Bill and Jason's Excellent UK Adventure - 2015

[Talltim]

Struggling for a birthday present for my sister , remembered she is Doctor Who fan, remembered this thread and off I went to Galaxy 4. The guy in there remembered you Jason!

[MJI]

I think that needs an answer of its own Ben. 

 

Apart from the fact that they both ran/run on the WCML, are 25 Kv powered and they both tilt, not a lot. 

 

That's a rather simplified reply of course, but there is one big similarity that's not at all obvious in that they both use Prof. Alan Wickens' high speed wheel profiles developed during the late 60s and early 70s on HSFV1, POP-Train and E-Train. Almost every high speed railway in the world uses them as BR made the information freely available at the time.

 

From the tilt system point of view there's almost nothing the same, the 390s use electric stepper motors to drive their screw tilt jacks whereas P-Train used almost horizontal hydraulic tilt jacks. P-Train used accelerometers to measure the lateral accelerations on the bogies and from them derived a signal to drive the servo-valves which powered the til jacks. The 390s know where they are in the world from the balises in the track and know how fast they are going and derive a tilt signal from that information. P-Train's system was active all the time and would 'de-tilt' if the train came to a halt on a sharply canted curve, whereas a 390 is only allowed to tilt if the balise lets it.

 

The 390s use BIG disc brakes to stop them, I think with 4 discs on each axle, plus the rheostatic braking from the traction motors, whereas P-Train used HK and friction brakes, as described above, and rheostatic and HK brakes (maybe) in the Power Cars. As far as I know the 390s use coil spring secondary suspension, whereas P-Train used air springs on the trailer cars, but used long Flexicoil springs on the Power cars. The 390s don't have power cars as such of course as the traction power is distributed along the train, whereas P-Train had its two centrally positioned Power cars.

 

As you can see there are LOTS of differences, even though some people will cling to the idea that BR sold the technology abroad and we've now had to buy it back. Not the case I'm afraid, just another lost opportunity amongst the myriad similar opportunities in the UK engineering field.

 

The APT-P sounds more advanced than the 390s

[Mr_Tilt]

The APT-P sounds more advanced than the 390s

 

To an extent they were, but I am a tad biased here. 

 

From the tilt point of view the 390s don't compensate for slow speed traversals of slow speed curves, which can be common where track maintenance is being carried out, whereas  the P-Trains would 'de-tilt' so that floor stayed level as far as the passengers were concerned. The 390s are ahead of the P-Trains insofar as they don't fully compensate for cant deficiency and thus avoid the dreaded 'tilt sickness' for those passengers who are prone to it, but later in their lives the P-Trains had similar tilt controls, but perhaps not as well developed as those on the 390s. It's questionable if hydraulic tilt systems are 'better' than electric screw jacks, and there are as many opinions as there are engineers, but I've always been a hydraulic guy myself.

 

P-Trains were also faster than the 390s but one reason for that because the planned signalling upgrades on the WCML didn't happen as planned.

 

One place where the 390s are definitely more advanced is in their secondary vertical suspension. Because the P-Trains had their secondary air springs mounted on the outer ends of the long BT11 bogies any vertical motion tended to be amplified, especially if the leading vehicle was out of phase with the trailing vehicle. This may have been sorted with planned P-Train versions, both articulated and non-articulated, but sadly the programme never got that far as it would have needed a major re-design of the bogies.

 

It may be that the 390s show better braking performance than P-Train but we'd need some input from my colleague Martin Collins on that. But remember that P-Train was designed to brake from 155 mph and the 390s only had to stop from 140, and today they're limited to only 125.