Lima 4-8-6

[Overmod]

ShroomZed

You know, was there ever a locomotive built with 'Unitary Machine Support' as depicted in the proposal? 

None that I know of; the principal advantage of two 'huge' inside cylinders was much better achieved, and of course much much more easy to maintain, through simple outside rod connections with better balancing (post-Eksergian) and lightweight 'high-dynamic' rod steels and detail design.

Part of the story also involved the general turn away from higher and higher single thrust pressures, together with the absolute peak in usable boiler pressure in a staybolted firebox that was somewhere between 300 and 315psi, combined with the perceived need to have 'higher' road speeds than even a somewhat 'optimized' CMS locomotive would provide.  The evolving issue is the water rate associated with the 'achievable' single-unit horsepower (which, remember, is a function of speed; it can be thought of as a measure of drawbar TE at speed).  By the time you get into what might be available with big cylinders (with lightweight pistons, hollow rods, and all that jazz) at high pressure, you either run into impossible cutoff issues, or the need for some kind of staged steam admission, or such a heroic mass flow (and hence water rate) that you need an appreciable part of the TE just to pull the water you need.  Consider that the PRR Q2 had a higher sustainable horsepower than any contemporary articulated locomotive, and that out of only five driver pairs... and a thirst to match.

Better to divide the cylinder capacity into a couple of engines in an articulated chassis, once you've solved the stability problems (which Baldwin started in 1930, N&W finished by 1934, and Alco commercialized widely starting a couple of years after that) and have, say, the D&H's conclusive and final answer to the high-pressure experiments: its Challengers.

Or divide heavy 2-cylinder thrust into a duplex configuration (and, if you are wise, conjugate it) if you don't want the high overall length.  

What you don't see is anyone attempting to merge the joy that is an AMC Berkshire with the joy that is a UP Nine; that is, attempting to make a 'Berk-and-a-half' by extending something like the successful C&O T-class 2-10-4 into a 2-12-x.  Either with two big inboard cylinders or three balanced ones.  And I think there are a fairly wide variety of reasons, mostly NOT accidents of timing or circumstance, that account for that.

Frankly it is difficult to imagine any twelve-coupled simple 2-cylinder-quartered engine much 'better' than something the size of a N&W A class (for the sane) or an Allegheny (for those who can pay for high-mass overcomplexity).  

[ShroomZed]

You know, was there ever a locomotive built with 'Unitary Machine Support' as depicted in the proposal? 

[Overmod]

Paul Milenkovic

There was a "wild" proposal for a Lima 2-12-6

This was from the pre-AMC-inspired Woodard, 'of a piece' with outside dry pipes, articulated trailing trucks, and other thermodynamic besserwisser ideas that were not so hot when they actually had to be built and run.  

'Central Machinery Support' was little more than the idea of keeping the thrust lines of the cylinders as far inboard as possible to minimize the augment couples from very heavy cylinder thrust -- the same principle the late Belgian Atlantics used to permit higher ultimate speed.  If you look at the plan view of the 2-12-6 you can clearly see how this was implemented -- note the distance between the comparatively large cylinders, made as narrow as casting technology would permit.

The whole of the design is from the pre-Eksergian era where even 4-8-4s were almost necessarily an increase on drag-freight power ... or, as in the case of the NYC high-pressure 4-8-4, assumed to be run economically at what we consider lower speeds now, on a minimum of coal.

By the time of the 4-8-6, quite a bit of interesting wisdom, specifically including how to turn an earlier-era 2-10-4 into a reasonably fast road engine, was incorporated in design.

Tandem rods, here, are the earlier original idea: using the knuckles to divide the rod thrust from the pin thrust in a given wheel across two 'pins' via a divorced fork-and-blade connection strictly in the rods, and (via that fork-and-blade connection) keeping the thrust line along the rods as much in a straight line as possible.  (It was also valuable to keep as much of this 'straight line' as close inboard to the wheels as possible, net of projection of Brobdingnagian counterweights, for fairly easily recognized reasons...)

The later 'tandem rods' of the Timken configurations (as seen on the Niagaras, the earlier N&W Js, etc.) involved sandwiching the big end of the main rod itself between two lightweight intermediate rods, with a common rod arrangement behind that keeping lightweight rods inboard.  This of course had a certain amount of compromise whenever the main didn't bear on the leading driver, as you can see from pictures now that you know what to look for, and it is one reason the 'revised' arrangement on the Js puts the main rod entirely outboard of the rest of the rodwork, something a beginning student of balancing might think of as a huge step backward.

