Tech Info about BB 8 axle loco please .

[M636C]

I should have credited the Kratville "Steamliners" book as my source for the span bolsters on the later M10000 series locomotives, although I think the feature was mentioned in most references. However, the photos in the Kratville book made things quite clear. That book is an excellent source for most things related to the UP Streamliners, although the change from head end power in dedicated power cars to steam heating and axle generators, a retrograde step in nearly every way, is only indicated by a careful reading of the actual vehicle diagrams. This occurred between the LA 1-2-3 and SF 1-2-3 sets and the following 4-5-6 sets (so before WWII).

Regarding the use of "+" in wheel arrangements, the rationale used in Australia was that "+" was used where a hinge was present, and if not a "-" was used. Thus electric locomotives with connected bogies were Co+Co but those without connection between bogies were Co-Co. There were some diesel locomotives with bogies connected, but not many. Some of these had couplers carried by the bogies, and some did not. Some diesels with couplers carried by the bogies did not have an interconnection.

One very common usage was 4-8-4+4-8-4 for Beyer Garratt locomotives. This would be incorrect by the above definition, since Garratts were supported on pivots with no hinge involved. However most Mallets and simple articulated locomotives had a hinge connection and could be shown as 4-8+8-4 using this definition.

I'm not sure that even the very compact span bolster arrangement would suit the limited headroom of the general Australian loading gauge, as suggested by the original poster. Just the loss of fuel capacity would be a problem owing the the shorter tank required.

One further point about the Gas Turbines and U50s. My understanding was that the U50s used the same trucks as the turbines, these being fitted to the U50s and the Alco C855 units as the turbines that has used them were withdrawn and scrapped. When the larger two unit turbines were scrapped, their trucks were used under the U50C units.

Perhaps the U50C would have been built with span bolsters if more of the trucks were available from withdrawn turbines....

Peter

[Pneudyne]

Re the UP Streamliners, I retrieved my copy of the book ‘The Union Pacific Streamliners’ by Rank and Kratville.  This has detailed information, including good photographs, of the span bolster assembly used on the M-10002/3/4/5/6 power cars, which were in fact locomotives.

 

The UP had evidently chosen the articulated body arrangement generally for the streamliners because it was thought to aid stability at very high speeds (100 mile/h and above).  Presumably it wanted to retain this for the double power car case, and so the span bolster was required to accommodate two power trucks under the articulation point.  Evidently the span bolster assembly, with carefully controlled lateral motion trucks, was also sufficiently stable at very high speeds.  The streamliner span bolsters had 8’4” wheelbase trucks at 16’0” centres.  The conventional wisdom is that B-B locomotives with short truck centres are prone to oscillation (perhaps a combination of yaw and longitudinal side-to-side) at higher speeds, but this did not seem to afflict the span bolster B-B combination, perhaps because effectively, most of the mass it was carrying was concentrated at the span bolster centre, rather than distributed along and beyond its length.

 

This experience may have predisposed the UP to accepting the span bolster running gear arrangement for the GTEL4500.  Here, 9’4” wheelbase swing bolster trucks were used at 15’4” centres.  The same running gear then became its preferred type for its “double diesels”, so it would seem to have worked well in practice.

 

Those Streamliner power cars then belonged to three groups:

 

1.              Four-truck locomotives

2.              Locomotives with span-bolsters

3.              Articulated body diesel locomotives

 

The third group is quite small, the other examples I know of being two Krupp diesel-hydraulic prototypes, B-B-B (with the Krupp characteristic of the time of having a torque converter for each axle), one each for SNCFA, Algeria and EFVM, Brasil, and five Alsthom diesel-electrics, B-B-B, for FE, Ecuador.  On the other hand, there were many more  articulated body electric locomotives, mostly because FS, Italy had a very large fleet built up over 50 years or so.  (The FS locomotives had fairly short truck centres, and eventually FS switched to the single-frame tribo (triple bogie/triple truck) type for better stability at very high speeds.)

 

I think that the Streamliner power cars could also be described as being of the quasi-(articulated body) tribo type.  From the viewpoint of the body structure, its rests on three truck assembles, with the centre “truck” under the body articulation point.  The centre point of the body assembly does not “know” whether it is resting upon a single truck or on a span bolster in turn resting upon a pair of trucks.

 

 

Returning to the wheel arrangement designation issue, I had a quick look at various sources to see how that for the GTEL4500 and subsequently the GE U50 and Alco C855 diesels changed over time.

