Steamlined v End Gangway Door Trains.

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Envoy

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Obviously TOC’s might order end - gangway door trains because they give flexibility regarding splitting/joining at junctions and increasing/decreasing length according to expected demand. I wonder how much the almost vertical surfaces increase fuel consumption compared to a streamlined train like a Class 800 when travelling at speed? Does the increased wind resistance cause problems at speed v a streamlined train? Do end gangway trains create a greater pressure wave in tunnels? Which type of front end is safer? Do drivers feel rather confined in the small cabs of end gangway trains and prefer those with cabs the width of the unit?
 
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Energy

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Worth pointing out that just because it doesn't have a gangway doesn't mean its as streamlined as an 800, look at the 196/197 vs a 195.
 

craigybagel

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Obviously TOC’s might order end - gangway door trains because they give flexibility regarding splitting/joining at junctions and increasing/decreasing length according to expected demand. I wonder how much the almost vertical surfaces increase fuel consumption compared to a streamlined train like a Class 800 when travelling at speed? Does the increased wind resistance cause problems at speed v a streamlined train? Do end gangway trains create a greater pressure wave in tunnels? Which type of front end is safer? Do drivers feel rather confined in the small cabs of end gangway trains and prefer those with cabs the width of the unit?
I can't answer all of the questions, and even the ones I can are based only on my own experience and others may vary.

Certainly on the only long tunnel I sign (just under a mile long, and single bore) you can physically feel that the wind resistance is much stronger on a gangwayed train than one without. Also, at all times it's noisier in the cab of a gangwayed train than one without at the same (or even higher speeds), but that might just be a difference in age or build quality.

I much prefer the views from a non gangwayed train, but as I said in the TfW CAF thread, I accept that the operational needs of gangways are much more important then my own desire to look at the pretty views outside!

I do find it much easier to couple gangwayed stock though - the gangways give a much better visual reference point then a coupler you can't see underneath the cab.
 

Energy

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Certainly on the only long tunnel I sign (just under a mile long, and single bore) you can physically feel that the wind resistance is much stronger on a gangwayed train than one without. Also, at all times it's noisier in the cab of a gangwayed train than one without at the same (or even higher speeds), but that might just be a difference in age or build quality.
I'm assuming you work at TfW looking at the CAF 197 thread, worth pointing out there is a big age difference between the 175s and the sprinters.
 

craigybagel

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I'm assuming you work at TfW looking at the CAF 197 thread, worth pointing out there is a big age difference between the 175s and the sprinters.
Indeed, that could explain a lot of the difference. It'll be interesting to see how things compare with the 197s and their gangways.
 

Energy

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Indeed, that could explain a lot of the difference. It'll be interesting to see how things compare with the 197s and their gangways.
May be useful if any drivers of electrostars/desiros/172s can comment if its windy on them, 150s have both gangwayed and non-gangwayed versions although I suspect both let air in :D
 

coppercapped

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Obviously TOC’s might order end - gangway door trains because they give flexibility regarding splitting/joining at junctions and increasing/decreasing length according to expected demand. I wonder how much the almost vertical surfaces increase fuel consumption compared to a streamlined train like a Class 800 when travelling at speed? Does the increased wind resistance cause problems at speed v a streamlined train? Do end gangway trains create a greater pressure wave in tunnels? Which type of front end is safer? Do drivers feel rather confined in the small cabs of end gangway trains and prefer those with cabs the width of the unit?
The answer to this question is…

…it depends!

The resistance of a train to motion may be described in mathematical terms by an equation which has three components - one is a fixed value, one varies directly with speed and the third varies with the square of the speed. This can be written as

Resistance = A + Bv + Cv^2

where A, B and C are constants and v is the speed.

Thus the aerodynamic drag is around half as much again at 125mph as it is at 100mph. This is why high speed trains need such high levels of installed power.

As a rule of thumb a longer nose (or streamlined front if you will) makes a noticeable difference to the drag above 80 to 90mph. A long nose has the benefit of reducing the pressure wave generated when entering or leaving tunnels at speed, look at some photographs of Japanese and some European very high speed trains.

