Cock o' the North at Peterborough, 1935

Dawn of the new P2 age

Not content with bringing a Peppercorn class A1 Pacific back to life, the team behind Tornado are now building a new version of Britain’s most powerful passenger steam locomotive ever - the Gresley class P2

In early June 1934, Cock o’ the North, a huge new locomotive with eight 6ft 2in driving wheels, went on display at Ilford, Aberdeen then Edinburgh after its launch at King’s Cross. Crowds flocked to see the London and North Eastern Railway’s (LNER) No 2001, the first locomotive of the innovative ‘P2’ class designed by LNER chief engineer Sir Nigel Gresley to haul long passenger trains on the steep Edinburgh to Aberdeen route. Within a month, test runs had revealed Cock o’ the North to be the most powerful passenger steam engine ever seen on British rails - a record the P2 locomotive class retains to this day. Despite their early success, by December 1944 Gresley’s successor Edward Thompson had subjected all the P2s to a power-reducing conversion into a different locomotive class with six driving wheels in an effort to standardise the LNER fleet. The iconic Cock o’ the North was eventually cut up just a month after its withdrawal from service in January 1960. A similar fate befell the other five P2 class locomotives, and by July 1961 they were no more.

Now, thanks to the efforts of registered charity the A1 Steam Locomotive Trust, which created Britain’s newest steam locomotive, the Peppercorn class A1 Pacific Tornado, a new class P2 locomotive is emerging. No 2007 Prince of Wales is currently one year into its construction at the Darlington Locomotive Works (where the A1 Trust is based), and should be pulling passenger trains by 2021.

The P2 project

But why build a new P2? “We’d always had it in our plan to follow the A1 with a P2 because we’re about filling gaps,” says Mark Allatt, chairman of the A1 Trust, explaining that there were significantly fewer LNER locomotives preserved than from the other ‘big four’ companies - the Southern Railway (SR), Great Western Railway (GWR), and London Midland and Scottish (LMS). This, he says, is because the only scrapyard not to dismantle withdrawn locomotives almost immediately - and which consequently enabled over 200 steam locomotives to be rescued by preservationists - was Woodham Brothers scrapyard in Barry Island in Wales, and they had just one ex-LNER locomotive.

The short lifetime of the P2 class was another draw, says Allatt. “The P2s were almost mythical beasts because they were the most powerful [and] they survived in their original form with those enigmatic names for such a short period of time,” he explains, adding that polls of A1 Trust supporters’ views consistently showed people wanted a P2 to be recreated.

Developing the design

One of the main aims of the A1 Trust’s P2 project is to improve on the original design which, despite the outstanding tractive power it produced, was not without its problems. “In terms of engineering, the P2 was almost an uncompleted project. In many ways they were defeated by the technology of the day, particularly in terms of metallurgy, as the pre-World War 2 metals wore very heavily,” says Allatt, adding that the trust is already in conversation with Tata Steel to determine what modern steels would be best for Prince of Wales.

“Thanks to computer power and the fact that we have time, we are able to do the development that Gresley couldn’t,” states the P2 project’s engineering director David Elliott, a BR-trained graduate engineer. Data from 3D CAD drawings has already enabled No 2007’s frames to be profiled by Tata Steel using a gas cutting machine, and The Boro’ Foundry Ltd in Stourbridge to machine the edges and the required holes. The resulting increase in accuracy compared with Tornado’s hand-finished frames will make it much easier to add components during assembly, says Elliott.

The original P2s occasionally suffered derailments in tightly curved sidings caused by a ‘swing link’ suspension patented by Gresley which acts to centre the pony truck (the articulated support for the locomotive’s small front wheels) after the locomotive negotiates a bend. This suspension slightly lifts the front of the engine whenever the pony truck turns, then converts the resulting forces into a centring force. The problem, says Elliott, is that it also takes some of the load off the front set of driving wheels, so on very tight bends the locomotive can derail. To avoid this happening with No. 2007, Elliott’s new pony truck centres thanks to compression in side-mounted springs, as applied retrospectively to other Gresley pony-truck designs.

Meanwhile, finite element analysis by engineering consultants Mott MacDonald in Derby, is being used to investigate whether Elliott’s modified crank axle design will meet modern criteria for fatigue life. A crank axle failure resulting in a wheel falling off the axle occurred at least four times on a P2, fortunately only ever at low speed, says Elliott. Helpfully, a 1939 photo of a failure in P2 No. 2005 clearly shows the crack started at a sharp corner at the inner end of the ‘keyway’ where the axle goes through the wheel. So to relieve stress in that area Elliott has given the keyway a gently curved corner and added a pre-stressed shallow groove.

Two P2s in a pod?

