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The de Havilland Comet (greatdisasters.co.uk)
58 points by arunmp 3 days ago | hide | past | web | favorite | 53 comments

I still think the Comet manages to look more futuristic than other civil planes. Something about the look of those engines in the wing roots with not a nacelle in sight.

Such a shame it turned out to be doomed due to being first and the now well known metal fatigue story.

The article, as with everything Comet related, ends with noting that lesson is why airliners now have very rounded windows. Yet none ever wonder or look at why cockpit windows remain decidedly rectangular. :)

The Comet did go on in a military role as the Nimrod - I once saw an AEW Nimrod parked at the edge of RAF Kinloss - a staggeringly ugly beast:


They were an amazing example of a legacy system being maintained far beyond any reasonable expectation of life at gradually increasing cost, to a great extent because nobody could agree on a replacement and the one-off cost of a replacement was always a bit more than the endless "maintenance" and "refurbishment".

If I remember rightly the refurbishment project hit the problem that, because the original planes were hand-built to 1950s tolerances, building new parts off the original plans simply wouldn't fit. The only viable approach was measure the specific plane you wanted to fit, and build a custom part for it.

Eventually one simply caught fire in the air: https://www.telegraph.co.uk/news/1528109/Fire-was-reported-o...

The destruction of the airframes was controversial: https://www.bbc.co.uk/news/uk-england-12292390 but I see it as a symbolic driving of a stake through the heart of a project that should have been honorably retired a couple of decades previously but instead took on a vampiric, undead, and ultimately fatal life.

> Eventually one simply caught fire in the air

Full details in the Haddon Cave report [0], the official investigation into the crash of Nimrod MR2 aircraft XV230 in Afghanistan in 2006. The 'simply' here (as in 'simply' caught fire) was in fact a catalogue of known problems and missed opportunities. The Nimrod variant involved was originally intended to perform long-duration maritime surveillance and was designed to allow the crew to intentionally switch off one of the engines when the plane arrived on station (to save fuel while loitering for hours). To restart the engine there was a pipe routed through the fuselage that carried hot gases from the running engine to kick start the cold one.

A separate modification of the complicated tanks and plumbing that supported in-air refuelling led to a (leaky) fuel pipe that was routed right past the (very hot) engine cross-coupling pipe. Very minor leaks somewhere in the system were routine.

In this case there was a fuel leak near the engine cross-coupling pipe. The unfortunate crew of 14 had six minutes from initial fire warning to the eventual and unavoidable explosion that killed them all.

[0] https://www.gov.uk/government/publications/the-nimrod-review

The B-52 program is slated to have a 95 year operational time span. Partly as an experiment in maintaining old aircraft.

Yes, but Boeing built 744 of the things, and only 78 (or fewer) are still in USAF service (I believe NASA has one …). So the ones being upgraded are from a late production batch (the B-52H) and presumably by that point Boeing had standardized things properly.

Comet production ran to 114 aircraft in four major versions, of significantly different size and engine configuration (they started with a 36 seater, and ended up with 119 passengers in a charter-variant of the Comet 4C). No individual model of Comet got anywhere close to a triple-digit production run.

Oh, and 26 hull loss accidents!

Sometimes amazed at how old some of the aircraft still in service are with many airforces/airlines . Just about 3 weeks ago an Iranian airline crashed a 707 in active service.

Yeah but Nimrod was bloated, and positively covered with warts and radomes. I'd claim they spoilt the lines a tad. :)

The normal Nimrod's were quite handsome beasts - used to see them a lot when I was a kid as I grew up near Kinloss.

My school was right next to a runway (as in a couple of hundred metres at most) — whenever a Nimrod was taking off, class had to stop and wait for it to do its thing as there was simply no competing with it on volume. Loud buggers!

As with a lot of British war jets from the post War decades, there was something quite beautiful — almost organic — in their lines.

