Allen Hazen wrote:There’s the rub – just what was the actual weight of these two locomotive types?
Alco DH 643 supposedly 378,000 pounds. GE U50C perhaps 417,000: a difference of about 10%. Not really all that much more than the difference between the lightest and heaviest examples of a single locomotive model: customer options make it very hard to infer anything about the "intrinsic" weight of the design! (Note that about 5,000 of the 39,000 pound difference is due to the engines themselves: despite the similar specifications of the engines, the GE 7FDL-12 was significantly heavier than the Alco 12-251.)
Allen Hazen wrote: (Aside #1: English Electric's designers seem to have been extraordinary in their ability to come up with very powerful but light-weight locomotive designs)That was mostly close attention to detail, I think, particularly by its Vulcan Foundry subsidiary, and a capability honed by addressing the needs of the CM-gauge export market. But EE did miss the mark on the high side now and again, such as with the BR class 23.
Allen Hazen wrote: (Aside #2: I'd love to witness the fireworks at a debate between historians of British railways on the topic "Resolved: British Rail would have done better by ordering duplicates of DP2 from E.E. rather than asking for the design modifications that led to the Class 50." (Grin!))That would take us well off topic, so I’ll stay mute – perhaps try it on one of the UK forums – as a “light blue touch paper and run for cover” exercise. (November 05 would be good timing, I think).
Allen Hazen wrote: But it seems to me that British Rail ALSO performed something closer to "controlled experiments" to compare DE and DH designs: they acquired at least two pairs of DH/DE designs which, in other respects, were very, very similar.I suspect that the first pair was a simply happenstance situation. Quite probably even when it was planning the class 53 prototype – which was not compliant with the BR specification - Brush was confident of completing the “back door” deal that bypassed the BR design competition and resulted in the class 47. So the 53 was something of a red herring. It had Maybach engines simply because Hawker Siddeley, who owned Brush, was the UK licensee.
(1) The Class 52 Diesel Hydraulic used the very same engines as the Class 53 (one unit built: the Brush prototype Falcon) Diesel Electric. Class 53 weighed 115 tons: between 6% and 7% heavier than the DH.
(2) Class 22 Diesel Hydraulic (68 tons) and Class 21 Diesel Electric (72.42 tons) also used the same engine (well, slight variants of the same engine design)… and were built in equal numbers (58 units each), suggesting that they may have been chosen deliberately to allow a comparison of the merits of the two designs. Weight difference here is just 6.5%.)
mp15ac wrote:There is an excellent book about the diesel-hydraulics available, Southern Pacific and the KM Hydraulics by Robert Zenk. It covers the development of the diesel-hydraulic program with the D&RGW and SP, the original six units, the 21 "production" units, the 3 "Alco-haulics", and the one surviving unit. Also covered are the diesel-hydraulics sold to Brazil (meter gauge), and proposed versions.Thanks, Stuart. I wasn’t aware of that book; I have now ordered a copy.
https://www.amazon.com/Southern-Pacific ... 0984624791" onclick="window.open(this.href);return false;
Allen Hazen wrote: When I looked up the weights, I also noticed that the Diesel Electric Class 21 was a few feet longer than the DH Class 22. Did the components of the diesel electric transmission (generator, control switchgear, etc) require a bigger "box" to house them than the pieces of the diesel hydraulic's machinery?Looking at the respective equipment layout diagrams, that appears to have been the case. Clearly, there is an irreducible minimum box length required, but often locomotives are longer than that for various other reasons, such as the minimum truck spacing required for bridge loading, accommodation of underslung fuel tanks, and for weight balance. The latter may be more difficult for diesel-hydraulic locomotives, particularly the single-engined type. The transmission drop-box needs to be more-or-less central, and that means that in turn that the engine must be somewhat off-centre, immediately creating a potential weight balance problem. The situation was eased by the use of lightweight high-speed engines, which is perhaps another reason why they were often preferred for diesel-hydraulic locomotives.
Allen Hazen wrote:...I knew Falcon was hard to compare with anything, and it's over-all design is very different from that of the Class 52 diesel hydraulics. But I don't have many "data points" for dh/de comparison! And it was an example of what a d.e. design, for British service and with British designers of (I assume) similar feelings about weight saving, using the same engines as a fairly successful d.h. design, COULD be.!That’s a good point. The 53/Falcon represented a “state-of-the-art” attempt to build a twin-engined, C-C, diesel-electric locomotive of around 2700 hp within a weight limit of 114 tons. It came out just above this target, at 114 tons. The class 47, powered by a very heavy medium-speed engine, and using a generally similar carbody, came in at about the same weight, suggesting that at this power level, there was not a material advantage to using two high-speed engines. The 52 on the other hand could be seen as the best effort, using the K-M form of advanced light-weight construction, at a broadly similar diesel-hydraulic locomotive.
jr wrote:I've read that the hydraulics took longer to reverse direction, than a diesel-electric. Something about the gear boxes needing to get properly meshed, before the throttle could be opened. (Perhaps not a big consideration with road units, but another small drawback to add to the pile).The Voith transmission (as did the Mekydro) used air-operated dog clutches to engage the respective forward and reverse output gear trains. It was possible to have tooth abutment that prevented engagement, and some early diesel-hydraulic locomotives had operator’s desk warning lamps to show this condition, as well as an interlock that prevented converter filling until either forward or reverse was properly engaged. (I think that the usual remedy was “try again”.) In fact, early diesel-hydraulic locomotives seemed to have more warning circuits than diesel-electrics and so typically required more wires in the MU bundle. This may well have retarded the advent of mixed-MU operations, even though Baldwin had included that in its 1954 list of diesel-hydraulic locomotive desiderata.
Allen Hazen wrote:... And, one more that may have been a big one: I have read that d.h. transmission isn't as efficent as d.e., that a smaller proportion of engine horsepower gets translated into train-pulling horsepower. (I.e.: the fraction horsepower-at-rail/horsepower-of-engine is smaller for d.h. than d.e.)There is quite a bit of detail on the BR comparison in the book:
Don't have much in the way of documentation, but one source I have suggests the peak effective (i.e.: at rail) horsepower of the British Rail d.h. Class 52 was unimpressive when compared to that of d.e. types of the same nominal engine horsepower. Perhaps explaining why B.R.'s later orders for big diesels to finish the elimination of steam were for Class 47 and Class 50, both d.e. types.