An alternative to HS2 route, follow the M40?

[The Planner]

If the route would be hugging alongside the M40, wouldn't it face a problem when it went around Oxford. When the M40 was built, it had to be diverted so it avoided some nature thingy, this caused the awkwardly tight bends that adds on time between J9-10. How would a 196mph train try to negotiate these same alignments?

It was to avoid Otmoor plain north of Oxford, the bend is between junction 8A and 9 and prior to opening was tested by police cars which found that the bend could be safely negotiated at 120mph. It has probably only added 2-3 miles to the route which is what ? 2 minutes ?

 

[Bald Rick]

It was to avoid Otmoor plain north of Oxford, the bend is between junction 8A and 9 and prior to opening was tested by police cars which found that the bend could be safely negotiated at 120mph. It has probably only added 2-3 miles to the route which is what ? 2 minutes ?

The reason the M40 was routed that way was due to a VERY successful local NIMBY campaign. A number of individuals divided up bits of private land in Otmoor into small parcels (1m sq iirc) and transferred them between themselves every couple of months. The authorities couldn't keep track of it for compulsory purchase, gave up and went the great way round. Having said that it is a great corner to go round at speed.

Re the France>UK grid connector; it is rated at 3GW, which is broadly the same as the largest power stations in the country. Last time I was in the National Grid Control centre, they confirmed that the connector was used almost exclusively for import to the UK. The exceptions are when the french powerworkers go on strike, which if it's the same as their air traffic controllers is roughly weekly.

 

[Class172]

I fono know why i put J10, i know fully well that is Cherwell Valley and not near Oxford. silly me

 

[pablo]

The BritNed interconnector started to flow a few days ago.....

 

[digitaltoast]

I wonder if my questions will ever be answered? The offer was made and accepted, but answer came there none.

 

[coral reef]

^^ Re the drag question, yes any vehicle one would expect to have 8 times the drag at 250mph than at 125mph. However you wouldn't expect a train designed for 250mph to have 8 times the drag as one designed for 125mph precisely because of that - it will be mitigated for to some extent in the design stage because doing so produces benefits.

Our current crop of 125mph trains are merely legacy vehicles with sloping fronts. At 250mph it is worthwhile putting design effort into every component that faces the exterior.

 

[Sapphire Blue]

Can someone explain this to a layman then.

It was stated (and I have no reason to doubt the experts) that it takes 8 times more power each time the speed doubles.

So that would mean that:-

a train travelling at 256mph will use 16,777,216 times more power than a train travelling at 1mph.


That cannot be true can it?

 

[OxtedL]

8 times is a generalisation, very low speeds are different i believe.

Air resistance (drag) doesn't really kick in at 1 mph.

 

[j0hn0]

8 times is a generalisation, very low speeds are different i believe.

Air resistance (drag) doesn't really kick in at 1 mph.

I have often wondered when drag starts to make a difference, does anyone know?

With so many of our trains flat fronted with huge air scoop doorways on the front travelling at up to 100mph, they have to use more power than needed surely.
I accept that on commuter trains there is less time at the top speed, but lets say the Euston - Crewe LM service. Drag must be a factor at such constants, but seeing as so many of our trains are like that, I guess they dont see it as an issue

 

[Nym]

It does make a diference at any velocity of moving through the atmosphere, but if you where to model it properly it would be an 'N'th power' differential equation.

You can assume that it doesn't have much affect at low speed because the affect it is having is insignificant compared to the inirta of the moving parts of the train, but it is there. It also depends on what you would call 'noticeable' when moving at 70mph a change of 20mph due to winds is very noticable but only if it changes constantly, gusting makes little diference due to again, the inerta of having to slow the vehicle.

If you want to know any more than that I'd have to do some reading up myself on basic fluid dynamics, a number of books will be available at your local library...

 

[dalmahoyhill]

Lordy, this is getting technical now, aerodynamics. Any mechanical engineers who work in this field anywhere? I am trying to remember my university fluid mechanics (for civil engineering and therefore water side of things) and I remember the simple way of assessing drag was by the drag coefficient.

I would assume that as EMUs only travel at 90mph, aerodynamic streamlining and the practicalities of fitting is outweighed by the operability benefits of having connecting gangways and large doors. I remember in the spec for the class 91 that the snub end is restricted to 100mph due to the aerodynamics of the flat face, although the buffers and other equipment on the normal end will not be very aerodynamic.

Drag and aerodynamics are not just a result of the front of the train hitting the air there is also the surface drag (skin friction) of the whole length of the train. Things like the surface material, recessed doors and windows, undercarriage arrangments all will increase turbulence and skin friction. Not working in this area I don't know what the governing effect is on a train, the aerodynamics of the nose, or the drag over the whole length of the train.

The biggest issue with drag on high speed trains seems to be tunnels and the massive additional power required to drive a train through at 300km/hr with the piston effect. For instance the newer shinkansen trains N500, N700 and the new E5 have exceptionally long noses to reduce the piston effect in tunnels, which make up a significant percentage of the routes. I read in the HS2 spec that its doubles the power requirement at 300kmhr.

As for the power required being 8 times as much at top speed as starting off. Surely starting off you have to overcome inertia which takes significant power? I would assume, starting off the train uses a lot of power, this tails off at lower speed and then starts to creep up as drag increases. This is what the power curve is I assume? Roger Ford mentions it quite often in modern railways but I have not read up on what he is on about.

 

[LE Greys]

Presumably, it depends on how it's done. A4 streamlining works, but that's partly because a venturi effect behind the chimney generates an updraught and clears drifting smoke, which is why the streamlining stayed on under BR. Duchess streamlining was more for show than anything, while the Bulleid air-smoothed casing allowed locos to use carriage washers, so was fairly convenient, although it needed modification for a smoke-deflector effect. Bulleid also worked out tender-carriage interface (note the curved sides on cab and tender) which probably helped. However, all of this was forgotten for a while, although it's worth remembering that boxy diesels and electrics are naturally "slipperier" than steam locos with exposed boilers and motion. Deltic noses and Western curved sides (which exactly match a MkI) probably made a marginal difference, but streamlining becomes very effective at over 100 mph. Therefore, the first effectively-streamlined trains were the HSTs, where both the front end and loco-carriage interface are properly streamlined.