444/158 relative acceleration curves

[HSTEd]

We all know that units like the Class 395 are insanely quick off the mark, but I have been thinking more about "express" units lately, like the Class 444.

I was wondering if anyone had any information as to the relative performance of the Class 444 compared the Class 158, which is perhaps the typical unit that comes to mind when you mention secondary express services?

The power to weight ratio of the units is similar but the Class 158s horsepower rating reflects its engine power whereas the 444's reflects the power of its actual traction motors.
Additionally the Class 158 has a less rapidly accelerating mechanical transmission.

Anyone got any actual data?

 

[TheGrew]

I think this could be interesting to look at, am I right in thinking that the 158s no longer pull off under full power to save fuel?
As for the 444 don't they have to run sections with reduced power (due to lack of juice in 3rd rail) I imagine otherwise they would be capable of the same acceleration profile of a 350 which is very quick (I believe quicker than a Pendolino).

 

[HSTEd]

I think this could be interesting to look at, am I right in thinking that the 158s no longer pull off under full power to save fuel?
As for the 444 don't they have to run sections with reduced power (due to lack of juice in 3rd rail) I imagine otherwise they would be capable of the same acceleration profile of a 350 which is very quick (I believe quicker than a Pendolino).

They don't have sufficient power to match a Class 350.
They are 115m long (5 x 23) compared to 80m (4 x 20) but still have the same 2000hp.

I somewhat doubt they are able to make 110mph at all.

On the plus side they are likely light enough to benefit from differential speed limits similar to those given to Sprinters now in case of a line being electrified.

It appears they will accelerate like Class 158s but make 100mph eventually.

I do note that a Class 444-type train that received the Desiro City bogies would be only ~211t, which would put it into a similar power to weight range to Cl87/90 loco hauled trains, which would allow it tomake 110mph relatively easily.

 

[MCR247]

On AC preferably

 

[HSTEd]

It turns out they beat 2+9 HSTs in terms of power-to-weight (if you use the Cl43s wikipedia page as a guide to the at-rail horsepower available).

So 110mph in a reasonable time should not be much of a problem.

Do Class 444s drive all four axles on the driving motor vehicles or just one bogie?
It appears they will behave like Class 158s that keep on accelerating to 100/110mph.

 

[Peter Mugridge]

444s are Bo-Bo + 2-2 + 2-2 + 2-2 + Bo-Bo, so all four axles are driven on each motor vehicle.

 

[notadriver]

Based on the power to weight ratios it would seem the 159 has an advantage. However 171s are very slow to accelerate despite having a better power to weight ratio than a 159.

 

[455driver]

Power to weight is only a part of the equation, what about gear ratios?
That has a huge effect on acceleration!

 

[HSTEd]

Power to weight is only a part of the equation, what about gear ratios?
That has a huge effect on acceleration!

The fact that the 444 has an electric transmission should provide it with an advantage over the Sprinter in this department (as the mechanical transmission would have to slip the clutch when starting and can't produce max power at low revs).

But I don't know.

 

[455driver]

The mechanical transmission has 5? gear ratios plus a torque converter where-as a 444 has a fixed gear ratio.


Take your average (manual) car and try pulling away in 3rd gear (that should get you to about 100mph on full revs) and see how it accelerates from a standing start, its all well and good gearing something for 100mph but there is always a trade off when it is one fixed gear.

 

[notadriver]

Just had a look at some logs from the railway performance society. Both runs on the up departing Woking. The class 158 passed West Byfleet at 78 mph and 3m 07 seconds. The class 444 passed the same point doing 80 mph in 2m 48s s apparently very similar.

 

[455driver]

I would like to see the speeds and times for Byfleet and New Haw though, the 444 would still be well into its stride but the 159 would be running out of puff!

Dont forget the 444 is limited to about 70% power from about 10mph where-as the 159 would be using all 1200 horses.
A 455 can keep up with a 450 up to about 40-45mph! Trust me on that one.

 

[notadriver]

I would like to see the speeds and times for Byfleet and New Haw though, the 444 would still be well into its stride but the 159 would be running out of puff!

Dont forget the 444 is limited to about 70% power from about 10mph where-as the 159 would be using all 1200 horses.
A 455 can keep up with a 450 up to about 40-45mph! Trust me on that one.

The next timing point was Weybridge

Class 159 : 4m 53 at 90 mph
Class 444 : 4m 34 at 88 mph

This was its top speed on this run. Its possible the 444 wasnt in any particular hurry as the 159 was still doing 80 mph through Surbiton whereas the 444 had dropped to 76.

