|Weight – Loco||107t 3cwt|
|Driving Wheels||6ft 2ins|
|Boiler Pressure||220psi superheated|
|Cylinders||Three – 21in x 26in|
The P2s were designed to handle the express passenger traffic on the Edinburgh to Aberdeen main line, which is noted for its steep gradients and tight curves. Double-headed pacifics were prohibited from the line, so the heaviest traffic was usually handled by double-heading two smaller engines. Gresley sought to overcome this need with a 2-8-2 design with four driving axles for greater adhesion compared to an A3 pacific. Initial plans were drawn up in 1932, and consisted of a 2-8-2 design using an A3-type boiler and dual chimney. Whilst the design was still being finalised, two engines were authorised in February 1933. At the end of March, this initial order was reduced to one locomotive. The firebox was lengthened, and a double blastpipe was added. The Kylchap chimney/blastpipe arrangement was chosen, along with an ACFI feed water heater (instead of injectors), and smoke deflectors.
After the successful experiments with the Lentz rotary cam poppet valve gear on the D49s, Gresley decided to fit similar valve gear to the P2s and directed Associated Locomotive Equipment Ltd to design a set of Lentz valve gear for the P2s. The gear was powered by two camshafts above the cylinders and at right angles to the locomotive horizontal centre line. These camshafts were synchronised with the rotation of the driving axles. Admission and exhaust valves were controlled by six scroll cams mounted on these two camshafts.
Associated Locomotive Equipment Ltd also provided the Kylchap double blastpipe, which was designed to take different blastpipe tops, and taper blocks allowing different blastpipe cross-sectional areas to be tried.
The smoke deflector plates were moved forward so that they extended far ahead of the smokebox. Wind tunnel tests led to the deflectors being made vertical. A V-shaped cab front was also added. During these changes, five more P2 locomotives were ordered, but with a choice of valve gear left open.
This first locomotive, 2001 Cock o’ the North (Cock o’ the North was the nickname given to George, the Fifth Duke of Gordon. The name was previously used on C10 class engine 9903 which was renamed Aberdonian) was completed at Doncaster in May 1934. 2001 was fitted with a Crosby chime whistle which Gresley had obtained from Captain Howey of the Romney, Hythe and Dymchurch Railway, and which was originally intended for one of that railway’s Canadian Pacific style locomotives.
Early indicator tests showed low final compression pressures.
Shortly after being put into service, 2001 was tested with a 19 bogie carriage train of 649 tons on a return journey between Kings Cross, Grantham and Barkston. The locomotive hauled the train at an average speed of over 50 mph, with peak speeds of over 70 mph. Drawbar pulls of around 6 tons at around 60 mph were recorded – representing a peak power output of over 2,000 horsepower.
In December 1934, 2001 accompanied by O.V.S. Bulleid travelled to the locomotive testing station at Vitry-sur-Seine near Paris for two months of testing. The ambitious test programme had mixed success due to problems maintaining boiler pressure, and overheating axleboxes and bearings.
Modifications were then undertaken at Doncaster but this did not fix the problem. After further testing on its return, 2001 entered service in Scotland.
The ACFI feed water heater on 2001 gave a lot of problems, and was never fitted to the other P2s. The heater used exhaust steam to heat the water before it was injected into the boiler. To work properly, the locomotive had to run continuously with its regulator open. This was not possible on the Edinburgh to Aberdeen route which the P2 was designed for, and so the ACFI feed water heater was wasted.
The second locomotive, 2002 Earl Marischal (The Earl Marischal was the hereditary title of the Keith family, whose seat (Dunnottar Castle) was visible from the line near Stonehaven. The title has never been used since the family took the Jacobite side in 1715) was completed in October 1934. This was identical to 2001 Cock o’ the North but with piston valves, Walschaerts/Gresley valve gear, and the ACFI feed water heater was removed. This also ran a series of trials before entering regular daily service in Scotland in June 1935. Due to the use of Walschaerts and Gresley valve gear rather than the poppet valve gear, 2002’s draughting characteristics were different to those of 2001. Trials found that a combination of a 5¾in diameter blastpipe top and 3 taper blocks worked best. This combination was made standard for the remaining locomotives of the P2 class, and was also used on 2001 when it eventually had its poppet valve gear replaced.
At low cutoffs smoke clearance on 2002 was unsatisfactory: wind tunnel experiments led to an additional second pair of smoke deflectors being fitted inward of the first.
The remaining four locomotives were completed in 1936. As with 2002, they had piston valves and Walschaerts/Gresley valve gear, but they had streamlined fronts similar to those of the A4 pacifics. Although the A4 pacifics has only been introduced the year before, their shape was clearly superior to the P2 deflectors for lifting the smoke above the cab, and hence was chosen as the new P2 front-end shape. There were smaller differences between these four locomotives-
- 2004 Mons Meg (Mons Meg is the nickname for a famous 15th Century cannon which resides on the ramparts of Edinburgh Castle overlooking the railway line as it heads out of Waverley station towards the Forth Bridge) had a bypass valve to divert some of the exhaust from the blastpipe.
