YOU have Misunderstood The De Havilland Comet. It Wasn’t the Windows!

[@MentourNow]

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[@fredashay]

Petter, I remember watching a few documentaries a long time ago where they put a Comet in a tank of water and flexed its wings over a period of months and they stated in no uncertain terms that the fatigue cracks occurred at the corners of the "square" windows. Were these documentaries all biased or careless in their reporting?

[@williamshockley7692]

In business and any commercial enterprise or military endeavor, _"Pioneers get the arrows whereas settlers get the land"_ .

[@fafner1]

@@fredashay The key failure was not stress concentrations in the windows, but insufficient support of the skin with stringers. Similar to rip stop nylon, the stringers act to stop cracks in the skin before they become catastrophically self propagating. Boeing produced a video where pressurized Comet fuselage was sliced open with a guillotine and promptly split open. A 707 fuselage under the same conditions lost pressurization but did not fail catastrophically. De Havilland was rightly known for its aerodynamic expertise, but they spent WWII building unpressurised wood airplanes while Boeing was building pressurised aluminium airplanes.

[@fredashay]

@@fafner1 Well, I just said what I saw in a some documentaries...

[@RWBHere]

Thanks for setting the record straight, Petter. I almost landed a job, in the mid-1970's, working on radar equipment for the Nimrod. It was a beautiful looking aircraft, and even though it was officially retired from RAF service in 2011, a very few were still to be seen flying for a short while afterwards. The Comet design lineage was clearly evident, although they were quieter than their ancestors, presumably because of the different engines..

[@rstross]

My Dad worked for DeHavilland (later Hawker Siddley's). He said the biggest contribution they made to aviation was sharing all of the information they learned during the aftermath of the Comet accidents. One of the most important: the development of rip-stop (crack arrestor) construction. This proved to be a real life saver for the now infamous Aloha Flight 243. While they went on to develop the Comet 2 and eventually the Comet 4, he felt that the lines of the original Comet 1 were the most beautiful.

[@tomsear1]

interesting point, thx

[@alanhat5252]

"rip-stop"? I'd like to hear more about that

[@do-re-me-fa3258]

Beauty? Safety

[@howardosborne8647]

I don't think any other passenger jet has ever looked better for lines than the first Comets...fantastic looking aircraft

[@howardosborne8647]

@@alanhat5252 it is a structural crack arrestor often called a ''rip stop doubler'. Also used on naval vessel hulls to minimise and control stress cracks from propagating into something catastrophic. Read a bit more in the wiki link below: en.wikipedia.org/wiki/Crack_arrestor

[@robertfindley921]

As an engineer and project manager handling large production projects, I am always impressed at your thoroughness and organization. It's rare that I come up with a question you don't immediately answer in the next few seconds. You do your homework well.

[@MentourNow]

We do try!

[@tomsear1]

Early career as baggage 🧳 handler: I DO have questions ;) srsly tho would make an insightful Ep A?!

[@petermallm149]

I do agree 👍

[@Keepmywifesnameoutyafucknmouth]

Shut up

[@jimtaylor294]

Amen 😌👌

[@BerkeleyTowers]

As a young graduate engineer in 1982, I started at BAe working on the Nimrod project. If I needed original drawings for reference, it was down to the archives to pull the original Comet 4c items! The smell and feel of these original drawings, just conjured up the image of a smoke filled drawing office full of blokes sat at huge drawing boards in the decades before me.

[@MartinInAmsterdam]

Me too man. BEA Systems at Prestwick Nimrod MRA4

[@BerkeleyTowers]

@@MartinInAmsterdam 😀 Woodford for me, AEW conversions and post Falklands mods.

[@dipling.pitzler7650]

Imagine if nowadays an engineer at Airbus or Boeing would examine a fuselage with a lit pipe in one hand! I think he would be fired on the spot just for entering the facility. PS: I think DH chose the integrated engines and leading edge intakes on the Comet because they already proofed the concept on the jets Vampire and Venom.

[@BerkeleyTowers]

@@dipling.pitzler7650 Until relatively recently, the Airbus was built with ashtrays on the flightdeck for the pilots...........

[@fafner1]

@@dipling.pitzler7650 Everyone struggled with where to place jet engines. Boeing initially proposed the B-47 with engines enclosed in the fuselage, but the Air Force objected due to the difficulty in containing engine fires so Boeing looked at other options. They realized placing the engines in pods did not increase drag that much and helped to damp torsional vibrations in the wing. With the 707 they realized the podded engines allowed the landing gear and fuel to be located in the wing root. In contrast, de Haviland on later models of the Comet had to hang additional fuel tanks on the wings.

[@John-boy]

I flew from London to Majorca on a BOAC Comet as an 11 year old in 1963. My first flight and it was very exciting and stylish. A proper hotel style menu with choices, china, glassware and silver cutlery on a table with table cloths. And only one class back then. We were treated like royalty. I loved the Comet.

[@Mumbamumba]

Nice! That must have been quite an experience for a 11 years old boy.

[@zaco-km3su]

And loud noises and bumpy travel.

[@John-boy]

@@zaco-km3su it was as smooth as silk and pretty quiet too.

[@austindarrenor]

@@John-boy I have first hand experience why the selling point of the new jets to the public was how smooth they were. I flew on an SAS DC-7 from LAX to Copenhagen. Only four yrs old but still have vivid memories of the flight.

[@lcprivatepilot1969]

Imagine actually being royalty and rarely receiving such treatment. Regardless, your experience sounds grand!

[@mtbelly1972]

Glad you mentioned the Nimrod. My old boss use to work on them. Had loads of conversations about the Nimrod. Flew from 1969 to 2011. Was a fantastic aircraft to watch at displays.

[@davidaprians]

I still think the comet is one of the most beautiful airplane ever made, its sleek design because the engine placement being inside the wings...

[@rainscratch]

Without doubt together with the Concorde and Constellation, truly elegant and stylish.

[@TenorCantusFirmus]

Everyone actually likes its look. Unfortunately, it paid the price of being first in a totally unknown territory; and probably being rushed into service far too early.

[@ant2312]

@@TenorCantusFirmus irrelevant to what the guy was saying

[@poruatokin]

That design feature was a common element in many British aircraft of the time, Valiant, Victor, Vulcan, Hunter to name but a few

[@jaywalker1233]

@@poruatokin A close relative flew the Hunter in the RAF amongst many other types, but he always said the Hunter was the nicest to fly

[@steveknight878]

I flew on the Comet a few times - the first time was from Singapore to Heathrow (BOAC). It would have been in about 1960 or 1961, and I would have been 10 or so. It was a truly lovely looking aircraft. I flew on a couple of Comets about 5 or 6 years later, IIRC. They were charter flights. I remember thinking how small they were in those flights. What an aeroplane it was.

[@dannydaw59]

Was it loud inside the cabin?

[@JohnSmythe-od4gk]

Can you remember how many refuelling stops were required on that trip? Just curious.

[@steveknight878]

@@JohnSmythe-od4gk I think just the one, in Germany (possibly Frankfurt, but I'm not sure). There may have been an earlier one, but I don't think so. I do remember that we had to get off the plane in Germany, and I don't remember doing that anywhere else.

[@steveknight878]

@@dannydaw59 I don't remember it being very loud - I was in a window seat near to the front.

[@tomnisen3358]

I read in the 1960's about the grounding. It was before 1960. Boeing 707 was on 1958, followed by the DC-8 and a Convair four engine jet.

[@billotto602]

I went into aviation maintenance in 1976 & just retired in 2020. The changes, based on a constant learning curve just in my career was amazing. The Comet was way ahead of everything else. Thanks for clearing that up. I've believed for decades that it was the windows that caused it.

[@GregWampler-xm8hv]

I'm going to have to disagree on the "way ahead" statement. The Comet was like our Bell XP-59. Basically a prop plane airframe and jet engines scabbed on. And no need to compare the Comet to the 707. Although the 707 got it right the first time whereas even the Comet 4 stuck to a failed late 40's design. The late 40's Boeing B-47 was the look of the future and 80 or so years later still is. And let's never forget the B-307 Stratoliner a late 30's pressurized cabin airliner from, you guessed it Boeing. FYI Boeing warned DeHavilland about the windows. And before anyone flames me DeHavilland was an innovative company and the DH Mosquito possibly the greatest overall, general purpose, do everything excellently aircraft of WW2. One other thing ol' Boy. The Comet came from the Barbizon Committee who formed what about 1943. So while we Yanks threw everything into the war effort our brothers in arm were stealing a march and planning for after the war. I say poor form ol' boy. Old school tie and all that eh what?? The Midnight Rider

[@billotto602]

@@GregWampler-xm8hv you do make some very good points that I wouldn't dare to disagree with. But I was referring to the story that it was the windows that caused the death of the plane. Perhaps I didn't word it right. 😔

[@jimtaylor294]

