LNER Class A1/A3
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 The most famous of the LNER Class A1/A3 locomotives, 4472 Flying Scotsman |
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| Power type | steam |
|---|---|
| Driver size | 80 in (2.03 m) |
| Length | 70 ft 5 in (21.46 m) |
| Axle load | 45,000 lb (20.4 t) |
| Weight on drivers | 34,500 lb (15,600 kg) |
| Total weight | 332,000 lb (151 t) |
| Tender capacity | 18,000 lb (8 t) coal, 5,000 imp gal (23,000 L) |
| Boiler pressure | 180 psi (1.24 MPa |
| Fire grate area | 41.25ft² (3.83m²) |
| Superheater area | 525ft² (49m²) |
| Cylinders | 3 |
| Cylinder size | 20×26 in (0.51×0.66 m) |
| Tractive effort | 29,385 lbf (13,329 kgf, 130.7 kN) |
The London and North Eastern Railway (LNER) Class A1/A3 is a class of 4-6-2 steam locomotives, designed by Nigel Gresley. The A3 was a refinement of the earlier A1, and the two are often considered together; all surviving A1 locomotives were eventually rebuilt as class A3.
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[edit] Development of Class A1
The Great Northern Railway's (GNR) A1 class wa the brainchild of Nigel Gresley, who became Chief Mechanical Engineer of the GNR in 1911. The intention was to produce an engine with ample capacity for mainline express services while being was more economical to operate than existing locomotives.
A total of seventy-nine of the class were ordered between 1921 and 1934, the first A1 entering service on the GNR in April 1922. The first ten of the A1 steam locomotives cost an average of ₤8,560 compared to the ₤6,840 for each of the first ten of the GWR's comparable Castle Class.
In the 1923 Grouping, the GNR became part of the newly-formed LNER with Gresley continuing as Chief Mechanical Engineer.
The A1 Pacific steam locomotive had 3 cylinders: 2 on the outside and 1 in the middle connected to the middle driving wheel. Gresley was as much artist as engineer and gave the locomotives an aesthetically pleasing design, decking them out in an attractive livery and giving them evocative names, mostly taken from racehorses of the era.
The A1s set new standards of performance with the heavy expresses on the East Coast Main Line, and the famous No. 4472 Flying Scotsman was the first British locomotive to officially reach 100 mph (GWR 'City of Truro' may have reached 100mph at an earlier date, but records are not verifiable). However the class suffered from a number of engineering problems. They had a stiff "all or nothing" regulator which, combined with the absence of any compensating levers near the rear pony truck and driving wheels, made them liable to slipping. This tendency to "wheel burn" resulted in the rails having to be changed every few weeks at points where the A1s habitually started from rest.
The A1s had a chronic tendency for the "big end" of the inside connecting rod to run hot; this was partly due to the design of the conjugated valve gear. The problem was largely cured eventually by replacement with a GWR design of big end. There were also such significant faults as broken lubricator pipes, which could only be replaced by lifting the boiler off the frame. However, the clearest proof that improvements were possible came with a comparative test in 1925 against a GWR Castle Class engine, in which the Castle performed better despite being smaller and lighter.
[edit] Class A3 Super Pacifics
After a preliminary period of disbelief [citation needed], Gresley began to experiment with modifications to the A1s. A successful result was obtained with No. 2555 Centenary, by reducing the cylinder diameter slightly, changing the valve settings to give freer steam flow, and increasing the boiler pressure from 180 psi to 220 psi with a larger superheater. The results included freer running and conservation of coal, thus reducing the need to change locomotives mid-run. A side-effect of the changes was that the axle load was slightly increased. A new class of locomotives was then built to this design; the class was designated A3, sometimes known as the Super Pacifics. All the original A1 Pacifics were eventually altered to A3 form as they went through the shops.
The A3s were even more successful than the A1s, handling the largest and heaviest expresses on the LNER. On a test run No. 2750 "Papyrus" set a new British rail speed record of 108 mph. This provided the impetus for a further development, the streamlined A4 Class.
As World War II broke out there was a requirement for 24-car freight trains to run on the East Coast Main Line and the A3s' (and the remaining A1s') performance on these freight trains was a vindication of their design, although lower standards of maintenance emphasized their detailed weaknesses.
After the war there were calls to overcome these troubles but they were mostly ignored, as the locmotives' performance was still good. The appearance of the A3 did change slightly when smoke deflectors were fitted to each side of the smokebox, and they performed better with the double chimneys which were fitted in 1958-1960. But even in the 1960s they were easily recognisable as being brethren to the class A1 Pacifics which saw service 40 years before.
The prototype locomotive had been rebuilt into what was virtually a new design and one other had been withdrawn in 1959, but otherwise the class remained intact until 1962, still on express passenger work. The last to go was No. 60041 Salmon Trout, in December 1965.
No. 4472 Flying Scotsman is the only survivor of the class. Its activities since being purchased for preservation in 1963 are such trips to USA and Australia have made it one of the best known and widely recognised steam locomotives in the world.
[edit] In fiction
In Thomas the Tank Engine and Friends, one of these locomotives was the basis for Gordon the Big Engine.
[edit] External links
| Locomotives of the London and North Eastern Railway | ||
| Pre-grouping railway designs | ||
| Great Central Railway: | A5 - B18 - D11 - J11 - O4 | |
| Great Eastern Railway: | J65 - J16 - J17 - Y5 - J17 - N7 - ?? - J69 - B12 - J66 - D13 - E4 - J15 - J70 | |
| Great North of Scotland Railway: | D40 | |
| Great Northern Railway: | C1 - C2 - J6 - J52 - K3 - N2 | |
| North British Railway: | D34 - J36 - Y9 | |
| North Eastern Railway: | B16 - E5 - D17 - J21 - J27 - J72 - Q6 - Q7 - X1 - Y7 | |
| align=left | align=leftLNER designs | |
| Gresley:
align=left|A1 - A3 - A4 - A8 - B17 -D49 - J38 - J39 - J50 - K4 - P1 - P2 - U1 - V1 - V2 - V3 - V4 - W1 - |
Thompson: | A2 - B1 - B2 - K1 - K5 - L1 - O1 - Q1 |
| Peppercorn: | A1 - A2 - Peppercorn A9|A9 - K1 - V5|V5 - | |
| Raven: | A2 - H1 | |
