LMS 4-6-2 Locomotives in Great_Britain

Class Details by Steve Llanso of Sweat House Media

Class Duchess - 8P (Locobase 1052)

Data from "Pacific Type Locomotive Hauls 'Coronation Scot'", Railway Age, Volume 106, No 14 (8 April 1939), pp. 819-821. See also [] (2 September 2004), quoting [Powell, A.J. Living with London Midland locomotives. 1977] ; Hollingsworth (1982); The CSA Illumina website -- [] (visited 12 July 2005), later found at [], last accessed 4 January 2018; and G. Freeman Allen (writing in Great Railway Photographs of Eric Treacy, 1987) .

Developed from earlier "Princess"-class locomotives, these were often described as the Princess Coronation class and nicknamed "Semis". These express four-cylinder engines, designed by William Stanier, ran easily on any service till the end of steam.

The Coronation locomotives showed the tapered boiler and Belpaire firebox typical of Stanier's design, but here the firebox was carried over a trailing truck and hence was wider than usual. Four piston valves of 9" (229 mm) diameter each allowed for relatively free steaming, although the RA account notes that the "exhaust passages in the cylinders have been carefully designed to give free exit to the steam without providing an excessive volume which would act as a reservoir." Many later received the Kylchap double blastpipe stack.

Steamindex noted AJ Powell's comments on this design that notes Stanier 's need "to produce a bigger boiler and then adapt the 'Princess' chassis to carry it. Bigger grate, bigger firebox volume, bigger free gas area, bigger barrel, bigger superheater + all these were incorporated in that delightful boiler. It was pushed upward so that the front corners of the Belpaire firebox were up to the limit of the loading gauge, just enabling 6 ft 9in wheels to be accommodated underneath it".

Powell then paused to ask: "(Incidentally, what was it so magical about 6 ft 9in diameter coupled wheels for express passenger engines in this country?)."

He continued by noting that Stanier retained the divided drive, but adopted a more conventional cylinder layouts that used rocking levers fitted behind the cylinders to actuate the inside valves. This avoided "valve setting troubles due to thermal expansion."

The US-published RA's 1939 impression of the 6220 was quite positive. The reviewer was duly impressed by the power in such a small package as LMS loading gauge limits came to 13 ft 2 5/8" (4.03 m) maximum height and 8 ft 10 5/8" (2.71 m) width. For comparison, the tightest of the three loading gauges described that constrained US 4-6-4 passenger locomotive size measured 15 ft 1 in high (4.60 m) and 10 ft 5 in (3.18 m) wide on the New York Central.

The CSA Illumina website summarizes the details of an article by W Alexander on the boiler's steel composition. It's included here to show just what care went into the development of a modern steam locomotive:

"Number 46235, LMS Steam Locomotive City of Birmingham: Metallurgical Notes

Alexander, W Hist. Metall. Vol. 19, no. 2, pp. 196-198. 1985

"The 125-ton No. 46235 locomotive, built in 1939 at a cost of 9437, was retired from service after covering 1,650,000 operational miles [2,656,500 km) and is now in a Birmingham museum. The metallurgical features noted include use of a 2%-Ni [nickel] steel giving a weight-saving of over 2 tons in the boiler-shell and firebox structures, arsenical [As]--Cu [copper] plates in the inner firebox, a Cu-bearing steel for the ashpan and other components subject to attack by hot ashes, and cast iron cylinders produced from a 50:50 mixture of cylinder scrap and a special low-P [phosphorus] iron."

Recitation of the periodic-table quality of the manufacturing process continues with: "Analytical and other details are given of these and the Vibrac Ni--Cr--Mo [nickel-chromium-molybdenum] steel coupling rods, the acid-steel tyres, the Si--Mn [silicon-manganese] steel leaf springs and the fatigue-resistant high-Sn [tin] -base axle-box bearings.--J.R. "

Hollingsworth (1982) reported a 1939 run pulling 605 tons of train (20 coaches) in which the Duchess of Abercorn (6234) showed 3,330 indicated horsepower. This was the most ever measured in a British locomotive. G. Freeman Allen (writing in Great Railway Photographs of Eric Treacy, 1987) comments that this run was part of a test to push the design to its limits after she'd been modified with the double blastpipe. Two hours after her climb to the Beattock summit, she returned with the same rake in a snowstorm, travelling 102 miles (Glasgow to Carlisle) in 116 minutes, including a run up 1% grade at 62 mph (100 kph). OS Nock (Allen reports) once timed the City of Nottingham down Beattock slope as she ripped through Beattock station at 105 mph (169 kph) and managed the 10-mile descent at an average of 91 mph (147 kph).

Five of the class were built with streamline casings for the special trains run during the coronation of King George VI in 1937. No. 6220 "Coronation" set a speed record of 114 mph (184 kph) that stood only briefly.

Class Princess Royal (Locobase 1486)

Data from Edward Cecil Poultney, British Express Locomotive Development (London: George Allen and Unwin, 1952), pp. 158-159. (Thanks to Patrick Shively for his 17 May 2021 email reporting that 6202 was Stanier's Turbomotive. See below and "The Turbine Locomotive", Wonders of World Engineering, Volume 1, No 2 (6 July 1937), archived at [], last accessed 20 May 2021; and O S Nock, Railways of the World in Color, Volume VI [6]--Railways at the Zenith of Steam-1920-1940 (London: Blandford Press, 1970), pl. 183 and p. 177.)