 

Railway Age (RA) 1948 November 27 and 1949 June 18 had the GTEL4500 as B-B-B-B.

 

Locomotive Cyclopedia 1950-52 had the GTEL4500 as B-B-B-B.

 

RA 1963 September 09 had the diesels as B-B+B-B.

 

RA 1963 October 07 had the diesels as B-B-B-B.

 

Railway Locomotives and Cars (RLC) 1963 November had the diesels as B-B+B-B.

 

RLC 1964 July had the diesels as B-B-B-B.

 

Lee, in ‘Turbines Westward’, 2^nd, 1975, had the GTEL4500 as B-B-B-B, I suspect copied over from UP documentation.

 

Kratville & Ranks, in ‘Motive Power of the Union Pacific’, 1977 had the GTEL4500 as B-B-B-B, again I suspect copied over from UP documentation.

 

Keekley, in ‘Roaring U50’s’, 1978, described the U50 (or U50D, as he called it), as having a B+B B+B (space, no sign between the two B+B groups) wheel arrangement.

 

Cockle, in ‘Giants of the West’, 1981, used B+B B+B for the GTEL4500, Alco C855 and GE ‘U50D’.

 

Marre, in ‘Diesel Locomotives: The First Fifty Years’, 1995, used B+B-B+B (with a dash between the two B+B groups) for the GE U50 and Alco C855.

 

I think it is a case of ‘take your pick’ from:

 

B-B-B-B

B-B+B-B

B+B B+B

B+B-B+B

 

Whether the changes were the results of rethinking the situation or just random errors is unknown.

 

I have not seen any GE literature in respect of the BB40 series export models, so do not know how it described their span bolster wheel arrangements.

 

 

As the ‘U50D’ alternative designation for the U50 has come up in some of the above sources, the earliest use that I have seen was in the RA 1969 February 24 and RLC 1969 March articles on the GE U50C.  Both referred to its predecessor as the U50D, without further explanation.

 

Keekley said:  ‘The U50D was originally introduced to the Union Pacific by General Electric as simply the U50.  It was only after General Electric built the U50C model in 1969 that the earlier model was referred to as the U50D.’  He does not say by whom, though.

 

And Cockle:  ‘While properly classified as U50’s, when the U50C was introduced this model became known as the U50D (improper, as it did not have D-type trucks) or sometimes called a U50 B+B B+B’.

 

Early GE literature (e.g. GEA-7842 of 1963 September) referred to the model as simply the U50.  And its never-built successor was the U56, e.g. as referred to in RLC 1965 September and 1966 March.

 

But GE did use the U50D designation in its 1985 May ‘Universal World Users Brochure’ and again in its 1991 September 21 ‘World Users List’.  How that came about is unknown, but de facto it legitimized this designation, notwithstanding its origin, whether it was from GE, the trade press or the railfan world.

 

 

In general though, the evidence over many years is that the span bolster wheel B-B-B-B arrangement is quite satisfactory in riding and tracking terms for high-powered diesel-electric locomotives in situations where eight axles rather than six are required in order to meet axle-loading constraints.  And as the EMD case shows, they can be built without requiring a higher frame height than for homologous C-C locomotives, and with tandem-mounted traction motors.  Whether the extra axles and extra complexity for extra power is justified in any given situation would be for the individual railroad operators to decide.

 

 

 

Cheers,

[Pneudyne]

Thanks for adding the UP Streamliner case to the span-bolster list – I was previously unaware of those.

 

Regarding the CEM locomotives, as best I can determine the builds (all CM (Cape/metre) gauge) were:

 

27 of the 4B (two span bolsters) type with SACM AGO 230 V16 or 240 V16 engine.

22 of the 3B (one span bolster) type with the SACM 195 V12 engine.

20 of the 2B (no span bolsters) type with the SACM 195 V12 engine.

 

More powerful standard gauge diesel-electric as well as electric 4B types were proposed, but none of those were built.

 

On the use of the ‘+’ sign in wheel arrangements, this from an article ‘Electric Locomotive Classification’ in ‘Railway Age’ 1926 February 27, pp.525-6, proposing a new system for electric locomotives:

 

‘The connection between trucks or motive power units, constituting an articulated joint (a flexible connection through which propulsive forces are transmitted to the drawbars) is indicated by a plus (+) sign.  Example B+B – two trucks connected by an articulated joint.’’

