APT tilting train: A laughing stock that changed the world | Hacker News Reader

APT tilting train: A laughing stock that changed the world

bbc.co.uk

63 pointsdarrhiggs25 comments

What this article left unsaid was that the project was started before the time of Margaret Thatcher but ended in production during Margaret Thatcher's premiership. Margaret Thatcher is well known to oppose the public rails and all other kinds of public works. It would have been very easy and popular then to vilify any large public project as a boondoggle.

The result is that the English still use trains (because their large population requires them) but get to import their trains from France, Italy and Japan.

Rail privatisation was a John Major initiative, not Thatcher.

Quote from OP

"The Italian firm Fiat bought the patents for the APT's tilting technology and used it to help develop its Pendolino trains, now manufactured by the French multinational Alstom."

Export of technological know-how is something of a UK speciality (ARM chips, fluidised bed furnaces for efficient combustion of coal &c).

"A six-car APT, including a driving trailer and buffet carriage, is in place at Crewe Heritage Centre. It's clearly visible to passengers passing by on the adjacent West Coast Main Line where it ran for a few months."

I go through Crew on a regular basis, and the APT is easily seen from the track. Along with the rather impressive dents along the side of the coaches resulting from a failure of the tilting mechanism.

Small world :) I live there and got to go on board the APT with my Grandad when I was younger, as well as run the model railway at the Heritage Centre with him.

Excellent. Now this is really a long shot - do you know of the llama farm (or farm keeping about a dozen llamas) that is one the way into Crewe from Stafford? They always surprise me on the way up to Liverpool...

The APT was rushed into service before it was ready and suffered from initial glitches which ultimately led to bad press killing it off.

On the other hand I use the descendent of the APT (the Virgin Pendelino) to commute into work and back. The tilting mechanism is really sublime and incredibly comfortable. It was ahead of its time.

I'm sorry, I hate to be a pain, but it's a pet peeve of mine. They weren't "glitches". They were defects.

Glitches are errors that happen outside of the design parameters of the system. For example, when you touch the antennae on an AM radio and you hear a pop or buzz from your own electrical field in the radio.

Defects are errors that occur within the design parameters. So a train that can't handle some snow on the tracks, or a national health insurance enrollment site that falls over after only a few users show up, those are defects.

Bugs are a type of insect. Using the word "bug" to describe a defect implies that the "bug" showed up, an external factor that got in and gummed up the works or something. But that doesn't happen in software. The defects were always there.

I think it's important to use the terminology correctly and make a habit of using it correctly because I think it puts the emphasis on the fact that we create the defects, and the defects were always there, they didn't just develop, they just had to be found. That's also why I don't like the term "software maintenance". When you have to take a site down for several hours every 3 months for "routine database maintenance", that's a defect in design, not just "changing the oil".

It was our fault. Calling them "bugs" or "glitches" or "maintenance issues" diminishes that.

The reason "bug" is used is because the first computers were programmed through hard wiring and mechanical switches, and they were actually insects that were present. This is from Grace Hopper in 1947:

http://www.computerhistory.org/tdih/September/9/

Convention has stuck which is why we have software debuggers, and the word bug in computer science has come to mean any unintended result, not just the presence of insect wildlife.

(I myself debugged a floppy drive in '87 which had an earwig stuck behind the read head backstop resulting in the read head being misaligned to the sectors)

Use of "bug" to mean "defect" goes back a lot further than the computer age:

http://www.etymonline.com/index.php?term=bug&allowed_in_fram...

At the time of Grace Hopper, the term was used in engineering contexts to refer to defects in general, quite unrelated to insects. Per your link, that's why she wrote "first actual case of a bug being found" -- it was amusing and unusual to find a bug (defect) caused by a bug (insect). If this were not the case, there would be no need to use the words "first" or "actual", or even note the event.

Well ... unless they were caused by stray transient electrical spikes changing the state of the system. These could be a defect but it might also be caused by improper input signal conditioning (which would be a defect elsewhere in the system). In either case, we've traditionally called these defects glitches and that lexicon has been broadened to more generally mean "unintended behavior".

As well as the glitches, there's a story that the tilt was initially set to entirely cancel the lateral acceleration from the curve. The press on the demo train was well lubricated with free booze -- result: headlines about the new train making them sick.

