Saturday, 5 April 2014

On the buses! And another look at APT.

Crewe Heritage Centre this weekend are holding a vintage bus event and I decided to go along for a look, and to have another poke around the prototype Advanced Passenger Train they have there. I recently managed to get hold of a copy of 'Advanced Passenger Train; A Promise Unfulfilled' by L H Williams through Cheshire Library inter-lending, a book long out of print, and I wanted to have a closer look at the train armed with my new knowledge.

A near-full Virgin Pendolino from Wilmslow whisked me to Crewe, where the vintage Routemaster bus operating a free shuttle between the station and the Heritage Centre rolled to a stop just as I emerged from the station.

Please click on any picture for a larger image.

Upper deck of the Routemaster at Crewe station

Rail House, Crewe, from the upper deck of the Routemaster

The Routemaster at the Heritage Centre ready to return to the railway station

Not too many buses on display, and some of them not that old!

View of Crewe station from the observation window of the old Crewe signal box at the Heritage Centre. Look carefully (click to enlarge) and you'll see the Routemaster on the road bridge in front of the station

A southbound Pendolino passes the Crewe Arms as it enters the station

General view of the Heritage Centre site from the old signal box balcony

A4 Pacific locomotive 'Bittern'. This engine is frequently used on steam specials.

A look at Bittern's corridor tender, enabling crews to be changed during non-stop runs from London to Edinburgh back in LNER days.

A promise unfulfilled; the only remaining prototype Advanced Passenger Train (APT)

Standard class interior of the APT. Compare with that of the Pendelino in the picture at the end of this post

The rather spartan drivers' cab, complete with second man's seat insisted on by the rail unions of the time, an issue which caused massive delays to the APT - Experimental project. The APT-E was built with single-crew cabs.

I had my sandwiches in the first class carriage of the APT; here, a train of VSOE (Venice Simplon Orient Express) Pullman coaches passes, southbound on the West Coast Main Line, topped and tailed by class 67 diesel locomotives. This train had dropped off Grand National-bound customers at Runcorn (for onward travel to Aintree by coach) and was returning to Crewe for servicing before returning to Runcorn later to pick up the passengers after their day out at the 'National'.

The train ran in service with two power cars in the centre, and six passenger coaches either side of these; a total of fourteen coaches. It was effectively two separate trains, separated by the power cars with catering in both 'trains'. The power cars do have a narrow corridor through them (shown in the picture above) but only train staff, not passengers, could use these.

The Heritage Centre has placed information sheets in the power car to explain how it operated (click on the picture to make the text legible in a larger image)

The traction motors are mounted in the power car body, with cardan shaft drive to bogie-mounted gearboxes to minimise the un-sprung weight for a better ride at high speed and less wear on the track.

One of the 4 traction motors per power car (nearest the camera). The ducting for the the traction motor blower is mounted on top of the unit. The transfer gearbox to drive the cardan shaft is the blue section on the far end of the motor, and the section beyond that is the hydro-kinetic brake.

Hydro-kinetic brake nearest the camera, the transfer gearbox in blue, and beyond that the traction motor with its blower trunking

The non-powered bogies carried hydro-kinetic brakes on the axle. The large drum with vanes fixed to it internally rotates with the wheels and has a vaned 'stator' inside it which does not rotate, a form of torque converter. To apply the brake, a glycol / water mix is pumped into the drum by compressed air causing drag between the non-rotating stator and the rotating drum, and the liquid pumped to radiators to dissipate heat. As the train slowed, final braking was achieved by wheel-tread friction shoe brakes applied by compressed air.   

A power bogie showing the cardan shaft drive from the body-mounted traction motor to the bogie-mounted gearbox

An external view of a power car. Each power car was fitted with a pantograph to pick up traction current from the 25Kv ac overhead wire, but only the leading one was used. If both pantographs were raised, the first one would set up a mechanical flex (a 'wave') in the overhead wire which would cause the second one to bounce on the wire. The 25Kv ac power was supplied to the other power car by cables, and it was this need to cable-connect the high voltage between the power cars that necessitated the power cars to be adjacent. On today's Pendolinos safe and reliable coach-top cables connect the non-adjacent transformer cars in the train again with only one pantograph raised, and modern technology allows all of a Pendolino's traction equipment (transformers, motor drive electronics, and traction motors) to be mounted under the train's floor so they don't impinge on the passenger space. Like APT, Pendolino uses (under) body mounted traction motors driving bogie-mounted gearboxes through cardan shafts. 

I returned to the railway station on the lower deck of the Routemaster

One Routemaster seen through the door of another

The Routmaster's driving cab

A Virgin Pendelino took me home to wilmslow, a modern version of what the APT perhaps should have been. The APT was a brave attempt to provide British Rail with 150mph tilting electric trains running on the West Coast Main Line. The project started with APT - E (E for experimental), a gas turbine powered 4-coach train of revolutionary construction. It was designed by engineers from the aerospace industry using lightweight but strong aluminium construction and tilting bogies to reduce the sideways forces for passengers on curves. APT - E was followed by three electrically-powered prototype trains (APT - P) which actually didn't inherit a great deal from APT-E (different tilt system, power, and traction system). British Rail management forced APT-P into service long before the trains were developed enough for that. Although they suffered from unreliability due to their not being sufficiently developed, they were fast and an APT - P still holds the London to Glasgow rail speed record despite a modern Pendolino having a go at the record a few years ago (APT - P also holds UK rail speed record of 162.2 mph for conventional, as opposed to High Speed, rail).  The unreliability gave BR management and Government the excuse they were looking for to 'pull the plug' on APT (instead of completing developing it into the reliable train it by then nearly was) and concentrate instead on the successful but conventional HST (High Speed Train), or Inter City 125 based on the non-tilting Mk3 coach of steel construction with a maximum speed of 125 mph and much lower acceleration rates than APT.

APT - E went to the National Railway Museum in York. One of the ATP - P sets is this one at Crewe (its second power car is with the NRM at York). The other two APT - P sets were scrapped.

The bulky electrical equipment of the time was not in APT's favor, with the requirement for the adjacent power cars to house it, which divided each unit into effectively two separate trains whereas on today's Pendolinos all the equipment is below floor level and the two transformer cars distributed in the train use a 25Kv coach-top connection to the single raised pantograph. The under-floor mounting of the traction motors on Pendolinos allows for most of the train's wheels to be powered, rather that just those of the power cars on APT. This gives better acceleration and resistance to wheel slip on gradients than on APT.

In addition the APT's hydro-kinetic brake was far from ideal, being impossible to control with enough finesse to prevent wheel slip, and continuing to cause drag after brake release due to residual fluid still in the system. The regenerative brakes of modern electric trains, made possible by developments in electronic technology were not available in APT's day. Regenerative brakes provide retardation by the traction motors operating as generators, recovering energy to be put back into the overhead wire as current for other trains to use rather than dissipated as heat as the hydro-kinetic and friction brake does.

However, APT has a far more pleasant interior than the Pendolino (see the picture above). It has a spacious, airy feel compared to the cramped claustrophobic Pendolino interior, with its tiny letter-box windows. Compare the picture below with that of the APT interior above.

Pendolino interior - cramped and claustrophobic compared to APT

So probably the ideal train for UK main lines today would be an APT with modern traction and braking technology. If the UK government of the 1980s had more vision and belief in rail's future, and had backed APT instead of burying it, perhaps that's what we'd have by now instead of Italian Pendolinos.


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