​@GregWampler-xm8hv If Boeing "warned" DH about the windows (which weren't the source of the problem), then they didn't heed their own "advice" if looking at the 707 😂 . (see video for example) It's also worth noting that the American view of the Comet when she debuted - according to aviation historian James Patterson - was typically that the UK had sized a 20 year lead on the US; that was how seriously they took it. I'd also dispute the "not innovative" line, as the Comet was - as pointed out in the video - flying at an altitude higher than any other commercial aircraft had *ever* done, as well as higher than basically all WWII Bombers, *and* was one of the first uses of swept wings on an airliner, among other new features. Objectively speaking DH went all in with innovation, whereas others in the industry were still making prop' 'planes with straight wings and tailsitting landing gear. Tis of note also that the Comet set a quantum leap in aviation safety measures and investigation methods, while by contrast the contemporary Soviet passenger jet TU-104 remained a temperamental death trap right up until full retirement in the 1980's. (the TU-104 also has the weird accolade of having killed more Soviet admirals than the Germans did in all of WWII) Last off: the Brabazon Committee makes sense as a wartime move, when considering the UK saw the efforts of chaps like Kaiser in the US, and knew that the US would be robust industrial competition after the war. Thus any kind of an edge was rather important, and being the smaller nation also requires an emphasis on innovation. That said the US didn't ironically take over in Shipbuilding after the war, for while Kaiser had proved he could build entire cargo ships faster than some aircraft companies could build a single aircraft, overall the US still wasn't peak competitive on *cost* (of labour & of end product), relative to the British. We both lost in the latter ultimately though, with wartime shipping loser Japan starting from scratch with an all new approach, while us westerners were slow to adapt and now only really build warships domestically.

[@WilhelmKarsten]

de Havilland was a deeply troubled company and decades behind in aircraft technology, the fact that they were still trying to build jets out of wood and fabric is undeniable proof of this. d-H made several critical design errors based on their lack of experience in producing all-metal aircraft and pressurized cabins.

[@WilhelmKarsten]

@@GregWampler-xm8hv The success of the Mosquito is based more than anything on the fact that Britain had no domestic supply of Aluminum and key imported sources were cut-off. The Mosquito was cheap to build but also lacked durability, they were essentially disposable aircraft which is why so few survived after the war. Their success with the Mossie does not transfer well to building commercial jet aircraft either. Good point, it's hard to believe just how out of touch with reality the British were about their future in the aviation industry, there were only two winners in WW2 and Britain was not one of them.

[@rudolfabelin383]

Hej Petter! My father's very good friend, John "Cats Eyes" Cunningham, made the maiden flight of the Comet. He was then the chief test pilot of de Havilland. They met when my father attended the de Havilland Aeronautical Technical School prewar. Best Greetings from Skåne!

[@Cobraguy321]

Thank you for a very accurate synopsis of the De Havilland Comet. I joined the De Havilland aircraft company at the Hatfield aerodrome as an apprentice photographer in 1958 and briefly met Sir Geoffrey one day when photographing some model aircraft. The comet water test tank was based on the other side of the airfield where a section of fuselage was put under stress tests to find the cause of the structural failure. I later joined the film unit which then became Hawker Siddeley. The airfield is now a housing estate, but the main art deco headquarters building still exists. The Comet will always be the pioneer and symbol of the jet airliner age.

[@anneest]

I think we can see the headquarters building in Mentour's video here? I had a closer look when I saw it was art deco ish, and immediately thought 'I hope they did something cool with this building!'. Thanks for sharing this information, cheers 👍😀

[@livethefuture2492]

Please definitely do more of these deep dives into historical aircraft! You a bring a new perspective to things that you cant find anywhere else. Love the work that you're doing!

[@NicolaW72]

👍

[@pablopeter3564]

EXCELLENT video, as usual. As a former Mexicana Air Lines pilot, I had the pleasure and honour to fly with pilot who had flown the Comet 4C, let me tell you that all of them liked it very much because its handling qualities but at the same time they told me that it was a mechanics nightmare. Greeting from Mexico City.

[@eucliduschaumeau8813]

When I was a kid, we flew the Comet in Mexico. I was impressed by the engines built into the wings and wondered why all planes were not built like that.

[@TmnTyler2020]

​@@eucliduschaumeau8813 maintenance on the engines becomes a nightmare when they're not easily accessible or removable which drives cost way up.

[@austindarrenor]

A mechanics nightmare, lol 😆 I imagine it would be with the engines hidden away in the wings. Good on Boeing and Douglas for putting practicality over aesthetics.

[@alfredomarquez9777]

As an 11 years old kid, my first fight was on a Mexicana DC6B, and some months later on the Mexicana Comet 4C MEX-HMO in 1965... The service was excellent and called: "Servicio Azteca de Oro", with a large Aztec golden calendar on the bulkhead separating the galley from the passenger cabin, very elegant and beautiful stewardesses and all passengers well dressed and behaving properly! Those flights marked the love for aviation, and I still have my PPL certificate valid. In 1967 Mexicana hd changed to the 727, which became my favorite!

[@pablopeter3564]

@@alfredomarquez9777 I am glad you had a good experience flying as a passenger in my former and beloved Mexicana Airlines. Let me tell you that I flew as a Fist Officer in the B-727 for 12 years, then jump to the A320 in 1991 to the present day as a Captain. Take care.

[@terryrainer2213]

A very interesting, thorough, and accurate analysis of the “Comet”problem. I have a copy of the book “The Comet Riddle”, by Timothy Hewat and W.A. Waterton, which not only describes the preceding incidents that led to the grounding of all “Comets”, it also gives an excellent report of the Court of Inquiry. Interestingly, it also explains that the first cracks at the very start, the “Ground Zero” of the metal fatigue, more than likely stemmed from the two square-cut Automatic Direction Finding (ADF) “Windows” situated in the forward top section of the fuselage, at least in the case of Yoke-Peter (G-ALYP) and Yoke-Uncle (G-ALYU). The book was published in 1955 and is long out of print, but it is well worth reading if you can get hold of a copy.

[@steve-marsh]

This is unbelievably good, so excited for the series, the best there is! (please just drop the swipy sounds) :D

[@klaasvanmanen8214]

Having watched several of your earlier video's and many of your more recent ones, I have to say that you have become so much better at presenting. It's incredible how easy it is to follow your story lines, how well you seem to fit into everyone's household (ease of watching), and how well illustrated your video's are. As just an example: in your early video's you used to say "Okay?" a lot, as if asking your viewers if they were still with you, which was of course superfluous. You now seem to be much more confident of the story you tell, so that you no longer pose this question. And very much rightly so, because your stories nowadays are clearly very well prepared. Big thumbs up from me.

[@reannereida974]

Please do more of these deep dives in historical aircraft! Im a junior (days away from being a senior) in college, majoring in aeronautical engineering because I absolutely love learning everything about aircraft! I always find it fun when I can relate what you are talking about to something i learned in class. Keep up the amazing work!

[@tedsmith6137]

A few points if I may. The higher cruising altitude of the Comet was to allow improved fuel efficiency for the engines. Higher altitude means colder air, colder air is easier to compress and, since compression is a big part of what a Gas Turbine does, the efficiency is greatly improved. Higher altitude means a higher pressure differential between outside air and cabin air pressure, increasing the loads on the structure. As an Aircraft Maintenance Engineer, I was taught about the history of design and the failures involved. We were shown the Comet history and saw how the structures and manufacturing techniques laid the groundwork for the issues met. The Aerial windows were shown to be the cause of the 2 in flight breakups, although it is clear that the water tank test article tore along the windows. I am still struck by the total lack of tear stoppers in the Comet fuselage. After staring at Boeing 747 structure for 36 years, the lack of Comet bonded doublers and tripellers, acting as tear stoppers, is so obvious.

[@phonicwheel933]

@Ted Smith well put. I believe they did embody tear stoppers on the Comet 4.

[@paulreichers847]

Another fabulous video, Petter, and I was one of those who always thought that the structural failures of the Comet were mostly related to the size and shape of the cabin windows. Thanks for setting me straight. Please DO keep these videos coming! Thank you.

[@Wannes_]

They still were The failures around the windows are plainly visible in the footage It need not have started there, but they ended the Comets by extending the ripping along the fuselage If it had just been the ADF panels blowing out, they'd have landed with some popped ears and scars from flying debris being sucked out. Remember : a 737 went partially topless and most aboard survived !

[@mnxs]

​@@Wannes_ you're sort of contradicting yourself, I think. As I understand it now, it didn't have anything to do with the particular _shape_ of the windows, as OP said. What _was_ the problem was that the aircraft was, overall, just not built strong enough: wrong alloy, insufficient skin thickness, insufficient (lacking?) rip-stopping measures, insufficient structural strength sans the skin, and there's probably more I'm forgetting. When the hull failed at the aerials, the breach could continue to develop largely unimpeded, and it just so happened to do so along the points with an already higher concentration of stress: the windows. In other words, it wasn't the windows that failed, it was everything around them. That 737 going topless (lol) was then, in actuality, a remarkably similar accident to those of the Comet. There was an old (albeit known) manufacturing defect in the skin adhesive bonding, along with some absolutely terrible maintenance on an old, overworked, corroded hull - meaning that the aircraft was, arguably, so weakened that one could aptly call it "the Hawaiian Comet" in reference to its weakened state. The saving grace there was that that aircraft did have sufficient structural strength remaining to not fall apart entirely, although it was a close thing.

