Comet 1 fatigue problems

[A30yoyo]

Were cracks emanating from the ADF aperture in the Comet 1 forward roof the common cause in all the fatigue related crashes. Did the Farnborough tank specimen fail there too ,or at a different 'cut-out'. How significant was the change from rectangular windows with slightly radiused corners to fully rounded windows ? Is it correct that the RCAF Comet 1s were satisfactorily modified and how?

[Blacksheep]

No, the ADF cut-out was not common to all failures. The tank specimen ruptured from the corners of the forward escape hatch cut-out.

http://www.tech.plym.ac.uk/sme/interactive_resources/tutorials/FailureCases/images/CM7ALYU3.jpg

http://www.tech.plym.ac.uk/sme/interactive_resources/tutorials/FailureCases/images/CM8ALYU2.jpg

[WHBM]

Is it correct that the RCAF Comet 1s were satisfactorily modified and how?
Yes, the two RCAF aircraft, which had been delivered some 12 months before the grounding, were modified to Comet 1XB standard. They lasted in RCAF service until the end of 1964. One went on to a US dealer and got a US registration N373S, being finally scrapped at Miami in the mid 1970s.

http://www.abpic.co.uk/photo/1388321/

The three Air France Comet 1s were returned to the UK, two were rebuilt and served for various non-airline trials purposes. One was being flown by Hawker Siddeley, De Havilland's successors, until 1978, and is the one now in COSford museum in faux BOAC colours, which it never carried in service.

This webpage says a bit about the rework that was done

http://www.rafmuseum.org.uk/research/archive-exhibitions/comet-the-worlds-first-jet-airliner/last-comet-1.aspx

[oftenflylo]

r u sure about that

[Planemike]

The one in Duxford is a genuine BOAC Comet 4 (via Dan Air). Think you may be thinking about G-APAS which is in RAF Museum Cosford.

Planemike

[WHBM]

You're right, of course. Wrong ---ford. Silly me.

[4Greens]

Check out Neville Shutes book 'No highway'. Its is eerily connected.

[A30yoyo]

Well here's another slightly unlikely websource on the Comet 1 fatigue problems...seems to know something about it.
http://www.visit-gloucestershire.co.uk/boards/topic/62-de-havilland-106-comet/

[Tinwacker]

Neville Shutes book 'No highway'

Great read for a youngster.......mmmm

Good radii, holes correctly de-burred, rivet edge margins and improved riveting just to mention a few

TW

[Wander00]

Neville Shute (Norway) was a distinguished aircraft and airship engineer and designer. "No Highway" was very prescient, and I still recall the film although I was quite young when I persuaded my Dad to take me to see it.

[mrloop]

In case you haven't already found it, the report of the tank test will be of interest: http://naca.central.cranfield.ac.uk/reports/arc/rm/3248.pdf

[evansb]

This cutaway from Popular Mechanics magazine, circa 1950, was sadly prophetic:
http://i141.photobucket.com/albums/r68/convair640/Comet-Cutaway-1950_zps2b251a21.jpg

[chevvron]

There was a complete Comet 1 fuselage at Farnborough up until the early '80s. Part of the mothballing had peeled away revealing Air France markings. Can't remember if it had square or round windows. I'm not sure what happened to it but last time I saw it was near the airfield fire service practice ground.(not the present one, this one was on the north side in what is now Qinetiq), previously it had been in 'the dump' on the north side and prior to that near the test tank on the south side.

[WHBM]

There was a complete Comet 1 fuselage at Farnborough up until the early '80s. Part of the mothballing had peeled away revealing Air France markings. Can't remember if it had square or round windows. I'm not sure what happened to it but last time I saw it was near the airfield fire service practice ground.(not the present one, this one was on the north side in what is now Qinetiq), previously it had been in 'the dump' on the north side and prior to that near the test tank on the south side.
This was the third of the Air France fleet of the 1950s, as described above two were rebuilt and flew again but one, F-BGNX, was left derelict at Farnborough. It was eventually given to the De Havilland museum at London Colney. Here it is there about 15 years ago

Photos: De Havilland DH-106 Comet 1A Aircraft Pictures | Airliners.net (http://www.airliners.net/photo/Air-France/De-Havilland-DH-106/0199805/&sid=b6a4e86c79f461212061f528a88f66f1)

Both Air France and the independent French carrier UAT had three Comet 1s. AF used them from Paris to the Middle East, while UT ran them to the French colonies in West Africa. The UAT ones were stored at le Bourget when the type was withdrawn and lay there for years, finally being scrapped in the 1960s.

