How is a class's maximum speed assessed?

[Harlesden]

For example, the stated maximum speed of a Class 377 unit is 100mph.
Exactly what would happen if a Class 377 unit was driven for half an hour (on a suitable stretch of track) at 110mph?
How was the prototype Class 377 unit tested at 110mph for it to be determined that the safe maximum speed is 100mph.
Genuinely curious.

 

[ainsworth74]

Exactly what would happen if a Class 377 unit was driven for half an hour (on a suitable stretch of track) at 110mph?

Nothing as all rolling stock is specified to include a 10% overspeed above the specified top speed!

So for a unit with a specified top speed of 100mph it will also be tested and safe up to 110mph (which is why LM's 350s are being tested for 110mph operation without much difficulty).

As for how top speed is assessed units are specified and designed to reach a certain speed. So the 377s will have been specified for a top operational speed of 100mph and there for designed to reach that speed by using components whose tolerances are sufficient for the wear and tear of 100mph running.

 

[dubscottie]

As stated above the max is usually 10% above the general speed. The Class 91 for example was tested to 154mph (140mph + 10% = 154mph)

There are odd ones though.. The design speed of the Class 86/4 was 125mph! (but only did 110mph max in service)

 

[BestWestern]

I understand that braking capability can be a governing factor, or so I was told once. A class 150 has tread brakes and wouldn't pull up sufficiently if it were doing, say, 85 or 90mph rather than it's design speed of 75. Might be complete tosh though!

 

[WatcherZero]

A class could have been designed with higher tolerances and margins and later have its top speed recertified as is happening with the 350's but for the most part they design the top speed in at the beginning.

 

[dubscottie]

I understand that braking capability can be a governing factor, or so I was told once. A class 150 has tread brakes and wouldn't pull up sufficiently if it were doing, say, 85 or 90mph rather than it's design speed of 75. Might be complete tosh though!

There might be some truth in that although I think it maybe more to do with wear on the brake blocks.
The Mk2's that were used with class 27's on the Edinburgh/Glasgow runs in the 70's were fitted with disc brakes as the tread brake blocks would have worn within 2-3 days! I think the disc pads still required replacing every week.

Back to the OP's question, a good example of something running at its limit for long periods of time is the above class 27's.. I am amazed they lasted as long as they did! 24 locos were needed to cover 10 diagrams

More here.. http://www.6lda28.com/shove.html

 

[MCR247]

So for 350s to be certified for 110, would they have to be able to run at 121?

 

[Nym]

Yes, but I get the feeling, (and thanks to the control systems used) that they can probably get up past 125 without too much effort...

 

[Yew]

Dont forget that for 125mph (maybe even 110?) there cant be any passenger accommodation in the first 1/3 of the leading car. For example its not a problem in HST's as their 'leading car' is the locomotive, that pax cant usually access. However in a Voyager, they have the long noses, the cab, and the restaraunt/bike space in the leading 1/3 of each driving car.

Intercity 225's where built to the regulations of the day that didnt allow any passangers in the front car of a formation, so thats why there are no seats in the DVT. However bizzarely, if you look at the APT designs, they had seats in the driving cars (the motors where in the middle) as the no pax in the leading car rule was put in place after an accident that happened between the development of the APT-P and the APT-U (intecity 225)

 

[A-driver]

It's all to do with braking distances, crash worthiness and maintenance costs. 377's were tested at over 140mph (must have been higher but I know they tested them at 140 with no air suspension) but in service they can't go above 90. This is largely due to maintenance costs-wear on wheels, brake pads etc. Recently the have been allowed to do 100 on the WCML and FCC run them at 100 up north but the brighton line is only cleared at 100mph for 319s.

365s are capable of 110 and this was considered when they were planning using them on runs to Doncaster but they can't exceed 100 at the moment as there is not enough of a crush zone between the front and the passenger. To be honest I wouldn't fancy being in the leading coach during a crash at any speed-can't see what the extra 10mph will really do!

Creature comforts also come into it. Low speed units like 455/456/313 etc are limited to 75 mainly because they have less suspension equipment around the boogies. Running one at 100 could result in severe rough riding.

 

[A-driver]

Dont forget that for 125mph (maybe even 110?) there cant be any passenger accommodation in the first 1/3 of the leading car. For example its not a problem in HST's as their 'leading car' is the locomotive, that pax cant usually access. However in a Voyager, they have the long noses, the cab, and the restaraunt/bike space in the leading 1/3 of each driving car.

Intercity 225's where built to the regulations of the day that didnt allow any passangers in the front car of a formation, so thats why there are no seats in the DVT. However bizzarely, if you look at the APT designs, they had seats in the driving cars (the motors where in the middle) as the no pax in the leading car rule was put in place after an accident that happened between the development of the APT-P and the APT-U (intecity 225)

Should have read that before posting my post.

Infact the regulations are that the manufacturer must prove the crash worthiness at higher speeds. It's a bit of a myth that you can't have passengers in the leading 1/3rd of the coach. The reason voyagers etc don't have passengers in the front is to do with design-the best locations for galleys and guards vans etc is at the end-out of the way.

There seems to be talk that the new Siemens Thameslink trains will be 100+ with pax in the front.

 

[Roylang]

It's all to do with braking distances, crash worthiness and maintenance costs. 377's were tested at over 140mph (must have been higher but I know they tested them at 140 with no air suspension) but in service they can't go above 90. This is largely due to maintenance costs-wear on wheels, brake pads etc. Recently the have been allowed to do 100 on the WCML and FCC run them at 100 up north but the brighton line is only cleared at 100mph for 319s.

