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Andrews Web Site
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Date: 4-9-2021
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Number of Hours: 8.00
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Manual Reference:
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Brief Description: Rebuilt Lower Engine Mount Fittings
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While I was reworking the lower engine mount attach fittings, I changed the design somewhat. First, let me mention that my current airplane (an RV-4) had very similar fittings early in it's life, but the design was modified when cracking became an issue (not on my plane, but others had experienced it) as a result, the design was made more robust. In the case of the Nexus fittings, I was concerned that welding a bent leg to a flat plate would result in a requirement for significant "bridging" in the weld. I was concerned that difficulty in getting good weld penetration into the corner of the bent part would lead to cooking of the upstanding leg and potential embrittlement. I thought it would be much easier to get a good weld in a simple 90 degree leg than one that was bent under. By adding another leg that could be welded with a 90 degree intersection while retaining the bent leg, I still have a fairly robust leg even if the weld were to completely fail. This design change does rely on the rivets between the legs to provide the stiffness needed to direct the loads to the welded leg, but the load in the rivets is well within their capability. Yes, there are other issues with this design, but this is the way I went.
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Showing typical weld on the 90 degree leg
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Completed Lower Fittings
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Typical Backside Penetration
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