\tangent another solution is camber or cant, where the outer rail is higher, banking into the curve, as an aeroplane turns.

A problem is the beginning of a curve. If the straight simply becomes an arc of a circle, the lateral centrifugal force (see xkcd) goes instantaneously from 0 to maximum. One might think an Euler spiral, whose rate of turn increases linearly, would fix this; but now, although the lateral force increases linearly, the onset of change in force is instantaneous, and is felt as a jolt by passengers. Apparently it is possible to create turns giving a smooth ride, but requires sophisticated dynamic models that are presently beyond me.

I started making a game with very smoothly transitioning banked turns, but it's a lot more complex than I thought! (Other games use tilting-like mechanisms, such as suspension, and the natural averaging over the four contact points of a car, but that's not applicable to what I want to do). If anyone has some pointers, I'd love to hear them!

P.S. Re trains: Of course, another problem is that banked turns are "static", the same for all trains regardless of velocity; whereas the "dynamic" tilting can adjust to current velocity, on-the-fly (in addition to smoothing out transitions). The rail camber/cant can remain suited to the typical velocity of non-tilting trains using the same track.

> the onset of change in force is instantaneous, and is felt as a jolt by passengers

An instantaneous change of force (and thus acceleration) create a jolt, I understand that. But taking the derivative again - 'the onset of change in force' - I don't see how that is felt as a jolt.

I thought so too; but that's what I read, as what happens when Euler curves were used in practice (which they were). Unfortunately, I didn't get to the point of trying it out for myself in my game.

[BTW: Like a bob-sled track, I did find that cross-sections that were sine waves or quadratic did feel strikingly smooth - those being smooth, with smooth deviratives, smooth derivatives of derivatives, and so on.]

If you imagine an x-y graph of force over time for a track that went like (start in a straight, an Euler curve to begin the turn, some time in an circular arc, and a reverse Euler to straighten it, end in a straight), the graph would be (level, slope up, level, slope down, level):

    _
  _/ \_

Apparently, humans are sensitive to the change between levels and linear slopes. Lines are uncommon in nature [though gravity is constant acceleration...?]. Perhaps related to inverse kinematics in limb movement? "Jolt" may be the wrong description.

To some extent the tilting was a side-show. It was the hydrokinetic brakes which really allowed the train to travel faster while still meeting the stopping distances necessary for the conventional signalling used on the line.

While the brakes are important, the tilting is most definitely not a side-show. I've been on a train when the tilting is not working, and the lateral forces are significant. They make it unpleasant to ride, and impossible to work. Certainly drinking coffee is no joke.

I stand (or preferably, sit) corrected.

Can't you just camber the track rather than make the trains actively tilt? I suppose the camber could be problematic at very slow speeds.

The idea was that it is much cheaper to change the trains than to rebuild existing tracks.

They do camber tracks but you have the problem of dealing with different train speeds. It the UK case the lines were old and not very cambered.

>In its brief life the APT, with its futuristic sloped front, was vilified as a waste of money - £47m in total - and mocked by the press.

When I read stuff like this, I want to kick people.

You advocate violence against people who don't agree with your views on public spending?

If I was advocating violence, I would have said so. That said I have a deep frustration for people with not only a negative can't do attitude. But more obsessively look for reasons to say I told you so. There are vast numbers of people like this and it gets worse decade by decade. And these people do vast damage to society.

And also spending £47m for heavy industry technology project is what I would call cheap. And except for the rare exceptions where the engineers nail the design all of these are janky initially. Which of course provides a lot of cud for the naysayers.

You'd have to correct the 47m GBP for nominal GPD/capita growth to get a clearer sense.

Using the data from http://www.theguardian.com/news/datablog/2009/nov/25/gdp-uk-... and picking 1975 nominal GPD (28,742 mGBP) vs 2013 nominal GDP (399,834 mGDP), the 47 mGBP in 1975 become 654 mGBP in 2013.

The Swedish developed train X2, launched 1990 in Sweden as X2000 is still in service and is using tilting technology to increase speed. It's been running the most popular commuter line (Stockholm <-> Gothenburg) for 25 years at 200 km/h. https://en.m.wikipedia.org/wiki/X_2000

Sadly it's replacements focuses on efficient brakes over tilting.

Move fast and break stuff doesn't work for infrastructure projects. If you cannot get good PR on day 1 then delay until you can.

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