Tail post assembly and NAS bolts

[mfazio]

I am assembling the tail post on Waiex #63. On the service bulletin to strengthen the assembly the top bolts call for NAS bolts rather than AN. NAS bolts appear to be close tolerance bolts. I am not questioning the use of these bolts but curious why these bolts would be used rather than the AN bolts in this location. Is it their close tolerance, strength, or other properties? Just wanted to understand what is going on with the loads, construction and the differences in bolts.

Thanks
Mike Fazio
Waiex #63


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[Bryan Cotton]

NAS bolts are stronger. About 160ksi vs 120ksi.

[mfazio]

NAS bolts are stronger. About 160ksi vs 120ksi.

How does the close tolerance factor in? What does a close tolerance bolt bring to the party that an AN3 doesn’t?

Is it a stronger bolt just based on its metallurgy?

Thanks for the response Bryan.


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[Bryan Cotton]

Without looking at the analysis it is hard to say. Tight fit holes always bring better shear strength as the loads are transferred more evenly. The beefup was in response to the Waiex that shed its tail I think. The original design was probably fine but did not take into account poor workmanship or envelope exceedence. Most likely the NAS bolts were chosen for their better shear strength due to material properties. That is controlled, hole tolerance is up to the builder.