The not-so-gripping tale of Thompson’s A2/2
Hornby's all-new LNER A2/2 models remind Pete Kelly of the debate which has surrounded these locos for decades, and of the P2 Steam Locomotive Company's new version of the Gresley 2-8-2s from which they were built.
Hornby’s all-new OO-scale versions of LNER A2/2 Pacifics remind Pete Kelly of the debate which has surrounded these engines for decades, and of the P2 Steam Locomotive Company’s rapid progress in building a brand new and much-improved version of the Gresley 2-8-2s from which they were built. He also looks at Bachmann’s new Class 20s.
WHEN the first of Sir Nigel Gresley's mighty P2 mikados, No. 2001 Cock o’ the North, emerged from Doncaster Works in 1934, it made a truly astonishing sight with its eight 6ft 2in driving wheels and unbroken lines extending around its prominent eight-nozzle, doublechimney Kylchap exhaust.
With a larger firebox than the Gresley Pacifics, it also featured Lentz rotary-cam poppet valve gear, allowing for continuously-variable cut-off, although excessive wear later forced a modification to a steppedcam arrangement with limited cut-off settings.
While the following five P2s – Nos. 2002 Earl Marischal, 2003 Lord President, 2004 Mons Meg (a huge cannon built in 1449 and located at Edinburgh Castle), 2005 Thane of Fife and 2006 Wolf of Badenoch – reverted to two sets of outside Walschaerts valve-gear with Gresley's derived motion to the middle cylinder, there were other differences too. Larger diameter fire tubes gave Earl Marischal, completed in 1935, a greater superheating area, and while visually the locomotive followed much the same design as Cock o’ the North, smoke drift at lower cut-offs forced experimentation with an extra set of smoke deflectors.
The remaining four P2s, completed in 1936, appeared with A4-style streamlining whose wedge-shape front had no problem in lifting exhaust, and the two pioneers also became similarly clothed.
Background
Conceived with one major purpose in mind – working heavy express trains without the need for doubleheading over the demanding main line between Edinburgh and the Granite City – individual members of the class boasted minor modifications of their own. With an outstanding tractive effort of 43, 462lb, they were certainly well up to the job, but even the P2 Steam Locomotive Company acknowledges that they encountered problems in service, the most serious of which was premature crank-axle failure on five of the six locomotives.
The first incident occurred when one of the class with 133,000 miles on the clock broke its crank axle at slow speed while leaving Stonehaven station in 1939, but to avoid this happening with the brand new P2, a modified crank axle made from the strongest A4T material rather than the standard A1T was assembled at the South Devon Railway.
While all Pacifics have a tendency to slip, the whole point of an eight-coupled express passenger locomotive is its superior adhesive performance with heavy loads, but as has been suggested by the A1 Steam Locomotive Trust and its P2 Steam Locomotive Co., excessive power has to find a weak spot somewhere – and in the P2s' case, rather than slipping the strain went onto the crank axle.
Evolution
While claims that the P2's long driving wheelbase caused track maintenance problems on the winding route to and from Aberdeen have been dismissed as highly exaggerated by several notables over the years, Edward Thompson decided to rebuild the 2-8-2s into Pacifics incorporating his own ideas, rather than put the mikados on straighter routes where track spread would have been much less of a problem. During the wartime conditions that prevailed, he probably saw the small class as opportune test-bed fodder on which to try out his ideas.
No. 2005 Thane of Fife was the first P2 to be rebuilt as an A2/2, spending 85 days in Doncaster Works between October 26, 1942, and January 18, 1943. The pony truck and first set of
driving wheels were removed and replaced by a new front bogie, the boiler barrel was shortened by just over 2ft, and, unlike the P2 design in which all three cylinders drove a single axle, Thompson decided to split the drive between two sets of driving wheels, with the inside cylinder acting on the first axle and the two outside cylinders on the second pair of driving wheels.
Retaining the original same-length connecting rods meant that the outside cylinders had to be placed right behind the front bogie, giving the front end of the A2/2s their notably odd look.
Thompson also decided to remove Gresley's conjugated set-up and instead fit three separate sets of Walschaerts to his engines, reducing the cylinder sizes from 21 x 26ins to 20 x 26ins diameter in the process.
Even though the second P2 mikado, No. 2002 Earl Marischal, with its two sets of Walschaerts valve gear, proved more efficient than Cock o’ the North because of its lower cylinder clearance volume, the P2 Locomotive Co. is continuing with Gresley's pioneering spirit by sticking to rotary-cam poppet valve-gear path, this time with a redesigned Franklin version of the Lentz gear that has already been substantially modified to address the cylinder clearance volume issue. A 3D printed model of the redesigned modified cylinder block has already been completed.
So how did the A2/2s measure up, especially during the latter years of the war and the long period of austerity which followed? There is no doubting that, with their high power-to-weight ratio, the Thompson rebuilds, which were lighter by several tons and had excellent freesteaming boilers, were capable of fast main line work, but the Achilles' heel was their serious tendency to slip. Even though their tractive effort still exceeded 40,000lb, their diminished grip was in total contrast to the massive pulling power of the original P2s.
The only A2/2 I ever saw, during a loco-spotting visit to York in 1960, was a grimy No. 60502 Earl Marischal which arrived with a northbound train. I was struck by its brutish appearance compared with the many graceful Pacifics I'd seen that day, and when it set off it had a tough time getting to grips with the tight curve. Little did I know back then that Nos. 60503 Lord President and 60501 Cock o’the North had already been withdrawn and disposed of (on November 30, 1959, and February 28, 1960, respectively), and that the remaining four A2/2s would all be gone by the end of July 1961. Combining its two guises,
Earl Marischal was the only one to clock up more than a million miles – 360,907 as a P2 and 673,947 as an A2/2.
Developments
How wonderful it is to see a brand new and much-improved P2 coming along so steadfastly in the shape of No. 2007
Prince of Wales. We simply can't wait, but there are still many ways to speed this exciting project along; visit www. p2steam.com to see how you can help.
Hornby has just introduced two newly-tooled versions of Thompson's A2/2 rebuilds, representing No. 60501
Cock o’the North in early-crest BR green (R3830) and No. 60505 Thane of Fife in later-crest BR green (R3831). These will be followed by No. 60502
Earl Marischal in late-crest BR green (R3977). All have a recommended retail price of £189.
To many who remember the P2/2s, especially in their later years, the well-applied pristine paintwork seems at odds with their generally unkempt appearance, and for those who feel so inclined, a little professional weathering would definitely improve matters.
The models each have a five-pole skew-wound motor and are DCC ready. Well-detailed body shells and underframes, along with detailed cab interiors and NEM couplings, complete the picture, but just as with the real-life locomotives, quite a debate is going on among modellers about which detail features they might have preferred.
Numbers, works plates, tender crests and so on are crisply applied, and the models will fill motive power gaps on many early BR layouts with an Eastern or North Eastern Region bias.