<tonyrenshaw@optusnet.com.au>
>
> I am supposed to attach it with 2 holes for AN3-12A
> bolts, 1/2" apart, and am wondering if people reckon
> I need a machine shop to make it an interference fit
> (extra tight requiring a hammer to tap them home),
> or whether conventional drilling and bolting would
> be OK.
Assuming you have a drill press and cutting oil, an accurate 3/16"
drill is an interference fit by default for an AN3 bolt, but in thick
steel, you'll likely have to ream it out a few hairs to be able to
even hammer it in. However, I've never encountered a small bolt on a
production aircraft that's an intentional interference fit requiring a
hammer, with that installation method specified in the service manual.
Or at least not in the presence of one ornery, old airframe mechanic I
know!
Or, how about a numbered drill? My chart suggests #12 (.1890"), and
you'd want a new one anyway. Or, the "NAS" bolts I have are tighter on
the shank than AN3, making a 4.8mm drill OK. I think they're called
NAS, or close-tolerance, the kind with the big dimple on the top.
I can't help on your other questions, and even a picture of the setup
may not help this nonengineer. You're adding a 4" extension onto
something subject to stresses nine ways from Sunday. But I checked
several taildraggers at the airport, and I saw AN3's on all of them,
in pairs or even just one in various places in the different designs.
Especially on the Luscombe there, most similar in gross weight to
Europa, it sure looks like something should have broken or the 3/16"
holes enlarged since 1946, but the guy will tell you no.
Reg,
Fred F.
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