 

And:

 

‘The separation between swivel type trucks is represented by a minus (-) sign.  Example B-B – a locomotive with two swivel type trucks.’

 

On that basis, one may see why GE used B-B+B-B to describe for example the VGN EL2B, and B-B-B-B to describe the GTEL4500.  In the EL2B case, the two span-bolsters are connected by an articulated joint through which passes all buff and drag forces, which completely bypass the main structure.  But under each span bolster, the two trucks are independent of each other.  In the GTEL 4500 case, the two span bolsters are unconnected, hence the minus sign in the middle.  As with the VGN EL-2B case, the two trucks under each span bolster are also independent.  The pathway for buff and drag forces is coupler to span bolster outer section to span bolster pivot, thence via the mainframe to span bolster pivot and via the span bolster outer section to coupler.

 

 

Cheers,

[M636C]

One other, much less obvious use of span bolsters not listed above was in the Union Pacific Streamliner trains.

The two units of M 10002 were articulated onto a span bolster which carried the end inner trucks, although from the outside, it looks like a pair of locomotives coupled together.

This feature also applied to the two units of the M10004 series, although these later received a genuine third booster unit coupled to the leading pair.

Amazingly, it appears that the first booster unit for the M 10004 units was run (in undercoat) coupled by span bolster to the M 10002 lead unit for trials on the City trains. M 10002's "booster" was only 900HP, so this might have been to get early test results from a 2400HP pair.

Peter

[M636C]

In the late 1960s, French builder CEM developed a span-bolster B-B-B-B locomotive for service on the African Outre Mer metre and Cape gauge lines.  The B trucks were of the monomoteur type.  Lateral motion swing links were placed between the body and the span bolsters, not between the span bolsters and the bogies(?).  Also, I think for the first time on a span-bolster locomotive, the couplers were mounted on the mainframe, not the outer ends of the span bolsters.  This locomotive, designated the 4B type by CEM, was part of a family, which included the 2B and 3B types.  The 2B type simply used two of the B trucks with swing link assemblies.  The 3B type had a single B truck, as on the 2B, at one end, and a span-bolster B-B assembly, as on the 4B, at the other end.  This made it the most ersatz form in the tribo group, and probably the most asymmetrical of the asymmetrical wheel arrangement locomotives – certainly more so than the Hungarian and British C-B examples.

 

 I recall this design. I don't think any locomotives were built to this design. I seem to recall that it was to be offered, among others, with a Pielstick 18 PA6 engine of 6000 HP and was available in standard gauge form as well. The feature that comes to mind is that the monomoteur bogies, like all of their type, were quite tall, projecting up into the locomotive cab type body well beyond the base of the engine and generator and the span bolsters were above this, occupying most of the locomotive up to the roof mounted radiators and air intakes at both ends. Given how far up into the body the span bolster was located, it would have been easy to arrange swing hangers reaching up from the base of the body to the span bolsters.

 

This was in the same tradition as the huge french prototypes 69001 and 70001. These, built in 1964, each had two Pielstick 16PA4 engines, 69001 driving through hydraulic transmission and 70001 driving through a contrarotating alternator suspended between the two diesels to DC traction motors. (what could possibly go wrong.) BB69001 was 30 tonnes lighter but was limited to 3510HP but CC70001 had a full 4000HP. Only prototypes were built, two of each.

 

The four monomoteur design just left out the prototype stage and disappeared without any examples being built.

 

Peter

[Overmod]

As far as I know, the use of + to denote articulation comes from Wiener, in Articulated Locomotives (1930), in part as revived and promulgated by Bob LeMassena around the time Kalmbach republished that book in 1970.  I recall a certain amount of pushback and mockery expressed from the railfan community about this, as they were used to 2-8-8-2s and 2-6-6-4s and were upset when they sprouted plus signs.

Note might also be made of the convention of using subscript o for unconnected powered axles in a truck, as in Bo-Bo or Co-Co for most American diesel-electrics.  This is where that term 'tribo' comes from (it has nothing to do with lubrication).

I don't have my copy of Wiener handy, but as I recall he used an apostrophe for individual powered axles in a common frame, so the B&O constant-torque W-1 would not have been 2-Do-2 but 4-2'2'2'2-4.  This is kinda like different forms of calculus notation...

Can you edit the post to clarify where the swing links run on the CEM locomotives?  I think that last word is meant to be 'trucks' or 'truck bolsters'...

