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Date: Sun, 05 Dec 2004 19:47:30 -0500
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From: "Dan Schaefer" <dfs155@adelphia.net>
Subject: re:Cowl fasteners
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On my 235 (yes, there are still some of them out there) I installed hinges
and SS wires on the sides of the cowl and non-floating steel MS21069 anchor
nuts (nut plates) to attach both upper and lower cowl to the fuselage
flange. I have almost always used MS24694C7 SS screws (8-32) in the 11 - 12
years the airplane has been flying.

In my experience, there are several things to consider if you go this way.

First, with all those screws most folks will resort to a power driver to
install and remove them. Over time, some of the SS screws will refuse to be
removed and, because I believe the SS is slightly more malleable than the
non-SS screws, will cam out (or even twist off) before you can get your
finger off the trigger of the driver. So, always keep an Easy-out and the
correct size drill bit handy when removing your cowl. I'm not sure what's
going on but it seems that the locking feature of the anchor nut (slightly
out-of-round) eventually eats the slightly softer SS threads.

Second, depending on the cowling material (my early 235 cowl seemed to be
made of quite different and softer stuff than the airframe) the screw heads
will eventually enlarge the countersunk holes and get to be a bit messy. I
heartily recommend embedding SS Tinnerman washers (or equivalent) at the
screw holes. I've seen it done on several LNC2's and wish I had done the
same when I built. The nicest ones were installed prior to finishing,
flushed to the surface and had the inside of the countersink masked so the
screw souldn't bear on the paint and peel it around the hole.

Third, if I were to do it over today, I think I'd use some sort of flush
type Cam-lock if for no other reason than making the R&R of the cowlings
easier and quicker, and I believe, less prone to messing up the paint from
the inevitable slipped screw driver - because it WILL happen!

Dan Schaefer
Early 235, N235SP