King Air windows...

[ILLINI]

I was told that the polarized windows in the main cabin should be left "open" so you could see through them because if they were left "closed" or blacked out, for long periods of time it would shorten the life of the polarization and over time they would not be able to block out as much light. Is this true? I found it hard to believe because these are two seperate panes of polarized plastic and couldn't understand how their position, whether open or closed, would affect their life. Is there any truth to this, or is somebody just blowing smoke up my arse?

 

[ArmyC12]

Good question. Flying BE-200's for the Army, they said the same thing. So, since they owned the airplane and signed my check, I said "yes sir" Now we have a plane that has shades. Some of the airplanes in the feet did report probles with leaveing them "closed" sitting out on the ramp all day, over the years. I say, if Beechcraft says dont do it, dont. What does you book say? Then, what does the mechanics maint. manuals say?

Hope I helped

 

[flyingtoilet]

My Simuflite manual recommends leaving the polarized windows open. We always did it at the 135 operation I was at for a while.

 

[CorpJetPilot]

I fly an F-90 with polarized windows. The previous pilot left them closed all the time stating it kept the cabin cooler. What it did was in fact cause them to have to be replaced in a much shorter period of time. Leave them open.

 

[ILLINI]

I did the same thing as ArmyC12... your plane+your signature on my check=your way. I didn't matter to me one way or the other if they were open or closed, but I was interested to learn if doing so would really shorten the life of the polarization. It just didn't make sense to me on how keeping them closed would affect their life.

I guess my next question would be... How??? How does closing the windows shorten the life of the polarization? Anyone know?

 

[Andy Neill]

When I first read the post, I thought it couldn't be based on fact. How could two panes of polarized plastic interact to cause their failure.

What follows is the reslut of an exercise in trying to have an open mind. I have no idea if it is true, but IF blocking the sun DOES IN FACT result in failure, this is my best guess as to why. With the panes arranged to let the light through (polarization in parallel) all (most of) the heat energy goes through also. With them in the blocking position (polarization perpendicular) a significant amount of the light and heat energy is trapped between panes and the reslutant overheating would cause an earlier failure.

Does that sound plausible?

 

[ILLINI]

Andy-

I hadn't thought of that, but it does sound like a reasonable explanation. The light is allowed to pass through the first pane of polarized plastic, but when it hits the second pane, which is perpendicular to the first, the light is stopped thus trapping the heat between panes as well. This trapped heat causes damage to one, or both of the polarized panes and they become less effective.

This leaves me with yet another question. I'm not familiar with the properties or characteristics of light or heat energy, so please excuse me if this is a silly question. But, if the panes are perpendicular to each other and the light is stopped at the second pane, wouldn't the light be allowed to exit back out through the first pane it went through? If so, wouldn't this also allow the heat to pass through the first pane as well? Or is the heat energy trapped between the two panes, thus explaining the possible dammage?

Things that make you go hmmmmm

 

[Andy Neill]

First. some of the physics of light involves light waves being more than two-dimensional. For this reason, when light is relfected (or passes through a layer of polarization) the light wave is modified so that it becomes planar (two-dimesnional). When it hits another layer of polarization not aligned in the same plane as the first, then all light is blocked.

Try this visualization. You have two sections of picket fence. You place one of them so that the slats are vertical on one and the other four feet behind it so that the slats are horizontal. The distance between the slats is such that a tennis ball coming at it has 50% chance of getting through. Now facing these sections of fence are all the tennis ball serving machines you can imagine and they are barraging the nearest fence section with tennis balls. Half of them get through the first section and half of those get through the second section. Those that don't get through the first section bounce back toward the machines. Those that don't get through the second section bounce back toward the first section with less energy and some of them bounce through to the machines but most are trapped inside.

From a given barrage, we see that about half are short of the first section about a fourth are in the middle and about a fourth made it through both. With repeated barrages of tennis balls. the middle section will get increasingly full (hot).

 

[bart]

So the point is put your kingair in a hangar far, far away from tennis courts with picket fences?

 

[ILLINI]

LOL!

Andy-
Thanks for your explanation. I understand it a little better now.

bart-
Thanks for the laugh! I'll make sure I remember that next time i'm putting the plane away.