I confess to having been impressed at the principle of CEM standardizing on one type of span-bolster arrangement and using it on their smaller 'tribo-size' locomotive.  It certainly gets around issues of lateral accommodation, even if swing is greater at one end than the other...

[Pneudyne]

Not directly addressing the primary topic, but I think providing some pertinent background, here is a “potted history” of span bolster running gear.

 

As far as locomotives are concerned, span bolster running gear appears to have originated in the first half of the 1920s in American interurban practice.  A non-exhaustive search shows that in 1924, Piedmont Northern used the B-B+B-B wheel arrangement, with articulated span bolsters, whilst in the same year, Illinois Terminal used B-B-B-B, with independent span bolsters.  In some of these cases then span bolsters may have been associated with lateral motion trucks.  There may well have been earlier applications.  Span bolsters were also used for freight cars, in for example 4-4-4-4 and 8-8-8-8 configurations, but I do not know the timelines.  Four-truck interurban locomotives were built until at least 1941-42, e.g. Piedmont & Northern #5600 by GE,

 

The NYC T class electric locomotives of 1913 and up had a single-frame B-B+B-B wheel arrangement, but it was not of the span bolster type.  Rather the inner axles were rigidly mounted to the beams, with the outers in non-lateral notion trucks that acted as pilots to the inners.  (1)  One could say that it was more-or-less a 2-B+B-2 wheel arrangement but with powered outer trucks, although 2-B+B-2 itself did not arrive until 1921 (GE for Paulista, Brasil).

 

The solitary EMD (Winton/GE/St. Louis) model T (was it painted black?) transfer locomotive of 1936 for the IC had the span bolster B-B+B-B wheel arrangement, with as best I can tell, rigid bolster trucks.

 

Post-WWII GE used the B-B+B-B span bolster wheel arrangement, with articulated span bolsters and rigid-bolster trucks, for the VGN EL-2B electric locomotives.  (2)  Then it used the non-articulated B-B-B-B form, with swing bolster trucks, for the Alco-GE GTEL4500 prototype (3), carried over to the GE production machines.

 

In that time period, Brown Boveri also proposed various GTEL designs, including some aimed at the US market which had span-bolster A1A-B-B-A1A running gear, as well as a D-D. (4)

 

Overmod has mentioned the Westinghouse non-span bolster B-B-B-B wheel arrangement used on its solitary GTEL prototype.  That was derived from a Westinghouse proposal for a homologous series of electric locomotives (AC and DC) that all used the same standard B truck with non-lifting lateral motion.  The range went from B-B, through B-B-B to B-B-B-B, and most improbably to articulated span bolster B-B-B+B-B-B and B-B-B-B+B-B-B-B versions.  (5)  The single-frame tribo form – with extended lateral motion centre-truck - was by that time well-established, although not widespread, in worldwide practice (GE appears to have been first, with a B+B+B for Mexicano c.1924).  The Westinghouse B-B-B-B was an extension of that.  (In respect of the tribo form, the articulated body type was also known pre-WWII, but the semi-articulated body form was yet to come.)

 

The Baldwin STEL prototype for N&W had (non-articulated) span bolster C-C-C-C running gear.

 

In 1962, the UP proposed using (in fact re-using) the same GTEL4500 B-B-B-B running gear for its desired twin-engine 5000 hp diesel-electric locomotives. (6)  It had to order prototypes from Alco and GE, who thus did use this running gear.  EMD chose to build prototypes on its own account, thus got to choose, and developed its own D-D approach.  There is some evidence that UP might have preferred B-B-B-B for the DDA40X, but not unexpectedly, that followed EMD’s preferred D-D approach. (7)

 

In the late 1960s, French builder CEM developed a span-bolster B-B-B-B locomotive for service on the African Outre Mer metre and Cape gauge lines.  The B trucks were of the monomoteur type.  Lateral motion swing links were placed between the body and the span bolsters, not between the span bolsters and the trucks.  Also, I think for the first time on a span-bolster locomotive, the couplers were mounted on the mainframe, not the outer ends of the span bolsters.  This locomotive, designated the 4B type by CEM, was part of a family, which included the 2B and 3B types.  The 2B type simply used two of the B trucks with swing link assemblies.  The 3B type had a single B truck, as on the 2B, at one end, and a span-bolster B-B assembly, as on the 4B, at the other end.  This made it the most ersatz form in the tribo group, and probably the most asymmetrical of the asymmetrical wheel arrangement locomotives – certainly more so than the Hungarian and British C-B examples.