These were the first Stanier Pacifics and, according to Grove (1967), were in their original form too long of wheelbase. See also [] (viewed 2 September 2004), which has a useful distillation of Cecil Allen's discussion of this class.

The class was at first difficult for LMS crews to handle as they learned that "their new and imposing 4-6-2s needed a good deal of 'nursing' if they were to give of their best." Moreover, the location of the cylinders over the bogie's trailing axle apparently exposed them to a wracking motion that caused them to work loose. Even a reinforcement strip failed to fix the problem entirely.

In addition, the original domeless boiler required the regulator ("throttle" in North America) to be located with the superheater. Not only were there heat-induced cracks, but the regulator was generally quite stiff in action. Allen is quoted on this as follows:"In fact, I used to watch little Lawrie Earl of Camden on occasion; he was about as tall as six penny-worth of coppers when he got the rightaway' at Rugby, run across the cab and positively launch himself at the regulator handle." Combined with the design's low factor of adhesion and the tall drivers, he had a very ticklish machine to get underway.

Such limitations didn't keep the LMS from working the Princesses hard from the start. Railroad Magazine for March 1937 described a 401-mile (646 km) non-stop run from Glasgow to London in 5 hours 44 minutes. "Even when she was doing 99 m.p.h [160 kph]. the train did not give any sensation of excessive speed," Railroad gushed. " The usual glass of water, filled to the brim, was placed on a table in a vestibule; not a drop was spilled!" Other noteworthy statistics from the trip: "The fireman had shoveled more than eight tons of coal into the firebox during the trip. More than 15,000 gallons [56,775 litres] of water were used. "

Refitting the design with a boiler reduced to the dimensions shown here (e.g., a 19 ft 3 in tube length rather than 20 ft 9 in, the difference being made up by a combustion chamber) helped considerably as did increasing the individual tube diameter to 2 3/8" (from 2 1/4") while simultaneously reducing their number from 170. They retained the Belpaire firebox (now with 217 sq ft of heating surface). In the fifties, all Princesses were fitted with a domed boiler.

In LMS Journal #5, author David Jenkinson notes that this class had almost as many boiler variations as the entire stud of LNER Pacifics - domed and domeless, high and moderate superheat.

The missing number 6202 in the class's road number list belonged to Stanier's turbine locomotive, which debuted in 1935. Although successful in many respects, the design was not repeated because maintenance costs escalated and, wrote O S Nock, it "was not justified by the relatively small improvement in overall efficiency."

British Rail converted the 6202 (later 46202) to a standard Princess Royal in August 1952. Alas, 46202 was the train engine of the double-headed Liverpool Express that collided with the wreckage of the Perth Express in the tragic Harrow and Wealdston station accident of 8 October 1952 that claimed 112 lives and injured 364 others, of which 88 were hospitalized. 46202 was scrapped soon after.

Principal Dimensions by Steve Llanso of Sweat House Media

ClassDuchess - 8PPrincess Royal
Locobase ID1052 1486
CountryGreat BritainGreat Britain
Number in Class3813
Road Numbers6220-62576200-6201, 6203-6212
Number Built3812
Valve GearWalschaertWalschaert
Locomotive Length and Weight
Driver Wheelbase (ft / m)14.50 / 4.4215.25 / 4.65
Engine Wheelbase (ft / m)37 / 11.2837.75 / 11.51
Ratio of driving wheelbase to overall engine wheelbase 0.39 0.40
Overall Wheelbase (engine & tender) (ft / m)62.92 / 19.18
Axle Loading (Maximum Weight per Axle) (lbs / kg)50,400 / 22,861
Weight on Drivers (lbs / kg)150,304 / 68,177151,200 / 68,583
Engine Weight (lbs / kg)238,336 / 108,108234,080 / 106,177
Tender Loaded Weight (lbs / kg)127,568 / 57,864
Total Engine and Tender Weight (lbs / kg)365,904 / 165,972
Tender Water Capacity (gals / ML)4800 / 18.184000 / 15.15
Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT)11 / 1010 / 9.10
Minimum weight of rail (calculated) (lb/yd / kg/m)84 / 4284 / 42
Geometry Relating to Tractive Effort
Driver Diameter (in / mm)81 / 205778 / 1981
Boiler Pressure (psi / kPa)250 / 17.20250 / 17.20
High Pressure Cylinders (dia x stroke) (in / mm)16.5" x 28" / 419x711 (4)16.25" x 28" / 413x711 (4)
Tractive Effort (lbs / kg)39,997 / 18142.3640,286 / 18273.44
Factor of Adhesion (Weight on Drivers/Tractive Effort) 3.76 3.75
Heating Ability
Tubes (number - dia) (in / mm)129 - 2.375" / 60123 - 2.375" / 60
Flues (number - dia) (in / mm)40 - 5.125" / 13038 - 5.125" / 130
Flue/Tube length (ft / m)19.25 / 5.8719.25 / 5.87
Firebox Area (sq ft / m2)230.50 / 21.41217 / 20.16
Grate Area (sq ft / m2)50 / 4.6545 / 4.18
Evaporative Heating Surface (sq ft / m2)2785 / 258.742516 / 233.74
Superheating Surface (sq ft / m2)852 / 79.15598 / 55.56
Combined Heating Surface (sq ft / m2)3637 / 337.893114 / 289.30
Evaporative Heating Surface/Cylinder Volume200.95187.17
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation12,50011,250
Same as above plus superheater percentage15,37513,388
Same as above but substitute firebox area for grate area70,87964,558
Power L128,26221,719
Power MT1243.62950.04

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