Originally published at: https://boingboing.net/2017/12/11/the-fascinating-history-of-the.html
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This reminded me of the old-timey air crash thriller novel No Highway by Neville Shute, which I assumed was based on the Comet. Actually though, Wikipedia says the novel came out a few years earlier.
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Interesting to see how modern the Comet looks, and how little the form factor has changed in 65 years.
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Pretty much all modern big jets owe a lot to this plane:
It’s unfortunate that the Comet I had a killing design flaw, considering that the later versions were reasonably successful. It is a really beautiful plane, something DH was well known for.
During WW2, the British aircraft industry concentrated on combat planes, letting the Americans build all the transports. This gave the USA a massive lead in passenger aircraft design and construction experience at war’s end.
The Comet might well have reversed that trend were it not for that fatal flaw in those window corners, and DH’s failure to stress test the pressure cabin by repeated press-depress cycles.
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and they were much too warm.
De Havilland put the plane through an unparalleled testing process designed to identify metal fatigue. Sections of the design were put through more than 15000 pressurisation and depressurisation cycles and no flaws were found. Likewise, the windows were exposed to much higher pressure differentials than would have been found in service. It passed with flying colours. When it flew, it was probably the most-tested plane in history.
The problem lies mostly with the way the windows were constructed. They were originally intended to be glued and riveted into the fuselage, but during construction of the airframes the assembly process removed the glue entirely and substituted punch rivets for drilled rivet holes. This created tiny fatigue cracks around the holes, which combined with the high stresses around the corners of the windows led to metal fatigue developing within 1000 cycles.
The Comet wasn’t going to beat America to the big airliners - it was a very small airliner with a tiny cabin. The much bigger 707 was likely to win in a two-horse race with DeHavilland. The plane that should have won the lion’s share of the market is the original Vickers V-1000 designed in 1953. It was bigger, faster, carried more people and flew further than the 707. It was the first airliner to use bypass engines which were quieter and more efficient than the turbojets of the Comet and 707.
It was cancelled by the Minister of Supply when the prototype was more than 80% complete. As George Edwards, CEO of Vickers said at the time with complete accuracy: ‘We have handed to the Americans, without a struggle, the entire world market for big jet airliners.’ Fortunately, Vickers would come up with the most beautiful of all subsonic airliners - the VC10, but that never sold in the numbers needed to build a sustainable UK airliner industry.
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The original one, finished in bare aluminium is perhaps the most retro-futuristic object ever created. It’s impact on a country shattered by the War can only be imagined - it must have looked like it was beamed in from space:
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Thanks Mike, a couple of things I did not know. So DH changed the window install process -after- the pressurization cycle testing? That should have invalidated the test results.
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The Comet went on to have a long history in the RAF as the Nimrod marine reconnaissance aircraft, which is mainly notable for it’s third upgraded version, the MRA3, going £789 million over budget (and nine years late), before the decision was made to scrap all the finished aircraft.
MoD procurement in a nutshell right there.
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Well, now we know that. I’m guessing this is exactly the sort of thing that led to the rigorous auditing that happens now.
Yeah, pretty much the whole content of Eagle comics for the next decade looks like it was drawn by people with this photo on their desks.
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Should have, but I suspect a lot of people a DeHavilland said ‘well the plane is ludicrously over engineered, we can cut back on that without worrying’.
Compared to the horrible planes the rest of the UK airline industry was turning out at the time, the Comet was impossibly well designed. If you want to see the competition - may I introduce the Avro Tudor - the wings of a Lancaster on a new pressurised fuselage:
Somehow Avro got through nine variations of the Tudor and they were all terrible. Several were rejected outright by the airlines for being too appalling even for the immediate postwar era, and several that did go into service ended up crashing or just vanishing into thin air (and helped fuel the whole Bermuda Triangle myth).
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Good point, the Nimrod is based on the Comet 4C, which as the video mentions, was a much re-engineered airliner from the poor old Comet 1. The first couple of Nimrods were actually Comet 4Cs that couldn’t find customers. The MRA4 version that was cancelled in 2010 was probably taking things a bit too far. What was thought to be a cost-saving exercise in using old Nimrod fuselages with plenty of life left in them turned out to be a big mistake as, for reasons I can’t imagine, all of the planes had very slightly different dimensions and it was a nightmare to get all the pieces to fit.
21 planes ordered, nine eventually built, £3.8 billion spent and all scrapped with a further £3 billion then being sent to Seattle to get some Poseidons.
The Comet 4 deserves a place in the history books for offering the first non-stop transatlantic airliner in October 1958. When it arrived in New York, the locals, showing their love for a winner, booed the plane and its passengers.
Possibly more importantly it creates stress concentrations around the holes.
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I hate it when people say that the Comet failed “because it had square windows”. That’s not true. The windows had rounded corners, deHavilland engineers knew about stress concentrations. They even ran a full-scale fatigue test of the airframe! However…
(1) As MikeR said, they changed the window design between the fatigue-test airframe (used more bonding) and the production airplanes (used more rivets). The cracks started from those rivet holes close to the corners of the “square windows”.
(2) The fatigue test was run in a fuselage that was previously used for static stress (i.e. strength) testing, which included being pressurized to about double the operating pressure differential to make sure it held together. The high pressure test work-hardened/cold-worked the high-stress hot-spots on the fuselage: Places with locally higher stress - such as the window corners - yielded and were stretched plastically (i.e. permanently), meaning that the material at those spots became longer in the direction of the stress. As a consequence, any future loads (e.g. during the fatigue test) did not cause as high a stress at those locations. So the fatigue-test airframe “high-stress hot-spots” did not experience stresses as high as those on real airplanes. So the fatigue test did not crack, but the real airplanes did.
Not only does modern jetliner design owe a lot to the Comet; Modern fatigue-testing also owes a lot to the Comet!
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Speaking of square windows…
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Of course, rigorous engineering analysis may have drawbacks of its own.
http://www.tandfonline.com/doi/full/10.1080/19378629.2017.1408631
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