Passenger window (& small hole)

[cheapfuel]

I have often wondered what the "small hole" located near the center bottom of the window is for. And, also, how is that window constructed? Appears to be just a layer of plexiglass,and a layer of glass. There must be more to it than that. Thanks ahead (again!)

[rwm]

It is a vent. There is no glass in the passenger widows. They are made up of a large thick pain of lexan, and two or sometimes three thin pains with the middle or inner pain on a two pain window that has a vent hole in it.
The front windsheild in the cockpit is made similar to a car windsheild were it is laminated glass several layers thick. Inbetween a layer there is gold flake and this is attached to wires and this is used to heat the windsheild.

[eyeinthesky]

window PANE

WindSHIELD:p

But thanks for the explanation...

[T_richard]

I was flying to DCA last week, hadn't flown into that town in years. I really enjoy the birds eye view you get from a plane on approach. Why can't they make the passenger windows bigger in a commercial plane? Is it money or physics?

[BlipOnTheRadar]

T_richard

remember the deHavilland Comet? beautiful aircraft, nice large windows... the rest is history. :( shame.

BlipOnThe Radar

[NineEighteen]

Why can't they make the passenger windows bigger in a commercial plane? Is it money or physics?Yes it's all about structural integrity. An airframe would be more far more robust and far easier to construct if no passenger windows were included...but passengers like to have windows! :8

Any 'hole' in a pressurised tube will affect the integrity, so the smaller the better. :ok:

[T_richard]

Blippie

Sorry I know less than nothing about a/c's Actually joining PPRUNE was the trigger that got me to start paying attention o aircraft. Can you direct me toward history of the deHaviland Comet. Also has anyone ever seen a good cheatsheet for IDing commercial a/c's

Upon reflection, I see the issues related to window size, sorry for the dumb question. I still want more visablity though, that is until I read about the deHaviland Comet. Then I'll probably shut up and go back to my seat:O

[Flying Boat]

I've found any general a/c ID books (Ian Alan are good) get you started, but you can't beat hours at an airport with a radio, binoculars & sandwiches to get to know civil aircraft well. As well as their variants (Sad I know).

If you want more vis, perhaps try to find operators still using Vickers Viscounts or Fokker F27 Friendships. The last time I flew in an F27 was in 1998, a return trip, Cancun to Cozumel. The return flight was brill 10 mins @ 1,300ft.
The Shorts S360 is unpressurised & has big square windows too.

I loved the structure part of my recent JAR/ATPL Aircraft General Knowledge paper (Hate Electrics though).

The Comet a beautiful plane but square windows added to the structural problems, once they went for oval windows the aeroplane was wonderful, unfortunately Boeing had already flown transatlantic with a stonger & larger aircraft, the B707. Prospective Comet buyers went the Boeing route.
An usual story for the old British Aviation Manufacture Industry, wonderful Aeroplanes and craftsmen, but awful salesmen.
The Comet was flying commercially until the late1970s/early 1980s.

Have fun in your new found obsession.

FB:ok:

[Departures Beckham]

Cheapfuel: Have a look here (http://www.pprune.com/forums/showthread.php?s=&threadid=67235) at the same question I posed about seven months ago.

[AlanM]

Have a loook at this Twin Otter - Vistaliner DH-6 (http://www.airliners.net/open.file/188029/L/)

Are they made by DeHavilland like this or modified? The larger windows here must change the structural rigidity? Obviously not being pressurised must help.

[T_richard]

okay let me see if I have this all lined up correctly, at 30,000 ft ambient air pressure is approx. 4.3 psi, humans feel comfortable a 14.7 psi so a/c is pressurized to adjust for the differential which means a positive pressure of approx. 9.6 psi. The cabin window is actually three panes; inside scratch screen, inside window with vent hole and outside window, all made of thick acrylic. If the outside window pops out(?) the inside window retains cabin pressure while still venting excess pressure out of the cabin without sucking me through the hole.

What would cause the outside window to pop out, structural failure of surrounding materials, external force applied to a/c skin aka collision. Did I miss anything.

[Genghis the Engineer]

Pressurisation is a big player.

As you pressurise a vessel - whether it's an aeroplane or a boiler, you get stresses forming in the skin which are a function of shape and pressure difference across the skin. They are called hoop stresses.

By introducing windows, which tend to be made of material that doesn't take tensile loads (hoops stresses are entirely tensile) the load which still has to go somewhere becomes concentrated around the windows. Bigger windows, or with sharp corners, tend to suffer bigger stress concentrations.

The Comet design teams didn't understand this well enough (it wouldn't be fair to say that they didn't understand it at-all). This isn't all that surprising since nobody until then had built large pressurised cabins to routinely fly to that sort of altitude.

So, cyclic hoop stresses, concentrating around the window corners, created large and unexpected fatigue damage areas. The fatigue cracks eventually joined up and the whole aeroplane unzipped with catastrophic consequences.

The DH design teams at the time had realised that their analysis was not as good as they would like, so had been happily testing a fuselage in a water tank to many times the number of cycles that the real aeroplanes (which broke up in the air) had been to. What they'd missed - which really was unknown at the time - was that by using the fuselage that they'd already used for limit strength tests, they were inadvertently using structure whose metallic/crystaline structure was modified by overload and had become much more fatigue tolerant than before. So the fatigue test fuselage was not representative of the flying aeroplanes.

A lot of lessons were learned from that, specifically...

- Use small windows which are as round as possible.
- Controlled overload of a structure tends to improve fatigue life.
- Non destructive testing of aircraft structure needed to be a lot better than it was. I've heard the Comet called the "Father of NDT", which isn't far wide of the mark.
- Be very very careful about the history of your test specimens, they need to be as close as possible to flight hardware.

G

[PaperTiger]

The Twotter 'Vistaliner' is an aftermarket mod (STC). None were built like that by DHC.
For the story, see (scroll down a bit): http://www.grandcanyonairlines.com/about_us/air_fleet/

[rottenlungs]

T_Richard

The best way to improve your view out of a plane is to sit up the front.

Learn to fly. Its wicked...

Lungs

[maninblack]

RWM mentioned that aircraft windows were made from Lexan, unfortunately this is not generally true as aircraft transparencies are either cell cast acrylic or glass/cell cast acrylic laminates.

Lexan is one of GE Plastics tradenames for their polycarbonate resin. Polycarbonates are, in the initial investigation, the perfect material for manufacturing a passenger aircraft window or military canopy. They are dimensionally stable, environmentally inert, can be easily coated to provide stealth or scratch resistant characteristics etc.

A few years ago tests were made on behalf of the US DoD with polycarbonate canopies as it was felt that the much improved scrath resistence over acrylics would improve pilot visual target aquisition and reduce ground crew workloads. This was all true. Sadly the problem that was not overcome was the breakdown of the plasticiser in the resin under UV light, hence, after a year or so in service the canopy lost its elasticity and became brittle. Too great a risk of explosive decompression for an airliner or certain loss of a military aircraft and crew as the pilot would not survive a shattered canopy at high altitude and speed.

Here endeth an overly long explanation.
:8