These maintenance practices tell you about composite repair processes and how to repair Class 2, 3 and 4 damage to the composite structure. Refer to
Section 51-10 for data about damage classification. Class 1 damage may only be repaired in accordance with a repair scheme approved by the manufacturer. All repairs must be carried out by approved persons. You must only use the materials approved by the manufacturer when repairing the airplane. Refer to Section 51-30 for data about approved materials. Inspect the damaged area. Look specially at the adjacent structure. Damage can go a long way under the surface. Use the techni ques given in Section 51-10. You must take care to do the repair correctly. The outer shell of a composite structure is stressed. Failure of the structure can cause an accident.
You must use the correct quantity of mixed resin for the repair. Weigh all the cut cloth patches that you will use for the repair. The ratio for glass cloth to mixed resin is 100 : 70. For example, 100 grams of dry glass cloth require 70 grams of mixed resin. The ratio for carbon cloth to mixed resin is 100 : 85. For example, 100 grams of dry carbon cl oth require 85 grams of mixed resin. Measure the quantities of resin and hardener accurate ly (± 0.5 % by weight). Mix the resin and hardener thoroughly before laminating, or adding fillers or other additives. Always use clean containers for mixing resin and only mix as much resin as you can use within its “working life”. When using a large quantity of resin put it into a shallow container. This will increase the ratio of surface area to volume which will reduce the risk of an exothermic reaction. For parts made from self extinguishing resin use the same resin system for repair (refer to Section 51-30).
3. Glass and Carbon Cloth
You must always use the correct cloth for the repair. Refer to the lay-up drawing of the repair area for
data about the type of cloths you must use. The lay-up drawing will tell you: ) The correct type of cloth. ) The fiber direction. ) The dimensions of the layer. Make sure that the fibers in each layer of cloth point in the direction given in the lay-up drawing. This gives the correct strength to the laminate. Only use sharp shears or scissors to cut the cloth to size. Make sure that the fibers in the cut cloth point in the correct relative direction. Make sure that the fiber strands are not broken or damaged. The cloth mu st be free of any damage or contamination.
4. Core Material
You must always use the correct sandwich core for the repair. Refer to the lay-up drawing of the repair area for data about the type of core you must use. Make sure that the core material is not damaged or contaminated. Use a sharp knife to cut the core to the exact size for the repair. The edges of the cut must be clean so that the core will bond correctly. You can profile the core by cutting or sanding.
A prescribed stack of resin impregnated cloth makes a laminate. A laminate which is used to repair an airplane becomes an integral part of the airpl ane structure once the laminate is hardened and fully cured. You can make the laminate in place directly on the repair or you can make the laminate on a work table and then apply the wet laminate to the repai r. When you make the laminate on a table: ) It is easier to do. ) It is easier to control and correct the laminating process. ) You can make sure that the cloth layers in the stack are correct bef ore you apply the resin. ) You can make the repair neater. ) You do not have to work upside down.
B. Laminating on a Table
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