Locomotive suspension systems

Discussion of specific prototype locomotives and other equipment of all gauges.
Chester
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Locomotive suspension systems

Post by Chester » Sat Mar 09, 2013 3:27 pm

In a thread I was reading on the mylargescale forums talked about the way the pilot and trailing truck effect the running of the locomotive into and out of curves. A couple of posts said that the four wheeled pilot trucks basicly acted like our models, but that doesn't seam right.

Does any one have info on the suspenion system of the 4-4-0's?

Thanks

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James
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Re: Locomotive suspension systems

Post by James » Mon Mar 11, 2013 3:54 pm

Are there models with prototypical suspensions? If so they must inhabit the upper end of the price range. The only model 4-4-0's I've ever owned (cheaper models admittedly) had the driving wheels rigidly attached to the frame and a "floppy" lead truck with excessive side play for the purpose of rounding sharp curves.

A 4-4-0's suspension is rather more complex than might be expected and I can't really describe it adequately in mere text while making sense. You want a drawing. Basically the locomotive's weight was carried on three points--a single point for the lead truck, and a point on each side for each pair of drivers. As such it was extremely stable for the same reason as a camera tripod. Suspensions evolved over the years and by the time the 4-4-0 matured it was common to see systems of links and levers allowing the proportion of weight carried on the drivers versus on the truck to be altered.

Smooth tracking was a large part of why the 4-4-0 maintained such dominance in the United States into the 1880's. Good tracking and steady running doesn't simply keep the locomotive on the track; it also reduces rail wear. That latter advantage was probably even more important than the former during the era of iron rails and questionable roadbeds. "Modern" 2-6-0's and 2-8-0's with equalized suspensions appeared during the mid 1860's but they only gained popularity slowly due in part to having a reputation for being harder on track than 4-4-0's.

4-wheel pilot trucks, specifically, by the 1870's tended to be made most often with swing bolsters to allow side-to-side play. The gravity-powered centering motion inherent to the swing bolster naturally steadied the locomotive. Often a radius bar was used to further assist the truck in guiding the locomotive through curves. Sometimes though the truck was made with a rigid bolster and the first pair of drivers left without a flange instead. You can see this latter construction method on the Santa Cruz Railroad's "Jupiter" in the image gallery on this site--the first set of drivers clearly has no flange.

Trailing trucks don't necessarily do much to guide a locomotive. It depends on the job the locomotive was intended to do. Some locomotives with even 4-wheel trailing trucks (like NKP's Berkshires) weren't really meant for running in reverse and did so only slowly for the most part.

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Re: Locomotive suspension systems

Post by John Coker » Mon Mar 11, 2013 8:26 pm

Yes, there were several models produced with working suspension systems, all (as far as I know) were produced in On3. Most were made by a Japanese builder, Kodama, in the 1970s. From what I understand he made a D&RGW K-27, a NCNG #5 2-6-0, a Class 8-18 4-4-0 and a Ma and Pa 2-8-0 in O scale. The 2-8-0 is extremely rare. San Juan Car made a plastic C-16 that had full suspension. Hardly anyone built the model, and they are also rare.

The K-27 is perfect. It has a Bissel post (weight over the pilot truck), transverse equalizers, connected into 1 and 2 drivers. 3 and 4 drivers were tied to the trailer truck, as in the prototype.

The NCNG #5- well, not so complete. The Bissel post and transverse equalizers are not on the model, though 2 and 3 drivers are equalized. The prototype had the pony and #1 driver equalized.

The 4-4-0 has 1 and 2 equalized. Apparently there was no equalization from the drivers to the 4-wheel pony truck on the prototype. The 2-wheel pony gave 4-4-0s an extremely stable ride, and made them very popular. The model has working Stephenson valve gear-how cool is that?!

All of the Kodama models run beautifully. I am fortunate enough to own the three described. Most larger live steam models have equalized spring rigging.