It is also important to consider the shapes of the parts of the trains. Sharp corners generated vortices which add drag. BR found that even at speeds of around 60mph and above rounding off the corners of the cab fronts reduced drag from this source, that is it reduced the value of ‘C’ in the equation above. Doing this at the design stage costs nothing but is difficult afterwards. Most train design from the late 1960s onwards, as speeds rose, used rounded corners in one form of another .

This ‘rounding’ is also effective in the inter-coach gaps, and even more effective is reducing the inter-vehicle gap as much as possible - some Swiss trains have been very good at this.

The nose drag is but one component of the total aerodynamic drag. ‘Form drag’ caused by air passing the train also plays a significant role (this depends on the total area of the side, roof and bottom of the train and its ‘roughness’) as well as do eddies dragged along at the rear of a train travelling at speed. So the longer the train the less significant is the part played by the drag caused by the nose shape.

It is difficult to put a figure for improved fuel consumption on all this, but the attention paid to detail in the HST design, including totally enclosing the gubbins under the coaches in a smooth casing, meant that the drag came out significantly lower than originally calculated. This meant that with the same installed power 8 coach (and later 9 coach) trains could be operated with the same top speed (although with somewhat slower acceleration in the higher speed ranges) as the original 7 coach trains. So it does make a difference.

Regarding accident protection. All new trains, whatever the shape of the front, now have to meet the requirements of EN 15227, Railway applications - Crashworthiness requirements for railway vehicle bodies.

I can’t answer the questions about how drivers feel!
 

100andthirty

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To illustrate what coppercapped said above, if you stand on a platform as a 75 mph freight train passes you'll really feel the windage of the loco and the wagons/containers behind. By comparison a Pendolino at 125 mph would cause less windage on the same person standing in the same place. This is not exactly analogous to power, but the 75 mph freight train is disturbing the air a lot more than the Pendolino. I'd say the front of a class 66 loco is even more angular than a train with a gangway.

It would be great to be able to find out if there's any measurable difference in power consumption between a class 360 and the equivalent class 350 at a given speed
 

Envoy

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I thank you all for your detailed answers. I note that 195’s and 197’s will operate between Manchester and Crewe and wonder how they would compare regarding fuel consumption on the same day if tested running non stop. Presumably a headwind would make a greater difference than a tailwind or a calm day.

Craigybagel:> I presume that the tunnel to which you refer is Dinemore - between Hereford and Leominster. As a passenger, I feel a pressure wave on my ear drums going through this tunnel. Talking of tunnels, I also wonder whether drivers switch off the air intake into the train when going through tunnels to prevent the ingress of diesel fumes. I have certainly smelt diesel fumes when going through the Severn Tunnel.
 

coppercapped

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I thank you all for your detailed answers. I note that 195’s and 197’s will operate between Manchester and Crewe and wonder how they would compare regarding fuel consumption on the same day if tested running non stop. Presumably a headwind would make a greater difference than a tailwind or a calm day.

Craigybagel:> I presume that the tunnel to which you refer is Dinemore - between Hereford and Leominster. As a passenger, I feel a pressure wave on my ear drums going through this tunnel. Talking of tunnels, I also wonder whether drivers switch off the air intake into the train when going through tunnels to prevent the ingress of diesel fumes. I have certainly smelt diesel fumes when going through the Severn Tunnel.
Diesel fumes in the coach? Wimps!

Now the Severn Tunnel was an experience behind a Hall or a Castle, especially if one met an unfitted coal train heading up the long incline to Patchway...

Diesels don't cut it!
 

Spartacus

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I've also read something that suggests streamlining only makes a difference once you get to around 90mph, so I expect the difference between a gangwayed and non gangwayed front of an otherwise identical design would be minute; driving style would have much more impact on fuel consumption.

Regarding wind, it's actually much more of an impact if it's coming from the side rather than if it's a headwind or tailwind due to the vast difference in the area presented to the wind, even for a short train.
 
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