Steam & Excursion > Lima Articulated Truck/Frame Explained

There have been several threads recently mentioning Lima's articulated trailing truck and frame, so I thought I'd whip up
a couple of sketches showing what this is, and how it differed from more conventional designs.

Lima had a LOT of great ideas when it came to innovation and improvement in steam locomotive design, but this wasn't one
of them!

Conventional non-articulated "delta" trailing truck
A. Boiler attached rigidly to frame via cylinder saddle
B. Sliding pads on frame at 4 corners of firebox allow boiler expansion/contraction but no lateral movement
C. Tender drawbar attached to frame
D. Trailing truck hinges on frame
E. Tailpiece of frame which supports firebox is, itself, supported by the trailing truck by "heart rocker" centering
devices
F. Front 2 driving axles (on both sides) and two wheel pony truck are equalized together
G. Rear 2 driving axles and trailing truck are equalized together on each side, thus providing "three point" suspension
for the entire locomotive


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Lima Articulated trailing truck
A. Boiler attached rigidly to frame via cylinder saddle
B. Sliding pads on frame at 2 front corners of firebox allow boiler expansion/contraction but no lateral movement
C. Tender drawbar attached to trailing truck
D. Trailing truck hinges on frame
E. Tailpiece of trailing truck supports rear 2 corners of firebox by lateral sliding pads, allowing truck to swivel but
with no centering devices.  A centering device would put undue stresses on the firebox
F. All 4 driving axles and two wheel pony truck are equalized together
G. 2 axles of trailing truck are equalized together on each side, thus providing "three point" suspension for locomotive
H. On coal burners, the ashpan was attached to the top of the trailing truck, rather than to the mudring, and swiveled under the firebox along with the truck
No locomotives were built with articulated trailing truck and 4 wheel leading truck.  There would be major problems
equilizing such a locomotive

It's easy to see that the articulated truck bore all in-train forces, and why it was unstable, particularly when backing
on curves.

-Larry Doyle
 

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Thanks Larry, that really explains it and it certainly doesn't look like a good idea.
Maybe Will Woodard had a bad day.

One thing I can't quite understand, and maybe it is just because I am a little tired at the moment is the theory of three point suspension and equalization.
I follow the diagram with the equilizers, but not sure I understand the term "3 point" and am trying to digest the two diagrams and how the locomotive would react and track as well as apply tractive force in each case.

Also, were any locomotives constructed like this ever rebuilt to standard configeration ?  If so, examples ?

Thanks again for posting this information.

train1275 Wrote:
-------------------------------------------------------
> Thanks Larry, that really explains it and it
> certainly doesn't look like a good idea.
> Maybe Will Woodard had a bad day.
>
> One thing I can't quite understand, and maybe it
> is just because I am a little tired at the moment
> is the theory of three point suspension and
> equalization.
> I follow the diagram with the equilizers, but not
> sure I understand the term "3 point" and am trying
> to digest the two diagrams and how the locomotive
> would react and track as well as apply tractive
> force in each case.

All steam locomotives of conventional design (i.e., not Shays, Climax, etc) sat on the track like a three legged milking stool!

Below, notice on this Mikado that driver axles 1 and 2 are equalized together on each side, then cross-equalized behind the cylinders and linked to the leading truck.  This forms one leg of the stool.

The third and fourth driver axels on the left are linked together with the left trailing truck bearing, forming the second leg.  Likewise, on the right side to form the third leg.
>
> Also, were any locomotives constructed like this
> ever rebuilt to standard configeration ?  If so,
> examples ?

Yes, but I'll leave it to others to describe their favorites.
>
> Thanks again for posting this information.

You're welcome!!  Thanks for reading it, and showing your interest - you might entice me to post more.

-John

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Ahhhh !!

Yes, I get it now !!

 Thank you for this explanation!  I've often heard about the spring rigging, but this explains it.

Hi, All..

My hallucination is that the Lima Articulated truck preceded the complex art of casting the one-piece 'engine bed'.
The articulated truck was a design compromise that had to be made.... There was no alternative, at the time.
To support that large grate area, Lima had to use the 4-wheel trailer truck.

The process of successfully casting huge loco engine beds took many attempts and failures.
it was several years before there were reliable cast, one piece engine beds......
A lot of the structural flaws in the cast engine beds only showed up under continuous, hard use.
Improvements were constantly added.

Today, Replicating reliable cast frames are an almost lost art....especially for large castings.

LarryDoyle's explanation is superb. 

Wes C.

 

wcamp1472 Wrote:
-------------------------------------------------------
> Hi, All..
>
> A lot of the structural flaws in the cast engine
> beds only showed up under continuous, hard use.
> Improvements were constantly added.

> Wes C.

Wes, 

the New Haven's 10 Baldwin-built Hudson's were afflicted with the malady that you describe.  It plagued them throughout their service lives.

Bob Callahan
Monticello, IN

You can really bewilder people explaining what a change to one point of the spring rigging can to throughout.  It's kind of an art when you think of it.

A recent thread showed that a handful of the Texas & Pacific 2-10-4s were rebuilt with new frames and the standard trailing truck.  I don't know of any others similarly rebuilt in kind (i.e. 2-10-4 to 2-10-4).  That of course doesn't mean such an animal doesn't exist.

Illinois Central hatched a plan to rebuild its 51 Limas into high speed freight 4-6-4s with new frames, Boxpok drivers and conventional trailing trucks.  The prototype rebuild turned out to have too low a factor of adhesion and, being a very slippery engine, it was not duplicated and was retired after a few years.  The rest of the Limas were modified in kind and renumbered from the 7000 to 8000 series.  7050/8049 was the original A-1 of 1924 and, given its status as the original Super Power locomotive, it is a shame that it wasn't preserved.

Mary McPherson
Dongola, IL
Diverging Clear Productions