On Mon, Sep 01, 2003 at 08:01:54PM +1200, cr wrote: > On Monday 01 September 2003 08:28, Pigeon wrote: > > > > > I don't normally disagree with you Pigeon ;), but here I do. If > > > > hydraulics had proved reliable, and cheaper, or significantly better in > > > > any way, d'you think they wouldn't have been more widely adopted by > > > > now? They were certainly tried in enough areas. > > > > So was the 68000, and look what a POS chip PCs ended up using... it is > > all too common for non-technical considerations to result in a > > technically suboptimal solution becoming the most widely used method. > > So we get VHS for VCRs, telescopic forks for motorcycle front > > suspensions, Windoze, incandescent light bulbs... > > I *knew* you'd say that. Or rather, I thought you'd say "So's Linux, and > look at the crap everyone else uses". > > But the case isn't the same. In the case of the PC (which uses the Intel > chip), or MS Windows, there's a strong motive for everyine to use the same, > whether for interoperability or just because, as a new user, they just use > what's being marketed and have no idea whether there are better ways to do > it. > > I assume the people who buy diesel locomotives aren't as ignorant as > first-time computer buyers, and evaluate the technical merits in rather more > depth, including comparing running costs.
Well, in the British case, at the start of dieselisation neither manufacturers nor operators knew very much about diesel locos. The LMS had a couple of experimental main line diesels, the Southern had three, and that was basically it, apart from shunters. So the sensible method was chosen of buying a small number of a large variety of different designs for evaluation. They were all more or less experimental, and they all more or less sucked, diesel-electrics and -hydraulics. Because of this lack of knowledge, and the fact that current motive power shortages could most easily be met by continuing to build steam locos, it was a long-term scheme. The original deadline for the elimination of steam was 1985, I think. Unfortunately, political pressures put paid to this plan. There was a "rush to dieselise", which resulted in many of these experimental orders being extended to full production runs regardless of their suckitude. Suddenly BR had thousands of crap diesels all breaking down all over the place, and maintenance and repair facilities were hard put to it to cope. Trying to maintain diesels in steam sheds didn't help either. One pillar of the Western Region's hydraulic policy had been to copy the system of unit replacement used by the DB on whose designs those of the Western were based. A stock of overhauled power components would be held and locomotives repaired by swapping out the old unit and repairing it in background. The overloading of the maintenance system by failures of crap designs, mostly diesel-electric, and political difficulties connected with the manufacture of German designs, meant that this system never got off the ground and hydraulics had to be repaired in foreground on an ad-hoc basis, for which neither the locomotives nor the depots were designed. Nor was it always possible to ease the problems of running unreliable locomotives by using them on freight trains. The Western's hydraulics were mostly lightweight machines designed in the expectation that the unbraked freight wagon was about to be abolished. When the programme of braking freight wagons were abolished, even the heaviest diesel-electrics had problems controlling unbraked freights, and the lightweight hydraulics were at a serious disadvantage. There were some half-decent diesel designs; those with some history. The English Electric and Sulzer Type 4s, which were based on the LMS and SR prototypes, were somewhat heavy and clumsy, but basically competent. From these were derived the English Electric Type 3 and the Brush/Sulzer Type 4, which were designed after the first mad rush and drew on experience to produce extremely solid designs. The only practical way to sort out the diesel chaos was to standardise on a few good types and scrap the vast variety of crappy ones. Any numerically small classes, anything vaguely non-standard, didn't stand a chance. The Western's hydraulics merely suffered the same fate as many a diesel-electric: development was replaced by scrapping. The later builds - the D800 and D1000 classes - were quite well debugged by the time this decision was taken; they were still scrapped as being "non-standard", but managed to hang on for longer than the dodgier early builds. There were surprisingly few comparisons of costs between electric and hydraulic transmissions; those that were done were generally made after the policy decision to eliminate hydraulics had been taken, and failed to provide a particularly level playing field, but from the data one could conclude that neither type had a decisive advantage. In the US, it seems to have been the case that locomotive design was dominated by a few large manufacturers who knew how to do diesel-electric and didn't want to know about anything different. There were a few hydraulics imported from Germany, and they seem to have worked pretty well, but the American manufacturers weren't interested in the concept and the few hydraulics eventually suffered the fate of any nonstandard item with greatly different maintenance requirements from the rest of the fleet. Currently US manufacturers seem to have a large share of the international market, so there's not much scope for buying hydraulics anywhere these days. > (Incidentally, I quite agree, the 68000 chip (or the Acorn RISC chip) are > both way superior to Intel's ad-hoc box of complications.) I haven't used the Acorn chip, but from their OS design on the BBC Micro I can believe it'd be pretty good. > > > > You're not a Great Western enthusiast by any chance? <vbeg> > > > > Me - Southern. ;) > > > > Certainly as far as technical developments are concerned. As for the > > more general view, I'm both Western and Midland - coming from "border > > territory"! > > Then we'll *never* agree, will we? ;) I dunno, Midland and Southern - we could run the Somerset & Dorset :-) > Well, it seems to be an odd an unfortunate coincidence then, that all the > reliable hydraulic systems happened to be hooked up to unreliable > mechanicals. ;) Most diesel-electrics were just as unreliable - there were just more of them. I reckon if the LMS / SR prototypes had been hydraulics, that's what we'd have today... > Underground trains don't run very fast, nor does their acceleration or > deceleration last very long, nor do they have long gradients, so regen > braking has less to offer. On some lines though, they put the stations at > the top of 'humps', to assist acceleration and deceleration. But I don't > think there'd be any risk of trains going too fast due to voltage - > that's controlled by the driver. My source for this was written by a driver - he reckons it can catch you out occasionally. Regenerative braking on the Underground has an extra advantage which doesn't apply to overground systems - it reduces the amount of heat dissipated in the tunnels, which is a serious problem. > All new stock? Including high speed trains? Yep, we've got 125mph DMUs and 140mph EMUs now (though the EMUs are currently limited to 125mph in service because the signalling and trackwork aren't good enough for 140mph yet). > > > > The Southern Railway's early electric locos had a > > > > motor-flywheel-generator set ingeniously wired in series with the > > > > traction motors to overcome the break in traction. But that's DC, > > > > I'm not sure it would work so well on AC. > > > > Given that the technology of the time made a rotary convertor a good > > solution anyway, it was a brilliant idea. It'd work just as well on AC > > or DC. It would still be quite a good solution, though I suspect a > > dirty great bank of batteries that you could also go on/off shed with > > would be preferred. > > Apparently it allowed them to make *brief* trips down unpowered sidings to > pick up the odd wagon and presumably go on shed. Useful. Coming off shed's a bit harder though... > I imagine batteries would > cost quite a bit more in maintenance and renewals, since lead-acids don't > last very long. They do have the advantage of commonality though; and industrial types aren't necessarily "disposable" like car batteries - you can take them to bits and put new plates in, recycle the old ones. -- Pigeon Be kind to pigeons Get my GPG key here: http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x21C61F7F
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