365s are capable of 110 and this was considered when they were planning using them on runs to Doncaster but they can't exceed 100 at the moment as there is not enough of a crush zone between the front and the passenger. To be honest I wouldn't fancy being in the leading coach during a crash at any speed-can't see what the extra 10mph will really do!

Creature comforts also come into it. Low speed units like 455/456/313 etc are limited to 75 mainly because they have less suspension equipment around the boogies. Running one at 100 could result in severe rough riding.

Consideration also has to be given to the "kinetic envelope" of the train. It may be physically possible for a unit to have its speed increased and be able to stop etc, but if suspension movement etc. allows it to exceed the loading gauge (hope that it the right phrase for the side-to-side profile) then it will be out of tolerance at speed.

Roy

 

[A-driver]

The kinetic envelope is addressed with the suspension so you are correct. That's what I mean by 313/455 etc limited to 75. Higher speed stock like 377s have hydraulic pistons on the bogies limiting sideways movement. I have gone blank though and for the life of me can't think what they are called and havnt got the energy to dig out my traction manuals and look it up!

 

[Nym]

lateral dampers?

 

[Mike C]

365s are capable of 110 and this was considered when they were planning using them on runs to Doncaster but they can't exceed 100 at the moment as there is not enough of a crush zone between the front and the passenger. To be honest I wouldn't fancy being in the leading coach during a crash at any speed-can't see what the extra 10mph will really do!

Creature comforts also come into it. Low speed units like 455/456/313 etc are limited to 75 mainly because they have less suspension equipment around the boogies. Running one at 100 could result in severe rough riding.

I think 365's would run at 110 fine. Their acceleration up to 100 seems convincing enough that 110 wouldn't pose any problems.

Anyway - yes, yaw dampers are required for running over 75mph.

 

[jopsuk]

It's all to do with braking distances, crash worthiness and maintenance costs. 377's were tested at over 140mph (must have been higher but I know they tested them at 140 with no air suspension)

Where was this done? Were they taken to one of the big test circuits on the continent? Wouldn't have thought it possible at Old Dalby.

 

[A-driver]

No idea were it was done, just know it was-when I learnt the traction we were going over the rules and regs for isolating secondary air suspension and the relevant speeds and was told its a pure creature comfort rule as they had to be test at 140mph with it isolated. The 377 will quite easily top 120 with little effort, especially on the AC. I will check with my mate who was one of the 'test pilots' when they were introduced on the southern but I'm pretty sure thy ran them at 110 up on the WCML before handing them over to the Thameslink.

 

[swt_passenger]

Dont forget that for 125mph (maybe even 110?) there cant be any passenger accommodation in the first 1/3 of the leading car.

Not true any longer. The 395s are the most obvious evidence.

The basic rule in GM/RT2100 Issue 2 July 1997 was:

"4.8 Passengers and catering staff shall not be carried in the leading vehicle of a train which has a maximum operating speed greater than 160 km/h without the sanction of HM Railway Inspectorate. A quantified risk assessment shall be submitted in support of any proposal to deviate from this requirement."

That was the basis of the design of the older generation of 125 mph MUs - and they still came up with a passenger free zone of about 1/3 of the coach length.

GM/RT2100 Issue 3 Oct 2000 dropped that paragraph completely, and the current version, which is Issue 4 Dec 2010 (and somewhat re-formatted), also no longer includes such a rule, or anything similar.

 

[jopsuk]

Thankyou for that one swt_passenger. I assume that any "passenger free" area in subsequent designs is down to convenience of layout of kitchen, luggage facilities etc- after all, that 1997 requirement puts catering staff on an equal level with passengers

 

[swt_passenger]

Thankyou for that one swt_passenger. I assume that any "passenger free" area in subsequent designs is down to convenience of layout of kitchen, luggage facilities etc- after all, that 1997 requirement puts catering staff on an equal level with passengers.

That's my understanding after browsing a few different group standards, yes.

 

[Hydro]

Consideration also has to be given to the "kinetic envelope" of the train. It may be physically possible for a unit to have its speed increased and be able to stop etc, but if suspension movement etc. allows it to exceed the loading gauge (hope that it the right phrase for the side-to-side profile) then it will be out of tolerance at speed.

Roy

Kinematic envelope. /pedantry.

 

[whhistle]

I wonder what would happen if you left it on full power for half an hour, how fast it would really get to.

 

[DXMachina]

a brand new 321 was speed tested on Stoke Bank to 117mph if i remember right

 

[ess]

what is the maximum speed and maximum theoretical speed of a pacer? (so at what speed will it derail going round a bend in a gale)

 

[Nym]

about 190mph if you drop it off a very tall cliff, or out of a C-130...

 

[TGV]

about 190mph if you drop it off a very tall cliff, or out of a C-130...

You'd need a bigger plane. C-130 cargo bay is only 10ft wide x 9 ft in height. And it's max payload weight is 19t. Or a shade over 20t if it's the C130-H.

The cliff idea I can't fault though.

 

[Nym]

OK then, lets push it out of a C-17 Globemaster... Since the RAF bought these while sick of waiting for the A400Ms to come and discovered the're cheaper and better

Still not long enough for a full pacer though... We'd need a C5 Galaxy for that, but it's not an air drop capable aircraft...

 

[jopsuk]

sling it under a chinook? can they lift the weight?

 

[Nym]

Not the mass of both carriages. You'd need a Soviet Heavy Lift for that...

Even then you could only lift one, a CH-47 can only realistically lift 10 ton.

(Spot the Ex. RLC)

 

[rf_ioliver]

Don't they test trains in a similar way to bridges?

First, build a fleet of trains, then run them until they break, subtract 10mph from the average speed at which they broke/disintegrated/crashed, then finally build a new fleet of identical trains with that speed as the maximum?

Ian

ps: sorry, been a long week