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The de Havilland Comet changed aviation for good
- mirimir 10y agoIt's indeed a beautiful aeroplane. But what's striking, and indeed rather UFO-like, are the small engine intakes. Anyone know what's up with that?
- will_asouka 10y agoCompact turbojet engines rather than high-bypass turbofans like modern airliners. Blended into the wing for less drag compared to underslung wing pods like the contemporary rival 707.
- justinph 10y agoThey're turbojet engines, not the turbofans that you see today. Turbojets have a smaller intake and the entire thing produces thrust. Unlike today's much more efficient turbofans, where a small turbojet turns the larger fans to produce most of the thrust.
- mirimir 10y agoOK, I get it. Thanks :) They are very cool looking.
- int_19h 10y agoFWIW, other turbojet airliners had larger intakes. E.g Tu-104 (which, coincidentally, was propped by Comet's fall, becoming the only jet airliner in service for a couple of years): http://i.imgur.com/L4KLas2.jpg http://i.imgur.com/L4KLas2.jpg
- cstross 10y agoThe Nimrod maritime patrol aircraft was a modified Comet airframe: https://en.wikipedia.org/wiki/Hawker_Siddeley_Nimrod https://en.wikipedia.org/wiki/Hawker_Siddeley_Nimrod In the early 2000s, BAe Systems had a project in train to upgrade them to the MRA4 spec, essentially remanufacturing the existing MRA2/MRA3 Nimrods around a new wing structure that could accommodate RR BR700 turbofans, doubling the aircraft's range: https://en.wikipedia.org/wiki/BAE_Systems_Nimrod_MRA4 https://en.wikipedia.org/wiki/BAE_Systems_Nimrod_MRA4 (Go look at the photos on the respective wikipedia pages and examine the engine inlets at the wing roots: the MRA4's air intakes are much larger.) The MRA4 upgrade was at least as radical as the proposal to re-engine USAF B-52 bombers with four GE high-bypass turbofans (as seen in the photograph on the web page below, showing a B-52 flying with the new engine in the inboard starboard pod): http://aviationweek.com/defense/ge-rolls-pratt-vie-b-52-engine-upgrade http://aviationweek.com/defense/ge-rolls-pratt-vie-b-52-engi... ... Which also got cancelled; in the case of the B-52 the USAF had so many old engines in mothballs that re-engining the B-52 would cost more than just swapping out old units, and in the case of the Nimrod MRA4 the program ran into nightmarish cost-overruns when it became apparent that the aircraft they were trying to remanufacture were all different — the RAF's Nimrod fleet had been hand-built then patched for half a century and simply couldn't be consistently upgrades. (Moral of story: upgrading a 50+ year old design is harder than it looks.)
- mirimir 10y agoDoh, I never really noticed how small those B-52 engines are. It makes the plane so elegant and insectile.
- gaius 10y agoFollowing the cancellation, the Defence Secretary Liam Fox used the Nimrod MRA4 procurement as an example of the worst of MOD procurement performance Ah those innocent days, before the QE carriers and the F35 made that look like mere pocket change.
- rjsw 10y agoI thought the consensus was that the construction of the carriers had gone really well.
- gaius 10y agoThey were supposed to have finished their sea trials by now. Also they were supposed to be convertible to cats & traps at the drop of a hat, which would have allowed the UK to procure a non-BAe fighter to fly off them, couldn't have that...
- FabHK 10y agoThere's a course on edX, Introduction to Aeronautical Engineering, that explains quite nicely why engines have these huge intakes these days: https://www.youtube.com/watch?v=a2PBOdTk3vE https://www.youtube.com/watch?v=a2PBOdTk3vE https://courses.edx.org/courses/course-v1:DelftX+AE1110x+3T2016/info https://courses.edx.org/courses/course-v1:DelftX+AE1110x+3T2...
- barking 10y agoPeter Duffey first flew during WW2 https://www.buckinghamcovers.com/celebrities/view/127-captain-peter-duffey.php https://www.buckinghamcovers.com/celebrities/view/127-captai... he also wrote a book about his flying experiences https://www.amazon.co.uk/Comets-Concordes-Peter-Duffey/dp/1888962100 https://www.amazon.co.uk/Comets-Concordes-Peter-Duffey/dp/18...
- gaius 10y agoSuch a wasted opportunity. Around the same time, the UK was throwing away its leadership in computing too. Weirdly, both ended up in Seattle.
