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Post by agoodcuppa on Feb 5, 2007 23:26:57 GMT
And bigger wheels make acceleration easier - hence the huge ones on mainline steam locos. Errrr, the larger the wheel the slower the acceleration and the more torque needed to get it rolling is how I've always understood it.
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Deleted
Deleted Member
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Post by Deleted on Feb 5, 2007 23:42:43 GMT
Whereas the smaller the wheel, the higher the rotational speed, leading to greater stress on the drivetrain (for locos and MUs) or the motion (for steam locos). Note that the GWR 4-6-0 'King' class locos had smaller drive wheels than the 'Castle' class, but the smaller wheels helped contribute to a slightly higher top speed.
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DrJimi
Virtual District Line construction engineer and arborist
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Post by DrJimi on Feb 6, 2007 23:46:01 GMT
And bigger wheels make acceleration easier - hence the huge ones on mainline steam locos. Errrr, the larger the wheel the slower the acceleration and the more torque needed to get it rolling is how I've always understood it. Exactly so - an example of mechanical advantage. Besides the discussion regarding C and D stocks, it's equally interesting to compare the C Stock to the Battery Loco. Both use 36" wheels, however the pinion ratio of the Battery is numerically higher, thus providing an overall gear ratio that acts as a torque multiplier so heavy loads can more easilly be moved from rest. Plus a Battery is designed to run at 48Km/hr (30mph) max. My understanding is that the D got the TS-sized wheels so as to reduce the number of required spare parts needed. The pinion ratio was designed accordingly to provide desired acceleration and top speed, within the limits of motor rpm. It's somewhat sluggish acceleration above 30mph is due to several reasons - motor design, rail friction and aero drag being among them. My research (for purposes of modeling and simulation) revealed A D produces max tractive effort at about 15-20mph (as initial inertia is overcome) and so it gets to typical line speed (30-ish) quite quickly. The roads where it might see 45mph are also those where weak field is used (to raise the natural balance speed of the motor), which tends to reduce the torque (acceleration) somewhat. /Jimi (simulation scientist at large ;D)
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Post by tubeprune on Feb 7, 2007 16:28:08 GMT
Dr Jimi, this is exactly what mreto type trains are supposed to do and designers have always tried to get high acceleration to a reasonable speed (20-25mi/h) to get the train out of the station and get the next one in (RORI - run out run in) which is critical to good operation. High top speed is not really needed unless you get an A Stock type route. That's why the flag switch was arranged to give low acceleration on open sections.
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Ben
fotopic... whats that?
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Post by Ben on Feb 7, 2007 19:13:39 GMT
I always though that larger wheels gave a smoother ride? If youve got a little wheel with one dent in, the dent will hit the track more often then a larger wheel with one dent?
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Deleted
Deleted Member
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Post by Deleted on Feb 7, 2007 21:33:30 GMT
My research (for purposes of modeling and simulation) revealed A D produces max tractive effort at about 15-20mph (as initial inertia is overcome) and so it gets to typical line speed (30-ish) quite quickly. That would tally with what they feel like to drive.
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Post by markextube on Mar 2, 2007 11:56:14 GMT
Here are the spec for the 1967 stock. Interesting in comaprison to the 09 stock!
Vehicle details and statistics Dimensions here are as designed in imperial units. The drawings show metric conversions. Driving Motor Car Trailer Car Length over body ends: 52ft 9ins 52ft 5ins Width of body: 8ft 8ins 8ft 8ins Car height: 9ft 51/4ins 9ft 51/4ins Tare weight: 30.4 tons 20.3 tons Tare weight of 8 car train: 202.80 tons Passenger door open width (double): 4ft 6ins 4ft 6ins (single): 2ft 3ins 2ft 3ins Car number series: 3001-3086 4001-4086 Car number series: 3101-3186 4101-4186 Vehicles in stock: 172 172 Grand total in stock: 344 It should be noted that 28 cars (14 driving motors and 14 trailers) were converted in 1987-1989 from Northern line crew-operated 1972 MKI tube stock Passenger accommodation Please note that standing capacity figures exclude seating capacity Seating capacity: Number of seats per train 304 Standing capacities: Floor area available for standing passengers (m2)a 132.24 Standing capacities: Maximum observed standing capacity (5 customers per m2) 661 Standing capacities: Maximum full load standing capacity (6 customers per m2)b 793 Standing capacities: Theoretical crush standing capacity (7 customers per m2)c 926
NOTES: a) Capacities here are figures calculated from floor area for design purposes b) For propulsion performance rating c) For structural and braking capacity
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Post by 100andthirty on Mar 4, 2007 11:29:20 GMT
Dear all
My first post!
Both 1973 tube stock and D stock have the same installed traction packages (PCM camshafts), and 12 traction motors (LT118) and are capable of the same performance as they weigh about the same. D stock's settings mean that it's a bit "slower" than 1973 tube stock. air resistance is a factor at high speeds, but can be neglected at speeds below 40mph.
Wheel size is irrelevant for performance - and smaller wheels just mean that a different gear ration is needed compared with big wheels.
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Post by District Dave on Mar 4, 2007 11:44:36 GMT
Welcome! And I very much hope it won't be your last!
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Post by 100andthirty on Mar 4, 2007 15:54:37 GMT
Thanks for the welcome and I promise to triple check my spelling in future
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Post by trainopd78 on Mar 5, 2007 13:20:42 GMT
I think I read somewhere that when new, the D stock motors were de-rated as they were far too quick for the District or did I make that up?
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Deleted
Deleted Member
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Post by Deleted on Mar 5, 2007 18:45:03 GMT
I think I read somewhere that when new, the D stock motors were de-rated as they were far too quick for the District or did I make that up? I have also heard that, but possibly I heard it from you!
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Post by tubeprune on Mar 5, 2007 20:27:59 GMT
I was involved with the stock when it went into service and I don't remember anything about that.
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Deleted
Deleted Member
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Post by Deleted on Mar 5, 2007 21:10:09 GMT
All I remember is that the use of both flags was banned, and only because the District did not actually have a maximum linespeed - there were fears that drivers giving it welly would not only SPAD various signals but also manage to plow through the overlaps entirely.
Now that the District has a maximum linespeed, using both flags is now only banned because the rules say so.
I think it was solidbond who mentioned this...
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Post by trainopd78 on Mar 5, 2007 21:16:28 GMT
I think I read somewhere that when new, the D stock motors were de-rated as they were far too quick for the District or did I make that up? I have also heard that, but possibly I heard it from you! Very possibly. I think I heard it from one of our long serving east end drivers. Thanks Tubeprune for clearing up that urban myth.
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