JEC COMPOSITES MAGAZINE - Issue #43 - September 2008 - 56

KNOW-HOW Materials Development of helicopter blade coatings Naval helicopters and vertical/short take-off and landing aircraft such as the V-22 Osprey operate in hostile environments. The leading edges of their rotor blade are protected with erosion-resistant materials to avoid rapid deterioration in sandy or dusty landing zones and severe sand, rain, or ice storms. The subject of this article is the search for a class of polymers offering superior erosion resistance and de-icing capability. conformable boot that is easy to apply. The Bell 210 medium utility helicopter is represented in figure 1. YOSIF GOLFMAN, New R & D Programs & Proposals Neo-Advent Technologies, LLC The problem The Navy is interested in replacing the metallic leading-edge strip with a polymer-based, field-serviceable, thermally-conductive and erosion-resistant boot material applied directly over the existing composite substrate of the rotor blade. This concept should reduce the overall blade weight and ensure uniform working strain and satisfactory fatigue life. Simplifying and allowing for repair and reapplication of the leading edge in the field could reduce maintenance requirements and costs. In the case of the V-22, the proposed coating materials/concept will need to meet the requirement for 250 flight hours of continuous operation in rain, dust and sand. Specifically, they need to demonstrate a superior resistance to surface abrasion and spallation caused by high-velocity impact of sand particles and raindrops [1]. Furthermore, the Navy has estimated that the thermal conductivity of the current erosion strip needs to be 12 W/mk or greater to maintain the current deicing performance (the titanium alloy portion is likely to be higher and the nickel lower), but Bell Helicopter can best say the precise requirement [2]. T he leading edge of the V-22 rotor blade is currently made of titanium and nickel abrasion strips bonded to a composite substrate. Although this bonded metal-composite hybrid is moderately effective for erosion protection and supports the de-icing capability of the leading edge, the current configuration limits the blade’s working strain and fatigue life [1]. The existing strips are unable to provide the 250 hours of flying operation required by the US Navy, and they also cause a de-masking glowing halo around the blades in certain night conditions. To summarize the required performance, Navy specifications call for a wear life of 250 hours in sand, dust and rain or 125 hours hovering in sand, plus 125 hours of forward flight in rain. It is highly unlikely that the current rotor blade will achieve this level of durability, however. The current strip element also requires frequent inspection to detect the accumulated fatigue cracks in the metal and ensure flight safety. Due to the nonoptimized bonding solution, field removal and maintenance of the strip is unfeasible, increasing the rotor blade’s operating and service costs. For example, the US army is replacing 20-25 helicopter rotor blades per month in Iraq and Afghanistan as a result of leading edge and blade tip erosion caused by sand. To improve the durability of composite-blade leading edges, the Navy wants to develop a high-strain, lightweight, thermallyFig.1: Bell 210 medium utility helicopter conductive and Reinforced thermoplastic materials The first wear-proof materials created, tested and patented [3,4] consist of a polyvinyl chloride, butadiene resin mixed with epoxy or phenolic resin and additives covering fibreglass. Thermoplastic resins have modest abrasion-resistance properties (see table 1). They recently gained popularity as an easy-to-produce replacement for structural aluminium components to reduce the weight of aircraft elements. They are rapidly replacing reinforced epoxy and polyester thermosetting resins. In the aerospace industry, thermoplastic prepregs were recently introduced for the Airbus A380 wing’s leading edges. The amorphous polymers used originally, such as polyethersulphone (PES), were later superseded by crystalline polymers such as polyphenylene sulphide (PPS). In reinforced thermoplastics like polypropylene, additive ingredients such as chopped carbon/fibre were used. For example, glass-reinforced and JEC Composites Magazine / No43 September 2008

JEC COMPOSITES MAGAZINE - Issue #43 - September 2008

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #43 - September 2008