- 2005 Thane of Fife (Thane of Fife is another name for the Earl of Fife, whose county the Aberdeen line passes through. This name was chosen by a competition in Boys Own paper, and was also used on C11 class locomotive 9871 which was withdrawn in January 1935) had a single (non-Kylchap) chimney.
- 2006 Wolf of Badenoch (Wolf of Badenoch was the nickname given to the 14th Century Earl of Buchan who burned down Elgin Cathedral in 1390 in a response to episcopal criticism) had a longer combustion chamber in its firebox, in an attempt to aid complete combustion of the coal.
All of these variations were covered by three sub-classifications of class P2. 2001 with poppet valves was classified as class P2/1. Class P2/3 was used for 2006 with the longer combustion chamber and piston valves, whilst the remaining four locomotives with piston valves were given the classification of P2/2.
The P2s were fitted with tablet exchange apparatus for use on the single line section between Usan and Montrose South that included the single track viaduct over the Montrose Esk Basin. The tablet exchanger operated through an elliptical hole cut in the cab end of the left hand tender side sheet. 2001-2 were fitted with the tablet exchange apparatus before they entered regular service. The other P2s were fitted when new.
In 1936 and 1937 the front ends of the whole class had their front ends converted to the streamlined style applied to the A4 pacifics introduced in 1935.2001 also had its ACFI feed water heater removed, and its poppet valves replaced with Walschaerts/Gresley valve gear to bring it in line with the other members of the class (P2/2).
In 1939 reports from the footplate on the performance of 2004 Mons Meg on the early morning Aberdonian non-stop from Edinburgh to Dundee; a train with gross weight of 320 tons. Peak speeds of over 60 mph were noted, with 55 mph on a 1 in 100 gradient, and an average speed of 44.25 mph. Despite the vehicle’s long wheelbase, 19 ft 6 in, and the frequent curves on the route, no reports of any serious issues with ride quality were noted. On the return trip with a load of 360 tons gross, recording a peak of 68 mph on a 1 in 100 down section, with an average speed of 38 mph including several stops and speed restrictions. The favourable reports on the acceleration of the train indicated that a speed of 50 mph was reached from standstill over 1.25 miles, with 60 mph reached in under 2 miles. Further Edinburgh to Dundee and return runs were made in the afternoon with 355 and 450 ton gross loads respectively with average speeds of 40.25 and 33 mph.
The P2s tended to suffer from a large number of damaged driving crank axles due to the overheating of the big-ends. This was partly due to the stresses at the front end caused by pony truck faults. The same swing-link pony truck mechanism employed on the K3 2-6-0s was used, even though this design had exhibited problems with both the springs and sufficient lubrication. Associated weakening would occasionally lead to failure of a crank axle whilst in traffic. These failures appear to be a major contributing factor to Thompson’s decision to rebuild the P2s as A2/2 pacifics. As a part of the rebuilds, Thompson used coil springs to centre the leading bogies, and which solved the problem as none of the A2/2 pacifics suffered crank axle failures.
Although often described as a mixed success, the P2s were a bold step forward for British locomotive design. They had a reputation for heavy coal consumption, but this was only really a problem with the prototype (2001 when it was fitted with its original poppet valve gear. The pony truck had problems, but as with the V2 2-6-2 locomotives, it could have been successfully redesigned.
It is said that they were unsuitable for the Aberdeen route for which they were designed but they did spend all of the time they were in service as P2 locomotives on this route. The longer fixed wheel-base did pose problems for the tight corners on this route, but the extra axle gave useful increase in adhesion for this steep route. As with all locomotive designs, the P2s were a trade-off between conflicting requirements.
After the death of Gresley in 1941, Thompson took over and began his standardisation plans. Due to their small numbers and mixed success, it was almost inevitable that the P2s would be rebuilt by Thompson. Between January 1943 and December 1944, all six were rebuilt as A2/2 pacifics.
|P2 class as introduced in 1934 by Gresley|
|P2 class after modifications in 1936-1937|
|P2 class as rebuilt by Thompson as the A2/2 class in 1943|
As rebuilt they retained their original boilers (although they were shortened by 2ft) and they were classified A2/2. Existing parts were used as much as possible, including the short outside connecting rods. This led to the outside cylinders being mounted relatively far back. The Gresley conjugated gear on the middle cylinder required a high level of maintenance, so Thompson replaced this with Walschaerts valve gear. For clearance, this meant the middle cylinder had to drive the leading driving axle. A Kylchap exhaust arrangement was fitted, as well as small wing-type smoke lifters.
Under the 1943 renumbering scheme, they would have been numbered 990-5, but they did not receive their new numbers until after the 1946 renumbering scheme when they received the numbers 501-6. They then received the British Railways numbers 60501-6 but retained the original names that they had carried as P2 class locomotives.
All of the former P2 locomotives were withdrawn from service in the period 1959 to 1961.