[Paul Milenkovic]

There was a "wild" proposal for a Lima 2-12-6

https://railroadlocomotives.blogspot.com/2010/12/blog-post.html

It was based on something called "unitary machinery support", which I supposed is another one of those things like "tandem rods" that I barely understand.

The most outrageous thing about the plan for a 2-cylinder 12-drivered locomotive (the Union Pacific type was 3-cylinder that kind of tempered the extreme forces on crankpins and balancing requirements), where the cylinders were way out in front ahead of the pilot wheels, if you could believe it.  Or don't believe it because it was never built.

[Overmod]

WM7471

I can't say for certain that there was never a proposal for a 4-10-6, but I have never heard of one.

Supposedly it was pitched to T&P.  (They are already notable for having supposed interest in a duplex-drive locomotive that is perhaps the ugliest approach to proposed streamlining in the often surprisingly-ugly pantheon of proposed examples -- a side view is in an older issue of Trains, and thankfully there are no perspective views.)

Meanwhile -- the thing I want to see is the drawings corresponding to the proposed Lehigh Valley 4-4-6-4 duplex -- complete with the little eight-wheel whatever-the-heck-it is as shown on the diagram.  (Knowing what I know about Q2s, I suspect it was a tender 'water bottle' in addition to the regular tender...) 

[Overmod]

IA and eastern

Where is the proposal for the counterpart 4-10-6 located.

Strange you should mention this.  There is a pencil sketch of just this 4-10-6 in the Casey Jones Museum in Jackson, TN.  

I believe it was developed using the side elevation drawing of Townsend's poppet-valved 4-8-6 published in Trains many years ago ... adding one driver pair.  All the universals and shafts for the type C valve-gear drive are faithfully rendered as there.

The locomotive could certainly have been built with 69" or 70" drivers (and appropriate lateral motion) with the double-Belpaire firebox and chamber expanded out to 'appropriate' clearances.  (The original Townsend locomotive in the ad was good for up to 76" drivers as lagged, but presumably for somewhat 'relaxed' clearances...)  

Expect it to have had the 'original' version of continuous-cam RC (as pictured in the '47 Cyc) rather than a stepped cam OC as was apparently applied to NYC 5500.  (Neither a stepped-cam RC design or the type D modification would have been particularly suitable for a fast, heavy freight locomotive with these characteristics.)

Note that the 6-wheel trailer would likely be similar in layout to an 'extended' version of the latter Niagara trailing truck, with comparatively short wheelbase and optimized axle placement.  It is needed because of the added weight of the double Belpaire, syphons/circulators, etc. and not because it's enormously 'bigger' than, say, a two-cylinder version of a Q2 chassis -- which involve as much horsepower as you practically need out of a rigid-frame locomotive before your water rate gets ridiculous for practical tender (or pan!) capacity.  That means, in part, that any increase in 'length' or perceived rigid wheelbase is relatively trivial compared to any other ten-coupled layout with similar driver diameter (say, the KCS 2-10-4s).

Note that a principal reason why the Lima designs didn't call for a 2-10-4 is the additional weight of the type C gear and tracting ... which was considerable and couldn't be located where it conveniently increased working adhesion.  Even on four-wheel lead-truck engines equipped with similar gear, the weight on the truck axles could be amusingly high.

 

[WM7471]

I can't say for certain that there was never a proposal for a 4-10-6, but I have never heard of one.   The Lima proposal for the 4-8-6 was an atempt to genterate in interest in a "2nd Generation" Super-Power steam locomotive by extending the trailing truck to increase the size of the firebox. 

The proposals came at the end of the end of steam power as Lima was trying to find ways save their locomotive building business.  Unfortunatly for them,  EMD had other ideas.  

Also consider that a straight frame 4-10-6 would be too long to operate on most railroads at that time.

T.

[IA and eastern]

There was proposals for Lima 4-8-6 but there was other proposals for 4-6-6s for the MP and Rock Island. There was aproposal for rebuilding 2-8-4s into 2-8-6s. Where is the proposal for the counterpart 4-10-6 located. Gary