9/27/01 AC 43.13-1B CHG 1

SECTION 3. INSPECTION AND TESTING

2-30. GENERAL. All components of the (2) Loose or wrinkled polyester fabric covering should be inspected for general con- covering, finished with coatings other than dition. Loose finishing tape and reinforcing dope, may be caused by inadequate or exces- patches; chafing under fairings; brittle, crack- sive heat application; excess slack when the ing, peeling, or deteriorated coatings; fabric fabric was installed; or bent or warped struc- tears and rock damage; broken or missing ture. Polyester fabric which does not meet air- lacing; and rodent nests are unacceptable. The craft quality specifications will very likely be- entire fabric covering should be uniformly taut come loose after a short period of time. with no loose or wrinkled areas, or excess ten- sion which can warp and damage the . (3) Glass fabric covering should be tested with a large suction cup for rib lacing a. Excess Tension. There are no methods cord failure and reinforcing tape failure caused or specifications for measuring acceptable fab- by chafing on all ribs and other structural ric tension other than observation. Excess ten- attachments throughout the airframe. Particu- sion may warp critical components, such as lar attention should be given to the area within , wing rib, and trailing edges out of the propeller slipstream. If failure is indicated position, weakening the airframe structure. by the covering lifting from the static position, the rib lacing cord and reinforcing tape must (1) Excess tension with cotton, linen, be reinstalled with double the number of origi- and glass fiber fabric covering is usually nal laces. caused by excessive dope film on a new cov- ering, or continuous shrinking of an originally NOTE: Temporary wrinkles will de- satisfactory dope film as the plasticizers mi- velop in any fabric coated and fin- grate from the dope with age. Heat from sun ished with dope, when moisture from exposure accelerates plasticizer migration. rain, heavy fog, or dew is absorbed into a poor-quality dope film, causing (2) Excess tension with polyester fabric, the film to expand. Temporary wrin- coated with dope, is usually caused by the kles may also develop with any type of combined tension of the heat tautened polyes- thick coatings, on any type of fabric, ter fabric and continuous shrinking of the dope when an is moved from a cold film as the plasticizers migrate from the dope storage area to a warm hangar or with age. parked in the warming sunshine, causing rapid thermal expansion of b. Loose Fabric. Fabric that flutters or the coating. ripples in the propeller slipstream, balloons, or is depressed excessively in flight from the c. Coating Cracks. Fabric exposed static position, is unacceptable. through cracks in the coating may be initially tested for deterioration by pressing firmly with (1) Loose or wrinkled cotton, linen, and a thumb to check the fabric’s strength. Natural glass fabric covering may be caused by inade- fibers deteriorate by exposure to ultraviolet ra- quate dope film; poor quality dope; fabric in- diation, mildew, fungus from moisture, high stalled with excess slack; or by a bent, broken, acid-content rain, dew, fog, pollution, and age. or warped structure. Polyester filaments will deteriorate by expo- sure to UV radiation.

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(1) Glass fabric will not deteriorate back side of cotton or linen fabric indicates a from UV exposure, but will be deteriorated by fungicide was present in the dope to resist de- acid rain, dew fallout, and chaffing if loose in terioration by fungus and mildew. the prop blast area. b. Polyester fabric conforming to (2) Cotton, linen, and glass fabric cov- TSO-C14b or TSO-C15d is whiter in color erings are dependent solely on the strength and than cotton or linen. The fabric styles adapted tautening characteristics of the dope film to for use as aircraft covering have a variety of carry the airloads. Dope coatings on heat- thread counts, up to ninety-four (94), depend- tautened polyester fabric will also absorb all ing on the source, weight, and the airloads because the elongation of polyes- breaking strength. Polyester is a monofilament ter filaments are considerably higher than the and will not have any nap or filament ends dope film. Polyester fabric that is coated with showing. materials other than dope, is dependent solely on the heat tautening and low-elongation char- c. Glass fabric is manufactured white in acteristics of the polyester filaments to develop color, and one source is precoated with a blue- tension and transmit the airloads to the air- tinted dope as a primer and to reduce weave frame without excess distortion from a static distortion during handling. Thread count will position. be approximately 36 threads per inch. Glass fabrics are monofilament and will not have any (3) Cracks in coatings will allow any nap or filament ends showing unless they are type of exposed fabric to deteriorate. Cracks inadvertently broken. should be closed by sealing or removing the coatings in the immediate area and replace d. When a small fabric sample can be with new coatings, or recover the component. removed from the aircraft and all the coatings removed, a burn test will readily distinguish 2-31. FABRIC IDENTIFICATION. between natural fabric, polyester, and glass Cotton Fabric meeting TSO-C15 or TSO-C14 fabric. Cotton and linen will burn to a dry ash, can be identified by an off-white color and polyester filaments will melt to a liquid and thread count of 80 to 94 for TSO-C14b and continue burning to a charred ash, and glass 80 to 84 for TSO-C15d in both directions. filaments, which do not support combustion, will become incandescent over a flame. a. Aircraft linen conforming to British specification 7F1 may be identified by a 2-32. COATING IDENTIFICATION. slightly darker shade than cotton fabric and ir- Nitrate or butyrate dope must be used to de- regular thread spacing. The average thread velop tension on cotton, linen, and glass fab- count will be about the same as Grade A fabric rics. When a small sample can be removed, (TSO-C15d). The non-uniformity of the linen burn tests will distinguish nitrate dope-coated thread size is also noticeable, with one thread fabric from butyrate dope-coated fabric by its half the size of the adjacent thread. When immediate ignition and accelerated combus- viewed under a magnifying glass, the ends of tion. Butyrate dope will burn at less than the cotton and linen fiber nap may be seen on one-half the rate of nitrate dope. Coating types the backside. The nap is also seen when the other than nitrate or butyrate dope may have coating is removed from the front or outside been used as a finish over dope on cotton, surface. A light-purple color showing on the linen, and glass fiber fabric coverings.

