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Pauls Railway Web

Advanced Passenger Train - Experimental

Tilting Trains

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One of the most innovative features on the APT was the trains ability to tilt the coach body upto 9 degrees off the vertical in either direction.     APT-E was the very first tilting train to be built anywhere in the world,   in fact because of the trains unique features the government regarded the train as a state secret until 1974,  although nearly all the railway paternity had seem information on the trains specifications by this time.

apt14s.jpg (10819 bytes) A central mounting point was fitted at either end of a bogie,   the bodywork was balanced on the mounting point,  two hydraulic rams were fitted at each end of the vehicle, and at either side of the mounting point , these supported the bodywork and held it level.    As the vehicle is needed to be tilted one pair of the rams are lifted and thus the vehicle tilts.   The whole assembly resembles a see-saw.

The diagram to the left shows the differences between the APT-E and APT-P tilting systems.   The APT-P tilt system has the advantage of adopting a vertical position during any tilt failure,  the APT-E would list over onto the coach buffer stops on an angle of 12 degrees,  although a fail safe system was added to APT-E to lock the vehicles in an upright position during failure.

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The advantage of the E train tilt system  over the P train version was the speed that the system could react to changes in the amount of cant compensation required at any given time. The E train high pressure hydraulics and the force of gravity meant that E train tilting was significantly faster in reaction times compared to the P train system.

TC2 can been seen here shortly after E Trains arrival at the National Railway Museum, York in what is now the Great Hall.   For a short while the tilting system was demonstrated to the public using a modified tilt pack and controller.

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On APT-E each hydraulic ram is supplied fluid by a TILT PACK which is fitted within the vehicle bodywork.   Tilting is controlled by means of an Accelerometer,  which acts like a spirit level, but is also affected by centrifugal force,  as the bubble moves off centre the electronics in the tilt pack compensate by tilting the vehicle into the curve,  a maximum tilt of 9 degrees can be achieved during everyday running, but the system is capable of tilting up to 12 degrees if necessary.    The tilt system allowed APT to run at between 25 - 40% faster while maintaining the conventional level of  passenger comfort,  but the train was also perfectly safe to run at the higher speeds even if the tilt system failed.    The tilt system on the APT was introduced only for the comfort of the passengers and had no effect on the trains ability to perform high speed cornering.

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While high speed cornering the vehicles would tilt over to maintain passenger comfort but the effects on the track and ballast had to be reduced,  conventional bogies would place large amount of lateral force on the track and ballast, this would have the effect of moving the track away from its correct position,  so a new design of bogies had to be produced.

The new bogies would have the ability to steer into corners and would also be articulated,   this means that adjacent vehicles would share a common bogie, this in turn would reduced the total weight of the train and drastically reduced the lateral forces placed on the track.

Active suspension was used to reduce the amount of pitch, roll, and bounce the supported vehicles would produce at high speeds on standard track.

The use of articulation, active suspension and steerable wheel sets are the main features which allows APT to run at significantly higher speeds without the need for special track concessions.

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The old Dalby test track were the APT-E was mainly tested was the perfect place for research and development of the APT project,  a 13 mile stretch of track with server bends, tunnels and various track sections maintained to different levels allowed the engineers to tweak systems on the train and develop there ideas.   Many high speed cornering tests were carried out with tilt system activated, de-activated and even tilted the wrong way into bends, all this was necessary to prove the safety and stability of the train during system failures and normal running operations.

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During a tilt operation a normal vehicle would protrude from the loading gauge,  the loading gauge being the imaginary tunnel that the train must pass through,  if any part of the train moves outside this loading gauge it would be able to strike trackside objects and even a train passing in the opposite direction.

To stop this from happening the top and bottom half of APT vehicles are tapered inwards, as can be seen on the photograph to the left.

The vehicles can be tilted up to a maximum of 12 degrees off the vertical in either direction and still not protrude outside the loading gauge.     During normal operation a maximum of 9 degrees was required to compensate for high speed cornering.

Although the tilt system on TC1 and TC2 had been commissioned just before the trains first run, it was decided that the train should run passive on its first trip out.

On return to the R&D sidings its a little known fact that the tilt system on TC2 was set to active for the short stretch between the mainline and the APT-E siding.

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Email me on Paul@APT-E.Org

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