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One-piece canopy on a commercial transport aircraft?

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  • One-piece canopy on a commercial transport aircraft?

    This caught my eye. Yes, I realize there are a lot of whack patents out there but it raises a question for me. What are the factors limiting window size on commerical jets? With cockpit windows, redundancy has been a factor (you get cracks or failure one the CPT's panel and you still have the FO's panel intact (this has happened). It appeared that early A350 designs incorporated a one-piece wrap-around panel but later gave way to multiple panels with the rather lame 'raccoon-eyes' compromise. Airbus also wanted much larger pax windows but later made them more conventional. I've always assumed these windows are kept small to prevent a passenger being ejected if one should fail.

    Now here is a company proposing to put a huge, one-piece plastic canopy on top of the pressure hull. What if it fails? What are the restrictions on this?

    http://edition.cnn.com/2015/12/14/av...aft/index.html

  • #2
    I think window size is limited by the need to carry pressurization loads on the fuselage around it.

    AFAIK the windows are not considered part of the structure. So everywhere you have a window opening, the perimeter of the opening needs to be reinforced to carry the load that normally would be carried by the fuselage skin or structural members if the opening were not present. The larger the opening is, the more load needs to be carried, and the heavier that reinforcement becomes. Each reinforcing structure may not weigh much, but multiplied by the number of windows in an airliner it adds up. The same is true of doors of course, but there are fewer doors than windows. Plus an airliner with no doors would probably run afoul of evacuation-time regulations.

    So something like that dome might be practical, because there's only one per aircraft. Of course that whole elevator dealie must add a *lot* of weight! And then there's the strength of the dome itself to consider...

    Oh and to give credit where it's due:
    Originally posted by The article
    We wanted to come up with a product that would provide a higher level of entertainment...
    Nice pun.
    Be alert! America needs more lerts.

    Eric Law

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    • #3
      Originally posted by elaw View Post
      I think window size is limited by the need to carry pressurization loads on the fuselage around it.

      AFAIK the windows are not considered part of the structure. So everywhere you have a window opening, the perimeter of the opening needs to be reinforced to carry the load that normally would be carried by the fuselage skin or structural members if the opening were not present. The larger the opening is, the more load needs to be carried, and the heavier that reinforcement becomes. Each reinforcing structure may not weigh much, but multiplied by the number of windows in an airliner it adds up. The same is true of doors of course, but there are fewer doors than windows.
      That is partially incorrect. Windows and doors carry pressurization loads almost by definition. Otherwise, being an integral part of the pressure vessel, they would fail under pressurization since there is no way to have a pressure differential of 10 PSI on the skin but zero on the window.

      The issue is the interface between the skin and the window (or door) which is a discontinuity that prevents the load to be transmitted from one part to another as if it was the same part. So to solve this, the skin (that works mostly like a membrane or balloon and withstand the pressure with tension) is fitted with a frame around the aperture that takes the load from the skin at one side of the window to the the other side, while the window rests on that frame and withstands pressure with flexion (as a thick plate).

      --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
      --- Defend what you say with arguments, not by imposing your credentials ---

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      • #4
        Originally posted by Evan View Post
        Now here is a company proposing to put a huge, one-piece plastic canopy on top of the pressure hull. What if it fails? What are the restrictions on this?

        http://edition.cnn.com/2015/12/14/av...aft/index.html
        1- Make it so it doesn't fail (it is not so difficult, there are many pressurized airplanes with bubble canopies).
        2- Keep your seat-belts fastened (in case it does fail).
        3- Make the rest of the structure (especially around the canopy) fail safe in case of a failure of the canopy.
        4- Do something to bring these two slobs back into the plane so they can receive O2.

        But basically it can be designed so it (almost) never fails, just as the windscreens (almost) never fail (catastrophically).

        --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
        --- Defend what you say with arguments, not by imposing your credentials ---

        Comment


        • #5
          Originally posted by Gabriel View Post
          1- Make it so it doesn't fail (it is not so difficult, there are many pressurized airplanes with bubble canopies).
          2- Keep your seat-belts fastened (in case it does fail).
          3- Make the rest of the structure (especially around the canopy) fail safe in case of a failure of the canopy.
          4- Do something to bring these two slobs back into the plane so they can receive O2.

          But basically it can be designed so it (almost) never fails, just as the windscreens (almost) never fail (catastrophically).
          1) Name a modern pressurized aircraft with a canopy where the occupants are not wearing oxygen masks. Also, the overriding philosophy in commercial aviation safety is not fail-proof, it is fail-safe (fault-tolerant or fault-passive).
          2) You're dreaming there.
          3) Definitely, but this doesn't keep the pax from getting hoovered out of the big hole in the roof.
          4) You mean the poor slobs who are now bearing the full blast of both cabin decompression and 490kt airstream?

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          • #6
            Originally posted by Gabriel View Post
            2- Keep your 5-point harnesses fastened (in case it does fail).
            Corrected.
            Be alert! America needs more lerts.

            Eric Law

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