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I just saw a comparison between the 787 and Concorde windows. I could be wrong but it almost seems like a hand could cover the majority of the window.

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George Clooney In a Mooney
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3 Answers3

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The Concorde flew above 15,000m. At this altitude a sudden reduction in cabin pressure would prove hazardous to crew and passengers with most falling unconscious within a few seconds. The low air-pressure would also render the oxygen supply system inefficient and most passengers would suffer from hypoxia.

Thus we have the reason for the smaller windows, should a breach occur then the size of the hole being small would reduce the rate if loss of air-pressure inside the cabin. This, combined with a reserve air-supply to augment the cabin-pressure as well as a rapid rate of descent manoeuvre to bring the aircraft to a safe altitude would reduce the the risk of hypoxia. So basically the small windows were designed to reduce the rate of air escape from the cabin should a hull breach occur.

John K
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DJAndersonZA
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    Nice first answer! Do you have a source for this? – Bianfable Jan 02 '20 at 09:47
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    I very much doubt that a descent to 4000 m from 15000 m within the time it takes to suffocate would had been possible. – Peter Kämpf Jan 02 '20 at 10:24
  • Please provide a reference. – Organic Marble Jan 02 '20 at 11:41
  • some reference from airliners.net – Rsf Jan 02 '20 at 13:28
  • Edited to add link with the information that I expect is the source of the post. – John K Jan 02 '20 at 15:51
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    @PeterKämpf in a rapid decompression at 55000 ft a fit person might last 15 sec, but a smoker, probably 1/3 to 1/2 of passengers at the time, would be out cold in about 5-10 seconds. Even if masks dropped, probably a third of the pax, those that failed to don masks immediately, would be unconscious before they got past 40000 ft. The little windows and secondary method to dump extra air into the cabin (I'm guessing an emergency bleed source) seems to be intended to buy a bit of extra time to give pax a chance to don masks. – John K Jan 02 '20 at 15:57
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    @JohnK: Thank you for the explanation, the window size was indeed part of the emergency procedure. I still wonder how much of that was wishful thinking and how much was proven procedure. – Peter Kämpf Jan 02 '20 at 18:40
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    Well at 40000 feet you might have 30-45 seconds to get your mask on, so they must've calculated they could slow the depressurization just enough to buy that little bit of extra time. Now I'm curious to find out how this supplemental air system worked. – John K Jan 02 '20 at 19:13
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    @John K In the comment above by Rsf is a link to an airliners.net discussion. There it is mentioned, that the size of the window of a Concorde is about the same as the cabin outflow valve. So if a window was lost, one of the two outflow valves would close, and all would be relatively ok. This is, of course, info extracted from an internet discussion, and as such, should be taken with a grain of salt. – Jpe61 Jan 02 '20 at 19:56
  • It gets worse. Oxygen at ambient pressure is only good up to about 41,000 ft. Above that you need a mask with overpressure to stay conscious. That's why there are additional requirements for flying higher (IIRC simply showing that probability of cabin altitude exceeding 41,000 ft is less than 10¯⁹ per flight hour). I am sure there is a detailed explanation somewhere around this site, but I am not sure I'll be able to find it given the general state of the search. – Jan Hudec Jan 02 '20 at 20:16
  • … I found mention here, and it actually says occupants must not be exposed to more than 40,000 ft, not 41,000 ft. – Jan Hudec Jan 02 '20 at 20:51
  • … I also can't find any decent reference (not just here, but anywhere) for the actual altitude above which ambient pressure pure oxygen is not enough for most people, but I am quite sure it is the reason behind that “must not be exposed to cabin altitude above 40,000 ft” rule. – Jan Hudec Jan 02 '20 at 20:52
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    @Jpe61 at altitude the outflow valves will be partially closed anyway, depending on how leaky the cabin is (door seals mostly, although I would have expected Concorde's leakage to be way less than the average airliner) and I would expect the outlet area at any given time would be less than with the valve fully open. But in any case, when the outflow valves close the rest of the way and supplemental air starts, it would be interesting to see what cabin altitude could be maintained with air dumping out a window. – John K Jan 02 '20 at 21:45
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    Losing consciousness and death are not the same thing. The plane might have time to descent to a decent altitude before people decease. – Déjà vu Jan 03 '20 at 16:54
  • Smokers have actually done better in thin atmosphere according to my experience. A two-pack-a-day friend of mine was solving logic and math problems while the rest of us were struggling to stay awake. They eventually just had to move on with the excercise because he wasn't being effected. – acpilot Jan 09 '20 at 05:01
  • Would the smaller windows really have significantly decreased the risk to Concorde passengers from a decompression, though? Don't the vast majority of decompressions result either from localised (one hopes!) ruptures in the fuselage skin resulting from accumulated fatigue damage, or from externally-caused damage to the pressure hull (either penetrating it directly [for instance, engine rotor burst] or weakening it to the point where it ruptures under normal flight/pressurisation loads [for instance, errant ground vehicles], and, in either case, again usually involving the fuselage skin)? – Vikki Jul 24 '20 at 23:50
  • @acpilot: Makes sense; smoking decreases the efficiency of oxygen transport, but also forces the body to adapt to a lower effective oxygen concentration. A smoker who's not smoking at that moment would have the beneficial effects of adaptation to (slight) hypoxia, without actually having to deal with the smoking-induced hypoxia (somewhat like athletes training at high altitudes). – Vikki Jul 24 '20 at 23:55
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From the wiki for Pressure Vessel

The fuselage is a pressure tank, the window is a hole in the construction of the pressure tank. Adding windows also adds weight: the pressure vessel construction must be reinforced around the hole. The window glass is obviously airtight, but does not contribute in absorbing any of the stresses of the pressure differential.

The window size is a function of:

  • The pressure differential. The higher the aeroplane flies, the larger the pressure differential between internal and external pressure.
  • The relative size of the hole, relative to the fuselage diameter, fuselage length, and aerodynamic bending forces.

For construction engineers, the best size of a window is zero. The windows in Concorde must be smaller because the fuselage diameter is much less than that of a B787 while it must handle a higher pressure differential.

Koyovis
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Airflow Rate through an Orifice will help give some idea of the time it takes for the cabin of the Concorde to evacuate after one window blows at 60,000 feet as follows:

Volume of the cabin: $50m × pi × 2m^2 = 620 m^3$, Diameter of orifice: $0.15 m$

Rate of outflow from calculator software, averaged for pressure difference from T0 to T fully evacuated: around $150 m^3/min$ yielding roughly 180 to 240 seconds to full evacuation, without pressure equalization (reserve air-supply), with debilitating unmasked hypoxia sooner.

The location of the orifice (open window), on the side of the fuselage, could possibly cause even lower evacuation time values due to the Bernoulli effect of the passing airstream.

This underscores the point of view that strengthening the windows was indeed of critical importance. Further examination of air replenishment capacity and emergency descent capability are in order, as newer versions of these supersonic transports may yet return to commercial use.

Robert DiGiovanni
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