He is also starting to re-design Cock o’ the North’s original valve gear. None of the six P2s built between 1934 and 1936 were identical because Gresley was experimenting with new technologies, and one disappointing performance result was from No 2001’s Lentz rotary cam poppet valve gear, explains Elliott. Valves let steam in and exhaust out of a locomotive’s cylinders, which in turn move the pistons that via a crank and connecting rod turn the wheels. A poppet valve can admit and exhaust more steam than a similarly sized piston valve (which most steam locomotives use), so should give greater performance. Plus the variable camshafts that operated the valves on No 2001 enabled the driver to finely control the amount of steam let into the cylinders when travelling at different speeds, so promised to optimise overall efficiency. However, these camshafts and other valve gear components wore so rapidly that Gresley replaced the Lentz system with conventional piston valve gear. Subsequently, in the 1940s, American rail engineers made improvements to Lentz valve gear that removed the earlier problems and worked successfully on US locomotives. Thanks to original drawings lent by the son of one of those engineers, Elliott will be incorporating these developments into No 2007’s Lentz valve gear.

One they built earlier

Meanwhile, to reduce the risk of the axle boxes running so hot that the locomotive is immobilised - something the original P2s suffered because their axles ran in plain bearings made from bronze and white metal - hardened steel roller bearings, as used on Tornado, will be fitted.

No 2007 will also have copies of Tornado’s tender, firebox, wheels (except for the coupled driving wheels), and boiler, as each was either identical or almost identical on the original P2s and A1s. Tornado’s tender - which is slightly modified from the original A1 tender to carry less coal but 1,200 extra gallons of water - has already proved to work well, while having identically sized boilers will give the option of swapping them between the locomotives during overhauls, says Elliott.

In terms of the overall design, like Tornado, No 2007 must have air brakes, and needs to be an inch lower in height compared with its original version to keep within the UK railway’s modern smaller loading gauge. It must also carry modern electronic safety equipment including specific types of LED head and tail lamps, the TPWS (Train Protection and Warning System) and the OTMR (On Train Monitoring Recorder), and - once Network Rail rolls the system out - the computerised ERTMS (European Rail Traffic Management System) equipment that will eventually replace the TPWS.

With no original template to work from as Gresley’s P2s had no electrics, the electrical system on-board Prince of Wales will copy that of Tornado which has, says Rob Morland, head of electricals for the P2 project, worked extremely well. “The biggest challenge has been keeping everything clean,” says Morland, a communications and electronics consultant by trade. “We’ve had quite a bit of water and coal ingress, and of course wet coal dust is a conductor. So on the P2 we’re looking at moving some of the sensitive equipment from the locomotive on to the rear of the tender,” he explains.

Another slight change from Tornado’s electrics will be to come away from using galvanised steel conduit for the electrical cables. This, says Morland, soon filled up when they had to add an extra half mile of wiring to Tornado’s initial three miles as new equipment - including air pump temperature sensors, outside frame LED lighting, and a GSM-R radio - was required. The flexible conduit that housed this new wiring resulted in “a complex set of different conduits on the A1”, says Morland. So to avoid this on Prince of Wales they intend using 3D CAD to design a simpler, structured trunking system made from box trunking and halogen-free plastic-covered steel flexible conduit that can easily accommodate extra cables if required.

In the meantime, Morland will be sourcing components for the system, including IP 66 and IP 67 die-cast aluminium boxes, military specification MIL-C-5015 bayonet connectors, and low-smoke zero-halogen wiring. He will also work with an optical physicist to design an LED luminaire system, which must function as both a headlamp and also as a (white) marker and (red) tail lamp, to go inside a replica of the original P2’s distinctive front headlamp casing.

Assistance required

Elliott is seeking components too, including a 1kW truck alternator to power No 2007’s TPWS, and “a small, reliable, 15kW modern turbine that will work off saturated steam to drive a compressor” as an alternative to using high-maintenance 1930s-design air pumps - as on Tornado - to feed the air brakes.

Human components are equally required, in the form of volunteers with expertise in any area the P2 project covers, from marketing and fundraising to 3D CAD drawing and carrying out stress calculations. In addition, more donations are being sought to help cover the estimated £5m build cost for No 2007. As with Tornado, supporters can donate the price of a pint a week (now £10 per month), and have the option to also sponsor individual components on Prince of Wales, explains Allatt, a branding and marketing consultant by profession. Meanwhile, to avoid borrowing money to purchase the boiler Allatt has opened ‘The Boiler Club’, which currently has a quarter of the 300 required members. “We are asking each member to give £2000 either as a single donation or in instalments,” he says.

The A1 Trust is also open to negotiating further sponsorship packages with service or component suppliers. Commercial sponsors for the P2 project so far include William Cook Cast Products Ltd, which has cast Prince of Wales’ wheels and several other steel parts, and road haulage firm L Hunt & Sons of Basingstoke, which is the carrier for No 2007’s larger parts and is helping publicise the P2 project via advertising billboards on the curtain sides of one of its lorries.

Assuming the planned schedule is met, 90 years after the first P2 was unveiled, No 2007 will have “realised the potential of the design that Gresley started, and be operating successfully on the Network Rail main line,” says Allatt. Like the original P2s, the tractive power of Prince of Wales will be its greatest asset, and will enable it to haul more carriages than other surviving steam locomotives. Since this will facilitate more ticket sales from each excursion, P2 No 2007 looks set to be, as Elliott puts it, “the supreme rail tour engine”.

For more information on any aspect of the project to build No. 2007 Prince of Wales visit, email or call +44 (0)1325 460163.

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