I remember seeing a Vulcan bomber doing aerobatics over our wee Scottish village - quite a site and the noise was incredible.

Some time in my teens I was at an air show with very relaxed views on where a crowd line should be compared to today. A Vulcan, howling away at full throttle, pulling into a max climb at what seemed just above our heads will never be forgotten, or unfelt. That display was definitely the highlight of the show. Ridiculously agile for the age and size.

No one had car alarms back then or they'd all have surely joined in. :)

As a youngster I was at an airshow "with very relaxed views on where a crowd line should be"* on the aforementioned very-close runway, watching a Harrier work its hovering magic less than a 100 metres away.

The noise was such that I now thoroughly believe the Brown Note might well exist, and back then was stunned to be able to imagine I could discern individual organs resonating inside of me. I've never felt such a level of bass since, not even in my later clubbing years, hugging bass bins in sweaty clubs, listening to dub techno or whatever it was that took my fancy twenty years ago... .

SUCH noise. It becomes so loud it's not even noise any more, just pressure waves and complete sensory discombobulation.

* love that, NeedMoreTea!

Back in the 70's, or perhaps early 80's when I was a kid, my family were on our usual yearly summer camping holiday on the west coast of Scotland. One day whilst out for a drive around Skye a Vulcan came up from behind us and flew very low over our family car (you could almost count the rivets) and then did a nose up into the sky. It was quite bloody amazing, it was loud and there was a thick black plume of exhaust as it powered up and away from us. Tremendous machines.

They used to do low level flying training in my parts. On at least on occasion I was walking in the hills and got to look down on a stream of jet planes tearing through the valley below, which was quite something to behold (especially as a youngster). Seems like they publish the timetables now[0], so it may be possible to plan a walk to co-incide.

[0] https://www.gov.uk/government/publications/operational-low-f...

Concorde is still the most beautiful aircraft ever, IMO.

As would the Spitfire. :)

And the TSR2 :-) could walk away from a lighting on a single engine.

To my eye IL62 is a beautiful airliner.
D_Alex 3 days ago [flagged]

>Yet none ever wonder or look at why cockpit windows remain decidedly rectangular. :)

Don't listen to the "aerospace engineer" that answered you.

The reason why cockpit windows are so angular is of course for visibility. They are mounted in a heavy load-bearing frame. Structural efficiency is sacrificed for a better view.

I tried to find a nice picture for you, but the best I could find is this https://polybull.com/product/genuine-boeing-747-400-full-coc...

These in turn are mounted on another heavy frame that attaches to the main bulkheads. You can see the angles are quite sharp, certainly no more rounded than the Comet windows were. But, once stress concentration and metal fatigue was understood, appropriate allowances could be made.

Conversely, for passengers, the view is compromised for better structural efficiency.

Hi, that's me you're insulting.

Do you have a problem with any of the facts I presented?

I have a problem with every statement you made in your first reply, starting with "aerospace engineer here", which implies you are specially qualified to discuss airplane structural design.

There are many disciplines in "aerospace engineering", and if you say work on instrumentation, then saying "aerospace engineer here" in this context is about as misleading as saying "circles are just squares with large radius corners" (they are also "triangles with large radius corners").

What do you actually do in our job?

>What do you actually do in our job?

I work in airworthiness and maintenance, so I deal with aerostructures on a daily basis. You?

>about as misleading as saying "circles are just squares with large radius corners"

What happens if you take a square with sides of length x, and smooth the corners down until the radius of each corner is x/2?

>I work in airworthiness and maintenance, so I deal with aerostructures on a daily basis. You?

I know you work in airworthiness from your post history. It also indicates you work with flight systems, and not structures. Amirite? What is your professional qualification?

You can see what I do in my profile.

>What happens if you take a square with sides of length x, and smooth the corners down until the radius of each corner is x/2?

Same thing as happens with any regular polygon with sides of length x.