- douche 10y agoIt's hard to keep up when you've lost the better part of two generations in a row, and most of the stockpiled capital of a century of imperialism - especially when you also lose the empire that generated all that wealth.
- Aloha 10y agoI've often argued that the root cause for loss of empire, was the best and brightest of a generation was left on Flanders fields. The best and brightest of the ruling class at the time was simple used up as cannon fodder, its also the cause for the decline of the aristocracy too.
- pjc50 10y agoAnd this was why postwar Germany lost its scientific and technical advantage and is now a ruined backwater - wait, no. Germany not only lost technicians and an aristocracy in WW1 and 2 but murdered those of its Jewish population that were not able to escape. Survivors defected to the US like Von Braun. The loss of empire was after WW2 not WW1, and partly due to the US insisting (Suez) and partly because it became morally and economically impossible to subdue (Mau Mau etc.). The postwar British disease was labour relations, which were handled far better in Germany with worker representatives at board level. (I might argue far more cynically that the aristocracy was by definition not a meritocracy, and that only its violent destruction by war enabled Europe to have a chance at becoming more egalitarian.)
- dba7dba 10y agoI agree with your assessment, pjc50. All major European nations lost most of their privileged/gifted young men in WW1 and WW2, not just UK.
- mcguire 10y agoThe British Nimrod, a submarine hunter, as well as other roles, was based on the Comet and was in service until 2012. Modified Comets apparently flew until 1997.
- cdegroot 10y agoMy biggest "surprise" always is how little we have progressed if you just look at how the planes look and how fast they fly (6h11m NY->London in 1958, that's pretty much what they do today, not?). It seems like the airline industry got a lot of stuff just right the first time and since then just has been doing performance tweaks (where I take "performance" to be very broad to include things like safety, economy, ...).
- cromulent 10y agoIt's down to the laws of physics. They still fly at around 80% of the speed of sound, as that is close to the so-called "coffin corner". https://en.wikipedia.org/wiki/Coffin_corner_(aerodynamics) https://en.wikipedia.org/wiki/Coffin_corner_(aerodynamics)
- frenchman_in_ny 10y agoIt's unrelated to the coffin corner. Planes in the ~80s were flying NY<>London faster than today -- the fuel savings generated by flying slower are what is driving the decision.
- cromulent 10y agoYeah, you are absolutely right :)
- dom0 10y agoWell the Concorde was twice as fast (record: 2 hours and 52 minutes), but it's decommissioned now.
- ak217 10y agoIn 1958, the cost of a ticket was about 4x what it is today (adjusted for inflation but not earnings growth), flying was at least 20x less safe in terms of fatal crashes per departure, and consumed at least 4x more fuel per passenger-mile. Those are some impressive performance tweaks.
- rwmj 10y agoThere is a "square windows" Comet 1A in the http://www.dehavillandmuseum.co.uk/ http://www.dehavillandmuseum.co.uk/ , next to the northern stretch of the M25. Well worth a day out to this quiet little museum (home of the former De Havilland factory) if you live in or around London.
- Animats 10y agoIt's surprising the designers made that mistake. Square inside corners were a known problem in shipbuilding.[1] Welding Journal, 1945: "Another contributing failure to welded ship failures is faulty design and in this category the inclusion of square corners is by far the most common and most detrimental. Occasionally some form of square corner will slip by the designer and and draftsman ... Supervisors should call it to the attention to the drawing room and request it be changed. ... would go a long way to solving our welded ship problems." Early models of US Liberty ships had that problem, big-time.[2] One broke in half before it got out of the shipyard. About 20% of the fleet experienced a square-corner fracture. Those were rush-job ships, built quickly with square corners to save construction time. It was well known in naval architecture to avoid that. Portholes are usually round. [1] https://books.google.com/books?id=P1IfAQAAMAAJ&lpg=PA473&ots=SumDmFcwfB&pg=PA473#v=onepage https://books.google.com/books?id=P1IfAQAAMAAJ&lpg=PA473&ots... [2] https://metallurgyandmaterials.wordpress.com/2015/12/25/liberty-ship-failures/ https://metallurgyandmaterials.wordpress.com/2015/12/25/libe...
- notahacker 10y agoAs I understand it, the problematic corners of the Liberty ship doors were literally square, actual right angles often close to a metal seam. The Comet's were rounded off, just not enough to cope with the stress of the speed and pressure differentials it was subjected to. I'm under the impression (but not certain) the rationale behind portholes being circular is/was more to do with concerns about the fragility of the glass than the surrounding metal.