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a. If the fabric type is determined to be width, regardless of the fabric grade. Fabric polyester, coating identification should start installed on aircraft with a wing loading of by reviewing the aircraft records and inspect- 9 lb. per square foot and over, or a Vne of ing the inside of the and the for 160 mph and over, will be considered unair- the required fabric source identification stamps worthy when the breaking strength has deterio- for covering materials authorized under the rated below 56 lb. per inch width. STC. The manual, furnished by the holder of the STC-approved fabric, should be reviewed c. Fabric installed on a glider or sail- to determine whether the coatings are those plane with a wing loading of 8 lb. per square specified by the STC. foot and less, and a Vne of 135 mph or less, will be considered unairworthy when the fabric b. Coating types, other than those breaking strength has deteriorated below 35 lb. authorized by the original STC, may have been per inch width, regardless of the fabric grade. used with prior FAA approval, and this would be noted in the aircraft records. The presence 2-34. FABRIC TESTING. Mechanical de- of dope on polyester can be detected by a sam- vices used to test fabric by pressing against or ple burn test. piercing the finished fabric are not FAA ap- proved and are used at the discretion of the 2-33. STRENGTH CRITERIA FOR mechanic to base an opinion on the general AIRCRAFT FABRIC. Minimum perform- fabric condition. Punch test accuracy will de- ance standards for new intermediate-grade fab- pend on the individual device calibration, total ric are specified in TSO-C14b, which refer- coating thickness, brittleness, and types of ences AMS 3804C. Minimum performance coatings and fabric. Mechanical devices are standards for new Grade A fabric are specified not applicable to glass fiber fabric that will in TSO-C15d, which references AMS 3806D. easily shear and indicate a very low reading regardless of the true breaking strength. If the a. The condition of the fabric covering fabric tests in the lower breaking strength must be determined on every 100-hour and an- range with the mechanical punch tester or if nual inspection, because the strength of the the overall fabric cover conditions are poor, fabric is a definite factor in the airworthiness then more accurate field tests may be made. of an . Fabric is considered to be air- Cut a 1-1/4-inch wide by 4-inch long sample worthy until it deteriorates to a breaking from a top exposed surface, remove all coat- strength less than 70 percent of the strength of ings and ravel the edges to a 1-inch width. new fabric required for the aircraft. For exam- Clamp each end between suitable clamps with ple, if grade-A cotton is used on an airplane one clamp anchored to a support structure that requires only intermediate fabric, it can while a load is applied (see table 2-1) by add- deteriorate to 46 pounds per inch width ing sand in a suitable container suspended a (70 percent of the strength of intermediate fab- few inches above the floor. If the breaking ric) before it must be replaced. strength is still in question, a sample should be sent to a qualified testing laboratory and b. Fabric installed on aircraft with a breaking strength tests made in accordance wing loading less than 9 lb. per square foot with American Society of Testing Materials (psf), and a Vne less than 160 mph, will be (ASTM) publication D5035. considered unairworthy when the breaking strength has deteriorated below 46 lb. per inch

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NOTE: ASTM publication D1682 has is cracked, it may be treated with rejuvenator, a been discontinued but is still referred mixture of very potent solvents and plasticiz- to in some Aerospace Material Speci- ers, to restore its resilience. The surface of the fication (AMS). The grab test method fabric is cleaned and the rejuvenator sprayed previously listed in ASTM D1682, sec- on in a wet coat, and the solvents soften the tions 1 through 16, has been super- old finish so the plasticizers can become part seded by ASTM publication D5034. of the film. When the rejuvenator dries, the The strip testing method (most com- surface should be sprayed with two coats of monly used in aircraft) previously aluminum-pigmented dope, then sanded and a listed in ASTM D1682, sections 17 third coat of aluminum-pigmented dope ap- through 21, has been superseded by plied, followed with the colored-dope finish. ASTM publication D5035. When repairing, rejuvenating, and refinishing covering materials approved under an STC, in- 2-35. REJUVENATION OF THE DOPE structions in the manual furnished by the mate- FILM. If fabric loses its strength, there is rial supplier should be followed. nothing to do but remove it and recover the aircraft. But if the fabric is good and the dope 2-36.2-41. [RESERVED.]

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