Railroading is like all technologies on a developing curve. As the heavier locomotives appeared, so did heavier rail. The Rio Grande narrow gauge main lines went from 30 pound rail , to 40, to 52, to 70, and finally 85 pounds per yard. While pony tucks did indeed work to guide engines smoothly and safely around curves, trailer trucks supported the larger fireboxes as well as kept engines from jerking through curves. Equalization? When working correctly, they keep all wheels on the track . When going down the railroad, the springs are equalizing quickly, in a jerky dance. Consequently the spring rigging wears out every few years and accounts for a lot of rebuilding.

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Curtis_F
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Re: Locomotive suspension systems

Post by Curtis_F » Thu Mar 14, 2013 2:16 pm

On early 4-4-0's (1850s - 1870s) is was not uncommon for the Engine Truck to be a rigid design with a bolster in the middle which would allow it to pivot around it's center point. When this was used the front drive wheels were Blind (no flanges) so the locomotive guided on the 4 wheels of the Engine Truck and the rear drive wheel set. This same arrangement was used, though in reverse, on 0-4-4's of the same time period

However, when negotiating tight curves the front drivers could, and would, slide off the rail head and put the locomotive on the ground. This setup also kept the weight on the drivers and on the Engine Truck constant.

I'm not sure when it was first implemented, however the design migrated to having flanges on all drive wheels, but giving the Engine Truck a Swing Bolster. Now the truck could pivot around it's center and travel left-and-right. The major advantage was not the travel horizontally, but the vertical travel that the swing motion induced.

Like a yo-yo at the end of a string when you swing it left-and-right it travels in an arc around your finger which also changes it's altitude. The further you swing it away, the higher it rises. Swing hard enough and it'll travel a full 360 degrees around your finger and over the top of your head.

The Swing Bolsters would pivot, move laterally and LIFT the front of the locomotives. Or the rear of the locomotives if we're talking about 0-4-4's. This takes weight off of the front drivers and puts more weight onto the Engine Truck. If you let the yo-yo hang it will always go the lowest point that it can, that is to say it'll hang straight down. The Swing Bolster is the same way, it doesn't want to be swung, it wants to return to its neutral, straight down, position.

Say a 4-4-0 goes into a left hand curve. The Engine Truck turns left, moves to the left, the bolster swings and lifts up the front of the locomotive. This raising of the locomotive transfers weight from the front drivers onto the engine truck, and like a yo-yo the Swing Bolster wants to return to neutral, this applies side-force onto the front of the locomotive which PULLS the front of the locomotive to the left. This also pulls the front driver flanges away from the rail head preserving the flange which otherwise would be grinding on side of the rail head.


I've seen lots of models that have trucks that pivot, and most have little slider plates which let the Engine Truck move left-and-right, but I've never seen a mass-produced G gauge or smaller locomotive that had a functional Swing Bolster which actually lifts and guides the locomotive just like the real thing.


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Curtis F.
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James
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Re: Locomotive suspension systems

Post by James » Fri Mar 15, 2013 4:48 am

Speaking of which, locomotives could be built with sliding bolster lead trucks. It doesn't seem to have been a particularly common style of construction though, at least not during the era I'm familiar with.

Chester
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Re: Locomotive suspension systems

Post by Chester » Mon Mar 25, 2013 4:59 pm

Hey thanks for all that information. I've known about the pilot truck used for guiding the locomotive in and out of curves, but never understood how. And for the trailing truck, I've always known that they were for supporting the firebox on standard gauge locomotives. I would imagine on the big mikados the trailing truck is used for support also. On the Sandy River & Rangeley Lakes 2-6-2's the trailing truck was also used for guiding when running in reverse which they had to do when working the branches.

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Curtis_F
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Re: Locomotive suspension systems

Post by Curtis_F » Tue Mar 26, 2013 2:39 pm

Chester wrote:On the Sandy River & Rangeley Lakes 2-6-2's the trailing truck was also used for guiding when running in reverse which they had to do when working the branches.
Chester,

The vast majority of trailing trucks, regardless of gauge of locomotive, do guide the locomotives as well. Though generally to a lesser degree than the front trucks. In the case of SR&RL 2-6-2s the trailing and lead trucks are very similar in design, construction, and have the same ability to lead the loco through curves. As you noted, that's great for bi-directional running.

