I flew in a Comet 4 from Athens to Nicosia in Cyprus a couple of times when I was a kid, back in the 1960s. I must admit it felt to me a bit like getting into a Victorian railway carriage after getting off the then very modern Trident from Heathrow to Athens, but that may have been down to Olympic Airways.
Note that there is another Comet (4B variant, so one of the later ones) preserved at the National Collections Center [1] near Swindon. However it is not available to view [2].
Such a beautiful plane. While perhaps the structural issues could have been better anticipated and addressed, the fact that the engines were incorporated into the wings would likely have been the next issue for the aircraft, with fires, seized turbofans, and proximity to fuel tanks causing further incidents or accidents at rates exceeding those of planes with their engines mounted on pylons.
There were later versions of the Comet. Version 1 was underpowered, and had too much weight reduction for that reason. By version 4, the design had been debugged. With more powerful engines and structural fixes, the Comet 4 went into service and did OK. 46 Comet 4 aircraft were built. Last flight in 1997.
Another DH106 Mk4C has been under restoration at the Museum of Flight restoration center in Everett, WA since 1995. I don't think that a single thing has been done to it since the outbreak of the pandemic in 2019. Allegedly they will be losing their lease in few years, no idea if they will do anything to complete the restoration before then.
I remember hearing that the square window cutouts in the original Comet concentrated stress in the corners and contributed to cracking. But Wikipedia seems to indicate that's not actually true. Nevertheless almost all pressurized aircraft now have round or oval window and door cutouts, or at least rounded corners.
>Many readers familiar with the Comet disasters might be wondering why, with this article drawing to its close, I have yet to utter the phrase “square windows.” But the truth is that “square windows” never had anything to do with the Comet crashes. The windows were not and never were square — in fact, you can see for yourself in the above image, which shows a Comet 1 window next to a modern Boeing 737 window. Can you tell which is which? You probably can, but not because one is any more “square” than the other.[0]
I've heard that counter-rumour before too but it never seems to make sense. The lengthy discussion by Admiral Cloudberg [1] seems to pin the blame on the corner of a window:
> De Havilland had calculated a maximum operating stress of 28,000 psi at the corners of the windows and doors, but investigators noted that this value was an average over an area of 2–3 square inches (13–19 square centimeters), meaning that in theory, highly localized stresses could be considerably greater. This “peak stress” could have been measured through the liberal application of strain gauges, but de Havilland had apparently elected not to attempt this, believing that any more precise measurements would be unreliable. Nevertheless, investigators measured it anyway, and from these data they calculated a localized peak stress at the window corners of up to 45,000 psi under normal pressurization conditions. Not only was this much greater than de Havilland’s predicted value, its relative proximity to the ultimate strength of the material (estimated to be 65,000 psi) produced an unfavorable stress ratio correlating to an expected fatigue life considerably below 10,000 cycles.
I think counter arguments come into one of two camps:
(1) when they replicated the problem in a pressure chamber at ground level it wasn't technically a window that failed but a "portal" (basically like a window but wires go through it instead of people looking out of it) - a pedantic technicality and not to say that all the failures in the air were for this same portal/window.
(2) The windows weren't don't have sharp corners anyway but rounded, not unlike some modern planes. True but you can see the failure was definely near a (rounded) corner.
Admittedly the Admiral Cloudberg article does seem to put more weight on the way the rivet holes were made than the angularity of the window corners. But it's still failing at a corner. I guess it depends how you look at it.
Cool, my local aircraft museum. The square-windowed Comet was rotting in the open for many years but (as the article notes) has been restored. They also have a Comet flight deck which you can walk around. It has 5 seats on the flight deck (it really is huge!), including a flight engineer and a navigator.
The wing-integrated jets, while not the most efficient, maintainable or powerful, are the best looking piece of commercial jet engineering in my eyes. Composite winglets are a distant second.
I flew in a Comet 4 from Athens to Nicosia in Cyprus a couple of times when I was a kid, back in the 1960s. I must admit it felt to me a bit like getting into a Victorian railway carriage after getting off the then very modern Trident from Heathrow to Athens, but that may have been down to Olympic Airways.
Note that there is another Comet (4B variant, so one of the later ones) preserved at the National Collections Center [1] near Swindon. However it is not available to view [2].
[1] - https://en.wikipedia.org/wiki/Science_and_Innovation_Park#Na...
