3M’s leading-edge innovation for helicopters

  • 30-Jun-2008 06:19 EDT

A BERP IV rotor blade with 3M's leading-edge protection system.

Operating helicopters in very difficult climatic conditions in Iraq and Afghanistan can result in the need to replace rotor blades after only 400 flying hours’ time because sand, grit, and gravel have such a severe abrasive effect. And sand on the blades can create sparks when helicopters land at night, producing a halo effect and making the aircraft’s position easy to spot, particularly when night-vision equipment is in use.

To improve the operating life span of the BERP (British Experimental Rotor Blade Program) III blades fitted to AgustaWestland Lynx helicopters, the type operated in both countries by British Forces, 3M has developed a protective polyurethane coating. Polyurethane is abrasion-resistant and, combined with a highly shear-resistant adhesive, can provide durable, replaceable protection that helps keep the helicopter fully airworthy for longer periods. The blades are now undergoing trials by British Forces.

Because of the complex shape of the blades, 3M worked closely with AgustaWestland to develop pre-shaped coverings (polythene protective tapes)—made in blade-shaped molds—used to protect the leading edge. The tough, light, sacrificial coatings can be flown for between 100 and 150 h and experience more than 400 landings without damage being sustained by the underlying metal, claims 3M. The tape can be removed and replaced in-theatre, giving another 120-plus flying hours until the next change. The capability avoids the need to remove the blades and, in some instances, ship them back to the U.K.

The development of the coverings marks the latest benefits to accrue from the BERP project, which started in 1976. BERP, a collaboration between AgustaWestland and the UK Defence Science and Technology Laboratory, has made other significant advances, including helping a modified Lynx to set a helicopter world speed record of 400.87 km/h.

BERP composite blades developed in the previous phase of the program feature a nickel or titanium strip at their leading edge—the area exposed to extreme conditions and where dimensional consistency is essential. Lessons learned from the use of polyurethane for the third-generation rotor blades have allowed designers to incorporate the material into the Phase IV design, but without a metallic leading-edge strip.

Andrew Marks, 3M’s Technical Specialist, said: “Polyurethane is one of the most resistant materials available. It is a cross-linked polymer that absorbs energy when it’s hit and is subsequently very impact-tolerant. The longevity and in-service availability benefits that we demonstrated by using polyurethane protective coatings on the last generation of rotor blades have been designed into the latest version.”

The incorporation of polyurethane rather than a metallic leading edge has helped meet several Phase IV performance targets, he explained. These include lower costs (both at purchase and throughout operational life), reduced rotor vibration, and enhanced damage and erosion resistance. And by using a composite rotor blade without a metallic leading edge, the nocturnal halo effect is avoided, allowing safer, stealthier operation at night.

Six AgustaWestland EH 101 Merlins purchased by the UK Ministry of Defence (MOD) from the Royal Danish Air Force are scheduled to become the first helicopters to enter service using the BERP IV technology. BERP IV is also being considered for the US101 project, designed to fulfill the role of the next U.S. presidential helicopter, and for the MOD’s Future Lynx project.

3M’s polyurethane protective tapes are also used on fixed-wing aircraft to prevent damage to body panels during takeoff and landing. The conditions being experienced by Royal Air Force (RAF) Lockheed Martin C-130J Hercules currently in service in Iraq and Afghanistan are particularly severe, with damage being caused by debris thrown up when using unmade runways. Replacing panels on the aircraft is slow and laborious; bullet proofing needs to be removed from the inside of the aircraft before the panels can be taken off. The process is further complicated because much of the exterior of the aircraft is structural, so an individual panel must be removed and replaced before work can begin on the next.

To minimize damage to the underlying panels, 3M 8641 tape is used to protect the underside of the RAF’s C-130s. The tape has an acrylic foam backing that offers impact absorption, as well as the abrasion resistance provided by its polyurethane surface. The U.K. aircraft also have the tape fitted to the sides and underside of the fuselage to offer greater protection and to reduce the need for panel changes.

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