|
|
<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
<< Lancair Builders' Mail List >>
<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
>>
Posted for "Lance A. Neibauer" <lancen@lancair.com>:
For the benefit of all IV-P builders, I'll comment on what we found with
the window that blew out of a IV-P a few weeks ago. A friend of the new
owner brought the door to our facility for inspection and repair. It's
worth noting that we have eight years of reliable service from not only the
company IV-P but also many others in the field with lots of total hours
(ours has around 2,000 hrs on it).
With that said, the review of this incident emphasizes the extreme
importance of doing the assembly work properly. We saw three key elements
that we believe caused the breakage. 1. The larger holes were made in the
window but soft plastic tubing was cut and inserted in the holes, with the
bolts going through the tubing. The tubing was cut a bit short in length
and the result was a hard epoxy "ledge" on one side of the upper bolt hole
on the top rear latch location. This ridge was very "crisp" and about
.050" - .070" high. More on this later. 2. The widow was not scuffed at
all on a large portion of the surface along the entire rear vertical bond
line as well as top and bottom bond lines, and appeared to have had no
adhesion whatsoever along these surfaces. 3. The bond flange area was
reduced overall by about 40- 50% - less than 1" in some areas.
I feel it was a combination of all of the above that caused the break. With
greatly reduced bond area and near zero bond integrity over much of the
area that was left, a lot of the membrane stress could have been focused
directly into the bolts. Had the bolt hole filler been consistent, that
load would have been spread uniformly and they may have taken it but with
the very soft tubing (taking virtually none of it) the small hard ridge at
the rear hole quite likely saw a sharp stress rise locally. I don't think
it was coincidence that the crack originated directly adjacent to that ridge.
This information reinforces the fact that proper technique is very
important and please don't adlib with techniques such as adding plastic
tubing in bolt holes etc. If the steps are performed properly, the result
is indeed proven reliability. While I'm on the subject, another general
area of concern is that of potential small stress risers caused from burrs
around a poorly drilled hole in the window. Please also pay particularly
close attention to this. A light smoothing with approx. 400-grit sandpaper
on the edges would help insure against such stress risers. Let's keep it
safe.
Lance
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
LML website: http://www.olsusa.com/Users/Mkaye/maillist.html
Builders' Bookstore: http://www.buildersbooks.com/lancair
Please send your photos and drawings to marvkaye@olsusa.com.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
|
|