2-8-8-2 - Survivor, Operation, Size - Boiler Capacity, Efficiency, Power, Speed Inadequacy - Inquiry

I am assuming that since I cannot find any mention of anything larger than 2-8-8-2 on frisco.org, such Frisco engines never existed.

But I want to know for sure.

1) Are there any surviving SLSF 2-8-8-2s?
2) If so, are there any SLSF 2-8-8-2s in operation - OR - retired but operational if it was not for those dang required boiler inspections similar to SLSF 1522?
3) Did the SLSF ever own a locomotive with a wheel arrangement larger than 2-8-8-2?

According to Wikipedia, which I know is not foolproof by a long shot, UP was the only railroad to own 4-8-8-4 Big Boys.

 

I did some more seat of the pants calculations just for fun to compare the spots to the mallets.

At 15 mph, the spots would have had a swept cylinder volume of 3854 ft^3/min, compared to the mallet's effective swept volume, high pressure engine only, of 2896 ft^3 per min compound. This means the mallets would have used just 75% of the steam as a spot engine, making the boiler stats look pretty good in favor of the mallets.

86% of THS vs spots, but used only 75% of the steam. Tractive Effort for the mallets was 83,500 lbs compound vs 71,480 lbs for the spots, no booster, giving 16.8% more TE in normal operation, thanks to compounding.

Now for the HOWEVER. The mallets could run simple, boosting their TE to an astounding 100,000 lbs. Just as astounding is that this increased the swept volume of the cylinders to 10,234 ft^3 per min! The actual steam usage wouldn't have increased 353% like the figures suggest, since the mallets would have had a pressure reducing valve for the LP engine while in simple operation.

However, even if the steam usage doubled, the boiler would have been woefully undersized. A spot engine with the booster cut in could generate 80,230 lbs of TE, although I do not know how much steam the booster would have used. This comes close to the mallets compound TE.

Tweaking could have resulted in a more successful mallet, but only if they were not operating as a simple engine at very low speeds trying to drag the tonnage over the hills. If they were operating as a compound on the hills, they should have been just as successful as a spot, assuming they were not leaking away their efficiency. I also cannot really quantify the effects of a mallet's softer exhaust blast on steaming ability due to lowered draft for the firebox.

Regardless, both series of engines were doomed to be obsolete as the drag era came to an end. The mallets had a 57" driver diameter that was going to limit their top speed regardless of boiler capacity. Compare that to the 1500's 69" drivers, the 4300 and 4400's 70" drivers and the 4500's 74" drivers. Even the rebuilt 180 series Americans had 69" drivers. The mallet drivers were just 6" bigger than many of the 0-6-0 switchers.

I bet the sight of a mallet going faster than 10 mph would make a section gang break out in a cold sweat!

James

 

Okay, I get this much.

1) Larger diameter driver = greater circumference = greater distance per revolution = increased speed. It is sort of like gear ratios.
2) Larger boilers needed larger fireboxes, correct?
3) 2-8-8-2s small driver size and small fire boxes led to their downfall, correct?

So why were the 4-8-8-4s seemingly so much more successful relative to the 2-8-8-2s?

I understand that boiling water produces steam and steam pressure was used to move trains but even though I had an "A" in Physics 101, I was a music education major, not a steam engineering major, so please, put it in layman's terms.

They must have increased the firebox. Larger box = more fire = more heat = more steam.

They also must have increased the driver diameter to increase speed.

 

Ken,

I think you summed it up very well. Now I will do my best to muddy the waters.

So why do 4-8-8-4s seem more successful than 2-8-8-2s? The UP articulates were a much more modern design than our beloved Frisco Mallets. They were not mallets, since by definition a mallet is compound and the UP Big Boy and Challenger locomotives were simple.

The UP engines were designed to be fast freight and passenger locomotives - products of the school of Super Power design. While the Frisco locomotives were designed to be drag engines. Who cares about speed, just give me the maximum tractive effort!

Other railroads also had early compounds that suffered from not enough boiler. The Erie Triplex is an example that springs to mind.

Lima pioneered the Super Power concept with a 2-8-4. The Berkshire was targeting fast freight, so it had to have a high TE and horsepower. For horsepower production at speed, an extra large firebox was needed so the four wheel trailing truck was used to support the weight. An appropriate driver diameter was used to keep rotational speed down at high speeds.

The development of lightweight disc drivers and lighter reciprocating parts also helped with balance at high speed to minimize the tendency of the steam locomotive to pound the track out of alignment. Higher boiler pressures were used for greater power and efficiency. All of these design refinements found their way into the later engines, such as the Big Boy and Challenger.

Comparing the UP articulateds to the Frisco Mallets is like comparing my 2009 Silverado to my Dad's 1946 Chevy 1/2 ton. Two different schools of design, from two different eras, for two very different uses.

Nevertheless, I wish I could have seen a Frisco Mallet in action!

James