AIRFRAME Greg Mellema | Contributing Author


Demystifying Composite Repair in Modern Rotorcraft


Unless you’ve been living under a rock for the past 20 years, the proliferation of advanced composite materials


in the rotorcraft industry cannot have escaped your attention. Throughout the 1990s and even into the new millennium, it seemed that with every new model helicopter introduced, yet another portion of the structure that we were accustomed to being made from aluminum was suddenly made from an advanced composite material like carbon fi ber, fi berglass or Kevlar. Perhaps it’s just my perception as an old sheet metal guy, but that trend seems to have increased dramatically in the last six to eight years. The trend towards advanced composite materials is not a conspiracy to make our sheet metal skills obsolete, but rather a natural evolution in the never-ending battle against the helicopter’s oldest enemy: weight. As such, we must embrace its coming and endeavor to expand our skill sets to include an understanding of how composites work and how to repair them properly.


Composite Basics


When we talk about advanced composite materials in aerospace, we’re referring to long-fi ber reinforcements such as glass, carbon or Kevlar (aramid) embedded in a matrix material, usually an epoxy resin. For the most part, the loads within a structure are borne by the fi ber reinforcement. This being the case, multiple plies of the reinforcement are typically laid up and oriented specifi cally to handle the loads imposed on the part (Figure 1). While short, chopped fi ber and polyester resin construction like you might fi nd in a hot tub or shower stall are also composites, we generally don’t refer to them as “advanced composites” because they simply aren’t able to achieve the same strength-to-weight ratios as their aerospace counterparts.


October | November 2015 HelicopterMaintenanceMagazine.com 29


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