Rail projects : Class 91 – a potential never fulfilled
The East Coast Main Line (ECML) has been for many years, England ’s rail gateway to the North starting from London Kings Cross to Edinburgh some 392.7 miles in length. Some of the worlds most famous trains and locomotives have plied their trade with evocative names such as the Deltic, flying Scotsman, Mallard and of course, the HST create wonderful images of times when rail travel was exiting, a symbol of national pride and dare I say it, romantic even.
Both the Diesel and Steam traction world speed records have been set on this legendary route and the billiard table flat and arrow straight four track section between York and Northallerton has always been nicknamed by train drivers and rail industry as ‘The racing stretch’ .
InterCity: building on success
It had always been the plan to electrify the ECML, a plan that had first been mooted back in LNER days, but following nationalisation, only the West Coast Main Line via Euston and Glasgow gained the ‘Sparks’ effect and even then opening in sections over a period of nearly 10 years. The ECML became fully wired in 1991 after much delays and Government dithering, and in hindsight following some serious problems with wiring and catenary either failing or at worst collapsing in poor weather conditions proved to be a costly cheap design. The stand alone InterCity division headed up by Dr John Prideux was proving to be a money spinner with the halo effect of the HST bringing valuable business custom to BR and unheard of leisure travel growth on the Eastern Region.
Across the Pennines, the Advanced Passenger Train (APT) was proving to be a problematic and costly experiment, especially as the tilting train idea had been in the pipeline since the late 1960’s. It was quickly becoming a reality that the APT was not so much too advanced for BR, but more the case that BR was simply not advanced enough for the APT.
With electrification well under way on the ECML, in 1984 the board of BR (BRB) decided that a fleet of high power locomotives and rolling stock would be required for the ECML once total route wiring had taken place to operate alongside the highly successful HST fleet. Invitations by tender were put out and GEC were the final winner to design and construct the locomotives which were to be numbered class 91.
The design was to be called Project Electra and the service would be called Inter City 225 as the operating speed was to be 140mph or 225km/h. GEC designed a new locomotive and had an operational example for proving constructed 1988. Because GEC has no capacity themselves to construct, the task of building this fleet was sub contracted out to British Rail Engineering (BREL) in Crewe. State of the art electronics and design saw the 91 fleet constructed ahead of time but problems with rolling stock production put the service introduction back by some time. Assembly of the new Mk4 designated rolling stock eventually became the responsibility of Metro Cammell (MCW) in Washwood Heath Birmingham.
In true political style, the promised Government funding for upgraded track and signalling that would allow these new trains to achieve their operating speed of 140mph was never acheived. The introduction of a flashing green aspect on the signalling (in effect turning four aspect signalling into five) on certain sections through Cambridgeshire and Lincolnshire, meant 140mph running for only proving tests were possible.
By the time a full 91 service came on line in 1991, journey times to and from London were cut back by nothing more than a few minutes, achieved by better acceleration times than the HST but hampered by having the same top speed in service of 125mph. With over 6300bhp available, the class 91 was still a high performing locomotive in every sense.
Even though these new trains looked utterly superb, in practice they failed to offer the same level of comfort of the proven HST. Whereby the 125 had been designed both in house and with a sensible budget, the class 91 and the Mk4 rolling stock felt lightweight and inferior to older designs. BREL engineers had been working on an updated bogie called the T4 which promised to be just as effective as the T3 on the HST.
Because of budgetary and time constraints, BREL bought in bogies from a Swiss concern called SIG that failed to offer a cosseting ride on our less than perfect track. Engineers could only tweak the design over time in service, but at best the ride quality at speed can only be described as fair. The actual locomotive featured some novel ideas and features to reduce wear on the track and vastly reduced unsprung weight.
The traction motors were mounted in the frame of the loco rather than the bogie with tractive power being fed to the axle gearbox by means of a short yoke jointed prop known as a cardan shaft. Primary braking was operated by rheostatic methods which in layman’s terms, turned the traction motors into generators thus reversing the torque and creating a retarding effect on the transmission.
The heat generated through the braking was dissipated through the resistor packs and this operated from maximum speed down to around 28mph after which, traditional tread brakes would automatically kick in to bring the locomotive to a halt.
The class 91 actually had two drivers’ cabs, it was initially planned to operate the loco as a high speed passenger train during the day and haul freight during the night. Only the leading end was streamlined meaning that locos operating ‘blunt end’ first were restricted to 110mph owing to aerodynamic buffering that could affect the roof mounted pantograph that collects the 25Kv electrical current from the overhead wire. Ideas of using the 91 as a mixed traffic locomotive were soon scrapped and this class of locomotive has only ever operated in passenger service.
Problems in service
Unlike the HST, the 91 class feature conductor operated power doors on the passenger coaches, but passengers who place cases or baggage too close to the doors continue to cause delays on overcrowded trains. Soon after introduction, it became apparent that fine snow could penetrate the air intake system at high speed, once enough powdery snow had got inside the electronics, it would subsequently melt and on a few occasions, short circuit causing the train to fail. The colossal power of the traction motor in both acceleration and braking caused heavy wear on the cardan shafts and bogie mounted gearboxes which required a redesign and even finer levels of assembly tolerances.
Still a record breaker
The complete 91 class went through a massive engineering upgrade known internally as ‘Delta 91’ during the GNER franchise which was completed in 2003, this comprised of various cab and equipment upgrades turning the class from below average to one of the best reliability records on the British railway infrastructure.
During the testing days, the 91 managed to achieve some record breaking runs when being type proved on the ECML. At a similar point in Cambridgeshire where the A4 steam loco Mallard broke the world record for steam in 1938, a shortened 91 set hit 162.4 mph – the fastest ever recorded speed for an electric locomotive in the UK. Another high speed test run saw this class run a time of just under 3 hours 30 minutes from Edinburgh Waverly to London Kings Cross, averaging just over 112mph point to point.
Sadly, GNER had their franchise withdrawn in 2007 following the parent company Sea Containers running into financial difficulty, the franchise was then put out to re-tender. A GNER management alliance with Virgin trains bid was turned down and the line was hand ed to National Express who also ended up suffering mounting losses. Nat Ex hand ed back the franchise to the Government during which time they had cut back dramatically on all operating costs allowing the fleet to become run down and problematic.
These events caused the Government to operate the line under the brand ing ‘East Coast Trains’ who have since put into place various plans to improve reliability and customer confidence. GNER represented a perceived image of style and quality that still seems to be much missed in the private railway sector.
With 6300bhp available, the BR class 91 remains the most powerful passenger locomotive in the UK, but prior to the Mk4 coaches being built, the 91 would operate with a surrogate HST power car recording the highest powered passenger train of its kind, at that time in the world having 8550bhp at the drivers’ disposal.
The refit programme of 2006 – 2007 has seen the class 91 sets turn from being an ugly duckling passenger wise, to a true elegant Swan with impressive new seating, total re-wiring, new spring and damper settings, improved electrics and features such as onboard WiFi and electrical charge points at every seat. These and many more refinements make sure that the class 91 despite its troubled life, remains to ply its trade on the ECML for years to come.