[@johnyoung1128]

@@Wannes_ You have missed the point, the discussion in this video is the point of origin of the cracks and the lack of “fail safe” features to limit crack propagation. The window to window cracks are what happened after the initial failure and were not the cause of the initial failure.

[@scofab]

I've argued this with so many people... no, they insist it was the window shape and won't be convinced otherwise. Well done and thanks again.

[@captainsunshine918]

Up until today I thought that everyone who knows anything knew it was the square windows! Your videos keep getting better, more informative, and more enjoyable to watch.

[@Gringuk]

I was fortunate enough to work as a steward on BOAC's Comet 4s starting in 1959. For several years I flew at times on each and every one of them (I seem to remember there were 19). I was later transferred to BOAC's B707 fleet which for me was a down-grade. The Comet was an exciting plane to work on, the pilots especially loved it; they said it was like driving a racing car! I later flew with British United Airways as a Purser on their VC10s. Another fantastic British built aircraft loved by both crews and passengers. What a beautiful plane it was. In those days these planes didn't do the long flight sectors today's big jets do. The plane would transit between five and ten different airports on its way to, say, the Far East or Australia. We had to refuel far more often and so sometimes stopped off at smaller airports where it was cheaper. We also obviously spent more time on the ground than in the air as we swapped crews at 'slip stops' where we waited sometimes for several days before boarding another aircraft and crewing it to the next 'slip stop'. Some of our trips away lasted three or four weeks. It was a tough life but we were so proud of our Comets and VC10s! Somehow I don't think I'd enjoy it so much working on these monstrous flying machines that carry so many souls onboard these days.

[@telstar4772]

Yes both of them beautiful aircraft, i think the livery of BOAC really helped accentuate the lines of the plane as well.

[@jimtaylor294]

Amen. According to quite a few flight crew of the period the Comet 4 & VC10 had the 707 beat on comfort and safety across the board, particularly when it came to takeoff and landing. The VC10 after all was designed for the shorter and more challenging airstrip of the empire routes, where high lift devices were a must. The 707 by contrast was known to "bang" down on the runway all the time, landing hard and at higher than ideal speeds due to the long sweep of the wings with few lift devices to mitigate it. Unfortunately BOAC & BEA spoiled things for a lot of our aircraft; setting requirements for the manufacturers before turning against the domestic aircraft they'd specified and going to Boeing instead. So much so that they were derisively nicknamed "the *Boeing Only Airline Corporation* " by those in the aviation industry. This negative trope befell the Ashton, Britannia, Comet, Trident*, VC10 and various would-be aircraft. *In the Trident's case, BEA changed their mind on the engines late in the design, resulting in the aircraft always being slightly underpowered and less competitive than she should have been.

[@Roland8879]

You must have flown with my father, Jim Manning.

[@bionicman2.0]

Fake! Story .maam

[@WilhelmKarsten]

@@jimtaylor294 A charming but completely meaningless anecdote. The Comet 4 had the worst safety record of any jet airliner in history except for the Comet 1 which had its airworthiness certification permanently revoked after just 2 years in limited service and 6 unexplained hull loss accidents. The VC-10 was sold in such few numbers, flew so few passenger/miles and was retired so quickly that it's safety statistics cannot be compared with the hugely successful 707 family, thousands were built and there are more than twice as many flying right now than the number of VC-10s ever built. The 707 series is still in RAF service and is expected to remain in USAF service until at least 2050. Comfort is subjective, and is completely irrelevant if airlines refuse to buy British jets because they don't make money, the bottom line rules and the 707 made money, lots of money for both Boeing and the airlines who bought them. The Boeing 707 had Fowler flaps and leading edge Kruger flaps nearly a decade before the first flight of the VC-10, the Comet had no leading edge lift augmentation devices. The Americans were at least a decade ahead of Britain in jet aircraft development in the mid-1950s.

[@sparky739]

Hi there. Hey, that was a great job on the Comets! I do very much enjoy your channel, and it keeps me in touch with aviation, after retiring so many years ago. I thought you’d like to know that my father flew the two RCAF Comet 1A’s for years. The RCAF acquired their two Comets in 1953. 5301 & 5302. Both were outfitted as VIP aircraft. Most flights were from Ottawa Ontario Canada to RCAF bases in France, but they also flew all over Europe and the US. Dad told one hilarious story about landing in Paris with a load of VIPs on the airplane. On approach, there was a Lockheed Constellation occupying the runway so they had to go around. The controllers were not happy, and dad jinked around all over Paris at low level, until they finally were slotted back in, low on fuel and time running out. They finally re-established their approach and landed. Before the VIPs disembarked one came to him and thanked him profusely for the incredible low altitude tour of Paris, thinking that the crew had done it just for him. After it was determined what the point of failures were, the two Comets were both ferried unpressurized back to De Havilland for upgrades to the windows and other apertures in the fuselages. They were then referred to as a Comet 1x. After, and despite being “fixed“, one pilot always had to be on oxygen above 10,000 feet at all times, which used to leave a mark on dad‘s nose for days after a flight. My mother lived in silent terror those years, as she knew the Comets history. At the end of their useful lives in the early 60s, dad flew each of them to a small airbase where they sat awaiting their fate. The squadron had been told that the aircraft were going to be broken up. The nose of 5301 was cut off and hauled away to the air museum in Ottawa. The left side control yoke of 5302 was removed and presented to my dad on an oak stand at a celebration at the officers club; we still have it today. To the Squadron’s horror, it was announced that the two aircraft had been sold, and were to be flown to Miami on a ferry permit! I remember there was quite a stink about that! Another control yoke was found and reinstalled on 5302, and my dad flew it down to Miami where it sat in corrosion corner until about 1965 when it was finally broken up for scrap. Dad returned from Miami on an Eastern Airlines Whisperliner 727-100 where he had become very friendly with the crew and had enjoyed many drinks on the flight home. My mom was somewhat terse with him on the way home. Those early jetliners did not have much range due to those thirsty early engines, especially at low altitudes. Instead of long 30 minute descents common today, Comet crews performed what was called a ‘jet penetration’ where they would arrive almost over top of the airport, and then descend rapidly from 40,000’ in 10 minutes or so, in line with the active runway around 3 miles out. He had all kinds of interesting stories of his times on the Comets. He did love flying them. Dad flew Harvards, Lancasters, Beavers, Otters, Expediters, C-47’s and Convair Cosmopolitans before retiring. He then went to Air Canada where he became an instructor on DC-8’s and the Lockheed TriStar 1011’s. He really loved those TriStars, especially the 500 series. For years he had his ‘own’ C-47 that he used to fly the Air Vice Marshal around in. Dad made sure that it was always extremely well polished, and it was known as the shiniest aircraft in the Air Force. I enjoyed many trips with him in that airplane. For some reason it had a speed kit installed with gear doors that, along with the polishing, had an extra 50 kn at cruise. This usually caused issues with the controllers, as they expected the aircraft to do the usual 150 kn so, we would usually get a call from ATC asking what our air speed was. Upon being informed, they would call back to confirm the type of aircraft. Lol. That old C- 47 built in 1943 is still flying. Apparently it has crashed a couple of times, but not damaged to a point where it had to be written off. The last photo I saw of it, it still had the speed kit and had undergone a Basler conversion. It continues to fly up north somewhere in Canada. Anyhow, keep up the great work! Old guys like me really enjoy your channel!

[@cr10001]

Excellent. And I wondered why earlier pressurised non-jet aircraft such as the DC-7 and Constellation hadn't had fuselage failures - thanks for explaining. The idea of fatigue causing the fuselage to split is actually the most alarming thought I get when flying, I wonder how many cycles the aircraft has had. Possibly fortunately for me I usually fly long-haul. But I can only recall one instance since the Comets of an unprovoked fuselage explosion, the 737 in Hawaii (Aloha 243). Two instances, the 747 JAL 123, though that was contributed to by a faulty repair. The rarity of such accidents seems to indicate that design and maintenance against fuselage failure is adequate. Cargo doors, on the other hand...

[@blatherskite9601]

Aloha 243 had corrosion problems by the door, finally leading to the top half of the fuselage peeling off - unfortunately, also with one of the cabin crew. Cracks are often found at the bottm corners of 737 doors - next time you enter one, look for the doubler plates rivetted at the bottom aft-most corner particularly! The y stop-drill the crack and add extra plating to fix it.

[@mahbriggs]

We learn from mistakes! When you are doing new things, new problems arise. Not all are caught in testing.

[@fafner1]

Since the Comet failures, much emphasis is placed on designing planes so that while cracks may occur, they cannot propagate catastrophically. Ironically, before smoking on airplanes was banned, fuselage cracks were often detected by the resultant nicotine stains on the outside of the fuselage.

[@billj5645]

How many cycles has it had? Each time the aircraft climbs to altitude then back to earth is one cycle. Fatigue life of steels are usually measured in the tens of thousands of cycles but aluminum can fatigue much faster.

[@dungareesareforfools]

The service ceiling of the B-29 was fairly high at 35,000ft, but I suppose its typical lifespan was much less than that of a civilian passenger plane.