I don't know to what extent these purchasers were given their money back when the type was withdrawn.

An interesting assembly of all the timetables of the Comet 1 users at point of withdrawl in 1954 is here :

http://www.timetableimages.com/ttimages/comet1.htm

[glendalegoon]

4greens

agreee about no highway

did you know nevil selected the name "REINDEER" because COMET was one of Santa's Reindeer? hmmmmm

great book, great movie. great scott!

[glendalegoon]

I remember there was a comet 4 sitting at KORD for many, many years...tied up in legal difficulties.

[Allan Lupton]

Dear Mr Goon

Please get a grip on the chronology:
"No Highway" was first published in 1948 by William Heineman, London.
I cannot remember when the DH106 was named Comet, but it was first revealed to the public in 1949. Norway would probably have known the name before that, but so what? The Rutland Reindeer was more Bristol Brabazon than anything else and the alliterative name was typical of the period.
The first Comet disaster was 1954.

[A30yoyo]

In addition to the Comet project being at the painful end of the learning curve for pressurized fuselage design didn't it also bring about the formalization of take-off procedures for jet airliners (V1, V2, rotate....)?

[WHBM]

In addition to the Comet project being at the painful end of the learning curve for pressurized fuselage design didn't it also bring about the formalization of take-off procedures for jet airliners (V1, V2, rotate....)?
I believe that was a result of the Canadian Pacific loss at Karachi on its delivery flight, which killed not only the crew but all the key members of the CP Comet purchase and introduction team who were on board. Their second aircraft was never delivered, and was sold instead to BOAC.

I remember there was a Comet 4 sitting at KORD for many, many years...tied up in legal difficulties.

That was former Mexicana XA-NAS, which worked through various dealers in the US from the 1970s-90s without ever being used. A onetime regular PPRuNe poster was the flight engineer on that last flight from Albuquerque into O'Hare - apparently none of the crew had even been in a Comet before !

'Black' Comet XM823 [Archive] - PPRuNe Forums (http://www.pprune.org/archive/index.php/t-374055.html)

[joy ride]

On a programme about the Comet I saw recently they talked about a TO crash at Rome. All survived, but programme said that flight crew were not familiar enough with early turbine acceleration compared to piston engines, and that exact TO angle was crucial.

[evansb]

The take-off angle and rotation speed was a different problem, and were easily resolved. This thred is about fatigue problems.

[johngreen]

A few years ago, the repositioned parts of the roof section including the ADF windows of G-ALYP were on display in the Science Museum as seen in this image. (They are no longer exhibited.)



File:Fuselage of de Havilland Comet Airliner G-ALYP.JPG - Wikimedia Commons (http://commons.wikimedia.org/wiki/File:Fuselage_of_de_Havilland_Comet_Airliner_G-ALYP.JPG#mediaviewer/File:Fuselage_of_de_Havilland_Comet_Airliner_G-ALYP.JPG)



It was a very sobering experience to be looking down on these pieces in such a very mundane and static state and yet not at all difficult to imagine something of the few seconds of utterly catastrophic trauma that surrounded and included them just over the period of my own lifetime ago.

No doubt those that have dealt or deal now with the aftermath of any such events will know well of such reflections...

