Obstacle Deflectors, not Air Dams!

[sirwilliamfrs]

Odd that so many posts about modern diesel & electric locomotives like the Class 59/60/66/90/92, when referring to the area under the buffers, call this an air dam. At the speeds involved such a device would be of negligible use! The usually reinforced plate is there to do exactly what the official description refers to as an obstacle deflector, it is probably effective in clearing light snow too. Indeed the Class 60 and the continental spec Class 66s incorporate a snowplough. Every time I see "air dam" used in connection with locomotives it puts me in mind of 'Max Power' air dam fitted Dimma-spec Peugeot 205s and 306s. Maybe an F1 DRS fitted Class 66 would use less fuel after all - less downforce ! 

Edited November 11, 2021 by sirwilliamfrs
correction

[rob D2]

Damn ! I thought they were dams - because I know they ain’t snowploughs - I thought obstacle deflectors were the “ lifesavers “, those metal bits that hang down ?

[njee20]

Whilst I would say the 59/60/66 is definitely an obstacle deflector, being a broadly flat piece; I would say the 90, and the 442 (for example) is an air dam, insofar as it serves an aerodynamic purpose. 

[Lemmy282]

Quite what aerodynamic purpose it might achieve on a slab fronted 442 is open to debate. Still more of an obstacle deflector.

[Nearholmer]

Without a “spoiler”, air-resistance around all the gnarly bits of the bogies and under-gear will be significant, because air flow will be horribly broken-up and turbulent, so adding a “thing” at the front, whatever it’s primary purpose, will help by leading to a smoother air-flow close to track-level.

 

Even quite small increases in speed add significantly to drag, because drag is a function of the square of the relative velocity, and modern train speeds are quite sufficient to make drag an important contributor to overall resistance. Even the apparently “brick fronted” MUs these days usually have a reasonable radius on the corners, partly I’m sure to get the air flow reasonably smooth down the sides of the train. Getting that smooth flow, and not having deep doorways, or deep “ins and outs” between cars, can reduce drag very significantly because it is turbulence that is the trouble-maker. You will see a lot of lorry cabs with a “spoiler” on the roof these days for the same reason, it helps to reduce turbulence around whatever load they are carrying.

 

 

 

 

Edited November 25, 2021 by Nearholmer

[njee20]

8 hours ago, Lemmy282 said:

Quite what aerodynamic purpose it might achieve on a slab fronted 442 is open to debate. Still more of an obstacle deflector.

I’ve no idea if they wind tunnel tested 442s (or 90s or 91s), but just because we’re not talking about something honed to within an inch of its life that doesn’t mean there isn’t a consideration for aerodynamics. As Nearholmer says, it’ll massively reduce turbulent air around the bottom of the unit/loco, where it’ll be most pronounced. Partially the same reason mk3/4 coaches have all the underframe equipment in boxes, rather than exposed.  

[Bucoops]

1 minute ago, njee20 said:

I’ve no idea if they wind tunnel tested 442s (or 90s or 91s), but just because we’re not talking about something honed to within an inch of its life that doesn’t mean there isn’t a consideration for aerodynamics. As Nearholmer says, it’ll massively reduce turbulent air around the bottom of the unit/loco, where it’ll be most pronounced. Partially the same reason mk3/4 coaches have all the underframe equipment in boxes, rather than exposed.  

 

I always find it strange that valances were fitted to the fastest trains in the 1930s - but this stopped happening and were in fact removed from those it was fitted to post-war (I'm thinking of the LNER Coronation/West Riding Limited sets specifically) - no doubt to reduce maintenance time and costs - but at what cost to fuel efficiency I wonder?

 

Didn't do anything for the looks either. I can totally understand the streamlined A4s having their valances removed during the war to aid maintenance and speeds weren't nearly so high - it's a shame they were never replaced afterwards though.

[Nearholmer]

Aesthetics are a very personal thing: I like the look of the A4 without valances, because it has a “leaping forward” feel about it, very reminiscent of the Jaguar bonnet mascot. With the valances, it seems to lack energy and dynamism. But then, I’m no fan of the look of heavily streamlined steam locos - they all look a bit like upturned bathtubs and/or jelly-moulds to me, and some are frankly weird.