You can keep up with a 450 up to 45 mph? Wow - they seem very slow around the areas I know especially uphills.

So the 444 weighs a hefty ~230 tons and only has 70% of its 2000 hp available? That works out to about 6 hp / ton. Based on 1600 hp a Class 442 has 8 hp / ton.

Looking at some logs for a 442 (10 car) and a 5 car 444 leaving Winchester on the up, Micheldever was passed in 7m41 for the 442 and 7m31 for the 444. Speeds were 85 for the 442 and 88 for the 444.

 

[HSTEd]

The mechanical transmission has 5? gear ratios plus a torque converter where-as a 444 has a fixed gear ratio.


Take your average (manual) car and try pulling away in 3rd gear (that should get you to about 100mph on full revs) and see how it accelerates from a standing start, its all well and good gearing something for 100mph but there is always a trade off when it is one fixed gear.

Yes, and this is because Internal Combustion Engines cannot produce maximum torque at zero revs.

An electric motor can do so, this is the primary advantage that lead to the current domination of Diesel Electric transmissions in the freight locomotive fleet.
Gearing in diesel electrics is determined by the maximum speed your motor can turn at without causing the rotor to disassemble itself and by the maximum speed.
The former limit is increasing all the time with increasingly strong rotors (especially PMMs which have a solid magnet) and innovations such as carbon fibre wrapping.

Also why is a Class 444 limited to 70% of available traction power above 10mph?
Is this to reduce its load on the system power supply?

 

[swt_passenger]

Also why is a Class 444 limited to 70% of available traction power above 10mph?
Is this to reduce its load on the system power supply?

Yes - it is because the famous 'Southern Power supply upgrade' was done on a basis of 'this is all you'll get', rather than 'what do you need'.

Same problems apply to all modern DC EMUs IIRC, 444s are not specifically different in this respect. As far as I know, SWT 450s are also significantly restrained. So when people mention that a 350/1 has far better performance on AC than DC it isn't actually the fault of the unit itself...

--- old post above --- --- new post below ---

The mechanical transmission has 5? gear ratios plus a torque converter where-as a 444 has a fixed gear ratio.

The Desiro's AC traction drive is variable voltage and variable frequency though (aka VVVF), and that effectively overcomes the limitation of having a fixed ratio drive on the bogie itself.

 

[notadriver]

I think there is always a final gear ratio in electric trains which affects acceleration and top speed. The 159s have a torque converter used from a standstill and then the direct drive takes over at around 45 mph.

 

[455driver]

Just had a look at some logs from the railway performance society. Both runs on the up departing Woking.

Were these "in service" runs or special "testing" runs, as drivers will drive it differently.

When leaving Woking on the up fast there isnt any real need to take a unit up to full speed too early as you just catch the train in front (this doesnt apply to the xx59 departure as you can race the xx59 departure on the up slow, but I digress ) and only intend to get to 90 at the M25 overbridge, coast for a while and then back up to 90 for Esher then let the unit reduce speed for the 85 at Hampton Court jn and 80 before Surbiton hold that through Surbiton and then let the unit slow down for the 75 before New Malden, the first time I touch the brakes is for the 40 at Clapham jn.
i wonder if a computer could be as smooth?

 

[notadriver]

They were just regular service runs. It might explain why the 444 was eased early and why the 159 continued at best possible speed.

Of course a computer wouldn't be as smooth or as efficient but I'm betting some expert rail enthusiasts on train simulator can drive their trains better than we can

 

[455driver]

He he he!

 

[cyclebytrain]

Were these "in service" runs or special "testing" runs, as drivers will drive it differently.

When leaving Woking on the up fast there isnt any real need to take a unit up to full speed too early as you just catch the train in front (this doesnt apply to the xx59 departure as you can race the xx59 departure on the up slow, but I digress ) and only intend to get to 90 at the M25 overbridge, coast for a while and then back up to 90 for Esher then let the unit reduce speed for the 85 at Hampton Court jn and 80 before Surbiton hold that through Surbiton and then let the unit slow down for the 75 before New Malden, the first time I touch the brakes is for the 40 at Clapham jn.
i wonder if a computer could be as smooth?

Hehe, speaking as someone who's designed control systems, I'd love to have the challenge of making one to outperform a human driver.

Sadly, I think the closest we're ever likely to get is a competition with model trains though! I'll stop hijacking the thread now!

