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1. 11:39 AM - Windshield (Gary Vogt)
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Sorry I got so condescending about windshield. No excuse.
By my count, I've installed 43 windshields since 1984. I've made a lot of mistakes
and learned a lot of 'tricks' to getting the windshield square with the bow
and getting the correct thickness of RTV.
I built my jig in 1984 in an attempt to simulate the location and shape of the
windshield as installed. At the time, I was trying too imagine how they were
done at the factory. I figured they had some sort of jig to put the windshield
on the bow. The jig has gone through 2 revisions. mostly to provide better
access to the underside. The version I have now guarantees an absolutely flat
windshield bow to which the windshield is bonded. I have a set of blocks of
wood to put under the forward edge of the windshield. These blocks locate and
lock the forward edge such that when the windshield is set into position, it
always falls on the same position at the windshield bow edge. The jig has dowels
that locate the holes to be drilled at the lower corners. Before the holes
are drilled, I tape a strip of .020 aluminum to the bow to simulate the thickness
of the RTV when installed. The holes in the lower corners are drilled
with the windshield in its
final location. With those holes drilled, the windshield can be positioned and
the two holes on top drilled. It's at this point that I use a feeler gauge
the determine the gap between the windshield and bow. Where it's too tight (meaning:
places where the forward edge of the windshield bow would project into
the RTV making the RTV too thin, <.020, in that area), I mark the windshield
so that any clamps in that area are not over tightened. I use two types of shims
to space the windshield from the bow and maintain the spacing during assembly.
Shims I've tried:
(1) self sticking foam that compresses to approx .025 inches. I punched out dots
using a hole punch. It worked, but left the dots showing. I did one like
this.
(2) .020 safety wire clips at the forward edge of the bow. It worked, but left
little holes when I removed the clips. The holes couldn't be filled with RV.
I did two like this.
(3) I made a spacer, .050 thick, the shape of the windshield bow, attached to
the bow through the holes used to hold the double bow seal on, that stuck up .030
above the aft edge of the bow (same surface the seal uses).
The idea here was to hold the windshield .030 away from the bow uniformly
from one corner to the other. At first, this sounded like a great idea (it wouldn't
work with an LP Aero windshield because
there is no lip at the bow). The biggest problem was: the bows are not all
the same shape. I used this for 4 or 5 windshields before it became obvious
this was not practical. I kept filing and adjusting the shape to get them to
fit.
(4) Then, I made little "L" shaped shims that can be placed under the aft edge
of the windshield between the bow and windshield. The long side is flush with
the windshield bow face.
The long side is 1 inch long and is .063 inches thick. The short side is
.050 inches long and several thicknesses. I have 10 sets in sizes from .025
to .040 inches.
These work pretty well. At first, I clamped them into place. Then, screws
through the holes that hold the double bead seal to the windshield bow. Then
tape. All work pretty well.
The gap can be filled with RTV after the shim is removed.
(5) My favorite is just too simple to believe. Again, using the holes that attach
the double bead seal to the windshield bow, I use a #6 screw onto which I
put a wide area #10 washer plus a wide area 5/16 washer.
I'd use just the wide area 5/16 washer but the hole is too big; the #6
screw won't hold it by itself. With the windshield in place, I can adjust the
gap between the bow and windshield with the washers tightened against the bow.
When bonding, I tighten the clamps, located at the shims, until the washer
just shows through the RTV and just touches the windshield. (NA for LP Aero
windshields)
After the RTV is applied to the windshield bonding area, the windshield can then
be set into place and located over the dowels on the bottom corners, the holes
line up on top for the top two screws and special washers. Clamps are applied
until I get either the "L" shim showing on the edge of the windshield or the
washer showing through the windshield. At this point, I know the gap at the
forward edge of the bow is about .020 inches. The gap is kept as uniform as
possible. After it's all done being bonded, I let the windshield sit for a week
before moving it. The maintenance manual says 3 days but I've found the RTV
to not be totally cured at 3 days.
The windshield in the $80,000 Cheetah was done in 2003 when John Rodgers owned
the plane. It has always been parked outside. It's a C.Bailey windshield. The
bond is still like new.
I've attached two pics of the jig after bonding the windshield. In the background
you can see my work bench on wheels. I keep all the tools I regularly use
on this bench. I also have safety wire, nylon ties, gloves, lube, and rulers
on that table. In the upper left you can see a couple of wheel pants for testing.
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