[A30yoyo]

I've retitled the thread to cover discussion of all the Comet I losses.
I know that De Havilland re-profiled the Comet wing leading edge to improve take-off characteristics, but what was the exact timescale of the introduction of 'V1, V2...rotate'. In the LIFE magazine series of photos of the first Comet 4 transatlantic service from Heathrow the Comets nose is off for several hundred yards before lift-off..was it a characteristic of the Comet 4?
Jet Comet - Hosted by Google (http://images.google.com/hosted/life/5502e428f0b4e7ea.html)
Jet Comet - Hosted by Google (http://images.google.com/hosted/life/d71b92dca0d22e2d.html)
Jet Comet - Hosted by Google (http://images.google.com/hosted/life/768ec902e2634482.html)
Jet Comet - Hosted by Google (http://images.google.com/hosted/life/a19282fb3665e0e1.html)
I watched that from the Public Enclosure you can see behind the Comet in the second shot
Finally has the Comet loss off India ever been linked to fatigue rather than extreme turbulence?

[glendalegoon]

dear mr lupton

I seem to not be alone in this.

No. 112: The Comet Failures (http://www.uh.edu/engines/epi112.htm)

and many more.

I guess we would have to ask nevil to be sure. try your ouji board!

[A30yoyo]

Hmmmm....they're still on about cabin windows....the point was that ALL the cut-outs in the pressure cabin had to be re-evaluated , redesigned and produced in thicker more fatigue resistant alloys with rip-stop features...the initial failures had been at an ADF window and an emergency hatch .
I think Pan Am started 707 services only about a month (edit) after the first Comet 4 transatlantic service...you can see a 707 parked discreetly by the fuel tank 'farm' (site now of T5) in the last of the Comet take-off sequence in #24

Here's some more shots from Mark Kauffmans 'Jet Comet' essay for LIFE mag
Jet Comet - Hosted by Google (http://images.google.com/hosted/life/f2310564a66734c3.html)
Jet Comet - Hosted by Google (http://images.google.com/hosted/life/66b5dafad4e8560d.html)
Jet Comet - Hosted by Google (http://images.google.com/hosted/life/8fbfeb8615c3159d.html)
Jet Comet - Hosted by Google (http://images.google.com/hosted/life/ad3d19fb68956b1c.html)

and these are from the same session but don't come up by searching 'Jet Comet'
BOAC Comet Captain Alabaster, BOAC Chairman Sir Gerard D'Erlanger and BBC's Reg Turnill in there
LIFE - Hosted by Google (http://images.google.com/hosted/life/c2588e84da67eba3.html)
LIFE - Hosted by Google (http://images.google.com/hosted/life/11d1c1212a1355c1.html)
LIFE - Hosted by Google (http://images.google.com/hosted/life/3543f819b8152170.html)
LIFE - Hosted by Google (http://images.google.com/hosted/life/a20b58736a7f8b9e.html)
LIFE - Hosted by Google (http://images.google.com/hosted/life/c6c5788894cc7192.html)
LIFE - Hosted by Google (http://images.google.com/hosted/life/09112e90462b808d.html)

[Airbanda]

I seem to not be alone in this.

No. 112: The Comet Failures

and many more.

I guess we would have to ask nevil to be sure. try your ouji board!

The linked article is a bit wayward with its facts and I very much doubt the connection to Rudolf. Apart from anything else it's not clear that the poem/book had reached the mass market at time No Highway was written.

Shute was not 'an engineer with De Havilland' by then although his early career in twenties included a spell at their Stag Lane works. He went from there to Vickers and then airships. After working on the R100 and abandonment of the airship programme following loss of R101 he co-founded Airspeed but parted company in late thirties. At the time it was majority owned by shipbuilders Swan Hunter. Only a couple of years later did they sell out to De Havilland leaving Airspeed as a division of the bigger company. After Airspeed he was able to live on his departure compensation and writing earnings until joining the RNVR at start of WW2 to work on various 'secret weapons'.

By 1948 he was again making his living solely as an author. He did though retain contacts at RAE and elsewhere including Professor Sir Alfred Pugsley who was working on fatigue.

No Highway is a good yarn but as much human story about the 'boffin' Mr Honey as about the science etc.

