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Found out FAA allows a 0.005 inch gap on some control surface hinges
Was digging through an old advisory circular last night and stumbled on that spec. Always assumed zero tolerance meant zero. Has anyone else run into a tolerance that seemed way looser than you expected?
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michael6691mo ago
You sure that spec isn't for a static unloaded condition? Because 0.005 at rest could turn into 0.010 or more once you get air loads pulling on the hinge line. I remember reading some old Mooney service bulletins where they had a similar spec for the elevator hinge gap and it only applied when the surface was hanging free at room temp. Did the circular mention any load condition with that number?
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margareto261mo ago
grays13 flutter dynamics are real but that 0.005 gap is just a static assembly tolerance, not a flight condition.
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oliverhernandez1mo ago
Has that old Cessna manual ever lead you down a rabbit hole of finding weird tolerances on unrelated parts? I once spent an afternoon trying to figure out why a 1960s 172 had a .003 gap spec on the rudder return spring bracket (totally not a flutter thing, just a manufacturing oddity).
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grays131mo ago
Wait, is that gap actually measured with the hinge under load or just sitting static? Because 0.005 inches sounds tiny until you think about flutter dynamics at high speed. I've seen some ancient Cessna service manuals give tolerances that look crazy on paper but work fine in practice. What kind of control surface was this for, aileron or elevator?
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