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Class 701 'Aventra' trains for South Western Railway

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OneTrackMinded

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OneTrackMinded said:
Demonstration of the acceleration on these units, a massive improvement from what it's replacing

Click to expand...
This is another example of the excellent acceleration of these units (although this is slightly lower power than the other video and not as good of an example ;) ). It moves off from a standstill so quickly! (skip to 0:07)
 
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RailUK Forums

WarrenTManager

WarrenTManager

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OneTrackMinded said:
Indeed they do!
Based off testing with a GPS acceleration monitoring device and comparing with a number of different results from all the other DC stock (desiro [444 and 450], desiro cities [700 and 707], electrostars [377, 378, 387, 376], networkers [465 [both motors], 466], junipers [458], 455, 777, the 701 is the fastest accelerating 100mph DC unit in the country, and the second fastest accelerating DC unit behind the 777, which is comparatively geared for 62mph (higher top speed gearing = slower acceleration and vice versa) (although I don't have data for the 710, so it might tie with that or be third because it has 90mph gearing).

It beats even the similar Desiro Cities (on DC of course) by a decent margin, especially when it comes to sustained acceleration at higher speeds.

It seems that the data provided on wikipedia is often wrong. The case with the desiros anyway is that the 0.85 figure is actually the AC acceleration rather than the DC, but this isn't specified on the Siemens specification sheet for the unit/s. Obviously they're trying to sell their product so they'd attempt to get higher figures in there without technically stating the power mode.


For the Desiro units, e.g the 450 and 444, they wouldn't ever be able to get to their advertised 1m/s^2 rate as they have such high power draw, meaning that the sub stations are unable to cope and therefore the power has been reduced significantly over the years. They’re quite close, but still behind.


In short, SWR’s “better acceleration” claim is indeed true after all, and to quite an extent as well.
Click to expand...
I did say they that I felt they were quick off the blocks!
 
H

hwl

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Nicholas Lewis said:
Desiros could have better acceleration rates they have the installed power but they were software restricted initially to follow VEP/CIG power profile and when the power system was reinforced that software restriction was never removed.
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The power supply was reinforced to an extent in places so in reality it would be swapping to a slightly lesser restriction. There would always be a restriction on DC, even the excellent Thameslink core area power supplies couldn't cope with no restrictions.

Samzino said:
From calculations in that video. It was accelerating at about 0.5m/s from standing start. Definitely wasn't on full power.
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Up to ~18mph* power draw is limited due to built in adhesion assumptions (max µ = 0.205) in the software (reduces risk of wheel spin and wheel wear) that cap the TE and hence reduce the power draw indirectly. TE is also considerably further software capped up to 2kmh.

*If the power supply is good this speed can be higher.

NR (and foreign equivalents) also restrict the max µ assumption for passenger timetabling (calculation) purposes.


Samzino said:
They're rapid indeed. Shame we don't have the Desiros unrestricted to compare.
Click to expand...
They can never be unrestricted on DC, the only question is on the level of restriction.
 
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Samzino

Samzino

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hwl said:
The power supply was reinforced to an extent in places so in reality it would be swapping to a slightly lesser restriction. There would always be a restriction on DC, even the excellent Thameslink core area power supplies couldn't cope with no restrictions.


Up to ~18mph* power draw is limited due to built in adhesion assumptions (max µ = 0.205) in the software (reduces risk of wheel spin and wheel wear) that cap the TE and hence reduce the power draw indirectly. TE is also considerably further software capped up to 2kmh.

*If the power supply is good this speed can be higher.


They can never be unrestricted on DC, the only question is on the level of restriction.
Click to expand...
Ah. I see. Well shows to a degree the performance limitations of DC, Thanks.
 
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hwl

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Samzino said:
Ah. I see. Well shows to a degree the performance limitations of DC, Thanks.
Click to expand...
The adhesion assumptions apply on AC too, on modern units power only makes a difference when you get faster than very fast human sprinting speed. You also get far more out every kW going into the train with modern units. Being 12-15t lighter than an equivalent 10car Desiro City or ~96t lighter than an equivalent 10car Desiro (if one existed) also helps.
 
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D

Dan G

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OneTrackMinded said:
Demonstration of the acceleration on these units, a massive improvement from what it's replacing

Click to expand...
That is impressive! I wonder what speed it has reached by the time the rear cab is passing?

Lightweight bogies + structurally optimised aluminium bodies = excellent power to weight ratio
 
Samzino

Samzino

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Dan G said:
That is impressive! I wonder what speed it has reached by the time the rear cab is passing?

Lightweight bogies + structurally optimised aluminium bodies = excellent power to weight ratio
Click to expand...
Believe it or not but I measured 22 mph
 
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norbitonflyer

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Dan G said:
That is impressive! I wonder what speed it has reached by the time the rear cab is passing?


