mk4 coaches

[Peter]

What is the difference from mk3 apart from the push button doors and the tilt profile?
also, why do they seem to wobble less than hsts'?

 

[devon_metro]

Different bogies means different ride quality. Mk3s don't seem to 'wobble' they just have softer suspension, pretty dodgy in the buffet car!

 

[class 313]

Mk4s don't tilt...

Only Pendolinos and Super Voyagers....

 

[devon_metro]

He didn't say they did

He merely said they have tilt profile, which they do

 

[class 313]

He didn't say they did

He merely said they have tilt profile, which they do

*whistles*

*walks away*

 

[ChrisCooper]

Mk4s are quite different to Mk3s. Mk3s are an evolution of the Mk2 design, wheras the Mk4s are based on the APT trailers. A big difference is the use of aluminium rarther than steel, although the Mk4s still weight about 5 tonnes extra than the Mk3s, and had they had tilt equipment would likely have weighed even more (tilt equipment on 221s around 10t to the weight).

 

[Turbostar]

Mk4s don't tilt...

Only Pendolinos and Super Voyagers....

Iirc, yes your right, Mk4s don't have tilt capability, BUT, they do have the facility to have it installed if required, not that they are gonna do it now, hence the profile of Mk4s. The option was there when they were built, but BR InterCity at the time didn't take up the option, think they said they'll look into it at a later date, & cost (zzzz...), but they never got round to it.

Mart

 

[Craig]

BUT, they do have the facility to have it installed if required

AIUI they had the facility to have it installed, but the space was used for something else during the Mallard refurbishment. I could be wrong though.

The ECML is reasonably straight south of Darlington, so tilt equipment isn't really required.

 

[ChrisCooper]

I think the tilting option was mainly for when they were planned for use on the WCML. Like I said, they were based on the APT, and the IC225 is really the APT-U, although re-branded due to the bad image of the APT. The 91s are also heavily based on the APT powercars, with features like body hung traction motors and an underfloor transformer. As has been said, the ECML only really gets curvy north of Newcastle, and thats where tilt would have givern an advantage. The extra weight of the tilt equipment though (as I said, it would possibly have been an extra 10t per coach, so 90-100t per train) would have had an effect on performance, possibly cancelling out the benefits, and it would have increased power draw and track forces, so the cost would have been high for little or no benefit.

 

[Peter]

so it's just harder suspention that stops them wobbling, nothing like harmonic occilations or whatever?

 

[ChrisCooper]

There are many factors that effect the ride of different stock. The suspension is one thing, particularly it's hardness or softness. Particularly with air-suspension, that can change over time if valves get clogged or the leveling system is not set up right (I was involved with an old 1960s bus which had air suspension on the back axle, and it use to ride awfully, particularly over speed humps, but after we had someone look at the entire air system, including the suspension, the ride was a hell of a lot better, although I still think the leaf springs on the front were better still). There is also the damping. Most trains have 3 sets of dampers, firstly damping the up and down and pitching of the bogies, secondly damping the roll and finally damping the yaw (twisting in relation to the body). Again, the tuning of these has quite an effect, and this can also change over time. The weight and weight distrubution of the coach body will also have quite an effect (the more weight, the more stable but the less smooth the ride tends to be).
Personally, I've never found the Mk3s to suffer from much roll, and actually I thought it was a criticism of the Mk4s. Perhaps when refurbished the bogies were overhauled and this has improved the ride, and if so the same is likely with the HSTs.

 

[Nick W]

AIUI they had the facility to have it installed, but the space was used for something else during the Mallard refurbishment. I could be wrong though.

Yes, the wi-fi and associated equipment used the space.