Bold, beautiful and faster than anything steam-powered on Earth.
The story of the London and North Eastern Railway A4 Pacifics is brought to us by LNER Encyclopedia.
By the 1930s, the railways were beginning to see increased competition from road and air travel. It was clear that services between the major cities had to be faster, more reliable, and more comfortable. Also, a number of high-speed diesel trains were attracting the world's headlines. In May 1933, the German State Railways diesel-electric Fliegender Hamburger entered service, with long stretches of 85mph required by the scheduled timetable. By 1934, the US Burlington Zephyr had reached 112.5mph during a longer 1015 mile journey
LNER Chief Engineer Nigel Gresley travelled on the Fliegender Hamburger and was impressed by the need for streamlining, although he realised it was only useful at the highest speeds. From this, he calculated that a streamlined and modified A3 design would be able to haul trains of eight or nine carriages at similar speeds. Both the Fliegender Hamburger and Burlington Zephyr were much smaller (2 and 3 carriage units respectively).
A series of trials were carried out, to confirm that a modified A3 design would be sufficient. During these, A1 Flying Scotsman broke 100mph, and A3 Papyrus managed average speeds almost as fast as Fliegender Hamburger but with a larger coach capacity! On this latter run, Papyrus managed to set a speed record of 108mph. With these trials under his belt, the LNER Board gave Gresley the go-ahead to create the "Silver Jubilee" streamlined trains.
The "Silver Jubilee" was designed as a complete streamlined train including streamlined coaches. These had valences between the bogies and flexible covers over the coach ends. Although this restricted their use, it maximised the streamlining effects and proved useful for publicity! The train had capacity for 198 passengers on 7 coaches: twin-articulated brake third, triple-articulated restaurant set, and a twin-articulated first class.
The wedge-shaped streamlining on the A4 was inspired by a Bugatti rail-car which Gresley had observed in France. The design was refined with the help of Prof. Dalby and the wind tunnel facilities at the National Physical Laboratory (NPL) at Teddington. As well as streamlining, it was important that the design lifted smoke up away from the cab. At first, there was a lot of difficulty in achieving this. Even smoke deflectors were considered! During the wind tunnel tests, it was noticed that a thumb print had inadvertently been added to the plasticine model, just behind the chimney. Only on impulse, was the model re-tested with the thumb print. Amazingly, the smoke was lifted well clear of the cab!
The LNER publicity machine had a field day with the new streamlined shape. Many saw this publicity as mere hype. Some thought the LNER was bowing to the latest craze. Others thought that it was not true streamlining and that the design team did not know what they were doing! In-fact, experimental data showed that a 40% reduction in horsepower was required when powering from 60mph to 150mph. The high speed of 150mph was used to simulate a headwind. This saving ranged from 41hp at 60mph to 639hp at 150mph.
As well as the characteristic streamlining, a number of other things were modified from the A3 design. All of the steam passages were streamlined. The boiler pressure was increased from 220psi to 250psi. The cylinders were decreased slightly in size so that the valve diameters could be increased to 9 inches. This produced free steaming within the restrictions of the 3 cylinder design. As with the A3, Walschaerts gear was used on the outside cylinders, and Gresley's conjugated gear was used for the inside cylinder. Further refinements were added at a latter date, including the Kylchap double-blastpipe exhaust,and Westinghouse QSA Brake Valves.
LNER 2509 Silver Link. Photo by Harry Green via Wessex Andy @ Flickr
A demonstration run from Kings Cross to Grantham on 27th September 1935 touched 112.5mph. The first service was on the 1st October 1935, hauled by No. 2509 Silver Link. A further three locomotives were built for the Silver Jubilee service to Newcastle. This service was a great success cutting the travel time between Kings Cross and Newcastle down to an amazing 4 hours. This success led to an extension of the service to Edinburgh, and the building of a further five A4s. By 1937, a third service to Leeds & Bradford had commenced. And thus, Britain's first inter-city network of fast train services was born.
On 28th June 1937, Stanier's streamlined Coronation Scot of the LMS set a new record of 114mph. Two days later, a press & publicity trip for the LNER's new "Coronation" service pulled by 4489 Dominion of Canada attempted to regain the record. Unfortunately, it only managed to reach 109.5mph on Stoke Bank.
LNER 4489 (BR 60010) Dominion of Canada preserved at Canadian Railway Museum. Photo by The Metal Merchant @ Flickr
With these increasing speeds, braking distances were getting longer, and so methods to improve braking were investigated. Gresley favoured the use of a system produced by Westinghouse (and already in use on the LMS), and so trials began in 1938. Trials typically required rapid acceleration followed by the brake test. On 3rd July 1938, the Westinghouse team arrived to find that the train consist had changed. Some of the coaches had been removed and replaced with the dynamometer car. Also, the locomotive had been changed to 4468 Mallard.
Only 4 months old, this A4 was the first to be fitted with the Kylchap double-blast pipe. The driver was also different - J. Duddington, who had been brought down from Doncaster and had a reputation for running trains hard when it was required. Duddington was joined by fireman T. Bray, and inspector J. Jenkins. When the Westinghouse team were onboard, they were told that they were going to attempt to break the speed record. Why the secrecy? One reason was so that the LMS did not hear of the attempt beforehand. Another might be that the LNER's civil engineering department were not keen on 120+ mph runs, when the track had official speed limits of only 90mph!
The Down journey consisted of conventional brake tests. At Barkston, the Westinghouse team were given the option of taking a taxi to Peterborough - they all refused! The centre big bearing was drowned in cylinder oil, and the return journey commenced. Grantham was passed at 24mph. By Stoke signal box, the speed had reached 74.5mph with full regulator and 40% cut-off. At milepost 94, 116mph was recorded along with the maximum drawbar of 1800hp. 120mph was achieved between milepost 92.75 and 89.75, and for a short distance of 306 yds, 125mph was touched.
Photo by W Hannabuss @ Flickr
A peak of 126mph was marked on the dynamometer rolls, and this speed was included in some unofficial reports. 126mph (202.8 km/h) is also the speed marked on the plaque BR mounted on Mallard in 1948. Gresley never accepted this speed of 126mph, and thought it misleading. The LNER only claimed a peak average of 125mph - so breaking the world record for steam traction held by the German State Railways (124.5mph) and the British record set by the LMS (114mph).
LNER A4 Mallard enters York Station on the 3rd July 1988 on her run to celebrate the 50th anniversary of her breaking the speed record for steam traction. Photo by W Hannabuss @ Flickr
When Mallard arrived at Peterborough it was found that the centre bearing had overheated. It was then towed to meet the press at Kings Cross behind an Ivatt Atlantic. This must have led to some confusion, but the overheated bearing was quickly re-metalled. A further check was made that everything was okay, and Mallard was back in revenue-earning service within 9 days.
Photo by FrMark @ Flickr
Over 60 years later, Mallard's record of 125mph still stands. The world's fastest steam locomotive is preserved at the National Railway Museum, York.
Photo by FrMark @ Flickr
And... did you know that the LNER A4's carried more liveries than any other British steam locomotive class?