the H135 system is the best on the market regarding maintenance effort and maintenace cost (DMC), it was the purpose to push this benchmark even further. To achive additional benefits, three major improvements needed to be successfully implemented and none of them was a given. First to mention is the concept of the blade being separated in three parts. In case of foreign object damage (FOD), most of the time only the outer part needs to be repaired. In parallel a new possibility to fold the system with a full folding capacity was introduced with the challenge to realize the extremely low DMCs of the H135, in a decisively bigger helicopter and to benefit from the experience of millions of flight hours and thousands of helicopters operated throughout the world. Second a reduced flapping hinge offset was introduced to improve the comport of ride. The third point is the attachment bearing stress laminate providing the benefit of slim shape in the connection area between Flex control unit (FCU) and blade airfoil section. All this with the reduction of vibration in mind that results from changing a four-bladed rotor to a five-bladed one [1]. We were motivated to include also a, for such kind of critical part, new liquid infusion molding technology, to have all process parameters in our own hands, to make the production of blades more reliable and at the same time reduce the number of nonconformities by introducing more and more automation in production, which was enabled using the bearing laminate design of the attachment [2]. This innovative new design, in combination with a new manufacturing process introduced in a different production site under considerable time and cost pressure, needed the dedication of a multi-disciplinary transnational team, to finally overcome all deviations that became visible throughout the industrialization and/or prototype phase. This finally led to a mature serial production within a two years time frame. The paper is intended to highlight the often shortened and only briefly recognized period of preproduction, prototyping and the serialization and maturation of critical composite parts.

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