 

Next came the GE export BB locomotives, which also had the couplers mounted on the mainframes, then the (I think – and this is strictly a layperson’s viewpoint – very neat) EMD export arrangement described above by Dave.

 

The D-D wheel arrangement (with true D trucks, not D wheelbases in a rigid frame), an alternative to B-B-B-B, was quite rare.  As best I can determine, EMD was the only user.  British Rail designed a swing bolster D truck c.1950, (8) but in the event never applied it.  Otherwise D trucks have almost always appeared in pilot-truck arrangements, such as 2-D+D-2 and B-D+D-2.  Baldwin also proposed, but never used 1-D+D-1.  There was a solitary Russian prototype diesel-electric (the so-called Gakkel locomotive) of c.1924, single-frame with the 1-C+D+C-1 wheel arrangement, so this did have a D truck (It was an actual truck, not part of the frame, but one could say that it was piloted by the outer 1-C trucks.) (9)

 

By the way, GE referred to the GTEL4500 and U50 running gear as B-B-B-B, not B+B-B+B, as used in some publications.  Whether the latter is a railfan derivative , or change made by AAR I do not know.  In the British Commonwealth wheel arrangement system, with which I am more familiar, it would definitely be Bo-Bo-Bo-Bo, no '+' sign anywhere.

 

 

(1)   See US patent 1026552.

(2)   The reasons for this choice were provided in ASME paper 49-SA-7, 'Motor-Generator Locomotives, Their Design and Operating Characteristics', by Fox (VGN), Gaynor (GN) & Gowans (GE).

(3)   See AIEE paper 50-77, 'The Alco-GE 4,500-Horsepower Gas-Turbine Electric Locomotive', by Morey (GE).

(4)   See Railway Mechanical Engineer, 1946 August, 'Gas Turbine locomotives', by Giger, p.394ff; also Brown Boveri Review 1945 October-November 'The Brown Boveri Gas Turbine Locomotive', p.353ff.

(5)   See AIEE paper 48-54, 'Electric Locomotives with Identical Basic Components', by Brecht & Kerr (both Wemco)

(6)   See: https://donstrack.smugmug.com/UtahRails/Union-Pacific/UP-Miscellaneous/i-T95bPCR/A

(7)   The span bolster possibility was mentioned in Railway Locomotives & Cars 1968 December in an item 'Two-engine, 6600-hp Locomotives for UP', pp5 & 6.

(8)   See IEE paper #967, 1950, 'Mechanical Design of Electric and Diesel-Electric Locomotives', by Cox (BR).

(9)   See Railway Mechanical Engineer 1927 July pp.435-437.

 

 

Cheers,

[BDA]

We already have weight and fuel tank capacity issues at 134 metric tonnes on 6 axles . From what I've read our new Evolution based units won't have the US std AC traction motors and are going to be limited to 7800 litres of fuel .

This won't work on our interstate trains without in line fueling so an even smaller (shorter) tank may not make much difference . 

Another two axles/traction motors and 44 tonnes definately would .

I can't see any other way around the performance issues on our lighter 60 kg/meter rail etc .

 

[bogie_engineer]

About 12 years ago I was tasked with designing a 4-axle meter gauge bogie for the SD70ACe-BB Progress Rail sold to VLI in Brazil. Axle load was limited to 24.5 metric tons. The meter gauge AC motors used were the SD70MAC cross-section with 43" wheels. I was able to keep the bottom plate height the same as the standard SD70ACe by using a fabricated span bolster that is partially tucked into the underframe and is hollow to distribute the cooling air to the TM's which receive full  ventilation regardless of bogie rotation. To keep the 2-axle sub-bogies compact and low, they use drop equalizers with the primary springs below the H-shaped bogie frame. The motor arrangement is unique in that all motors are on the same side of the axle as is common on low weight shift 3-axle bogies. To optimize weight shift performance with the axle hung motors, the motor nose supports are connected to the bogie frames at axles 1 and 3 - the nose supports for axles 2 and 4 are connected to the span bolster. Weight shift performance is equal to high adhesion 3-axle bogies, unlike the typical span bolster arrangement using two axle bogies with facing motors.

