ABSTRACT

Results of an investigation to determine whether thermal deicing methods (hot air, hot glycol, or radiative heat) would damage the composite materials in helicopter blades are presented. Samples from composite helicopter blades were thermally cycled in the regime of thermal deicing method temperatures and then mechanically load tested. A reduction in strength was determined as a function of number of thermal cycles and temperature of testing. It was observed that although C-scans cannot detect any damage, damage did develop along the bond line of the composite skin and the Nomex core and caused a reduction of mechanical strength.

INTRODUCTION

Helicopter deicing experiments conducted by Ryerson et al. (1999), have raised concerns about possible damage to the composites used as the skin materials of helicopter blade sandwich panels as a result of thermal deicing. Although heating strips are imbedded within the leading edge of some helicopter blades to alleviate in-flight ice accumulations, these systems are not effective for preflight deicing because ice and snow accumulate over the entire upper surface of blades. Also, these heaters cannot be powered prior to engine start, and engine start cannot occur when the blades are covered with ice and snow. Most modern helicopter blades are made of composite materials. Application of heat for deicing can cause rapid temperature changes in composites, which induces stresses that can invisibly weaken the multilayered, or sandwich aircraft structures. This paper discusses the results of an investigation to determine whether thermal deicing methods (hot air, hot water, hot glycol, or radiative heat) would damage the composite materials in helicopter blades. To assess the problem we prepared 98 samples from two used helicopter blades, then C-scanned them to establish a baseline for thermal defect analyses.

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