[2] - "[Some items] - including large aircraft - ... are therefore not featured on the tour." https://www.scienceinnovationpark.org.uk/visit-us/public-gui... (at the bottom, "Note on Large Aircraft")
Such a beautiful plane. While perhaps the structural issues could have been better anticipated and addressed, the fact that the engines were incorporated into the wings would likely have been the next issue for the aircraft, with fires, seized turbofans, and proximity to fuel tanks causing further incidents or accidents at rates exceeding those of planes with their engines mounted on pylons.
There were later versions of the Comet. Version 1 was underpowered, and had too much weight reduction for that reason. By version 4, the design had been debugged. With more powerful engines and structural fixes, the Comet 4 went into service and did OK. 46 Comet 4 aircraft were built. Last flight in 1997.
2011 if you count the Comet-derived Nimrod.
The Sud Aviation Caravelle is a sibling with a different engine configuration.
Another DH106 Mk4C has been under restoration at the Museum of Flight restoration center in Everett, WA since 1995. I don't think that a single thing has been done to it since the outbreak of the pandemic in 2019. Allegedly they will be losing their lease in few years, no idea if they will do anything to complete the restoration before then.
https://www.museumofflight.org/exhibits-and-events/aircraft/...
http://www.dhcomet.com/_main/main.htm
I remember hearing that the square window cutouts in the original Comet concentrated stress in the corners and contributed to cracking. But Wikipedia seems to indicate that's not actually true. Nevertheless almost all pressurized aircraft now have round or oval window and door cutouts, or at least rounded corners.
I thought that too until I read this
>Many readers familiar with the Comet disasters might be wondering why, with this article drawing to its close, I have yet to utter the phrase “square windows.” But the truth is that “square windows” never had anything to do with the Comet crashes. The windows were not and never were square — in fact, you can see for yourself in the above image, which shows a Comet 1 window next to a modern Boeing 737 window. Can you tell which is which? You probably can, but not because one is any more “square” than the other.[0]
[0]https://admiralcloudberg.medium.com/neither-money-nor-manpow...
I've heard that counter-rumour before too but it never seems to make sense. The lengthy discussion by Admiral Cloudberg [1] seems to pin the blame on the corner of a window:
> De Havilland had calculated a maximum operating stress of 28,000 psi at the corners of the windows and doors, but investigators noted that this value was an average over an area of 2–3 square inches (13–19 square centimeters), meaning that in theory, highly localized stresses could be considerably greater. This “peak stress” could have been measured through the liberal application of strain gauges, but de Havilland had apparently elected not to attempt this, believing that any more precise measurements would be unreliable. Nevertheless, investigators measured it anyway, and from these data they calculated a localized peak stress at the window corners of up to 45,000 psi under normal pressurization conditions. Not only was this much greater than de Havilland’s predicted value, its relative proximity to the ultimate strength of the material (estimated to be 65,000 psi) produced an unfavorable stress ratio correlating to an expected fatigue life considerably below 10,000 cycles.
[1] https://admiralcloudberg.medium.com/neither-money-nor-manpow...
I think counter arguments come into one of two camps:
(1) when they replicated the problem in a pressure chamber at ground level it wasn't technically a window that failed but a "portal" (basically like a window but wires go through it instead of people looking out of it) - a pedantic technicality and not to say that all the failures in the air were for this same portal/window.
(2) The windows weren't don't have sharp corners anyway but rounded, not unlike some modern planes. True but you can see the failure was definely near a (rounded) corner.
Admittedly the Admiral Cloudberg article does seem to put more weight on the way the rivet holes were made than the angularity of the window corners. But it's still failing at a corner. I guess it depends how you look at it.
Cool, my local aircraft museum. The square-windowed Comet was rotting in the open for many years but (as the article notes) has been restored. They also have a Comet flight deck which you can walk around. It has 5 seats on the flight deck (it really is huge!), including a flight engineer and a navigator.
Edit: flight deck photo on Wikipedia: https://en.wikipedia.org/wiki/De_Havilland_Comet#/media/File...
Other highlights of the museum are a fully restored Mosquito, and a Chipmunk (which will be nostalgic for RAF servicemen and cadets of a certain age).
The wing-integrated jets, while not the most efficient, maintainable or powerful, are the best looking piece of commercial jet engineering in my eyes. Composite winglets are a distant second.