GSR Class B1a

By a large margin, the Class B1a were the biggest and most powerful engines ever to run in Ireland. They were designed under the supervision of E.C. Bredin. His Chief Draughtsman, H.J.A. Beaumont, prepared the drawings.

Design

The engines had three 18½ in x 28 in cylinders and 225 lb/in² boiler pressure. The nominal tractive effort was 34 799 lbf, which corresponded with Great British main-line power. Further, it was the only design which exploited the full extent of the extra width afforded by the convert|5|ft|3|in|m|abbr=on gauge. Originally five were to be built, named Maedbbh, Macha, Tailté, Gráinne, and Deirdre, but only three were eventually turned out - 800 "Maedhbh" in 1939, with Macha (801)and Tailté (802)in 1940. They were intended for the Dublin-Cork route but wartime coal shortages and the early 1950s advent of diesels on main line services resulted in their never having had much chance to show what they were capable of. In the 1950s they gradually became neglected and even resorted to light goods trains on occasion, with little other work to do.

The locomotives have been described as "Queens", on the assumption that they were all named after mythical queens. This is partially incorrect. Maedhbh was a warrior queen referenced in the Tain Bo Cuailnge, The Great Cattle Raid of Ulster. Macha was the Goddess of Sovereignty of Ulster, and Tailte was the wife of Eochaid Mac Erc, the last Firbolg of Ireland. The nameplates were written in old Irish Script.

Maedhbh (pronounced "Maeve") was built in 1939 at the CIE Inchicore Works, Dublin and was withdrawn from service in 1964 and is now on display at the Ulster Folk and Transport Museum, Cultra, Northern Ireland.

Power

Tractive effort (TE) is the name for the force applied to the rail by the wheel of the train to cause movement. Thus Maedhbh's force of 35,000 pounds-force equates to 159 kN. TE is not constant throughout the speed range but reduces as the engine speeds up.

The TE is constant typically from stall speed up to 20 mph (32 km/h or 8.8 m/s) and during this time acceleration is constant. This is the region of "maximum tractive effort" and is indicative of the maximum output capability of the engine.

Power is measured as force times speed, hence the maximum power capable can be calculated from the maximum speed attained at the maximum tractive effort.

:Force (159 kN) × speed (8.8 m/s) = 1400 kW :Force (35,000 lbf) × speed (20 mph) × (22 ft/s)/(15 mph) = 1,026,667 ft·lbf/s. Since a horsepower is 550 ft·lbf/s, dividing by that gives 1870 hp

Thus convert|1870|hp|abbr=on is the theoretical "maximum power at rail".

Note that the actual power to the rail will be reduced due to friction, air resistance (drag), and power dissipated in sound, heat etc. In effect, Maedhbh probably had similar tractive effort to a GM refitted A Class.

Livery

The locos were turned out in a completely unique livery which no other locomotives ever carried. In the height of the Great Southern era, when every single locomotive in the Republic of Ireland wore a plain unlined battleship grey livery, these engines were turned out in a smart mid green, with a distinct bluish tint. The green was lined in black and light yellow, and the GSR coat of arms was carried on the tender, flanked by large pale yellow letters "G S", which appear to have been shaded in red and gold. The cabside number plates and nameplates had blue backgrounds, and raised polished brass rims and numerals.

In CIE days they received the 1950s standard green, somewhat darker than they had carried before, with black and white lining. This is the livery the preserved 800 carries, though rather than the CIE "Flying snail" emblem which would be appropriate to this later livery, she incorrectly carries the earlier "G S" without shading, and a replaced GSR coat of arms.

See also

* Diesel Locomotives of Ireland
* Multiple Units of Ireland
* Coaching Stock of Ireland
* Steam locomotives of Ireland