The span bolster has a pin on top that engages a pivot with fore and aft rubber pads that transmit the tractive force into the underframe but allow for lateral motion. Rubber compression springs on "wings" at the bolster ends support the underframe and transfer the load directly to a second set of rubber compression springs on the underside of the "wings" that engage the bogie frames. This allows for a simple bogie frame with short bending moments between spring sets. The equalizer suspension is unique in that the axle bearing adapters connect directly for traction thru a rubber bushing pinned to the equalizer and a rubber pad carrying the vertical load from equalizer to bearing adapter. Lateral thrust pads handle lateral forces between bearing adapter and bogie frame. A rubber bushed link connects the equalizer with the bogie frame to transmit tractive and braking forces. With this arrangement, there are no wearing friction surfaces that require weld build-up/re-machining at overhaul and provide consistent performance between overhauls.

Given the length of any 4-axle bogie and the resulting loco length with any reasonable fuel tank size, I doubt this would be seen anywhere in Australia except the iron ore RR's like BHP.

GBB Bogie

Dave

[Overmod]

Part of the reason for the double-B systems was certainly the traction-motor capability possible on the narrower gauge with wheelbarrow-suspended motors.  However, we should consider the EMD experimentation with the arrangement (at one end of a test locomotive) -- we have had both threads and informed discussion about this.

I think we've covered the 'alternative' to using span bolsters (which can increase height) on some of these locomotives.  One alternative is to pivot only the outboard trucks (the inside ones could be, but guiding would be sadly affected!) with the inner trucks free to 'float' transversely, as on the three-truck PRR experimental electric.  Those inside trucks could be allowed some controlled rotation as well as lateral accommodation without compromising ZWT tractive effort to the locomotive chassis.  I doubt you would see any modern diesel locomotive or conversion with the trucks articulated in line, with couplers on the truck framing, since the fuel tankage would be in the way.

[M636C]

BDA

Hi all , I was looking around earlier and noticed that Wabtec and Progress build export locomotives with 4 trucks and 8 powered axles .

I am interested to know how the four bogie systems work as in how they articulate for track curvature . 

Here in Australia our axle loads are lower at around 22-22.3 metric tonnes vs 30 plus in the US . 

I'm wondering how we would go with 8 axle units that would maintain up to 22.3 TAL (178T gross) but give us better adhesion performance . In theory it would allow us to use smaller lighter AC traction motors than current in US but still have decent performance . 

The down side could be less space for a decent sized fuel tank but that would depend upon frame length . Recently Progress made the narrow gauge GT46ACe for Adani and its frame was a bit longer than our standard gauge units . It'd be interesting to see what could be done with the same frame length but laid out more like the GT46ACe they are currently making for Australian operators , but in BB configuration . Wabtec has been doing similar things to Progress with GE Evo based units on Metre gauge export units .

 

Thoughts ?  

 

It was GE that originated the four truck design, using the standard truck they used on small narrow gauge units linked by a span bolster, much as the UP Gas Turbines used. EMD started off by building the DDM45, an SD45 on the four axle Flexicoil. Later they copied the GE design.

In the case of the DDM45, which ran on a metre gauge iron ore line, the problem was that the motors weren't powerful enough, so four motors were needed to deliver the engine power to the track. While the axle load was reduced, that wasn't the main problem.

Vitoria a Minas had a number of Krauss Maffei 4000 HP diesel hydraulics, basically the same as the second Southern Pacific order, which retained the three axle trucks and presumably, the same axleload on metre gauge.

The Australian GT46C-ACe units already have domestic USA traction motors, those used on the SD70MAC. Apparently, SD70ACe motors wouldn't fit within the size restrictions. 

In Australia, I think loading gauge restrictions would mean that there was no clearance for these double bogie locomotives.

Peter

[BDA]

Hi all , I was looking around earlier and noticed that Wabtec and Progress build export locomotives with 4 trucks and 8 powered axles .

I am interested to know how the four bogie systems work as in how they articulate for track curvature . 

Here in Australia our axle loads are lower at around 22-22.3 metric tonnes vs 30 plus in the US . 

I'm wondering how we would go with 8 axle units that would maintain up to 22.3 TAL (178T gross) but give us better adhesion performance . In theory it would allow us to use smaller lighter AC traction motors than current in US but still have decent performance . 

The down side could be less space for a decent sized fuel tank but that would depend upon frame length . Recently Progress made the narrow gauge GT46ACe for Adani and its frame was a bit longer than our standard gauge units . It'd be interesting to see what could be done with the same frame length but laid out more like the GT46ACe they are currently making for Australian operators , but in BB configuration . Wabtec has been doing similar things to Progress with GE Evo based units on Metre gauge export units .

 

Thoughts ?