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Found an old FAA advisory circular that changed how I think about wire routing
I was digging through some digital archives for a different issue and stumbled on FAA AC 43.13-1B, Appendix A. It has this whole section on wire bundle bend radius that I'd never really paid attention to. It says the minimum bend radius for a wire bundle should be ten times the diameter of the bundle, not just a 'gentle curve' like I was taught. I checked a harness I'd just installed on a Cessna 172, and my bend was maybe six times the diameter. It's a small thing, but it explains some intermittent faults I've chased on other jobs. Anyone else have a 'standard' they learned was actually wrong?
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eric_thompson5mo ago
Turns out my whole career has been based on "looks about right" engineering. Found out the hard way a tight wire bundle can act like a tiny little saw over enough vibrations. Makes you wonder what other specs we're all eyeballing.
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lucas2065mo ago
Yeah that "looks about right" thing @eric_thompton hits hard. I read about a bridge where the bolts were just a bit too tight from someone eyeballing it, and the whole thing had stress cracks in a few years. Makes you realize how many small choices add up. We trust that the person before us did the math, but sometimes they just made a good guess. Your wire bundle story is a perfect example of that tiny detail no one checks until it fails.
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