[@rbrucebicknell5038]

Nice mix of talking head commentary and relevant historical footage. Well edited. A pleasure to watch. Thank you.

[@AsymmetricThrust]

Wow, what a treat! I already love this as a secondary channel, but this video took mentour in an entirely new direction. Well done Petter and team! Excited to see more content along these lines in the future! It’s like a bonus third channel for us all wrapped up in the first bonus channel

[@scottnigh5056]

I still find the Comet to be a very beautiful shape. Would love to see a company recreate her with up to date systems.

[@JohnR31415]

Modern engines just wouldn’t fit…

[@computiNATEor]

As mentioned, today’s modern high-bypass engines wouldn’t fit, and the in-wing engines have major service negatives. Much harder to get to the engines themselves.

[@jfangm]

@@computiNATEor They could fit, it's simply a matter of engine size and wing design. And maintenance wouldn't be an issue. The mounting could be designed to allow the engines to be dropped out the bottom of the wing.

[@computiNATEor]

@@jfangm Sure, but what if you just need to change a leaking fitting at the top? On a normal cowling that hinges open that just means opening the hinge. On the Comet that’d mean dropping the engine

[@jfangm]

@@computiNATEor Not necessarily. The top of the housing could also be hinged to allow access. It's not an insurmountable issue. I think putting the engines inside the wings could actually be MORE beneficial now, given modern materials and design engineering. Some of the benefits of an in-wing mounting are: Increased speed and fuel efficiency resulting from reduced drag. Increased ground safety resulting from the engines being mounted higher in the airframe. Increased crash safety, as the engines would be inside the wing, not dangling beneath it, leaving nothing to snag on terrain during a belly landing. Whether or not the benefits outweigh the costs, I cannot say. I am neither an aerospace engineer nor a maintainer. However, as an engineering draftsman, I believe the concept DOES merit investigation.

[@martinda7446]

Mentour Pilots final words about failsafe design in aircraft systems adds to this bit of history. De Havilland after the Comet fiasco set about designing their next aircraft. They knew they couldn't survive another accident aircraft, so the whole philosophy surrounding their next project was safety. The DH121 was the first triplex aircraft. The Trident had three of this, that and the other. All critical systems had not one backup, but two. Three engines included. The worlds first autoland (except the Caravelle has gone down in history as the first CatII autoland), the De Havilland 121 Trident had completed large numbers of autoland flights except not in low visibility. The Trident was equipped with CatII in 68.. But history is a bit confused with approvals and various systems. The trident also had a rapid descent system available, which... deployed reversers to allow very fast rates of descent. A lot of firsts on the Trident too, and another design Boeing took some advantage of, so the story goes.. Re the Comet, the rivet holes were punched using poor technique. Even then they knew a dodgy rivet hole would be a bad thing. Not only that but the antenna windows were marked in the blueprints as being affixed by adhesive. Even though the aircraft may have survived much better, a final analysis showed areas in the cabin had stress levels many hundred percent above those calculated, so they had a fundamental structural design problem. The aircraft would likely have failed even if put together properly. Aluminium will always fatigue unlike steel, weid, but absolutely correct. Regardless of the stress/ strain, even if well within the elastic limits, unlike steel which will always return to condition before deformation (if kept within and even beyond elastic limits where it will deform but retain all properties), aluminium will eventually always fail. This is why airframes have a limited life and they are always testing for cracks and fatigue, flippin ally will fail even if you are nice to it!

[@hodgeheg480]

The “fact” about the windows being the cause is one of those things people will still argue as it’s become so engrained in people’s minds.

[@gingernutpreacher]

It's also made worse by one of the brake ups originated from a Ariel that was window shaped

Well I was a Documentary hoarder for a long time (20+ years) and I sure have Documentaries about aircraft, including the Comet and everyone of them blames the windows very clearly. In fact even I didn't know any better and you can hardly blamed normal people for the error if even old Documentaries that ran on TV 20 or 30 years ago got it wrong and a lot of the Documentaries are even older then that. So pretty sure this error will keep showing up over and over again as people do research and find the wrong facts and base there research on that.

[@hodgeheg480]

@ Yep, its one of those things that was set in stone many years ago.

[@NicolaW72]

@ Indeed.

[@solandri69]

While sharper corners are stress concentrators, the danger of larger windows was less well-understood at the time. I was part of a project analyzing a bunch of bearing (e.g. rivet) test data for Lockheed in the late 1980s (right when finite element analysis on computers was beginning). And the predominant assumption at the time was to simply (naively) take the total stress and distribute it evenly over the reduced cross sectional area when there was a cutout for a fastener or window. We know now that that's not how it works. So whenever these early designs had sharper corners or larger windows, the local stresses in certain regions would exceed design specs, eating into the safety margin. Add in a few fatigue cracks and you're into the failure range. To try to alleviate these uncertainties, Lockheed specified certain size and distance limits between sequential holes. I dunno if De Havilland had similar engineering guidelines.

[@heckelphon]

What a great video, which took me back to flying half way round the world on a commercial flight in a Comet 4B 60 years ago. The operating range was so short that the BOAC route from LHR to Singapore (not SIN back then, but Paya Lebar) hopped via Rome, Damascus, Baghdad (extra stop), Karachi, Kolkata and Rangoon, with a refuelling stop of 50 mins each time, so the whole flight left London at 13:15 GMT on day 1 and arrived in Singapore at 18:00 local time on day 2: a total of 36 hours 15m. But despite being cooped up for a lot of that time I don't recall it as other than very comfortable, and the fact that in those days you climbed down the steps, across the dusty tarmac and often into a transit lounge with one slow creaky ceiling fan stirring the flies about a bit just added to the charm of aviation. Oh, and in Karachi someone broke one of the fuel couplings when disconnecting the hose, so we had to wait in Kolkata for a replacement part to be flown in, and be an audience for the stirred-up flies in the lounge for a further 3 hours. It all added to the sense of adventure!

[@JohnJones-cp4wh]

I commenced my working days as an apprentice with De Havilland. 1953. So was directly connected to what happened and it`s affect on the workers, After the accidents there was simply no money spent on what might be called frivolous things, such as a works magazine, remember that the company had numerous divisions spread over the country, divisions such as engines, propellers, establishments producing wings, fuselage, tailplane and all the component parts with their attendent machine shops. Then all this had to come together in the final assembly workshops. One thing that did surface was the DHs553 works specification that referred to the finishing of cut edges, they were now all to be polished. Holes that were either drilled or punched were now to be drilled and reamed, this by a special combined drill reamer, still have some in my toolbox. Unfortunately the company never recovered from that and was absorbed into the Hawker Siddley group in 1960. The , I think. only part that exists today is the plant at Broughton in Cheshire that manufactures the wings for Airbus.

[@Low760]

So you're 86~? Wow! Did you go anywhere else in the aircraft industry after them? Involved in the concorde?

[@JohnJones-cp4wh]

@@Low760 88, went to a small sub contractor involver with Vickers, VC10 and also TSR2.

[@lithh5683]

Love the idea of the new series! Looking forward to see more!

[@JohnDrewVoice]

When I was an American teenager living in England, I got to fly on both the De Havilland Comet 4 and the Sud Caravelle. Of course, the Boeing 707 very quickly overtook the Comet in worldwide sales, including sales to BOAC. In fact, I'd initially flown to England on a BOAC Boeing 707. The Caravelle was thrilling to ride. Upon rotation, the Caravelle ascended at an angle steeper than anything I'd previously experienced.

[@LemonLadyRecords]

Huh. I remember the Caravelle *descending* suddenly at a frightening angle lol, but they also banged and yelled me out of the head and threw me in a rear seat, so I think some larger issue, like an evasive maneuver or too late descent. I couldn't speak French, so never found out, alas. Scared me good, though!

[@anniechrisbendy6000]

Cash briefcases / corruption beyond belief often was the boeing/ douglas/ lockheed biggest asset...in the 60,s 70,s Fully supported by jfk, nixon,ford,carter etc

[@bmc9504]

As a Brit whom flew on them all, I was quite excited for the 707 but was greatly disappointed as I always seemed to get very dry and hot and bothered on the 707 and DC8. I got upset when they retired the VC10. Later I fell in love with the 747 and after that the 767 due to its layout, only 2 seats by the window! Prior to jets the Viscount was the most amazing thing, you looked more forward to the flight than the holiday.

[@bmc9504]

Also I've taken off at London city on an RJ85, engines full and brakes too! Very scary as it was extremely steep and the plane only went slower as it got near to the skyscrapers

[@kueller917]

I love this series. You're fantastic at explaining the workings of aviation and older aircraft tend to have fewer good guides out there. Can't wait to see more.

[@stuarthall3874]

Fascinating story I would not have known if you hadn't created this video. Thank you! I clearly remember being taught as an undergraduate engineering student that the sharp corners in the windows were the source of the cracks. It's sobering to realize how incorrect facts can be promulgated through credible channels.

