Window design

[Shamrock 602]

Anyone around who can tell me a bit about the disign of passenger windows on commercial airliners?

I'm curious about how they withstand pressurisation. Also, despite the big temperature differences, it's rare to see any condensation/ice - presumably the space between the layers is filled with something very dry. But what gas, and at what pressure? There seem to be three layers, apart from the innermost layer of perspex.

It also seems that the pressure between the three layers is equalised, as there is a small hole in the middle layer (both on Boeings and Airbuses).

I'm all ears...

Shamrock 602

[Onan the Clumsy]

afaik, there's just a hole in the fuselage that they fill with a piece of perspex, nicely sealed around the edges. I guess the differential pressure isn't that great in fact it'd have to be pretty enourmous to flex the pane out of the opening.

The bit with the hole in it is simply the inside trim.

Unless I'm mistaken, there are only two layers as well. The fixed outer and the inner trim piece. I've seen the outers get replaced, but I don't know if it was because they were scratched or because they were a life limited part. If life limited, it'd be interesting to know if they track by cycle, flight time or calendar time.

[Mr @ Spotty M]

You have an Outer Pane, Inner Pane and a Trim Pane.
The Outer is the thicker of the two and is surrounded by seal, which sits against the window opening, with the inner sitting on the seal with a small gap between.
The inner pane has a small hole if my memory serves me, l think to equalise the pressure and it acts as a fail safe for the outer pane.
So no gas or pressurised air between the panes, they are not life limited, but get changed when they are scratched or become crazed.
The inner pane often becomes distorted and the outer a little too, they are changed also for this reason.
I hope someone will correct any errors in my post, as l did not have access to the manuals.

[Shamrock 602]

Thanks for the information...

... but having looked closely again, it really does seem as if there are three panes (the central one having the small hole in it), in addition to the perspex one closest to the passengers.

Also, if there was ordinary air inside the window assembly, wouldn't the outer pane become covered in ice on the inside due to the cold?

Just curious...

Shamrock 602[B]

[PIGDOG]

Níl a lán uisce...

Sorry, there's not a lot of water in the air and it is only air between each pane.

I've taken them apart a couple of times, and there are only three layers (definitely). A trim layer, an inner layer and an outer layer. Aparently the inner layer must be capable of withstanding 1.5 times the maximum pressure differential, although, during normal operation it has no pressure dirrerential across it. Therefore, it is purely a redundency.

'tis an interesting procedure de-crazing windows. A bit of a pane actually... More trouble than it's worth.

Slán leat.