Shute's biographer John Anderson (Parallel Motion published by Paper Tiger in 2011) quotes Shute on the subject:

You think that was my own idea? Look I'm getting a little embarrassed about being hailed a prophet of metal fatigue. It really happened this way. Someone sent me a couple of technical papers by Professor Pugsley and he forecast the whole thing. I thought it was a fascinating idea for a novel so I wrote it. If anyone was the prophet for that book it was the Prof.

His full name was Nevil Shute Norway, professionally in aviation he was Norway. Shute as a given name was taken from further back up the family tree, the family name of his paternal grandmother.

He used it for his early 'hobby' writing so as not to impinge on his professional work with Vickers/R100 etc and it is the name by which he is generally known.

[Allan Lupton]

Some of Mr Lienhard's flights of fancy are just that and I think Airbanda has nailed it pretty well, so can we leave the "No Highway" digression now, please.

[Airbanda]

Request noted

Given this is a thread in History and Nostalgia (as opposed to a professional/technical sub forum) I'd have thought an element of digression was permissible if not inevitable.

But I've no wish to offend, still less get in an argument.

[VX275]

I've been able to read the original series of Farnborough reports covering the Comet accidents and facinating reading they make. The one point that lept out at me that is rarely mentioned is that the cracks around the ADF and other window openings were occuring on the production line as evidenced by the number of stop drilled cracks, including one of the fatal cracks on Yoke Peter. It is obvious that the cracks propogated despite these measures, with some cracks having more than one hole.
The builders recognised that the material was prone to cracking and applied the industry standard preventative action whilst failing to recognise its ineffectivness and the subsequent consequences.

[Blacksheep]

There was a complete Comet 1 fuselage at Farnborough up until the early '80s.Come up to London Colney if you want to see it again . . .

We have it at the De Havilland Aircraft Museum, along with lots of other De Havilland aircraft and engine examples.

[Stanwell]

Allan Lupton,
Please come up with an interesting contribution then - OK?
See what I'm getting at?

[Allan Lupton]

Quote
See what I'm getting at?

Since you ask, young sir, no I cannot see what you find interesting.

[barit1]

I discovered this University of Washington visual package - good historical review of the science of fatigue:

http://www.aa.washington.edu/courses/documents/mae_winter2014/Safarian_2-3-2014.pdf

(For me, It took a while to load) :rolleyes:

[Discorde]

I seem to recall that the Comet's designer, Ronald Bishop, was reported as difficult to work with and intolerant of criticism or is that an unfair or inaccurate malignment? Is it true that some engineers questioned the light gauge of the aircraft skin and the square window design in a pressurised hull? The increase of stresses at sharp corners had been known about for many years.

[joy ride]

Interesting to note that the Sud Aviation Caravelle had triangular windows and the L1011 Tristar had square ones. I heard a while back that Redux was originally specified to secure the windows, but de H management were not convinced that this method alone was good enough to rely on, and insisted on the addition of rivet plates and rivets, and it was these additions that initiated the cracks.

I am not sure how true this is, but the record of the Cravelle and 1011 suggests that (within limits) the window's shape is arguably less important than its construction.

[Spooky 2]

That was former Mexicana XA-NAS, which worked through various dealers in the US from the 1970s-90s without ever being used. A onetime regular PPRuNe poster was the flight engineer on that last flight from Albuquerque into O'Hare - apparently none of the crew had even been in a Comet before !


I was the FO on this flight and it's true none of us had flown the Comet prior to that day. We did one takeoff and full stop at KABQ before heading off to KORD. BELARG was the FE and we use to keep in touch a little but I'm afraid he had some health issues that prevented his continued participation in this forum. His postings were always excellent by the way. The fellow who flew Capt on the flight passed away last year.

[WHBM]

I was the FO on this flight and it's true none of us had flown the Comet prior to that day. We did one takeoff and full stop at KABQ before heading off to KORD. BELARG was the FE and we use to keep in touch a little but I'm afraid he had some health issues that prevented his continued participation in this forum. His postings were always excellent by the way.
I'm sorry to hear of Belarg's problems, we had many a banter here, both serious and humorous. He had a great knowledge of the 707.