[@BogeyTheBear]

10:54 _"In theory..."_ indeed. The kicker is that, while the pods may be draggy, the overall wing can remain thin. Burying the engines within the wings makes the wing deeper and thicker, which is tremendously draggy. Another consideration addresses the very reason a four-engine podded layout placed the engines so far out on the wing-- to distribute the weight more evenly across the wingspan. Bear in mind that it is the wing and not the body which is lifting the entire structure into the air and concentrating all of the weight in the middle where the fuselage sits will cause the center of the wingspan to bend at that point. Spreading the weight out by slinging the engines farther along the wing reduces that bending force (this is one of the benefits in a flying wing design- little to no bending forces). The Comet, of course, clustered the engines close to the fuselage, requiring even more structural strength (thus weight) to resist bending.

[@jayykeyy]

I like how this channel is also Mentour 73YearsAgo!

[@Jack_The_Ripper_Here]

What

[@squ1dd13]

@@Jack_The_Ripper_Here They like how this channel is also Mentour 73YearsAgo!

[@kevinlock7108]

I remember flying in the Comet from London to Venice, operated by Dan Air. Such a wonderful aircraft. It felt like luxury at the time. Never forgotten. ❤

[@mandolinic]

Good old Dan Air. Flew on a few of their Comets to various holiday destinations in the 1970s.

[@selseyonetwenty4631]

@@mandolinic Or 'Dan Dare' as we used to call them 🤣

[@mandolinic]

@@selseyonetwenty4631 👍

[@lindabarrett5631]

Fascinating! I love these classics. The classics have helped us grow and learn, making our current aviation much safer. 😃

[@overvieweffect9034]

I'm really looking forward to this series, and I hope you cover the DC-10 in the future, as I believe there are a lot of misconceptions about it's safety issues too

[@phuketexplorer]

A combination of the wrong airframe material AND square windows, would be closer to the truth. It's much cheaper to produce square windows than round, so if they weren't an issue, we'd still be flying today in aircraft fitted with them.

[@Hybris51129]

I will admit I would love to see this series evolve into its ultimate form where you get some stick time behind some of these historical aircraft where possible and give a first hand account of how it feels to fly them. It's a unique path that I think you and your channel could potentially reach.

[@danharold3087]

Maybe start with Buffalo Air. They fly Douglas DC-3 Curtiss C-46 Commando Lockheed L-188 Electra

[@cjmillsnun]

@@danharold3087 and soon the Boeing 737!

[@danharold3087]

@@cjmillsnun I don't it will ever fly. Engines are about $2 million.

[@Alex462047]

It is a big undertaking. Even if you manage without getting a type rating, operating aircraft of this type and size is a terribly expensive proposition, especially since they are no longer in commercial use. There might be a way to do it, but it's not as simple as just jumping in and flying it.

[@deniermurch8693]

I flew in a Comet 4 many years ago on a charter flight of DAN Air. The other memory of that flight, was, It was the first time I was served a hot meal on a charter flight, steeak and kidney pudding, lovely. Normaly we would get sandwiches.The flight was to the Canary Islands. The best plane I have ever flown in, I loved it.

[@aimeedean1]

I've been waiting for this one!

[@MentourNow]

I hope you will like it!

[@WilhelmKarsten]

de Havilland admitted that they never preformed any stress calculations for the sections of fuselage that failed. British Airworthiness certification rules only required one section to be tested and d-H simply assumed that the other sections would perform the same... a shameful example of engineering incompetence and criminal negligence

[@johnmarshall6702]

Looking forward to you video on the Constellation. I flew from New Jersey to the Azores on a Constellation in 1971, and from there up to the UK. Given I'd flown many times on jets, I was surprised how quiet the Constellation was on the ground and how ungodly loud it was during takeoff and the rest of the flight. It was an old Air Force executive transport that had eventually ended up with the Pennsylvania National Guard, who still made a trip across the Atlantic and a tour of Europe every summer. Odd thing was I was traveling as an Air Force member, grabbing any ride across the pond I could, and they stuck me on that wonderful old plane. Others complained ( it was SLOW) but I loved every moment. Given there weren't many of us onboard, we could sit where we wished. I tried sitting in the seats that were inline with the props for a bit. That was torture, with the metal floor buzzing insanely and the noise, which included the continual drifting out of sync of the props before they were corrected. I heard after landing that the auto-sync (or whatever its called) on the engines was out of service, so the Engineer had to frequently tweak them by hand (ear?). Didn't notice the noise or vibration so much in the rest of the plane and the tail was pretty quiet. But there was a row or so of seats on all those piston planes that you did NOT want to sit in.

[@matthewwalker2100]

Thanks for emphasising the "lesson learnt" aspect (as often, the point). I flew (age 13) on Dan-Air Comet 4 flights in the seventies (Gatwick - Germany). Really well ventilated. Smokers didn't bother. There's a howling gale along the floor! Fine with me!

[@rainscratch]

Great coverage as usual, with excellent accompanying clips. Very stylish aircraft covered in this episode, the Constellation, B Stratoliner, B Stratocruiser and of course the subject of this video the Comet. I may be mistaken. but one of the problems I recall reading about with the Comet was the tail. It basically was a similar design and size to predecessors like the Electra. This did not translate well to a high speed, high altitude jet airliner. And there's something unnerving about a jet airliner with its engines embedded and hidden away in the wings. However major advancement in understanding metal fatigue, skin and join technology improvements and much more was gained from the unfortunate Comet disasters. Britain with the Comet together with the Concorde was often at the leading edge of technological advances, but unfortunately was not to be a world leader in the commercial side of aircraft sales.

[@anthonyvallillo422]

Indeed, both the original Comet and the Concorde were way too small to be commercially successful except as limited luxury transport for the very elite. American manufacturers tended to design to the actual needs of commercial airlines of the day, and this, as much as the engineering, led to their success.

[@fafner1]

The tail of the Comet is notable for not being swept. The tail is smaller than the wing and has a lower lift loading so the drag penalty is small. Still, modern designs generally use tails swept at the same angle as the wings.

[@johnrussell5245]

I flew in a Dan Air Comet in 1976. Inside the most notable feature was the structural partitions which divided up the interior, each with a restricted height opening you had to step over to reach the next interior compartment.

[@michaelh8890]

Hi Petter, thanks for another fine video, and the beginning of a new series. I just wanted to point out a few small errors. First ( I'm sure you know) you mentioned the Lockheed Constellation and pointed to your new merch shirt, which displayed a Comet : ) Second, the B707 entered commercial service in 1958, not 1955 as you noted. The KC135 entered service a bit earlier, in 1957. Thanks for all the great videos. As a former flight test engineer & NTSB investigator, I thoroughly enjoy you work, and can honestly say yours are the best and most definitive videos on the internet.

[@terryluckhurst4114]

The design and testing issue was that fracture mechanics related to cyclic loading and structural fatigue was not all encompassing to say the least. deHaviland did carry out 18,000 repeated loadings on a test airframe (static loading) that "removed any doubt about the fatigue life of the cabin". That's all very fine if the cabin was constructed to the highest levels of integrity. But the cabin (fuselage) was constructed by overlapping sections of plates mostly of thin (22 SWG) by rivetting not reduxed bonding. Any holes drilled and cut countersunk (as they were) for rivetting removes thickness that resists air loading (force/area) and should have at least been dimpled. The original source of the cabin failure was the forward escape hatch (window) forward lower and aft corners where stress raisers on cut countersunk rivet holes (caused burrs by a blunt rose bit) cracking forward to frame 13a and aft to frame 16. The window remained in place but the frame sprung outwards from the bottom two corners. It was concluded that DH did not make use of calculations in an attempt to arrive at a close estimate of stress distribution near the corners of the cabin windows. They used a sample of the fuselage 24-26 ft long by 3 ft wide from which they projected a life of 10,000 pressurised flights. The sample was not holistically represented as it was supported by a stiff bulkhed where many other fuselage panels were not. But what they did or could not legislate for was standard of workmanship and that cut countersinking 22 SWG reduced the skin thickness substantially and the resulting burr stress raiser reduced the safe life by over a half. My background was in establishing the first Def Stan 05-123 Repair Design Office capability in the RAF and was the fixed wing critical repairs liaison engineering officer for all three services working with design authority repair design and stressing departments.

[@phonicwheel933]

Wow Terry that is deep stuff. The Comet debacle must have horrified you.

[@billrivers3839]

In my admittedly dim recollections of Aerospace Structures courses in my college career, the ADF windows were never specifically mentioned. It was just « windows » (and rivets!). A fantastic video, especially for citing the UK crash investigation report, which made clear that the ADF windows were one of the culprits.

[@TheCoffeehound]

That same omission made it into my intro to engineering textbook back in the early 2000s.

[@super_slav91]

The most beautiful commercial plane ever in my eyes. Along with the tu-104, love me some wing mounted engines. VC10/IL-62 close second.

[@cathyburkart9395]

Thank you. History is important on many levels.

[@NicolaW72]

Yes, indeed.

[@bilalhijjawi8860]

This is great! Shedding light on the challenges aviators faced and resolved throughout history makes one appreciate today's aviation technology that much more. Thanks again for sharing with us your unique views and knowledge. Adding, my uncle piloted the de Havilland Comet, Boeing's 707s and 747s before retiring in the UK.

