CHAPTER 14AIRCRAFT NONMETALLIC REPAIRChapter Objective: Upon completion of this chapter, you will have a workingknowledge of the basic repair techniques associated with aircraft nonmetallicstructures.You will also have a working knowledge of advanced compositematerials, their unique characteristics, and special techniques and safetyprocedures associated with composite repair materials.This chapter deals with the materials andprocedures to be used in the repair of nonmetallic andadvanced composite materials used in aircraftconstruction. The procedures discussed are general innature. When actually repairing nonmetallic oradvanced composite materials, you should refer to theapplicable maintenance instruction manual (MIM)and structural repair manual (SRM).MAINTAINING AND REPAIRINGAIRCRAFT NONMETALLICMATERIALSLearning Objective:Recognize the proce-dures for cleaning and repairing orreplacement of aircraft nonmetallicstructures and surfaces.In the following text, we will discuss some of theprocedures used in the repair or replacement ofaircraft nonmetallic structures. Because no one set ofrules applies to all aircraft, you should refer to themaintenance instruction manual (MIM) and structuralrepair manual (SRM) for the materials and proceduresfor a particular aircraft.MAINTAINING TRANSPARENT PLASTICMATERIALSBecause of the many uses of plastic materials inaircraft, optical quality is of great importance. Theseplastic materials are similar to plate glass in many oftheir optical characteristics. Ability to locate andidentify other aircraft in flight, to land safely at highspeeds, to maintain position in formation, and in somecases, to sight guns accurately through plasticenclosures all depend upon the surface cleanliness,clarity, and freedom from distortion of the plasticmaterial.These factors depend entirely upon theamount of care exercised in the handling, fabrication,maintenance, and repair of the material.Plastics have many advantages over glass foraircraft application, particularly the lightness inweight and ease of fabrication and repairs. They lackthe surface hardness of glass and are very easilyscratched, with resulting impairment of vision. Youmust exercise care while servicing all aircraft to avoidscratching or otherwise damaging the plastic surface.Specific procedures are described later in thissection for minor maintenance; however, thefollowing general rules are emphasized:1. Transparent plastic materials should behandled only with clean cotton gloves.2. The use of harmful liquids, such as cleaningagents, should be avoided.3. Fabrication, repair, installation, and mainte-nance instructions must be closely followed.4. Operations that might tend to scratch or distortthe plastic surface must be avoided. You must takecare to avoid scratching plastic surfaces with fingerrings or other sharp objects.Just as woods split and metals crack in areas ofhigh, localized stress, plastic materials develop, undersimilar conditions, small surface fissures calledcrazing.These tiny cracks are approximatelyperpendicular to the surface, very narrow in width,and usually not over 0.01 inch in depth. These tinyfissures are not only an optical defect, but also amechanical defect, as there is a separation or partingof material.If the crazing is in a random pattern, it is usuallycaused by the action of solvent or solvent vapors. Ifthe crazing is approximately parallel, it is usuallycaused by directional stress, set up by cold forming,excessive loading, improper installation, improper14-1
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