Why isn't the DART Aerodynamic?

Niles

Niles wrote: »

I remember seeing pictures on the web (probably on a now defunct fotopic site) of LHB built EMUs in I think Germany (but maybe somewhere in Eastern Europe, sorry, it's a long time since I saw it!) which were very similar to the 8100 DARTs. Maybe it was a standard design or something, modified for the Irish gauge.

I think this is the foreign unit I referred to earlier, not quite the same but there does seem to be some family resemblance between it and our own 8100s. It's from the same era (1982/3) and seems slightly narrower, but that could be attributed to CIÉ having a wider gauge.

Then there's these units,which were built about ten years later, they seem slightly curvier at the front. You can still see the resemblance to the 8100s though.

PseudoFamous

Cookie_Monster wrote: »

how do you propose they do that then?

Install snowplows on every bus. It'll solve our problem of snow, and keep self important audi drivers out of the buslane, too

Cookie_Monster

Niles wrote: »

I think this is the foreign unit I referred to earlier, not quite the same but there does seem to be some family resemblance between it and our own 8100s. It's from the same era (1982/3) and seems slightly narrower, but that could be attributed to CIÉ having a wider gauge.

what happened to the right hand rail just in front of the unit?

It can't be actively operating that close to missing track can it?

Victor

Photos http://irishrail.ie/fleet_information/commuter_and_dart_fleet.asp

Class No. in Service Horsepower (HP) Date Built Manufacturer
8100/8300 Class 38x2 (originally 40x2) 690 1983 GEC and Linke-Hofmann-Busch (now Siemens)
8200/8400 Class 5x2 690 2000 Alstom
8500 Class 4x4 690 2001 Tokyu Car Corporation
8510 Class 3x4 690 2003 Tokyu Car Corporation
8520 Class 10x4 690 2004/2005 Tokyu Car Corporation

Much of the air resistence on a train is to the sides - surface area, open windows, fittings, panel joints, the gap between carriages - not the front.

As mentioned, DART is modular, so if you put a point end on every carraige, the train would experience more substantial air resistence every carriage / every second carriage.

A greater efficiency would probably come from reducing the number of end cars from about 78% to about 50% and using the current cab space for passengers.

Niles

Cookie_Monster wrote: »

what happened to the right hand rail just in front of the unit?

It can't be actively operating that close to missing track can it?

Not sure myself. Looking closely the rails seen in the foreground seem to be slightly higher than the rail near the unit, my guess is that these are checkrails or something similar, and the actual running rail is obscured from view by the platform edge? If you look closely you can just make out the chairs for the right hand rail along the platform edge.

Victor

Cookie_Monster wrote: »

what happened to the right hand rail just in front of the unit?

It can't be actively operating that close to missing track can it?

Hover trains. :cool:

Unusual rail type. Might it be third rail power and this is the boundary between two circuits? Actually, given that it is a terminus, I wonder if it is some sort of deliberate de-railing arrangement. The view seems to be within this train hall. http://maps.google.ie/maps?q=warschauer+strasse+s-bahn&hl=en&ll=52.506531,13.449476&spn=0.005485,0.027466&sll=53.401034,-8.307638&sspn=5.766735,19.753418&vpsrc=6&hq=warschauer+strasse+s-bahn&radius=15000&t=m&z=16&layer=c&cbll=52.505459,13.448795&panoid=_g68WPPg2tqC2arD_zpgbw&cbp=12,152.02,,0,-4.29

It is an unusual U-bahn set up. The station entrance is nominally at ground level, but the ground to the north is lower for S-bahn tracks and while it falls away steeply to the south to the river bank, meaning the first section of the U-bahn is actually elevated.

http://en.wikipedia.org/wiki/File:Ubahn_oberbaum.gif

CIE

PseudoFamous wrote: »

Install snowplows on every bus. It'll solve our problem of snow, and keep self important audi drivers out of the buslane, too

That's nice. Where will they store the salt for melting the snow and ice?

corktina

whereas you will no doubt save minute amounts of energy over many years by streamlining the DORT, the advantage of this is lost by losing probably 4 seats behind each driving cab. The overall most efficent configuration for a suburban train in terms of energy per passenger is therefore a flat front.

steamengine

OP has a point ok. The DART presents a flat surface to the oncoming air, so using the drag coefficient of 1.2 for this type of surface give a resistance of approx 190 lbs at 30mph. This increases to 750 lbs at 60 mph - figures based on an estimated frontal area of 64 sq.ft. The reason for the increase is that the resistance is proportional to the square of the speed. That is double the speed equals 4 times the resistance. In terms of power these figures equate to 120 horse power or 90 kw absorbed to overcome this resistance at 60 mph.

However the total drag coefficient for this type of train may be as high as 1.8,- still reading up on it. Some figures for streamlined trains may be as low as 0.2, so one can see how power could be saved by having a more aerodynamic shaped cab front.

Estimating an average speed of 30 mph for a DART equates to a 30 hp or 22.5 kw loss based on a drag coefficient of 1.2. - hardly significant in the scheme of things.

PS - I like the look of the original DARTs - heading for iconic status just like the 071's !

CIE

The DART presents a flat surface to the oncoming air

Actually, it's not flat. The outer thirds are slightly convex. Also, some extra bits were added; the new lamp assemblies with the rebuild feature some new interesting-looking external fascia.

I'd say the parts that cause the most turbulence are the doors that hang on the outside. Never understood that design; it's not even like a plug door design.

monument

In the event the reasoned answers to date are not good enough...

Stopping drag? How about maglev, fully in tunnels?

CIE

monument wrote: »

In the event the reasoned answers to date are not good enough...

Stopping drag? How about maglev, fully in tunnels?

I presume you mean the "vactrain"? Good for a laugh, that is, especially at the recent estimate of over €2 billion per mile for its infrastructure. Maybe when they get "cold fusion" to power it and what does this really have to do with DART anyhow?

monument

The op had a reasonable question but reasonable answers have already been given.

CIE

monument wrote: »

The op had a reasonable question but reasonable answers have already been given.

As far as the "vactrain" goes though, it could be any shape you want on the front and back, since there's no air to resist its forward motion. One estimate for average speeds was 2,250 mph, so you can go from Dublin to Cork in about 4.5 minutes

corktina

i can only hold my breath for three minutes...:(

Wild Bill

For what it's worth - I think the DART trains look very handsome.

The Luas also looks good; but would look a bit daft on a heavy rail commuter line.

Horses for courses.