[@mikepowell2776]

Thank you for producing a fair and accurately researched biography of a great but misunderstood aircraft. My late father was an instructor with BOAC on the original Comet 1 fleet. Later he served as Chief Instructor with East African Airways which had a fleet of three Comet 4s ( later augmented with additional aircraft.) I had the privilege of flying as a passenger in each of the three original purchases including several flight deck hours and even a couple of landings. Next to the DC3 (which Eastaf also operated on domestic services) it remains my favourite aircraft - a far cry from the samey Airbuses and Boeings filling today’s fleets. This must be the ‘go to’ video on the subject. Thanks again.

[@StevePemberton2]

I wonder why they kept the Comet name for the new variant. It seemed to add an unnecessary stigma to the newer plane. Perhaps Comet 4 would have sold better with a different name? I guess no way to know now. And it creates confusion in discussions because most people don't understand the differences between the Comet 1 and Comet 4. Whereas few if any people have concerns about the Nimrod, the average person will hear Comet 4 and not realize that it is different than the version that had the accidents. Actually I think the Comet 1 could have continued as the problems were solvable, but it needed an upgrade anyway just as the early 707 really needed the upgrades that were in the 707-300.

[@2000globetrotter]

Great video but there is one MAJOR piece of the story missing. At the start of the design process, the comet chief engineer, R.E, Bishop, insisted that the finished aircraft must be fitted with De Havillands own Ghost engine but, during the design process, it became apparent that the aircraft would be way too heavy for the power output of the Ghost. Many of De Havillands engineers raised these concerns and suggested that the engines should be the upcoming Rolls Royce Avon, which was way more powerful. However, Bishop would not hear of it and insisted that the airframe needed to be lightened instead. After having tried many different unsuccessful approaches, he then instructed the design team to make the aircraft's skin thinner, so thin, in fact, (0.4mm) that pilots of early production Comets commented on the strange ripples in the skin after a flight (due to the pressurisation and de-pressurisation cycle). Bishop and De havilland dismissed the pilots concerns and carried on regardless, with inevitable consequences. Bishop was never held responsible for this problem, despite it being entirely on his shoulders. He was warned by his own engineers but his arrogance never allowed him to admit that he was wrong.

[@phonicwheel933]

@ David Jackson Yes, this is a great video and what you posted is frightening. Just take a look at a piece of 0.4 mm aluminium: intuitively it seems insubstantial. Also, who authorised the use of punched rivets rather than drilled, and who authorised the omission of Redux bonding? Who designed the faulty aerial apertures? It seems that a cavalier attitude and a lack of quality control sadly wrecked the prospects of this beautiful and potentially world-beating aircraft, not to mention the loss of life in the inevitable accidents. The negative effect on the reputation of the whole UK aviation industry was also considerable.

[@phonicwheel933]

Update 2July2023 *_Hi David,_* did you mean to say 0.04" rather than 0.40mm? Most sources state that the Comet 1 skin was 22 SWG (0.711 mm) at the top and 20 SWG (0.911mm) at the sides. That is still fairly thin, but not crazy thin. By comparison the Boing 707 skin is 1.62 mm thick. The skin material was D.T.D.546B (AL-P2014A) which is strong and hard, but subject to cracking. It seems that the thin skin, material type, and punch riveting was a receipt for trouble.

[@shorttimer874]

Dad flew with the B29s in the South Pacific as a supernumerary Combat Camera operator (think newsreel rather than recon). He described crawling through the pressurized tunnel crossing over the top of the bomb bays connecting the front cabin to the rear one. He also mention the crew tradition that the person who used the latrine first had to empty and clean it after the 10+ hour flight, leading to a contest to see who had the worst bladder. Also it has been a few years since I have seen them, my sister has his photos now, but he brought back some pictures of the various planes' nose art, one of them was Bockscar shown in the clip and though it is black and white from what I remember it looked different.

[@20chocsaday]

I made up a small model of a B-29. The tunnel and pressurisation is what I remember most about it.

[@daigriffiths399]

I've seen Bockscar at Wright-Patterson AFB. I took a very long moment to acknowledge the mission it flew; everyone remembers Enola Gay but few know the name Bockscar.

[@AadidevSooknananNXS]

Yes, love this series!! Looking forward to more! Looking forward to your (potential) coverage of the 377 Stratocruiser and the Airbus A300

[@ricardobecker7028]

Hello Peter, Welcome back! - Comet 4 had retired after 4 planes were lost when I was around 10 years old. I remember the news on TV, since Aerolineas Argentinas ( my place of birth ) had recently purchased some. - Now, I agree that the "metal fatigue" had several causes, lining up to create a perfect combination to crack the fuselage. - By watching your video I learned that the aluminium used in the construction was somewhat thinner? to fly somewhat higher? Engines almost together exerting centrifugal forces over the joint area of the fuselage and wing. - Once again, the first thing it comes to mind as a Failure Analysis Engineer and Reliability and Maintainability Engineer, are the following considerations. Vibrations, do exists from the nacelles of the engines to its own surroundings. - Given the rotary natural configuration of the jet engines, one has to imagine a potential problem which is two fold : When needed to take a turn, or slow down an engine on , the vibration potentially would put out a "...balanced act..." within the wing's body and surroundings. Now, when this is compared to the other side of the wing. with a one side the engines running at a higher speed than the opposite side, during maneuvers one side would vibrate louder, harder and stronger than the other, - beginning to cause the known "...material fatigue..." Or what is its defined "work outside of the "...Az... ( Admissible Zigma ) Definition of material fatigue: when a material loses its period of elasticity and can not recover to get back to its original position. - Now this does not necessarily needs to to be evident suddenly, - In most cases, it is a sub-milimetric plastic deformation at the material bonding structure, (molecular level) which begins to rupture and cut through one little tiny bit at the time, with every unbalanced maneuver that the plane takes. - Plus with each one of this events taking root, the controls, by default would start to behave different than intended, thus the over maneuvers from pilots to correct the position out of time and or sequence. Definition of Admissible Zigma : It is the zone on which a material it is subject to active work loads, and can expand and contract normally. - Another portion of this Admissible Zigma is the prior of restriction, ( Zr ) which is the point of actual fatigue because the material can no longer restore its original position, and it is the most resistant moment prior to a potential crack rupture, and if is a crack already existing, it would continue its cutting through metal effect faster than the recovery of elasticity of the surrounding metal frame. Add to this the "...thinner aluminium..." at high altitude, and you have a recipe for disaster in waiting.. Off course the semi square angles from the windows did not help either, however due to the combination of the engine vibrations and the material fatigue, the crack will automatic look for the path of less resistant on the material. I hope you understand me. - it is a bit technical.

[@keyesnm]

i am not an aviation enthusiast. BUT i LOVE your story telling and enthusiasm. you are a great storyteller

[@phonicwheel933]

The Vickers Viscount turboprop was developed at the same time as the de Havilland Comet. It became one of the UK's most successful passenger aircraft, with 445 sales worldwide, including the US. The Viscount was solid and reliable and liked by airlines and passengers, but it didn't have the sex appeal of the Comet and looked similar to piston aircraft of that era. The Viscount 700 and Comet 1 were the first types to enter scheduled service. Both aircraft were pressurized and carried 40 passengers, with a payload of 12,000lb, and their ranges were similar at 1,400mi. The Viscount had 4 wing mounted Rolls Royce Dart 510 turbo prop engines, and the Comet had 4 Halford Ghost jet engines, embedded in the wing roots. The Viscount cruised at 300mph at 20,000ft, against 460mph at 40,000ft for the Comet. This meant that the 900 mile London to Rome flight took 3hrs in the Viscount, while the Comet did it in 2hrs. With the cabins normalised to 8,000ft, the pressure differential would be 4.2psi for the Viscount, versus 8.2psi for the Comet. Comet 1's fuselage did have to withstand nearly twice the differential pressure of the Viscount 700 and 53% higher cruising speed but, on the other hand, the Comet was 84% heavier than the Viscount at 70,000lb versus 38,000lb, so it should have been a lot stronger. In principal, the design, proving, and production exercise would be similar for both aircraft. So what I can't understand is, if Vickers could produce a reliable pressurised passenger aircraft, why couldn't de Havilland.

[@GregWampler-xm8hv]

Very good point, had never occurred to me. I enjoy your use of actual facts, so refreshing. 😎

[@Low760]

30,000ft vs 40,000ft is huge as is 160mph more.

[@SueBobChicVid]

I was skeptical of the need for ANOTHER historical aircraft video, but Petter (and his crew) made this better than usual. The history and comparison with other aircraft added a lot to the mix. And... where on Earth did you find the video of the guy pumping up the balloon? Creepy and funny.

[@MentourNow]

Hahaha! I will ask Alejandra, my editor 😂

[@rainscratch]

How about HM QEII looked like she was cleaning the window!

[@cieludbjrg4706]

Interesting video! Amazing what you manage to cram into a 13 minutes-or-so slot! From what I’ve read, it was the square windows that were at fault. But nowhere have I read that t was the «radio windows» that were the culprit! You din’t (have time) to mention that a whole aircraft had a water tank built around it, and then the cabin was pressurised and depressurized a lot (like when flying) to see where the cracks developed. We got a brief glimpse of it towards the end. What I didn’t know was that the military version flew until quite recently! Excellent video, looking forward to the one about «Connie»!😄

[@awuma]

@@cieludbjrg4706 The Nimrod was not the only Comet variant to see long military service.

