Thermal Deicing of Polymer Composite Helicopter Blades
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THERMAL DEICING OF POLYMER COMPOSITE HELICOPTER BLADES Piyush K. Dutta1, Charles C. Ryerson1 and Charles Pergantis2 U S Army Engineer Research and Development Center, Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, NH 03755 (Correspondence author) 2 U S Army Research Laboratory, Aberdeen Proving Ground, Aberdeen, Maryland
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Abstract This paper presents the results of an investigation to determine if thermal deicing methods (hot air, hot water, hot glycol, or radiative heat) would damage the composite materials in helicopter blades. Samples made from Blackhawk helicopter blades were thermally cycled in the regime of the temperatures of thermal deicing methods and then mechanically load tested. The strength reduction was compared with the number of thermal cycling and the temperatures of thermal cycling. The strength results and the modes of failure indicate that damages indeed do develop in the composites, especially along the bond line of the composite skin and the nomex core of the blade structure, and mechanical strength is reduced. 1. Introduction This study has been performed to identify potential damage to US Army helicopter main rotor blades due to prolong exposure to cold, as well as, ice build-up and its removal. Concerns arose by the accumulation of icing experienced by US forces on rotor aircraft based in Bosnia and the deicing procedures used by US Army maintenance personnel. Although, heating strips are imbedded within the nose/spar sections of modern blades, they are unable to heat the composite skin/honeycomb core section (tailing edge section), and are ineffective to melt large amounts of accumulated ice. Additional melt/removal systems are being utilized, although even these are very time consuming. It has been documented, that to accelerate ice removal, US Army maintenance personnel have been known to break and lift ice patches from blades using mallets, hammers and putty knives, causing irreparable damage to the structure. The knowledge from this project can be applied throughout the fleet of rotorcraft within the tri-services, including US Coast Guard, Medi-Vac/Rescue units, and SOF. Pin using the thermal techniques the thermally induced stresses caused by rapid thermal gain, and differential heating of dry and ice-covered surfaces, have the potential for invisibly weakening multi-layered aircraft structures made of composite materials. Many Army helicopter blades are made of composite materials. It is apprehended that the use of thermal methods, for example, the fielded Buddy-Start system, could damage these blades rendering the aircraft unsafe to fly. This paper discusses the results of the investigation to determine if thermal deicing methods (hot air, hot water, hot glycol, or radiative heat) would damage the composite materials in helicopter blades. We used two retired Army helicopter blades, performed thermal scans of those blades for gross defects and, after locating (and thus avoiding) the defects, cut the two blades into 98 samples.
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