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The British Experimental Rotor Blade (BERP) gives helicopters improved speed and lift
Lighter, Safer, Quieter Helicopter Blades
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Faster, Lighter, Safer Helicopter Blades
Companies in the Westland Group, together accounting for most helicopter manufacture in the United Kingdom, are increasingly using composites nowadays. These materials are lighter and stronger and have better load carrying and more durable properties than conventional metal alloys, while in certain rotary wing applications, design to more exacting specifications is possible.
Initial work towards the development of new aerofoils undertaken by the UK Royal Aerospace Establishment (RAE) incorporated sections that showed improved aerodynamic performance and delayed stall on the retreating blade, eventually including swept tips. This early expertise by RAE and Westland culminated in the British Experimental Rotor Programme (BERP), the intention beingthatWestland would design and build
a new blade using composite materials. Flight trials with a single blade modified to determine and confirm the characteristics predicted were an integral part of the early work. The design gives major improvements with both advancing and retreating blades and, when combined with distributed camber profiles, provides a significant increase in speed and lifting capability. One notable early achievement occurred in August 1986, when a Westland Lynx equipped with BERP blades set a new world record for helicopters at an average speed of 400km/h (precisely 216. 3 knots).
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Reduced Buckling Danger
The BERP blade spars are constructed from multiple layers of carbon and glass fibre, pre-impregnated with a modified epoxy resin and consolidated around an acrylic foam core in matched aluminium dies and cured at 120°c.
The use of pre-impregnated materials enables lay-up to be improved and consequently weight and thickness, so that the blades can be moulded to controlled dimensions in a repeatable process. The foam core is machined accurately to oversize dimensions and, when crushed in the moulding process, provides enough resistance to allow the pre-impregnated layers to be consolidated into shape without damage or distortion. The foam also increases the buckling stiffness of the blade and allows freedom of design since there is no need for core or mandrel removal.
At the trailing edge, an assembly comprising a Nomex honeycomb core, covered with a carbon fibre skin, is attached to the spar. Finally, erosion and lightning strike protection is added to the leading edge of the blade by a formed titanium sheet, electrodeposited nickel, or a thermoplastic.
Several improvements have been made to the blades as a result of experience and a rotor system of this type is now fitted to the Anglo-Italian EH101 helicopter, among many others. On theEH101thereis a five-blade main rotor of 18. 5m diameter compared with one of 12. 8m on the Lynx.
Variants of the EH101 will have a maximum takeoff weight of 14,288kg and although similar in sizeto Westland’s Sea Kinghelicopter, will have to be faster and carry a greater load over a longer range. These improvements in performance are in no small way due to the BERP composite main rotor which has an increase in thrust of up to 40% over that of conventional blades.
Improvements in aerodynamic and aero-elastic characteristics also reduce vibration. Composite blades weigh less and have better damage tolerance- particularly important in the military field.
Westland’s composite blade facility is meeting orders for new and retrofit applications from the United Kingdom and many other parts of the world. Six countries are already using Sea Kings with composite main rotor blades.
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