[@Grant-is2ge]

I love the videos on historical aircraft.

[@coreys2686]

Don't forget the Avro C102 Jetliner, built in Canada and flown in 1949, 13 days after the Comet.

[@bmc9504]

Beautiful aircraft, 2 engines I believe? God save the king.

[@coreys2686]

@@bmc9504 four engines, two per side, slung under the wing. Placement is similar to the 737, but no pylon. Mains retract into the nacelles too, very WWII.

[@eucliduschaumeau8813]

They only made one Avro C102 and Howard Hughes offered to build it under license, but the project was scrapped before the second one was finished. Even with four engines it only had a maximum speed of 417 MPH and a cruise speed of 376 MPH.

[@t5ruxlee210]

The Jetliner was mostly a hand built basic engineering testbed. The start of the Korean War crippled any chance it might have had going forward because it had no priority at all when it came to obtaining cutting edge aviation aluminum alloy sheets, etc., from US makers. Only the Avro CF-100 RCAF interceptor production facility and the Canadair RCAF Sabre jet assembly program were eligible to receive such scarce, vital, defense related materials in 1950s wartime.

[@yamilgacel6319]

I had the pleasure of flying as a passenger on a Olympic Airways Comet 4B from Athens to Beirut in 1968. I still have the postcard of a Comet 4B that was in the seat packet on that flight. Nice memories!

[@ndmb6333]

6:14 6:14 6:14

[@DrRichardKirk]

Both my parents worked on the Comet. They had a model of it on their wedding cake. Another person was Nevil Shute, author of 'No Highway'. The aircraft that failed in that book was called the 'Reindeer': 'Comet' was one of Santa's reindeer. The Reindeer in the book failed from a high-frequency fatigue from fluttering modes in the wing. Fatigue was typically seen as being a failure the resulted after millions of stress cycles rather than the few hundred cycles from cabin pressurisation. But Neil Shute correctly captured the general feeling that the aircraft was novel in so many ways, and some unforeseen combination of things might bring it down.

[@riderramblings]

I flew on the Comet 4 as a passenger a number of times (at least 4 that I have logged). It was a stunningly beautiful looking aeroplane. The main problems from a passenger point of view were: Speed, comfort and cruising height. She was relatively slow when compared to the VC10 and Boeing 707 and stopped much more frequently. The seats were quite uncomfortable especially as a flight to the Far East could be over 30 hours of which about 18 hours was in the air. Finally cruising height was quite low (I seem to remember 32,000-36,000ft being the norm) regardless of the design criteria, you could find yourself in some quite bad turbulence. Because she was quite uncomfortable, we'd always go to the Transit lounge at each stop. I remember having to often wait at the top of the stairs when re-boarding while the baggage door inside the cabin was closed and secured. For reference, I flew on G-APDL twice and (I think the Registration was) G-APDF twice. A total of 29,524 statute miles logged

[@Roland8879]

My late father was a BOAC Captain, Constellation, Boeing Stratocruiser and Comet. I had many flights in the Comet on the flight deck, his cruise was Mach. 75 at 42,000 very comparable to the VC 10 and 707.

[@riderramblings]

@@Roland8879 I have checked my log and I didn't fly as a passenger with your father. Interesting note is that, according to my log, the Comet 4 would take, on average, 18 hours to do the trip whereas the VC10 15 hours and 707 16 hours. The fastest trip by Comet 4 was 17.35 hours. The fastest trip by VC10 was 14.10 hours

[@Roland8879]

The routing Comet vs the other two was entirely different. Sector lenghts checking Dad's log book varied from an hour to five hours with an average roughly 2 to 4. This was not what the 707 or VC10 would economically do, this would give you the increased time. He flew New York London early '59 in 7 hours much the same as the early PanAm 707's.

[@RB747domme]

Sorry, I don't wish to argue any points here, but I wanted to say that London to Singapore and a comet 4c only took 13 hours. This included a fuel stop in Eastern Europe. As for the cabin, it depends on the airline, and which model seats that they fitted. BOAC fitted really luxurious seating, which is comparable to business class today, and on top of that they had a white tablecloth and cutlery foodservice, with really good food. I don't know how or why you had an unusually uncomfortable trip, but as I say, the comet 4c flu faster than 510 mph meaning that it could fly to the far East in 12-13 hours on average, I'm certainly would fly around 40,000ft - and this I'm absolutely certain of, meaning that I think you might have got that memory a bit confused or incorrect if you don't mind me saying. There is no real reason for pilots to fly at a lower altitude on a long-haul journey, as that was the point. it would have cost them a fortune extra fuel, and would have made it much less efficient. As an example Comet 4c used across the Atlantic at 42,000 ft at 520 kn. This is only a tiny difference between what airlines fly at today.

[@well-blazeredman6187]

A beautiful plane. One of my first flights was on a Comet 4, headed south for some bucket & spade in the Med. Later, I flew a couple of ASW sorties in Nimrods - described by the crewman serving me my hot rations as 'The Mighty Little Chef'.

[@acefox1]

Great video! I live near the approach path of a US Air Force base where I still see lots of upgraded KC-135 tankers with serial numbers dating back to 1958 flying all the time.

[@mahbriggs]

McConnell Airforce Base? I live near there, and remember when it was a B-52 base, Titan Missile base, B-1 bomber base and then the B-2 bomber! They use to fly B- 47s from there as well, but that was before my time. Watching one of those slowly coming into land at the base while driving down Kellogg was quite the sight! I have been aboard a KC- 135 at an airbase open house. Amazing how small the cockpit is. The 707 is basically the same aircraft with a slightly larger diameter fuselage.

[@boronsniify]

Fascinating! Your point about the antenna “window” is one I have never heard before….

[@chriss2777]

This is awesome! I'm looking forward to this series.

[@nurrizadjatmiko21]

When i studied and watch a documentary about the Comet, i think it's a very cool aircraft since it was the world's first jet airliner and it can carry 42 passengers and crew. Yes, i remember there is 2 BOAC Comet disaster back in 1954 and the cause is similar and those 2 accidents has change passenger travel forever.

[@Sjanzo]

Two Comet crashes caused the demise of the company... How many 737 MAX crashes ? Quite ironic that the 707 was once demonstrated at an air show doing a full roll in order to show it was sturdier than the Comet..

[@luca7069]

TLDR: the whole "square windows" thing is a bit of an hoax. The big issue was simply that the airplane was way too pressurized and that the project in general lacked any sort of wiggle room for metal fatigue (on the whole structure, not just the square windows). If the Comet had round windows, it still would've suffered from explosive decompressions, because again, the problem was the way too high cabin pressure (for the design). Perhaps it would've happened later, but still...

[@hederoth7883]

Flew one in 1973. Probably the most beautiful airliner ever built.

[@msmirandagirl]

I flew on a BOAC De Havilland Comet 4 when I was a child. It was 1964 and my Mom and I flew from Rome to London. We got a free upgrade to First Class because Coach was full. Great memory.

[@lancethrustworthy]

You have spoiled me with the quality explanations and fine animation. You've become my favorite aviation expert. Bravo.

[@AndorMilesBoard]

Absolutely fascinating. Easy to see how Aerial Windows would confuse journalists at the time, especially as the pictures were unfortunately of a fragment of fuselage so the placement would not be clear.

[@danharold3087]

It is still happening. The narrative of the 737MAX as told by the press is far from correct. Now the media has to be PC too.

[@GeorgeVCohea-dw7ou]

It would most probably confuse generalist journalists of the twenty-first century as well. Fortunately, there are experts to quickly and hopefully fairly clarify faulty reporting for proper amendment these days.

[@matsv201]

The strange thing is that this myth circulate to this day, despite most airliners still have square front window. If it was a problem with the fuselage, and not the window, this would have effected the front windows as well. (the real reason aircraft windows are round is because round windows are lighter)

[@danharold3087]

@@matsv201 As indicated by the video there was no one problem.

[@awuma]

@@danharold3087 It's usually the "Swiss Cheese model"... all the holes (i.e. causal factors) lining up.

[@Rob2]

You already mentioned the Süd Aviation Caravelle, but it is very interesting to trace that company into the later projects of Concorde and Airbus. Also an important aircraft is the Hawker-Siddeley Trident, the pioneer of autoland.

[@awuma]

The Lockheed L-1011 was also a pioneer in automated landing IIRC.

[@sjmachrihanish]

A second-hand Boeing 247D, a gift from Canada to the Uk during the war, was the original auto land pioneer. The research culminated in January 1945 - the world's first automatic orbit, approach and blind landing.

[@awuma]

Excellent video! Minor Correction: 19:50 The Comet 4 and Boeing 707 entered service in 1958, not 1954. The Comet 2 also had a long and successful career in the RAF, while ex-airline Comet 4C's were also used as transport and VIP carriers for many years. There is one Comet 4 left which could potentially be brought back to airworthy status, but British business and government are loathe to support old "complex" aircraft. The Comet in its variants was a genuinely beautiful jetliner. I was really impressed by your definitive debunking of the "square window" myth, especially when you compared it with that of the Boeing 707 airliner (not the prototype with a few funny little ovals).

