left-struck
a month ago
If you just want an answer to the question
> Bleed holes, Captain Joe explains, “allow for pressure equalization between the space between the panes of the window and the cabin interior. Without these holes, the pressure difference between the cabin and the space between the panes would lead to stress on the window.”
stouset
a month ago
And then to answer the follow-up, the double panes are not for safety in case one breaks. They’re for thermal insulation.
Arn_Thor
a month ago
This doesn't refer to the double-paned outer window, the pressure window. It refers to the innermost protective pane, the "scratch pane" that keeps greasy fingers and portruding camera lenses from reaching the two "real" windows. It's the hole in the scratch pane people are asking about
butvacuum
a month ago
doesnt mean the inside one isnt there to protect the outside one.
traceroute66
a month ago
> doesnt mean the inside one isnt there to protect the outside one.
The inner pane is typically half the thickness of the outer pane.
So whilst you could argue it cold be seen as a failsafe, I would say its primary purpose remains "double glazing" insulation.
The OAT at 30–40,000ft is very low and there is a lot of combined window area. So the importance of insulation is not to be underestimated. In particular on newer aircraft where efficiency is the name of the game in their design.
iso1631
a month ago
The inner pane (isn't it plastic?) is far easier to replace when some annoying kid devices to scratch their tag into it with a nail file.
traceroute66
a month ago
> The inner pane (isn't it plastic?) is far easier to replace
That's the scratch pane you are referring to.
Yes, it is made of cheap plastic and serves no structural or other purpose other than to protect the real stuff from annoying kids. ;)
HPsquared
a month ago
Also if it wasn't insulated, the windows might also steam up? Or does the air conditioning make it dry enough that this wouldn't happen. Foggy windows could also affect the pilot's ability to see, I suppose the flight deck windows must also be insulated.
traceroute66
a month ago
> Or does the air conditioning make it dry enough that this wouldn't happen. Foggy windows could also affect the pilot's ability to see, I suppose the flight deck windows must also be insulated.
Depends on the aircraft but a typical design would connect the space between the panels to an air supply or otherwise a self-contained desiccator system.
Flight deck windows are completely different, typically three layers, two full thickness and one half thickness. All fully heat/chemical strengthened with additional anti-fog, anti-ice and moisture absorption systems built-in. The fact that some of them are sliding (i.e. openable) adds to the design complexity.
Sohcahtoa82
a month ago
> OAT
For the non-aviation folks, OAT means "Outside Air Temperature".
mierz00
a month ago
My time in the military has made me hate acronyms with a fury.
butvacuum
a month ago
that's not what's being discussed. airplanes have a hull window and a passenger cabin window that are universally refered to as a single "double" window- at least amongst the general public.
The inner cabin window is absolutely there to protect the hull window.
jstanley
a month ago
Doesn't this just put the stress on the other pane of the window? I don't see how it helps.
EDIT: Oh. It helps because otherwise the bit between the panes would be at a different pressure to both the interior and exterior of the plane. It would work just as well if the bleed hole were on the outside, as long as both panes are equally strong.