Samples of Actual Compression Cracks
(These were found in a Citabria wing, but apply to all 7-, 8- and 11-series)
Sample 1 - Front Face of Spar
These failures are from about 5 inches inboard of the spar doubler plate. Note the differences in the face shots - one is much more subtle. |
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Sample 1 - Rear Face of Spar
Also, note the wood grain anomaly (a subtle wave in the otherwise straight line grain pattern) adjacent to the compression failure which is especially noticable in the view on the rear of the spar. Without this grain anomally, which acts to concentrate the stresses, there may not have been a failure at this location. |
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Sample 1 - Top Surface of Spar
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