The repair and return to operational status of military aircraft involved in crashes or serious accidents, or those having heavy structural damage discovered during depot level maintenance, may require the replacement of main structural components or assemblies. These components will have to be positioned, and attached to the aircraft, to very precise tolerances. The precise positioning of these assemblies or components is normally done during the aircraft manufacturing using massive assembly tools, called jigs, that are not normally found at repair or maintenance facilities. Therefore, the need existed for a method that will allow the precise positioning of the component while avoiding the use of expensive and complex tools. The IAF Depot developed such a method, using optical theodolites of the type normally used in surveying. Once hard (or reference) points are identified on both the component to be positioned and on the aircraft, a positioning setup is performed using two or three theodolites. A coordinate system is then specified, and the measuring of the precise spatial positioning of each reference point is determined. Using a six-degrees-of-freedom supporting cradle the component is then moved into its correct position, using an iterative method that calculates the spatial motion required to match the component’s current position to its required one. The use of optical theodolites was found to answer the strict tolerance requirements for major structural component positioning. The method was further refined using new-generation, computer-controlled theodolites that allowed for the automation of some stages, greatly reducing the time and effort required to perform this type of operation.
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