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Subject: Re: [LML] Re: Cabin Door Window-IV-P
From: Colyn Case <colyncase@earthlink.net>
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Brad do you have a pics of the old and new latches?

On May 6, 2010, at 5:11 PM, Brad & Tracy Simmons wrote:

> I have replaced 6 IVP windows; 5 from the inside and 1 from the =
outside. I have bodyworked and painted one additional door with the =
window replaced from the outside. =20
>=20
> Brent is correct in that replacing from the outside is actually easier =
in many ways. However, it is probably more difficult for a beginner to =
properly scarf in the carbon plies after reinstalling the glass, thus =
the door perimeter ends up a little proud of the fuselage.
>=20
> In the past, Lancair's position has always been to replace from the =
inside. When replacing oven cured prepreg skins (such as the cabin door =
skin)with hand laid wet layups, Lancair's rule of thumb is to rebuild =
with 1.5 wet lay-up plies for each original ply of cured prepreg. This =
gets pretty thick on the outside of the door. On the door window that =
was replaced elsewhere and brought to us for painting, we were not able =
to fair it in flush with the surrounding fuselage. Obviously the time =
and expense is much greater if you have to bodywork and paint the =
fuselage perimeter. If you can guarantee the shape can be retained, =
cutting the stiffner may prove to be less work overall.
>=20
> I have a jig to bondo the door into before we cut the stiffner away =
that guarantees the original shape. We'll also bolt a couple of =
temporary door latch receivers onto the door that allows the relocation =
of the latch to it's original location, minimizing or avoiding issues =
with latch adjustment. Typically two of the four studs can be saved =
anyway. If you cut the stiffner on the innermost angle, it can be =
rebuilt without even having to remove the seal!
>=20
> Some years ago, Lancair modified the latch brackets to eliminate the =
two countersunk screws per latch that were previously drilled through =
the plexiglass window perimeter. Every blown out window that we have =
replaced shattered because of these screws. I would encourage everyone =
to eliminate these by switching to the new style bracket if you have the =
opportunity.
>=20
> Regards,
>=20
> Brad Simmons
> Airframes Inc.
> Milan, TN
>=20
>=20
> -----Original Message-----
>> From: Brent Regan <brent@regandesigns.com>
>> Sent: May 4, 2010 3:23 PM
>> To: lml@lancaironline.net
>> Subject: [LML] Re: Cabin Door Window-IV-P
>>=20
>> Replacing the windows from the outside is the common practice and =
much=20
>> easier than attempting a replacement from the inside. This is =
especially=20
>> true for the door due to the stiffener and latch geometry and=20
>> placement.  I too had a bit of trouble accepting the concept but =
after=20
>> some thought and analysis it became clear that replacing the window =
from=20
>> the outside was the preferred option.
>>=20
>> The reason for original installation of the windows from the inside =
is=20
>> less a function of strength and more a function of labor and =
cosmetics.=20
>> Imagine the sanding work needed to fair in all the windows and the =
high=20
>> chance of slipping with some 60 grit. Ouch!
>>=20
>> Remember that the entire fuselage is a series of layers that are =
glued=20
>> together so it becomes a question of if you can get reasonably close =
to=20
>> the prepreg bond strength with a wet layup. A quick analysis shows =
that=20
>> the window area is about 400 square inches. If we assume a 10 PSI =
burst=20
>> pressure we get 4,000 lbs force. The window bond perimeter is about =
100=20
>> inches so the stress is about 40 pounds per linear inch of bond, =
which=20
>> is about the peel strength. But the loading is cantilever, not pure=20=

>> peel, and the tensile strength for Jeffco (now Rhino) 1307LV is =
better=20
>> than 2 KSI. Bottom line, no problem.
>>=20
>> The trick is to grind the door down about 0.060" around the window =
and=20
>> taper it out about 4" so that when the 6 bid carbon is applied the=20
>> original thickness is preserved. I made patterns to cut the wet =
layups=20
>> to shape to minimize the work around the window edge. Once the 6 bid =
is=20
>> on you can taper it back. The bid layers leave lines like a topo map =
so=20
>> it is easy to get an even taper BUT, this is NOT a repair for an =
epoxy=20
>> newbie.
>>=20
>> The BIG advantage of replacing the door window from the outside is =
that=20
>> you don't mess with the door shape or latches. When my friend blew a=20=

>> window climbing over Colorado he landed in a remote town. He removed =
the=20
>> door and shipped it to me. I was able to replace the window,  paint =
the=20
>> outside of the door in primer, reassemble and adjust the latches, =
pack=20
>> and ship it to Colorado in less than a week. He was able to install =
the=20
>> door in about an hour and flew the plane home.....pressurized! Once =
home=20
>> he removed the door and took it to the paint shop. Now you can't tell=20=

>> any work was done. You have to love composites.
>>=20
>> Regards
>> Brent Regan
>>=20
>> --
>> For archives and unsub =
http://mail.lancaironline.net:81/lists/lml/List.html
>=20
>=20
> --
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