[barit1]

Interesting to me:

Douglas DC-2 cabin windows had a small radius in the corners.
DC-3/C-47/C-53 etc. had square corners.
DC-4/C-54 had round windows.
DC-6 & 7 had square corners (first pressurized Douglas ships)

:rolleyes:

[Genghis the Engineer]

I seem to recall that the Comet's designer, Ronald Bishop, was reported as difficult to work with and intolerant of criticism or is that an unfair or inaccurate malignment? Is it true that some engineers questioned the light gauge of the aircraft skin and the square window design in a pressurised hull? The increase of stresses at sharp corners had been known about for many years.

(1) A great many senior people throughout the history of aviation have been reported as "difficult to work with and intolerant of criticism", hence CRM !

(2) Engineers generally communicate by criticising each other's work - so I'd be amazed if somebody hadn't asked those questions, along with lots of others.


Yes, increased stresses at corners were known. The impact of cyclic stresses in a pressure hull, relatively speaking, weren't however.

G

[joy ride]

One known example was the cargo hold openings on Liberty ships which originally had 90º corners. These initiated cracks, with at least one Liberty breaking into two. Later ones were built with rounded corners.

However, the examples of Caravelle, L1011 and DC6 / 7 do suggest to me that the shape itself is less important than its construction. I believe that Bishop did specify Redux alone, but management demanded a cautious "belt and braces" construction. It is sadly ironic that this cautious approach was what led to the failures.

[Volume]

The impact of cyclic stresses in a pressure hull, relatively speaking, weren't however.The impact of cyclic stress was well known from many railroad desasters. The appearance of cracks was quite well known, what was unknown at that times was what we use to call "fracture mechanics" today, the growth mechanism for cracks which may be explosive (instable) under certain conditions. Especially in a thin, highly stressed pressurized skin, the energy released from the skin which is unloaded due to the crack is higher than the energy required to enlarge the crack. It is the same phenomena that makes a balloon go pop if you inflate it high enough (enough energy stored in the rubber skin).

And of course it was the mechanism of coldworking by overstess not understood at that time.

[Shaggy Sheep Driver]

I have heard that when dH reworked the aeroplane to produce the Comet 4 they weren't going to risk another fatigue event so slightly over-engineered the airframe. This made it a bit heavier than it need have been, bad news for any aeroplane. But it made the airframe an ideal choice for Nimrod, which had to operate for long periods in thick air at low level.

Any truth in that?

[tdracer]

While metal fatigue was a well known phenomena at the time, I suspect what may not have been so well known was that aluminum has fundamentally different fatigue characteristics relative to iron/steel.
In short, with iron and steel, as long as you have adequate margin between the max stresses and plastic deformation, the fatigue life is nearly infinite, that's not the case with aluminum.

[Volume]

with iron and steel, as long as you have adequate margin between the max stresses and plastic deformation, the fatigue life is nearly infiniteThis is not entirely true, there are also iron/steel alloys around that will bite you if you try to prevent fatigue by static margin. Anway this philosophy will lead to structural weight inacceptable for an airframe. An airframe that heavy will have an infinite life because it will not be economic to operate and hence be parked all the time. Except for the military, where cost has not been an issue for some decades.

A Comet 1 with round windows would have had a longer life, but would eventually have failed catastrophically as well. As other airframes did. You can never reliably prevent a crack from happening, whether due to stress concentration, manufacturing flaw, accidental damage or whatever. The trick is to design the airframe in a way that you can allow cracks until you eventually detect and repair them. You need to prevent uncontrolled, instable crack growth. Which can be accomplished by adequate design without the weight penalty of low stress levels. A lesson that took a dozen hull losses and half a century to learn.

[washoutt]

Constructing the frames and longerons in such a way, that they divide the skin fields in "fenced-off" sections was the basic method to achieve that.
Previous construction methods had formers attached to the inside longerons or vice versa. That is catastrophic.