 

[O L Leigh]

Only Cl172s have a mechanical transmission. All other "modern" DMUs have a hydraulic transmission with 2 stages (Cl180s excepted, or so I believe). The first stage is a torque converter that holds the engines at constant revs. This takes the drive up to a certain speed (@40mph on 75mph Sprinter classes and @70mph on 100mph Cl170s) where drive is taken over by a fluid coupling to bring the train up to it's maximum speed.

I doubt a Cl159 could keep up with a Cl444. Having driven 3rd gen EMUs and now DMUs the difference in acceleration is very noticeable. If you give a Cl379 "the beans" from a stand it will be doing @65mph when the vigilance goes off after 1 minute. A good Cl170 might be doing 50mph by this time.

O L Leigh

 

[notadriver]

Don't forget a 444 has an extra coach and reduced traction power because of DC third rail limitations.

 

[O L Leigh]

I understand that.

But the disparity in acceleration rates are so great that it is not entirely explained by these factors alone. Power-to-weight ratios are only indicative of performance but, where power and transmission systems are so very different, they cannot be relied on to decide on which train sets off faster.

O L Leigh

 

[notadriver]

Hehe, speaking as someone who's designed control systems, I'd love to have the challenge of making one to outperform a human driver.

Sadly, I think the closest we're ever likely to get is a competition with model trains though! I'll stop hijacking the thread now!

There's no question that jubilee line tube trains stop at the exact point every time and can run closer together than with a human in control. In fact I agree with ATO for tube operations. Outside on the big railway where things can happen is a different story.

The problem with simulators is no matter how realistic they are - they can't emulate the real thing exactly. I found the million pound training sim has better brakes and accelerates harder than the real thing

 

[notadriver]

I understand that.

But the disparity in acceleration rates are so great that it is not entirely explained by these factors alone. Power-to-weight ratios are only indicative of performance but, where power and transmission systems are so very different, they cannot be relied on to decide on which train sets off faster.

O L Leigh

Congrats on your move to another TOC. Are you treated better there ? The logs seem to indicate only a minor difference between a 444 and a 159. In fact I believe a 159 held the fastest start to stop time between Clapham Junction and Woking and Woking to Basingstoke prior to the Desiros!

 

[michael769]

The most important factor in acceleration is not the power but the torque. It is torque that provides the force required (via Newtons 1st and 2nd laws) to accelerate.

The engine's power output tells us the amount of energy available to be transformed into the desired torque. While it is true that Torque is related to power to an extent, is influenced by other factors most notably how efficiently it can be produced and transmitted to the wheels. No system is 100% efficient so not all the power generated will produce useful torque.

The reality is that suitably designed electric motors can produce torque far more efficiently and more importantly consistently that a mechanical transmission, which means that electric traction is likely to accelerate better than diesel of the same power output, especially on a gradient.

It is a red herring to discuss gears in the context of electric traction. Gears are required in internal combustion engines because peak power (and torque) is only available at high revs which requires a mecanism (the gears or hydraulic transmission) to allow the ratio between engine rotation and wheel rotation to be varied as speed changes thus allowing the engine to run within its peak torque band.

High torque electrical motors have no such limitation with at least 90% of maximum output throught it's opertional speed range. The noise that sounds reminiscinet of a gear change on some A/C stock has nothing to do with gears the similarity in the sounds is entirely coincidental.

 

[O L Leigh]

The logs seem to indicate only a minor difference between a 444 and a 159. In fact I believe a 159 held the fastest start to stop time between Clapham Junction and Woking and Woking to Basingstoke prior to the Desiros!

Those are quite long sections and the running times are unlikely to be affected by differences in acceleration. In addition, both types of units are used for similar types of service and are likely to be timetabled to take the same amount of time between these points. Therefore the logs won't give much indication about differences in acceleration. Cl379s don't get shorter times between points A and B than Cl317s even though they accelerate MUCH faster.

O L Leigh

 

[455driver]

Don't forget a 444 has an extra coach and reduced traction power because of DC third rail limitations.

#More thread drift#

A 444 is set at about 70% power where-as a 450 is set at about 52% so they "should" be about equal in performance once on the move, a 450 will set off faster simply because the units are much lighter and both use 100% power(unless the driver wants a smooth set off and eases the power in) from a standing start.

 

[HSTEd]

So lets posit a 444 in the future operating under AC power, so that it has none of the power restrictions imposed due to the power supply issues on the Southern.

Would it thrash the Sprinter then?