Complex composites lighten NATO copter
Dutch consortium develops advanced composite critical landing gear that meets NH90 helicopterperformancerequirements.
• Lighter and stronger than existing metal design
• Braided reinforcement permits preform automation
• Performance testing validates finite element analysis predictions
The application of carbon fiber composites to the wings and fuselage of a newly designed aircraft is now standard practice. One area of aircraft design that continues to elude the composites community, however, is the landing gear. As primary structural elements with concentrated loads, conservativedesign practice has traditionally dictated metal in these components. This may change if a team of Dutch companies and scientists is successful in its quest to design and fabricate lightweight, durable composite landing gear for heli-copters and fixed wing aircraft. SP aerospace and vehicle systems (Geldrop, The Netherlands) is under contract for the development, qualification and production of a retractable, crashworthy NH90 Rear Landing Gear Assembly landing gear for the NATO NH90 helicopter, in both Army (TTH, or Tactical Transport Helicopter) and Navy (NFH, or NATO Frigate Helicopter) versions. A joint development of Eurocopter (France and Germany), Agusta (Italy) and Fokker (The Netherlands), this 10-ton-class helicopter will be used for a wide variety of tasks, such as troop transport, cargo transport and anti-submarine operations. Composites are widely used throughout the helicopter, such as in the airframe, stabilizers, and the rotor blades. Development prototypes of the helicopter have been flying since 1995 and the first serial production delivery is scheduled for 2004. The NATO Helicopter Management Agency (NAHEMA), consisting of France, Germany, Italy, The Netherlands and Portugal, has ordered 253 helicopters with an option for 124 more. The Nordic countries (Sweden, Finland and Norway) have ordered 52 units, with an option for an additional 17. The landing gear is currently designed in metal. In the mid-1990s, SP aerospace, in conjunction with the Structures and Materials Division of the Netherlands National Aerospace Laboratory, NLR (Amsterdam, The Netherlands) began exploring the use of advanced composites, convinced that composites technology had matured to a point where a landing gear application was practical, according to René Hekerman, engineering manager for SP aerospace. In 1996, the team initiated a technology development project to design, build and validate carbon fiber composite torque links and a trailing arm assembly based on NH90 landing gear specifications. SP aerospace is the lead company for the project, responsible for concept design component specifications, integration of components into the landing gear, and component testing and qualification. NLR is handling the conceptual design for the composite elements, development of design allowables, development and manufacture of the RTM production molds and the composite parts, and subsequent testing of the subcomponents. Two additional partners provide specific expertise: Eurocarbon (Sittard, The Netherlands) has responsibility for the development of a fully automated overbraiding technique for the fabrication of cost-effective preforms for the composite trailing arms, while MSG Software Benelux BV (Gouda, The Netherlands) provides the finite element analysis (FEA) of the mechanical strength of the composite structures.
Funded by the Dutch Government and the partners themselves, the program is split into two phases: technology development and validation. The torque link was developed from 1996 to 1999. This relatively simple component was used as a demonstrator in order to bring the design, analysis and RTM capabilities to a higher level. This enabled development of the trailing arm's very complex shape, which was had its beginnings in 1998 and was largely completed in 2002.
Tri-axial overbraiding of structural beams
Result: Labor intensive and bulky results.