- hydrogen18 10y agoDoes the BBC not even get the history of Britain correct? The aircraft never exploded. It just broke up in mid flight.
- phillc73 10y agoWhen I read the headline, I was really hoping this article was about the de Havilland DH.88 Comet.[1] That really was a beautiful aeroplane. [1] https://en.wikipedia.org/wiki/De_Havilland_DH.88 https://en.wikipedia.org/wiki/De_Havilland_DH.88
- aphextron 10y agoNot sure why the downvotes. I thought this as well. The DH.88 absolutely changed aviation in it's own way. The first fully monocoque, aluminum skinned, twin engine, variable pitch prop aircraft ever produced. We are still making aircraft with this same basic design to this day.
- phillc73 10y agoMany of the design elements from the DH.88 can also be found in the DH.98 Mosquito,[1] probably the most successful multi-role aeroplane of WWII. [1] https://en.wikipedia.org/wiki/De_Havilland_Mosquito https://en.wikipedia.org/wiki/De_Havilland_Mosquito
- WalterBright 10y agoThe other problem the Comet had was economic. It could only carry 36 passengers. The 707 could carry 140. The larger number of passengers meant the 707 per-passenger cost made it cheaper to operate. The 707 could do 5 times the work of a piston powered DC-6 at only double the cost. It was a huge money-maker for airlines. http://generalatomic.com/jetmakers/chapter7.html http://generalatomic.com/jetmakers/chapter7.html
- WalterBright 10y agoThe corner of a square hole in a flat plate has 4x the stress of the surrounding material. It's called a "stress riser". If you look at a concrete slab with such an inside corner, there's usually a crack there. Boeing solved the problem by using rounded windows, and riveting on a forged doubler around the window frame. The skin was also organized so a crack will not propagate far. The success of the latter has shown itself in various incidents where an airliner has lost a panel in flight, but went on to land safely.
- JshWright 10y agoReal Engineering has a nice explainer on this topic: https://youtu.be/7rXGRPMD-GQ https://youtu.be/7rXGRPMD-GQ
- dingaling 10y ago> Boeing solved the problem by using rounded windows, and riveting on a forged doubler around the window frame. Boeing was by no means the first to use radiused windows in pressurised airliners; the Avro Tudor was doing so in 1946 and there may well have been earlier examples. Conversely the Boeing Stratoliner was flying with square windows in the early 1940s and didn't suffer fatigue failures, nor did the later DC-6. Corner stresses were understood at the time. What really undid the Comet was that the fuselage skin gauge was insufficient to accommodate the increased rate of change of pressure differential that was introduced with jet flight. Whereas the preceding piston-engined airliners were lucky to hit 1000 feet per minute climbing to 20,000 ft, the Comet climbed at three times that rate to 35,000 ft +. The Comet had skin reinforced to 20 swg along the window belt, whereas the succeeding Comet IV had 18 swg with 16 swg framing.
- WalterBright 10y agoFatigue failure was poorly understood at the time. It still is incompletely understood, but much better models have been constructed to predict it. Fatigue damage goes up as the cube of the load, and the Comet was pressurized at 35,000 feet rather than 20,000 for the Stratoliner, meaning much more load.
- tajen 10y agoI like the De Havilland story in how it made the managers look like fools: 2 crashes in bad weather, +1 in good weather, a worldwide suspension of operations, resumed a fortnight later with reassuring words from the management, +1 another crash, then a more serious stress test (which should have been done since the beginning), with negative results, then a bankruptcy... Fortunately, that's what happens to the wrong companies. Another aircraft story I love is the Tu-144, the copy of the Concorde: "Critical alarms were so routine that pilots had to borrow pillows from passengers to stuff the cockpit siren". The full Wikipedia article is worth reading (or the Mayday episode worth watching), it's a good laugh. Each time I fly, I internally laugh at how crazy humans are, throwing a can of the most inflammable liquid we can find, at 900km/h. "Play with fire, mum says, ..." and play with fire we do.
- TheSpiceIsLife 10y agoCould be worse, at least jet fuel isn't hydrazine. It is possible to extinguish a small fire with jet fuel. Don't try this at home.
- jacquesm 10y agoF16's carry hydrazine as emergency fuel to maintain control in case of loss of power.