22 seconds to travel its own length from a standing start.
Click to expand...
According to the equations of motion, and assuming constant acceleration, we get s= (u+v)t/2
u (initial speed) = 0,
s (length or distance) = 200
t= 22 seconds
v = final velocity

v=2s/t -u = 400/22 = 18metres /sec or 40mph.

acceleration, using s=ut +1/2 at^2,
rearranged and u=0 gives t^2 = s/2a
a= 200/484 = 0.4 m/s^2. Barely half the maximum it is quoted as capable of, which is 0.7m/s^2

At 0.7m/s^2, it would have cleared the platform in 12 seconds. (t^2=s/2a = 200/1.4 = 144)

EDIT - correction t^2 =2s/a, so a= 400/484 = 0.84m/s^2
 
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wickham

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Don't think any are permanantly parked up at Wimbledon - there just is not the room. There are a few at Clapham Yard (3 x 10 car and 2 x 5 car a few days ago) and a number at Eastleigh Airport Sidings - all the rest (with a few oddities at other places off Region) are put out to grass at Marchwood, Long Marston and Bicester !
 
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swr455

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norbitonflyer said:
According to the equations of motion, and assuming constant acceleration, we get s= (u+v)t/2
u (initial speed) = 0,
s (length or distance) = 200
t= 22 seconds
v = final velocity

v=2s/t -u = 400/22 = 18metres /sec or 40mph.

acceleration, using s=ut +1/2 at^2,
rearranged and u=0 gives t^2 = s/2a
a= 200/484 = 0.4 m/s^2. Barely half the maximum it is quoted as capable of, which is 0.7m/s^2

At 0.7m/s^2, it would have cleared the platform in 12 seconds. (t^2=s/2a = 200/1.4 = 144)
Click to expand...
Think your calculations may be off slightly
s=ut+1/2 at^2, u=0 thus s=1/2 at^2
therefore a = 2s/(t^2)

I made the time to be more like 23 seconds so a=2*200/(23^20)=400/529 giving average acceleration of 0.76 m/^s, a bit better than spec
 
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norbitonflyer

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swr455 said:
Think your calculations may be off slightly
s=ut+1/2 at^2, u=0 thus s=1/2 at^2
therefore a = 2s/(t^2)

I made the time to be more like 23 seconds so a=2*200/(23^2)=400/529 giving average acceleration of 0.76 m/^s, a bit better than spec
Click to expand...
You are quite correct. I lost a factor of 2 somewhere. A-lavel maths was a long time ago, when Class 312s were the latest thing in EMUs.
 
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OneTrackMinded

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Crossing my fingers training has started now. I've seen quite a few 701s not in service out on about and I wonder if they're being used for driver assessment
 
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Meglos

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1D54 said:
How many of these things are parked up at Wimbledon?
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There is normally 3 or 4 in the long shed at Wimbledon, and all you can normally see from the outside is the drivers cabs. It's pretty rare to see one outside, except when it's about to ECS to Waterloo to operate the Monday-Friday double Windsor service (WAT-WNR-WAT-WNR-WAT).
 
Samzino

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norbitonflyer said:
According to the equations of motion, and assuming constant acceleration, we get s= (u+v)t/2
u (initial speed) = 0,
s (length or distance) = 200
t= 22 seconds
v = final velocity

v=2s/t -u = 400/22 = 18metres /sec or 40mph.

acceleration, using s=ut +1/2 at^2,
rearranged and u=0 gives t^2 = s/2a
a= 200/484 = 0.4 m/s^2. Barely half the maximum it is quoted as capable of, which is 0.7m/s^2

At 0.7m/s^2, it would have cleared the platform in 12 seconds. (t^2=s/2a = 200/1.4 = 144)

EDIT - correction t^2 =2s/a, so a= 400/484 = 0.84m/s^2
Click to expand...
Not far off from what I got.

I decided that acceleration truly is measured from a standing start. Tractive effort is suppose to be higher usually from a standing start and start to curve off.

Class 701, starts moving at 3:54
First intermediate car passes Front of where driving car cab was at 3:54 @ 4:01

Train takes roughly 6.78 Seconds to Travel 20.8 Meters(One Driver Unit car Length of 701/0)

If v=2s/t - u then
((2x20.8)/6.78) - 0 = 6.13 m/s or 13.71mph

Must account for the intermediate cars being shorter than the driving cars by 0.9 meters so:

((2x(20.8-0.9))/6.78) - 0 = 5.87 m/s or 13.13mph

In Acceleration: 0.87(0.865 non rounded) m/s^2 from a standing start to clear one 20.8m Driving motor car length.

Can expect that number to reduce quite a bit as the train gets faster.
 
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3973EXL

3973EXL

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Stabled Farnham Depot - from the Main Line 06/03.
701049
701042
701035
701047
701044
 
J

janahan

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Many videos (taken front front on) visibly show it's acceleration from a standstill just from the way you can see the front cab rise a little as it starts moving, similar to some fast accellerating cars, something I have not seen on many other, especially DC trains (barring the Pacer, though their bounciness is nothing to do with acceleration, or lack of, but down to its unique.. erm suspension).

When these were first announced, I admit i was dissapointed that we were getting these instead of getting more Siemens units, at the time I was not overly impressed by the Bombardier offereings compared to Siemens, plus the fact they were lossing the distictive lok of the other aventras (345/710/720). I was also rolling my eyes during the "difficult introduction" which didnt help with my impression of these units.

Whilst I have not yet had the opportunity to actually ride them, living on the windosr line, I have seen many and even seen them running past me at stations, and they are growning on me. I think that whilst it certainly had its build issues, that these are actually technologically good trains just marred by a poor build that hopefully can be fully sorted out.
 
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