HST & 91 jerking

[SkinnyDave]

Please excuse the possible rude title

I have been on a couple of HST trips recently and leaving the stations has been anything but graceful with really noticeable jerking of the coaches. I have had this with 91s when they are changing speeds en route but not at stations.

Is this driver technique or just a usual characteristic of the trains?

 

[hairyhandedfool]

As I understand it, the rear power car of an HST doesn't help with the initial getaway from the station and so there will be a little jerk as the rear power car kicks in. More knowledgeable folk may correct me on this though.

I imagine, scientifically speaking, the 91 is the part of the 225 set that slows the train more, when not providing tractive effort, than any other vehicle (due to it's weight), so when it accelerates it will remove any slack from the couplings (hence the jerk you feel as the power kicks in). When hauling, obviously it will allow the slack to expand, again creating the jerk as the coupling reaches the maximum tolerance.

 

[Crossover]

I think it may be a characteristic of the trains. I have certainly experienced the surging on the 91 + Mk 4 sets on many occasions before now

 

[edwin_m]

Do you recall if the weather was wet at the time? This can be caused by wheelspin - possibly more noticeable with HSTs because if the front power car loses traction the rear one will carry on pushing and the couplings will compress a bit, giving a bit of a shove especially to the coaches near the front.

 

[Mugby]

I experienced it one Sunday morning on the 0900 XC service from Leeds.
The jerking was so bad I really thought the 125 was going to fail but we made it to Wakefield where it stood for almost half an hour and I think a travelling fitter attended it.

After that it seemed to be ok.

 

[shedman]

As a rule the rear power car will get power quicker due to it providing ETS. With a class 91, I was trained when taking power (in the 91) to pull to the first notch, gain power and apply steady or (on the DVT) to apply very minimal power then once power is provided apply steadily. That apparently removes any jerking. How right this is I don't know because being on the shed getting up to 5mph didn't require too much power!

 

[BestWestern]

Certainly on HST stock the sensation is very much that the rear power car gives an initial push, indeed you can observe the carriage behind you (when there is one) ride up very slightly immediately before your carriage begins to move. That would suggest it is being shoved from behind, rather than pulled from the front. Quite why that would happen, when the throttle lever being pulled is in the front power car, I don't know. All acceleration, either from a standing start or when increasing speed, tends to be very 'jerky' when you're sat at the back, as you get the full force of the rear power car; it's less so the further down the train you get as the increasing number of coaches dampen the effect, and presumably the front power car begins pulling and evens things out before the shove from behind gets all the way down the train through all the couplings.

The braking on HST sets can be noticeably jerky when wheelslide occurs, or when a set has 'snatching' brakes, when they are rough in their application.

 

[455driver]

Quite why that would happen, when the throttle lever being pulled is in the front power car, I don't know.

Because the rear PCs engine will be reving slightly higher as the rear PC provides the ETS to the coaches.

 

[Zerothebrake!]

The rear power car on a HST runs the train supply or 'creature comforts' (heating/air con & lighting etc) so it provides less tractive effort than the leading one. Any jerks or snatching is usually caused by pulling away with too much brake still in the train..it can vary quite a bit from power car to power car as to how the train handles too - even when they're on the same train.

 

[ChristopherJ]

Was on a Greater Anglia Norwich loco hauled IC set the other week. Every station departure both down (loco pushing) and up (loco hauling) was a journey full of bang, crash, snatch, squeeze, rub, jerk between loco and carriages...

I was educated that on the 90s and 91s, it's best to just open the power handle to full and let the electronic gizmos work out the most efficient way of distributing the tractive effort to the wheels rather than interfering with gradual applications of power.

 

[dk1]

Was on a Greater Anglia Norwich loco hauled IC set the other week. Every station departure both down (loco pushing) and up (loco hauling) was a journey full of bang, crash, snatch, squeeze, rub, jerk between loco and.

Sounds like the driver was not in the best of moods or else just very poor at his profession.

 

[notadriver]

If the railhead conditions are poor I think it's best to use a lower power setting instead of letting the WSP work to try and gain adhesion. I've also been told not to use sand unless absolutely necessary. Maybe the rear loco was struggling to get grip and the WSP wasn't very good ?

 

[Zoidberg]

Sorry if I have missed it, folks, but what is ETS?

Google was not much help, referring me to things to do with model railways and educational services.

 

[notadriver]

Sorry if I have missed it, folks, but what is ETS?

Google was not much help, referring me to things to do with model railways and educational services.

Electric train supply. For air con, heating etc.

 

[GRALISTAIR]

Mathematically I was taught
Rate of change of displacement = velocity
Rate of change of velocity = acceleration
Rate of change of acceleration = jerk
Rate of change of jerk = jounce

Slightly OT but on American railroads they do not need banking locos for traction - more to even out the tension in the couplings.

I still would prefer a 91+DVT to a EMU though.

 

[Cherry_Picker]

Sorry if I have missed it, folks, but what is ETS?

Google was not much help, referring me to things to do with model railways and educational services.

Electric Train Supply. It's the system used for getting electricity from the locomotive to the carriages of a train. Stuff most people take for granted I guess, but there are no engines or motors to generate power on traditional passenger coaches (obviously DMU/EMU coaches do have a means) so there needs to be a system to supply them. It can also be referred to as ETH (Electric Train Heat) or HEP (Head End Power) sometimes all three acronyms will be on equipment on the same train!

*edit*

It seems Head End Power has a Wikipedia article.

 

[notadriver]

Mathematically I was taught
Rate of change of displacement = velocity
Rate of change of velocity = acceleration
Rate of change of acceleration = jerk
Rate of change of jerk = jounce

Slightly OT but on American railroads they do not need banking locos for traction - more to even out the tension in the couplings.

I still would prefer a 91+DVT to a EMU though.

I think EMUs with distributed traction are the future unfortunately

 

[Zoidberg]

Electric train supply. For air con, heating etc.

Electric Train Supply. It's the system used for getting electricity from the locomotive to the carriages of a train. Stuff most people take for granted I guess, but there are no engines or motors to generate power on traditional passenger coaches (obviously DMU/EMU coaches do have a means) so there needs to be a system to supply them. It can also be referred to as ETH (Electric Train Heat) or HEP (Head End Power) sometimes all three acronyms will be on equipment on the same train!

*edit*

It seems Head End Power has a Wikipedia article.

Thanks chaps - such helpful folk here

 

[BestWestern]

Because the rear PCs engine will be reving slightly higher as the rear PC provides the ETS to the coaches.

I hadn't really thought about it since I was half asleep, but now you mention it I suppose it's rather obvious! Good simple explanation