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9/8/98 AC 43.13.1B CHAPTER 2. FABRIC COVERING SECTION 1. PRACTICES AND PRECAUTIONS 2-1. GENERAL. Cotton and Irish linen fab rics were the airframe coverings of choice from WWI through the 1950’s. However, in creases in cost and the short lifespan of natural fabrics became the driving factors which re sulted in almost 100 percent replacement of original airframe fabrics by man-made, STC-approved, polyester, and glass filament fabric. 2-2. PROBLEM AREAS. a. Deterioration. Polyester fabric dete riorates only by exposure to ultraviolet radia tion as used in an aircraft covering environ ment. When coatings completely protect the fabric its service life is infinite. Therefore, it is very important to thoroughly protect the structure from deterioration before covering and provide adequate inspection access to all areas of fabric-covered components to allow inspection for corrosion, wood rot, and mice infestation. Multiple drain holes in the lower ends of all fabric-covered sections also provide needed ventilation to remove condensation. b. Tension. Polyester fabric obtains maximum tension on an airframe at 350oF, and will not be excessive on aircraft originally covered with natural fabric and 12 coats of Nitrate or Butyrate Dope. However, dope ap plied over full heat-tauted fabric can develop excess tension after aging and damage light aircraft structures. Coatings other than dope will not increase fabric tension after aging. The heat-tauting instructions given in the manual of each STC-approved covering proc ess should be followed. 2-3. AIRCRAFT FABRIC-SYNTHETIC. a. STC-Approved Covering Materials. There is a wide selection of STC-approved covering materials available which utilize synthetic fabric falling within the generic class “Polyester” and may vary in characteristics. Difference in the fabric may be denier, tenac ity, thread count, weight, shrink, tension, and weave style. b. Polyester Filaments. Polyester Fila ments are manufactured by polymerization of various select acids and alcohols, then extrud ing the resulting molten polymers through spinnerets to form filaments. The filaments are heat stretched to reduce to the desired denier or size. It is the heat stretching that im parts a memory in the filaments causing them to try and return to their original shorter length when reheated at a controlled temperature. Overheating will cancel the memory and melt the filaments. c. Covering Procedures. Coating types, covering accessories, and covering procedures also may vary; therefore, the covering proce dures given in the pertinent manuals must be followed to comply with the STC. The FAA STC-approved installation takes precedence over instructions in this advisory circular. d. Installation. Initial installation of polyester fabric is similar to natural fabric. The fabric is installed with as little slack as possible, considering fittings and other protru sions. It may be sewn into an envelope, in stalled as a blanket, or installed by cementing to the airframe with a fabric cement. Each STC may differ in the cement seam overlap, type of sewn seam, heat shrinking procedures, and temperature. Par 2-1 Page 2-1PDF Image | AFS-640
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