
The de Havilland Comet changed aviation for good - nairteashop
http://www.bbc.com/future/story/20170404-the-british-airliner-that-changed-the-world
======
WalterBright
The 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.

~~~
dingaling
> 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
Fatigue 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.

~~~
RugnirViking
I assume I am wrong on this, but surely if it pressurized to 35000 feet, then
that would be _less_ load? As they pressurized it to that it would be closer
to the air at its altitude?

~~~
WalterBright
The cabin pressure inside is 10,000 feet, the air pressure outside is 35,000
feet, making for more of a pressure differential than at 20,000 feet altitude.

------
WalterBright
The 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)

------
phillc73
When 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
Not 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
Many 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)

------
gaius
Such a wasted opportunity. Around the same time, the UK was throwing away its
leadership in computing too. Weirdly, both ended up in Seattle.

~~~
notahacker
Classic case of first mover disadvantage. Their failures helped Boeing learn
some tough lessons about metal stress, and Boeing got many aspects of the
fuselage of their first jet liner so right they're _still_ used on the latest
generation of the 737 which will finish in the top two biggest selling
aircraft this year. Of course, us Brits learned tough lessons of a different
kind with the Concorde: no matter how brilliant the engineering is, you need a
mass market to break even on an aerospace programme.

It's not as if the UK's contribution to Airbus or other parts of the aviation
supply chain today is insubstantial though.

~~~
jacquesm
Airbus is one of the companies that will be hit hard by brexit. Arguably the
single market is what made Airbus possible to begin with.

~~~
josst
Airbus is based largely in France and Germany. BAE will likely suffer more as
a contractor.

~~~
jacquesm
[http://www.airbus.com/company/worldwide-presence/airbus-
in-u...](http://www.airbus.com/company/worldwide-presence/airbus-in-uk/)

------
barking
Peter Duffey first flew during WW2
[https://www.buckinghamcovers.com/celebrities/view/127-captai...](https://www.buckinghamcovers.com/celebrities/view/127-captain-
peter-duffey.php)

he also wrote a book about his flying experiences
[https://www.amazon.co.uk/Comets-Concordes-Peter-
Duffey/dp/18...](https://www.amazon.co.uk/Comets-Concordes-Peter-
Duffey/dp/1888962100)

------
cdegroot
My 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, ...).

~~~
ak217
In 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.

~~~
lostlogin
Those of us with legs suffer at least 4x more - The price has been at least
partly compensated for by cramming more people in.

~~~
slededit
A first class ticket is about double the cost and has the traditional leg
room. If you can live with only half the cost of the 1950s then its an option.

------
mirimir
It'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?

~~~
justinph
They'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.

~~~
cstross
The 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-engi...](http://aviationweek.com/defense/ge-rolls-pratt-
vie-b-52-engine-upgrade)

... 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.)

~~~
gaius
_Following 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
I thought the consensus was that the construction of the carriers had gone
really well.

~~~
gaius
They 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...

------
rwmj
There 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
It'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...](https://books.google.com/books?id=P1IfAQAAMAAJ&lpg=PA473&ots=SumDmFcwfB&pg=PA473#v=onepage)
[2]
[https://metallurgyandmaterials.wordpress.com/2015/12/25/libe...](https://metallurgyandmaterials.wordpress.com/2015/12/25/liberty-
ship-failures/)

~~~
notahacker
As 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.

------
tajen
I 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
Could 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
F16's carry hydrazine as emergency fuel to maintain control in case of loss of
power.

------
mcguire
The 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.

------
hydrogen18
Does the BBC not even get the history of Britain correct? The aircraft never
exploded. It just broke up in mid flight.

