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Original Date: 05/08/1995
Revision Date: 01/18/2007
Information : Airbag Shimming on the F-18E/F Wing
The F/A-18 E/F requires 100% liquid shimming between composite and mating structures. McDonnell Douglas Aerospace (MDA)-St. Louis applies an airbag shimming method which uses a large, low pressure, pneumatic tool to apply constant, uniform pressure over large, irregularly shaped surfaces while the liquid shim material cures. Previously, MDA-St. Louis performed liquid shimming by using wedgeloks which produced localized pressure on the skin, resulting in undesired thickness variations in the liquid shim. The new method uses an airbag shimming tool, which has C-channels containing airbag inserts, and is attached to the assembly jig. When the airbag is inflated, it produces even pressure against the composite skin.
With this airbag shimming method, two holes are drilled prior to liquid shimming to maintain the skin/substructure relationship. The gap check is performed by attaching the airbag tooling and pressurizing the airbag. While the liquid shim is curing, the pressure on the composite skin is uniform and constant, so the quality of the liquid shim thickness is improved over that obtained through the wedgelok method. After the liquid shim is applied to the opposite surface, the wing is moved to the Automated Drilling System for final drillout. This method eliminates the need for installing large numbers of cumbersome wedgeloks.
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