You said "It's not the shape of the window but the radius of the corner". This, like every other statement in your initial comment, is a misleading half truth at best. The true picture is complex, but the shape definitely matters, because you want to avoid abrupt local changes of stiffness in the direction of most stress (this can happen without any openings even, for example by adding a local bracket).


You are not quite rite, no. "Flight systems" is ill-defined but if you mean flight controls like elevators and ailerons and whatnot, then yes. I also work with structures as a routine part of maintenance, repair and overhaul. Why would you assume my HN comments are a good way to accurately determine my area of professional expertise? Most of my comments are just shitposting about javascript anyways.

>The true picture is complex, but the shape definitely matters

Of course it matters in a general context, but what matters more in the context of fatigue-related crack growth and stress concentration is the radius of the corner. This is why we stop-drill cracks. This is basic undergrad stuff.

In any case, I see from your profile you work in oil and gas. Not sure why you have so much emotional investment in this topic but this quote of yours:

>Don't listen to the "aerospace engineer" that answered you. The reason why cockpit windows are so angular is of course for visibility.

Doesn't refute or rebut anything I've written on this topic. In fact I was not attempting to explain why cockpit windows are polygonal in shape, only that the corners aren't as sharp as it might seem at first glance/long distance because it seemed like OP was equating "rectangular" with "causes structural problems".

I probably won't reply again, have a great day bro.

> Not sure why you have so much emotional investment in this topic

I can't sleep when someone is wrong on the internet!! :)


>Yet none ever wonder or look at why cockpit windows remain decidedly rectangular. :)

Aerospace engineer here. It's not the shape of the window but the radius of the corner. A circle is just a square with large-radius corners, really, and it's the sharp corner that causes stress concentrations.

If you look closely at modern jet liner cockpit windows you'll see they are in fact still rounded at the corners.

The radius of cockpit windows doesn't look that different than the radius on the Comet's square windows.



Perhaps not, but remember that the metal fatigue phenomenon responsible for cracking in the Comet was not yet fully understood at that time.

Nowadays we have a very good understanding of how metals degrade/respond to repeated load cycles and can design around it. I have not personally worked on airliner window structures but there are a number of avenues that one could take to retain the general shape of the window and still avoid structural compromise due to cracking.

I'm sure my brain had another sentence that never made it to keyboard when I was writing that, as I've given completely the wrong impression, opposite to intended. No idea what I was thinking. :)

Comet windows did have rounded corners, as seen in the wreckage photo, similar to the 707's and others. The cause was stress at rivet holes and lack of strength in those areas. After strengthening it had oval windows. The popular view continues to believe the cause was windows with corners.

I believe you're correct, but they did also find that the magnitude of stress concentrations around the windows were much higher than design analysis predicted.

Which, although technically correct, is still quite misleading and misses out the fact that this was done purely as a precaution, since the actual crack causing the failure did not come from a passenger window [0] but rather the ADF aerial square cutouts in the roof. These are what the photograph in the article shows, and the position is also highlighted in the diagram there. The 'square' passenger windows, as pointed out in the wiki link cited above, had similar corner radii (or smaller in some cases) to those of the Boeing 377 and Douglas DC-7 aircraft.

0. https://en.wikipedia.org/wiki/De_Havilland_Comet#Window_shap...

My intent had actually been to point that out in the first place when TFA concluded, as is often the case, it was the windows. See my brain fail comment somewhere downthread, as I only came back too late too edit the original:


> Something about the look of those engines in the wing roots with not a nacelle in sight.

Quite a few early jetliners lacked normal nacelles.

Can you give some examples? I'm curious as I also find the de Havilland Comet design to be quite remarkable for this compared to modern jetliners, and this is the first time I'm encountering the design.

EDIT: I found this wikipedia page [1] and clicked around, and the only jetliners I found without nacelles are the Tupolev ones -- the Tu-334, Tu-104, Tu-110, Tu-124 -- and the Tuplev supersonic Tu-144.