Both the SP 4449 and UP 844 have Commonwealth "Delta" style trailing trucks that swing side-to-side on large "Heart Rockers" which do lift a tiny amount, so they can carry a lot of weight but guide very little.

The Sumpter Valley Ry 2-8-2's #19 & #20 have trailing trucks that slide left-right, but don't lift so the weight on them is constant, and they use a pair of large springs between the loco frames that push against pads on the trailing truck to act as a centering device, so they do help guide the locos also.


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Loco112
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Re: Locomotive suspension systems

Post by Loco112 » Wed Mar 27, 2013 8:00 pm

" The Sumpter Valley Ry 2-8-2's #19 & #20 have trailing trucks that slide left-right, but don't lift so the weight on them is constant, and they use a pair of large springs between the loco frames that push against pads on the trailing truck to act as a centering device, so they do help guide the locos also".
The D&RGW K-28 and K-37 (that has the K-28's trailing truck?) both have the slide left & right trailing truck that also has the "big spring" centering devise (behind the trailing truck).

I was told buy a guy (who should know if anyone does) that the K-27 will derail often when backing through turnouts, he said "because its trailing truck is not very effective in centering or guiding it in reverse".

The ultimate in NG trailing trucks (in the 1920's) has to be the Uintah's #50 & #51 cast steel delta link equipped commonwealth style trailing truck (did I get all those typically Std gauge terms correct?). Its too bad that work of art didn't come along a few years earlier and make it onto the later Mikados, and there is no reason for it not making it onto the K-37's except for some bean counters economy measures. He must have seen that the end was near and saved those few extra beans for the Std gauge steeds.
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Re: Locomotive suspension systems

Post by Curtis_F » Thu Mar 28, 2013 9:55 am

Loco112 wrote:cast steel delta link equipped commonwealth style trailing truck (did I get all those typically Std gauge terms correct
hehe. Trailing Engine Trucks are a rather over looked area of research regardless of gauge.


Type: Commonwealth

"Commonwealth" is a type of frame design/construction developed and patented by the Commonwealth Steel Company (later General Steel Casting Co.). The hollow cast frame design which would become synonymous with, and carry the name of, the company was developed for tender trucks, then adapted to Trailing Trucks, then front Engine Trucks, and later diesel locomotive trucks.

Several thousands of standard gauge locomotives were built with Commonwealth tender trucks.

Style: Delta

"Delta" style are 1, 2 or 3 axle Trailing (or Front) Engine Trucks designed and patented by the Commonwealth Steel Co., so all Delta are Commonweath, but not all Commonwealth are Delta. The design uses a Commonwealth hollow cast frame, internal equalization arms that tie into the locomotive driver suspension, outside-of-wheel bearings (Plain or Roller), and large Constant Resistance Heart Rockers for steering and load carrying capacity. Many standard gauge Delta Trailing Trucks had the mounting pads for Franklin Locomotive Boosters cast into them as a standard practice for possible retro-fits later in the service life of the locomotive.

I'd venture to say the "Delta" was the most successful Trailing Truck design in the history of steam locomotives, and possibly the most produced.


The Uintah 2-6-6-2s had "Commonweath Delta Trailing Trucks".

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Curtis F.
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Re: Locomotive suspension systems

Post by John Coker » Thu Mar 28, 2013 2:05 pm

Interesting thread. Since I am familiar with some NG engine design I add my 2 centavos.

4-wheel pony trucks had a slightly complex and ingenious swing design so they could move laterally through tight curves. Hard to describe but but makes sense when one see the truck. As Curtis says the swings lift the locomotive front as it tracks into a curve.

Chester is also right- trailers act well as a guide truck as well as support. Alco used a trailer design that mainly supported the frame directly by means of a plate on the truck sliding on a plate on the frame. SV 2-8-2 s, K-28s and K-37s all had this crude but effective design. It accounted for a smooth ride. Slather on the gear lube, though.

K-36s had a Hodges truck. The truck supported the frame by means of a swing , a lever as well as equalization. These engines ride rough but stay on the rails(most of the time). I worked on 463 a LOT, switched with it a LOT. I never had any problems with its trailer derailing. Maybe other engines in this class did.

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