Ralph Johnson's The Steam Locomotive Appendix C HP Calculations

[bcrawford]

https://babel.hathitrust.org/cgi/pt?id=mdp.39015004535301&view=1up&seq=580&skin=2021

According to Mr. Johnson, the potential horsepower of some steam locomotives is as follows (Unfortunately, some of them are cropped out):

PRR K5 4-6-2: 3822

C&O L-2 4-6-4: 4465

B&O T-2 4-8-2: 5064

ATSF 3765 4-8-4: 5344

Milwaukee Road S-2 4-8-4: 5499

ATSF 5001 2-10-4: 5964

S.A.L. R-1 2-6-6-4: 4877

C&O Allegheny 2-6-6-6: 6980

Western Maryland M-2 4-6-6-4: 6345

Western Pacific M137/151 2-8-8-2: 6463

DM&IR M-3 Yellowstone 2-8-8-4: 6801

Union Pacific Big Boy 4-8-8-4: 6167

PRR T-1 Duplex 4-4-4-4: 4627

 

My question is how close to tested performance are these figures for those that have been tested? The Big Boy and Allegheny appear to be close to tested figures, but what about the others?

I ask this because I pretty sure that some of these engines were never tested, so I'm curious as to whether one can ascribe the potential figures to the untested locomotives?

 

Thanks for any help, 

BCrawford

 

 

[timz]

You mean, how reliable are his calculations?

He gives his formulas, earlier in the book. He would figure so many pounds of steam evaporated per square foot of heating surface, and so many horsepower per pound of steam, and so on. By coincidence, his estimates for the 2-6-6-6 and 4-8-8-4 are close to the engines' drawbar horsepower on test. But his figure for the 4-4-4-4 is low, as is his figure for the NY Central 4-8-4, and his figure for the SFe 3751-class 4-8-4 as built is high.

But his formulas are as good as any we know of, if you're trying to estimate horsepower from engine dimensions.

[bcrawford]

Thank you for your help

Its just that some of the figures suprised me, notably the Missabe Yellowstone at 6800 and the WM challenger suprassing the Big Boy, which is why I asked if those figures should be taken seriously or with a grain of salt.

Also, if you can, what horsepower figure did he attribute to the NYC 4-8-4? Unfortuantely, the person who scanned the book didn't get it in the scan.

Again, thank you for your help.

[selector]

From my reading, both the S1b and the T1 were in the 6000HP range, although 
I read one account that pegged the former closer to 6500.  I don't recall that those claims came from a particular author offhand.  And I agree that the claimed HP for the ATSF Northern is high by as much as 800 HP.

[timz]

When I mentioned Johnson's figure for the NY Central 4-8-4, I meant the figure you get, using his method. I'm guessing he didn't include it in his table.

Using his method--

NY Central S1b had 499 sq ft direct heating surface; Johnson multiplies that by 80 (see page 93 of his book) and figures the direct heating surface produces 39920 pounds of steam per hour.

The S1b had 4320 sq ft of heating surface in tubes/flues, and the tubes were 20 ft long, so (see page 93) Johnson figures the tubes/flues produce 9.2 pounds of steam per hour, per sq ft, so 39744 pounds per hour from them.

So 79664 total pounds per hour, except (on page 103 and 107) he says to increase that by 8% because of the feedwater heater. So 86037 lb/hr.

On page 166 he says since the engine has 275 psi boiler pressure and a type E superheater, it needs 17.75 pounds of steam per hour to produce a horsepower. (See also p176.) So his horsepower estimate is 4847.

His estimate for a SFe early 4-8-4 is 5203 hp. The only caveat: he says "modern" engines produce 80 lb of steam per sq ft of direct heating surface; I'm assuming he considered the 4-8-4 built 1927-28 "modern".

So, should you take these figures "seriously"? No. Should you ignore them entirely? No.

[bcrawford]

Thanks for breaking it down (the formula) timz, I was a little lost on how to calculate the horsepower, but I understand how to now.

With the talk of the niagara, I decided to look up the horsepower of the locomotive and I found a variety of drawbar hp values.

275 psi 79 in drivers 5050 (5070) dbhp @ 63 mph

290 psi 79 in drivers 5300 dbhp @ 63 mph

275 psi 75 in drivers 5200 dbhp @ 61 mph

https://nycshs.files.wordpress.com/2016/01/niagara21.pdf

from page 11 through the pdf reader(pg 23 on the document)

You were both indeed correct that the value is low using the formula.

Thanks for the help

[Overmod]

Keep in mind that there are three 'horsepowers' -- indicated horsepower, which for the Niagara can be the indicated 6680, and is derived from (as 'indicated') an indicator mechanism; wheelrim (usually measured as torque, not 'horsepower', and including some difficult/impossible-to-calculate variables like machinery and valve losses; and drawbar... which is the only thing that actually 'matters' as it is the thing that counters train resistance, e.g. as calculated from the Davis formula.

PRR in fact did not use 'horsepower' considerations, but charted drawbar pull directly against speed (you can get horsepower by simple calculation from any point on the resulting graph).  I have posted the comparison graph for the V1 turbine design multiple times here (although not in the delightful colors that the original at the Hagley is plotted with).

Note the discussion of the Collins method in Gerbracht's article, and what it implies.

I have wondered many times if a great deal of misery and misapplied capital could have been saved if appropriate practical testing of the Franklin System (at least the four-valve type-A version of it) had been done independently.  LeMassena is not of particular value (imho) in discussing this in relation to the Niagara; I have always thought the detail design of 5550 was to achieve 'comparable horsepower' to the piston-engined versions,with the advantage being greater operating economy (which was observed) -- in part this was to make poppet and Baker engines 'comparable' in making up trains for road service, and in part -- at least potentially -- to see if a 'sufficiently advanced technology' 4-8-4 could match the expected performance of the C1a (and thereby if given the 64-ton tender from that design, make Harmon-Chicago reliably without stopping for coaling...)