[@briandbird6339]

I was tutored by Alexander "Sandy" Jack in the early 70's when studying for ARB (as it was then) certification. Sandy was an aviation pioneer, veteran of the Paris air service and involved peripherally in the Comet inquiry. He strongly believed that the aircraft was periodically over pressurised due to a design flaw and icing of the dump valves. A subsequent redesign, for other reasons, cleared this problem. Sandy Jack was a serious aircraft man so I always remembered his view and am inclined to believe it.

[@joshuaknight1748]

We studied this at uni. Hate how everyone assumed it’s the windows. The 707 windows were only slightly more radiused.

[@sandervanderkammen9230]

Actually, aircraft in production today have the same radius.

[@LtNduati]

Can we take a moment to appreciate how involved in aviation Petter has been? Like he was an airplane firefighter, baggage handler, had to have been a first officer, captain, line captain/training captain, youtube pilot, I think a co-founder in an flight school, and his wife was a flight attendant. He genuinely loves aviation, lives aviation and cares about educating everyone and anyone interested in listening about all aspects of aviation - what a man, and what a person - I hope I get to fly on one of his planes someday.

[@barbaradavis393]

I always understood that the issue was the window shape. Thanks for explaining it so clearly. Seeing those rivet holes sure tells a different story. Have you read Nevil Shute's "No Highway"? He was a British engineer and author. The story concerns a new airliner that has a couple mysterious crashes. A research engineer at a government facility blames them on metal fatigue.

[@michaelplunkett8059]

They made it into a 1951 movie with Jimmy Stewart, Glenn's John's and Marlene Dietrich. Guess nobody at Dehaviland saw it.

[@turricanedtc3764]

@@michaelplunkett8059 - I'm sure at least some of them did, but the problem as specified in the book and movie didn't really relate to what happened in reality with the Comet 1...

[@carlramirez6339]

0:04 What do I think about when I hear the name "de Havilland Comet"? I think it's a great way for me to ensure a life insurance payout for my family.

[@matthewsjardine]

I am so glad you are making this series. I look forward to learning more about the classics.

[@patrickradcliffe3837]

18:30 gonna jump in here as a retired airframes mechanic. The skin and the structure of the 707 is MUCH different then the Comet. There sections of the skin that are thicker then the rest to stop propogation of cracks around the windows frames and other openings through the fuselage

[@rolandbogush2594]

Well done - I thought that it wouldn't be possible to cover all the nuances of this complex story in such a short time but not only did you include all the main points, you did it with great clarity and in an easy to understand manner that doesn't duplicate the many other videos on the Comet story that have been produced over the decades. Really good job! The Comet 4 that inaugurated the first trans-Atlantic passenger jet service (shortly ahead of the Boeing 707) can today be seen in the Imperial War Museum in Duxford, England - well worth a visit!

[@TIMMEH19991]

Without doubt the best looking passenger aircraft ever, closely followed by the VC10. I can just remember seeing Comets flying as a kid, and I was lucky enough to fly on a VC10 a couple of times. Now they were amazing planes. I hope you do a video about them!

[@edwardmccall1032]

I also loved the Lockheed L-1011 Tristar with the one engine in the tail and the two pods.

[@NicolaW72]

The De Havilland Comet is indeed a Classic, a very important step in Aviation History - but unfortunately she will forever stay in the Shadow of her Crashes and her Grounding. She was therefore also a monumental failure, too. Thank you very much for leading us into this Chapter of Aviation History!😃💛👍

[@QuicknStraight]

Was it, though? The Comet 4s stayed in passenger service until 1980, fully 26 years are the initial flights of the Comet 1.

[@NicolaW72]

@@QuicknStraight Yes, it was. There´s no history, even no naming of this Aircraft model without that sad story and she became therefore a monumental economic failure, too.

[@QuicknStraight]

@@NicolaW72 I disagree. Once they had sorted out the initial issues, it was a superb aircraft, only it's early reputation causing it to fail economically.

[@NicolaW72]

@@QuicknStraight Yes, exactly - that´s my point.

[@BeechHouse]

Very informative. Thank you! I am a newly-graduated Docent for the Seattle Museum of Flight and this information is really good to know. We have a DH-C still in the restoration facility that we hope to bring into the museum shortly.

[@ernstoud]

It is easy to criticize past technologies, so this was a very nice balanced view. Thanks!

[@heidirabenau511]

To answer your question at the start, no, I think of how the De Havilland Comet pioneered aviation forever.

[@harveyh3696]

Looking forward to the new series. DC-3. 'Nuff said. Still flying.

[@awuma]

The fact that updated turbo-prop conversions, such as the Basler BT-67, fill a very useful niche today points to the astonishing excellence of the DC-3 design. Of course, not being pressurised gives an aircraft the possibility of almost unlimited life span if properly designed and built. They got it right with the DC-3. Funny how "DC-3 replacements " have come and gone, while the DC-3 keeps on doing its thing.

[@harveyh3696]

@@awuma Wondering how long the B-52 will actually be flying.

[@Petriefied0246]

It would be interesting to see how the last version of the Nimrod would have affected potential later versions of the Comet.

[@FutureSystem738]

Awesome video thanks Petter, I thought I knew everything about the Comet but still learnt a bit more. Big 👍👍

[@camptube7621]

Went to see the comet at Duxford. Beautiful plane that cut an amazing shape. Those engines built into the wings were just class. Thanks for featuring this engineering pioneer. Breaks my heart what happened. Also saw the prototype Concorde there too! If any of you enthusiasts get a chance to visit RAF Duxford Museum in the U.K., please do. You will love it.

[@DoktorBayerischeMotorenWerke]

The de Havilland Comet Disaster remains the worst engineering failure in the history of commercial jet aviation. de Havilland admitted that they never performed the necessary stress calculations for the fuselage sections that failed, CEA regulations only required one section of fuselage to be tested, d-H estimated the stress based on faulty test data. D-H was still building aircraft made primarily from molded plywood and linen fabric... they simply had no experience building large all metal aircraft or riveted aluminum alloys.

[@Dad_Lyon]

Those rivets around the cutouts induced cracks even before stress induced fatigue, leading to today's Damage Tolerance assessments. It's a classic and has genuinely saved countless lives from the diligence of the investigations.

[@davidpowell3347]

My understanding is that the engineers specified that the holes for the rivets would have been made by a more elaborate process such as drilling or even by heat/melting but that in construction the rivets simply got punched through.

[@Dad_Lyon]

@@davidpowell3347 That's brutal when doing a D&DT assessment. Wouldn't surprise me though. Edit: Should have been caught in MRB/liaison activity.

[@turricanedtc3764]

@@Dad_Lyon - Alas, such processes did not exist then. I think D.P. Davies (in "Handling The Big Jets") alludes to a tendency within British aircraft manufacturers at the time of the Comet 1 to have the design engineering team and production engineering team operate in a manner which we would call "silos" today - in other words, there wasn't as much communication between those teams as there should have been. He also alludes to a tendency in the UK in which engineers deferred a little too much to to the senior designers and credits Boeing for having a more open approach when he made his early visits. That said, Boeing's Dash-80 prototype first flew in 1954 - the same year the Comet 1 was permanently grounded. Neither the B707 nor the Comet 4 entered service until 1958, which strongly suggests that it took both design and production engineering teams on both sides of the Atlantic four more years to work through the engineering problems to the extent that they were satisfied the end product was safe for commercial passenger service.

[@WilhelmKarsten]

*The Comet was the worst engineering failure in commercial aviation history.*

[@Jelmerize]

They we’re simply unknowing… This plane was the fuse that lit the jet-era. Things wouldn’t be so safe this day if it wasn’t for this aircraft.

[@WilhelmKarsten]

@@Jelmerize *This plane was the **_bomb_** that destroyed the British aircraft industry...* *Not true, the facts are irrefutable, the Comet Disaster could have been easily prevented if de Haviland had simply followed well-known and understood industry standards for the design and construction of pressurized cabins made from riveted aluminum alloys.* *de Havilland was decades behind in aircraft technology and was still building aircraft primarily from wood and linen fabric.* *The only thing that was learned from the Comet Disaster was that aircraft manufacturers could no longer be trusted to conduct their own crash investigations, de Havillands behavior and attempts to cover-up or hide its incompetence and criminal negligence was simply reprehensible.* *The real tragedy of the Comet Disaster was that hundreds of innocent people died unnecessarily because de Havilland did not want to admit that it never preformed the stress calculations for the sections of fuselage that failed.* *A truly shameful and humiliating chapter in British aviation that has led to the total collapse of the British aircraft industry.*

[@PsRohrbaugh]

My grandfather was a military pilot. On rare occasions, they would be repositioned on civilian aircraft. They wore their flight suits, which included a parachute. Anyway, apparently my grandfather wearing his parachute when getting on board a Comet caused a bit of a stir...

[@phonicwheel933]

😊