[1] https://en.wikipedia.org/wiki/List_of_jet_airliners

The Avro Canada Jetliner is another example, though it never went into production, and if you are including the Tu-144 then the Concorde belongs as well, and the original 737 also had its engines mounted directly under the wing, without pylons. While it is not quite the same, I think all trijets except the DC10/MD80 had the third engine buried in the tail.

There were many military designs, such as the British V-bombers, with engines mounted in or directly on the wing, without pylons.

Interesting point: the 737 was originally designed to take off from gravel runways.

Hrm, I thought the Sud Aviation Caravelle also lacked them, but I was wrong (though they're in an unusual place on it).

One amazing story about this is that the film 'No Highway in the Sky' [1], which (almost) predicts this exact problem, was made a couple of years before these actual events took place.

[1] https://www.imdb.com/title/tt0043859/

The film was based on the novel "No Highway" (1948) by Nevil Shute, who had worked as an aeronautical engineer at De Havilland.

It's good that not all of Nevil Shute's predictions were so accurate:


How do you know? As far as it goes, this novel might be actually an accurate prediction (except for the year).

The foreshadowing was obvious when they called out the square windows in the first few paragraphs. Everyone who's ever slept through an engineering class knows corners cause stress risers.

One story I heard was that one of the production engineers added a rivet in the skin near the corners of the window. This was added because he thought it would strengthen the structure. Unfortunately it actually acted as an additional stress concentrator. I'm not entirely sure there wouldn't have been an issue without that extra rivet. The guy that made that change thought he was doing the right things but in fact made things much worse.

According to Wikipedia:

> The accident report's use of the word "window" when referring to the Automatic Direction Finding (ADF) aerial cutout panel[121] has led to a common belief that the Comet 1's accidents were the result of its having square passenger windows. In fact, Comet 1's cabin windows were very similar in shape, with similar corner radii, to those of the Boeing 377 and Douglas DC-7[122], both of which were pressurised aircraft. The windows in Northwest Airlines' B-377 were in fact larger and notably more rectangular[123] than those of the Comet 1. While stresses in the area of the passenger windows were significantly higher than de Havilland had calculated, nowhere in the accident report is it claimed that the fatigue failure of the Comet fuselage occurred was a result of the shape of the passenger windows, but instead from excessively high localised stress at bolt and rivet holes, for which insufficient reinforcing (and therefore structural load distribution) existed.

Chester Wilmot, author of "The Struggle for Europe" who was an Australian War Correspondent during the Second World War was one of the passengers who sadly lost their lives in the crash of the Comet over the Mediterranean Sea.

I can recommend "The Struggle for Europe" - he wasn't just writing about the history, he was actively taking part.


Such a shame Nimrod is no longer flying. But it replacement(Rivet Joint) makes a mockery of regulations introduced because of Nimrod. Basically the MAA would like more information on adhering to regulations at time of production, they'd like an idea of when things start to fail. The RAF may not have even fully qualified for to fly because they were built in the 60s! They don't want the same mistakes like Nimrod because of fatigue

I wonder why all the planes were names in some variation of Yoke [name, including Yoke]? Maybe:

yoke: NOUN; Irish informal; A thing whose name one cannot recall, does not know, or does not wish to specify.


It looks like it's based on their registration "numbers" written out in the phonetic alphabet in use at the time: https://www.smithsonianmag.com/history/comets-tale-63573615/


Comet 1—registration G-ALYP, dubbed “Yoke Peter,” from the phonetic alphabet then in use in Britain (George-Able- Love-Yoke-Peter)

When I first saw the headline I was thinking it was this Komet :-) https://en.wikipedia.org/wiki/Messerschmitt_Me_163_Komet

Also an interesting aircraft.

My Dad was a riveter in the Vickers Viscount factory in the 50s/60s. Ok, not Comets, but close.

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