WEIGHTING A LOCOMOTIVE PART 2

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JKreider
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Re: WEIGHTING A LOCOMOTIVE PART 2

Post by JKreider » Fri Jun 10, 2016 1:44 pm

Not really sure why Don was offended, something I certainly did not intend on doing.
Don and Ed Yungling are very accomplished builders.
I thought that John Pennington and I were talking about weight distribution while Don was talking about fine tuning the equalization system with springs and such, something which was done on the prototype. I thought that we were talking about two separate things.
The equalization system is initially designed to provide three point suspension for stability and to properly distribute the weight of the locomotive over the wheels. It is done under static conditions.
I often hear somebody say that when a locomotive goes into a curve, the centering device throws more weight on the front of the engine. But the math shows (to use what I have discovered is a dirty word) that the weight on the pilot truck is merely converted to a vertical weight component and a centering component. The overall weight cannot change because the equalizing levers and components have not changed. That is assuming that the spring rigging is floating freely and nothing is bottoming out or not flexing as it should. (Don had a situation where he made an adjustment because the spring rigging was stiffer than anticipated and the engine was being lifted in the front.)
But as Ed has pointed out, when a locomotive starts moving, static equilibrium goes out the window and the spring rigging really can take a beating from shock loads. As the locomotive rattles, bangs, shifts, and bounces down the track, obviously weights and loads shift, springs compress and extend. The very purpose of leaf and coil springs, and changes such as what Don did, is to dampen that shock and to provide the necessary flexibility. Otherwise a locomotive would beat itself to death and not track very well. Those of us who have had a lot of cab time in the prototype at speed often wonder how these things stay on the track. However, changing or adding a spring is not going to change the static weight distribution. Leaf springs have a lot more damping capability than coil springs. Leaf springs are there to soften the heavier loads.
I’M MERELY EXPRESSING MY OPINIONS HERE. I’m not an expert on any of this. I thought that our discussions here on Chaski were meant to be fun where we learn and exchange ideas. But it is no fun when people get offended or they offend you. I have received calls where I have been told that they did not give a “you know what” about any math to the point of being insulting. Who needs that?
Jim Kreider

optigman
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Re: WEIGHTING A LOCOMOTIVE PART 2

Post by optigman » Sat Jun 11, 2016 2:15 am

Seems that math would have been used to engineer the prototype's spring and equalization systems. Pretty hard to argue with equations that show proof. I doubt I would want to run down the track at 70mph without someone doing the math to prove proper distribution. We are fortunate that Alco, Baldwin, Lima, & others had exceptional engineering departments to develop such fine machines and that the blueprints / information have been preserved for those who are interested in learning or modeling may do so. The only way a hobby such as this can survive is to share knowledge / information so others can learn and understand. The hobby has grown over the years and there are so many fine models that rival their big brother in many ways that engineers of the past would be impressed. :D

RET
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Re: WEIGHTING A LOCOMOTIVE PART 2

Post by RET » Sun Jun 12, 2016 10:37 am

Hi,

I'm not sure if I want to get embroiled in this controversy, but here goes.

As far as I know, English locomotives had individually sprung axles with no equalization. I believe things grew up this way because English track was better. In contrast, because of the greater distances, North American track was inferior so equalization had to be incorporated in addition to springs. The best example of this was the American 4-4-0 where the lead truck was one support point and the equalizers between the two driving axles provided the other two for a three point suspension. As more drivers were added, the equalization system had to be extended, but the goal was always to have a three point suspension.

From my own experience, I have found that for our models, proper suspension is essential. If the wheels can follow the track, the locomotive will stay on, no matter how much it dances and bounces about. If the axle travel is restricted in any way so the wheels can't move properly, the locomotive will come off every time.

For models without equalization, soft coil springs are the best, usually mounted below the frame as is the practice in some full size English locomotives. Where leaf springs are used in full size, there are two ways I know of to make them flexible so they will work as they should in a model.

In the first method, you use a combination of thinner leaves (the longest ones) together with black plastic "fake" leaves to get the performance you need. In the second method, you again use thinner material, but you combine that with bending each leaf to a different radius with the largest radius on the bottom (shortest leaves). This produces a "progressive" spring where the load is taken gradually by each leaf as the deflection increases. Very thin spacers between the leaves will help performance with this method. Both methods work, just choose the one that is appropriate for your situation. You can also conceal a coil spring inside a dummy spring to get the performance you need.

As an example, my 3 1/2" gauge Boston & Albany tanker uses a combination of equalization together with the progressive springing described above. The leaf springs actually work and work well! You can take this model and rock it over five degrees each side of center without having any of the drive wheels come off the track. That may not seem like a lot until you use a protractor to see how much 5 degrees really is. In this case, because the model is stationary, all of the flexing takes place in the leaf springs (not the equalization) and you can see the springs move and flex as they are supposed to.

With equalization, the whole idea is to keep the load on the axles constant as the track goes up and down and to make the suspension a three point system if possible. As the number of axles increases, this equalization gets much more complicated, but if you look at it a bit at a time, it is still basically the same.

For the main axles, the equalizers are just bars that are attached to the leaf springs at the spring ends with a pivot in the middle of the bar to keep the load on each drive axle the same. If the pivot wasn't in the middle, the load on the axles wouldn't be the same and in some cases (leading or trailing trucks), there are alternate pivot holes to allow for adjustment of axle loading.

To sum up, provided the equalizers are correctly made and installed, the springs work as they are supposed to and there is enough travel (more is needed on models) so nothing bottoms out, the loads on the axles will not vary even in corners. Generally, more vertical travel has to be allowed for in both leading and trailing trucks to prevent the situation Dave found before he made the changes.

Put simply, if the action of the heart rockers or swing links on the lead truck lift the front of the locomotive, there is insufficient vertical travel in the suspension. On Big Boy, I have added a concealed coil spring to the lead truck king pin and also to the caterpillar tender truck to give more vertical float. The equalization doesn't extend to the lead truck in either case.

Hope this helps a bit.

Richard Trounce.

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Loco112
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Re: WEIGHTING A LOCOMOTIVE PART 2

Post by Loco112 » Sun Jun 12, 2016 2:35 pm

There is an old spring truism that might be useful to remember when pondering our projects:

"A Shorter spring is a Stiffer spring".

That is true for: leafs, coils, torsion bars, etc.. If you shorten it, you stiffen it.
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Dick_Morris
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Re: WEIGHTING A LOCOMOTIVE PART 2

Post by Dick_Morris » Sun Jun 12, 2016 5:19 pm

In the first method, you use a combination of thinner leaves (the longest ones) together with black plastic "fake" leaves to get the performance you need.
Just last night I was deciding the proper lengths of alternating leaves of .040 spring steel and black Delrin for the springs on my Consolidation.

On the USATC Consolidations the front two axles and lead truck were equalized. The rear two axles were also equalized, but were independent of the front part of the spring rigging. I believe this was to make the suspension very flexible for the expected damaged track in Europe at the end of WWII.

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