Can anyone provide me a simple explanation of how the size of locomotive driver counter weights was determined? I'm sure it has much to do with the weight of the rods involved, coupled with the force of the stroke. On big locomotive, the main driver has an enormous counter weight, and the others are lesser. Still, how was this determined?

Richard, it is my understanding (and hopefully everybody will correct the parts of this that I get wrong) that in typical "compromise" counterbalancing, about half the weight of the reciprocating parts being carried by each driver gets compensated. The large counterweight on the main driver is due to having to compensate for the weight of the combined set of reciprocating components as they pass the front and rear limits of the stroke. Since the weights are not applied in the same plane as the reciprocating parts, there is a rocking couple from side to side which results at each driver, and this has to be further compensated by cross-counterbalancing the opposite driver. The amount of cross-counterbalancing needed is a function of the effective lever arms from driver to rods and from driver to driver. In practice the cross-counterbalance weight and compensating weight get combined which results in the angular offset of the weight from being opposite the crankpin. Sorry for any terminology errors.

PC

From Mastering Momentum, edited by Louis Sillcox, 1941. “Dynamic augment is defined as the difference between maximum dynamic and static forces directed vertically downward upon the rails-generally referred to the driving wheels of reciprocating steam locomotive. Dynamic augment is always present in the operation of this type of motive power. The ideal design can limit and accurately control its value but it can not eliminate dynamic augment in any steam locomotive of conventional pattern if a part of the unbalanced force arising from the weight of reciprocating elements is to be balanced by inserting counterbalance weights in the driving wheels. Perfect rotating balance of a steam locomotive individual driving wheel is impossible to obtain without the equivalent duplication of existing unbalanced weights on the opposite side of the wheel and doubling the counterbalance weight. This is for the reason that the necessary elements of rotative unbalance are represented by the crank pin and the weight of the valve gear and the rod portions which attach to it. These masses rotate in a plane outside that of the wheel, yet any effort to counterbalance must insert weights within the wheel itself.”

And later, “Ideal theoretical dynamic balance of self contained weights can be obtained and the problem would not be difficult were there no forces present which require compensation, other than those introduced by rotating elements. The reciprocating piston, rod, crosshead, and excess reciprocating component of the main rod, however, introduce horizontal fore and aft forces and these, if not absorbed within the axle assembly upon which they directly react, or distributed among all driving wheels, transmit unbalanced couples, tending to rotate the locomotive about a vertical axis and to tear the structure apart.“

Later yet, “Maximum allowable dynamic augment for any locomotive driving wheel is generally defined as a percentage of static weight at a specific speed in excess of the actual static weight on the rail. For instance, for a passenger locomotive, maximum dynamic augment may be given as forty percent of the static load at eighty-five miles per hour. If the axle load is 60,000 pounds, the specification requires that the momentary wheel load must not exceed 42,000 pounds at the rail. Some such excess is unavoidable and increased speeds is one factor favorable to the trend toward the Diesel-electric locomotive.”

Mr. Cook and Mr. Johnston, thank you for the explanations. While reading, I had to graphically picture the rod and driver componenets in various planes and angles as they would crank. Hard to believe that these are "simple" explanation, but I get the picture. Steam locomotive design must have been an art form of standards and hidden little "tweaks" that master locomotive men knew, and squirreled away for further exploitation. When you got to locomotives like the PRR Q2 duplex, the extreme engineering must have been fearful. Given steam locomotive building in a computer age, perhaps much of that knowledge would have been plugged into ideal design programs, and Baldwin, Lima, American, or Juniata, might have planned a locomotive with a design fabrication coming out in numbers and drawings. The tweaking of the design would be left to the masters and the operations department. I suspect the two technologies would not be incompatible, but we'll likely never see such a thing come together in this world; a bit like dinosaurs and mammals, they lived in diverse ages.

Thanks for your research, time, and explanations.

I'm an electric guy and readily admit ignorance of things that reciprocate.

However, the thought came to mind. With today's computers I'm sure someone could come up with a program that could fairly quickly calculate all the factors and result in a solution determining the weights of the varios counterweights on the drivers for a given locomotive.

At this late date the results of this exercise would be academic but I wonder if someone could do the computer figuring to see how close the engineers at Baldwin, ALCo, et al, came using their slide rules and hand cranked calculators.

Maybe someone has done this already?

Baldwin blew it on at least two designs, the Atlantic Coast R-1 Northern was so bad that it was actually hopping off the rails at speeds of 80 to 90 mph. This was determined by high speed photography done by BLW. In this case, the R-1 was over compensated and had weight removed. But even so, they were limited by rule to no more than 90 mph although some authors report higher speeds in actual service.

The other design was the NH I-5 Hudson class which had counter balance problems that appear to have been resolved.

Both of these engines had 80" drivers which in theory are easier to counter balance. On the other hand, N&W engineers were able to correctly calculate the counter balance on the J Class 70" drivers so that speeds of 100 mph were routinely achieved.

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Just out of curiosity, what is a gently curved track? I thought the J's were capable of negotiating the typical 10 or 12 degree turn-out in a yard. I know that during the 611's first trip to Norfolk in the Steam Program, they couldn't turn it the because some of the turns were made tighter since the days of steam in the Lambert Point yard but I don't know the radius of the turn that stopped them.

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I think you are quite accurate with your comments Kelly, a good friend who is an avid student of steam locomotive design made very similar comments about the construction of the "J" to me some time ago.

I believe you. Just I was trying to observe that an engine that can't navigate through a standard yard is an operational headache. Do you have any idea what the maximum curvature the "J" could handle? As my screen name indicates, my real interest is in the very little engines.

I long ago became very suspicious of speed claims about steam engines. Many of the engines that Mr. Linwood Moody reported doing 50 and 60 mph had no counterbalancing at all that can be discerned in photographs. The reality was probably closer to the non-foamers of the time reporting that they were better than walking … but just barely. <G> But I still find them charming.

I can't answer the question about the degree of curvature, but I can assure you that the derailment occurred on Labor Day weekend in 1982. We had driven to Roanoke in a rental car with another couple to ride back to Alexandria behind 611. When we saw two dirty GE's pull the passenger train into Roanoke station on Sunday evening, there was much concern as to whether or not they would get 611 back to Roanoke in time to head to Alexandria. Fortunately they did, and the four of us had a great time riding home in the observation car. I did sneak to the baggage car on a couple of times so I could catch cinders.

I can't believe that it's almost 25 years ago.

Kelly,
Do your spread sheets take into consideration cross counter balancing. Could you talk a little about this as well.

Thanks

Circa 1987 I walked along side 611 as they turned her on the Y in Watkins Yard, south of Columbus, Oh. Recent highway construction had forced a regrade of one leg of the Y since the year before. At one point, the trailing truck started to ride up on the top of the rail even though the rail was greased. Crew climbed under and hammered wedges (I think) that somehow forced the flanges to drop back down as the crept the rest of the way. It seemed the crew knew just want to do. I've aways wondered what they did.

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