 

 

[Bucoops]

9 minutes ago, Nearholmer said:

Aesthetics are a very personal thing: I like the look of the A4 without valances, because it has a “leaping forward” feel about it, very reminiscent of the Jaguar bonnet mascot. With the valances, it seems to lack energy and dynamism. But then, I’m no fan of the look of heavily streamlined steam locos - they all look a bit like upturned bathtubs and/or jelly-moulds to me, and some are frankly weird.

 

 

 

That's why I didn't mention the LMS

[njee20]

I much prefer unvalanced A4s too! And rebuilt Merchant Navies.

[Dunsignalling]

22 minutes ago, Nearholmer said:

Aesthetics are a very personal thing: I like the look of the A4 without valances, because it has a “leaping forward” feel about it, very reminiscent of the Jaguar bonnet mascot. With the valances, it seems to lack energy and dynamism. But then, I’m no fan of the look of heavily streamlined steam locos - they all look a bit like upturned bathtubs and/or jelly-moulds to me, and some are frankly weird.

 

 

I agree, and the Jaguar mascot comparison sums it up well. A de-valanced A4 looks like it's going some even when standing still.

 

Maybe its about what we are/were familiar with, but an A4 with valances looks almost architectural to me and rather puts me in mind of something I'd use to take the creases out of my clothes.

 

After all, "streamlining" was applied to pretty much all consumer goods in the 1930s.... 

 

John

Edited November 25, 2021 by Dunsignalling

[jcm@gwr]

8 minutes ago, njee20 said:

I much prefer unvalanced A4s too! And rebuilt Merchant Navies.

 

I was under the impression that the Southern Pacifics were designed for

going through the carriage washing plants,

and were called air smoothed only to please the publicity department!

Edited November 25, 2021 by jcm@gwr

[Dunsignalling]

2 hours ago, Bucoops said:

 

I always find it strange that valances were fitted to the fastest trains in the 1930s - but this stopped happening and were in fact removed from those it was fitted to post-war (I'm thinking of the LNER Coronation/West Riding Limited sets specifically) - no doubt to reduce maintenance time and costs - but at what cost to fuel efficiency I wonder?

 

Didn't do anything for the looks either. I can totally understand the streamlined A4s having their valances removed during the war to aid maintenance and speeds weren't nearly so high - it's a shame they were never replaced afterwards though.

There would obviously have been a trade-off between the two, but balance between cost (and availability) of labour and fuel inevitably changed over time, an effect further exacerbated by the outbreak of war.

 

There is also the point that 1930s "streamlining" was in many instances a fashion statement and that, at some point, a feature that once generated an impression of modernity began to have the opposite effect; the rather lumpen LMS locos being an obvious example.

 

Maybe we should count ourselves fortunate that the A4s did not lose their elegant casings entirely... 

 

John

 

 

Edited November 25, 2021 by Dunsignalling

[Zomboid]

I think once the A4 had been done, that was pretty much as good as steam locomotive streamlining could get, aesthetically speaking. We certainly never bettered it in the UK, and none of the foreign streamlined locos I know of were better.

 

At that point there was no point anyone else trying...

[Jim Martin]

2 hours ago, Nearholmer said:

Aesthetics are a very personal thing: I like the look of the A4 without valances, because it has a “leaping forward” feel about it, very reminiscent of the Jaguar bonnet mascot. With the valances, it seems to lack energy and dynamism. But then, I’m no fan of the look of heavily streamlined steam locos - they all look a bit like upturned bathtubs and/or jelly-moulds to me, and some are frankly weird.

 

 

The valances also create a big, slab-sided vertical surface that I don't find particularly aesthetically pleasing.  By the same token, I prefer the look of the GCR "Directors" after the LNER removed the splasher over the coupling rods.

 

Jim

[Zomboid]

The A4 has a kind of curved "running board" that nothing else had. Removing the valances emphasises that, whereas the flat line along the bottom of the valances creates more of a jelly-mould appearance. I suspect that they were aerodynamically significant at 126mph though.

 

As for rebuilt Bulleids, they look very nice in a different way to the "air smoothed" versions. With the BFB wheels you just have to paint them black (with optional silver smokebox) and a dirty great headlight and you've got something very American looking. Which I like.

[Nick Holliday]

1 hour ago, Zomboid said:

The A4 has a kind of curved "running board" that nothing else had.

Nothing else, apart from the 2 streamlined B17 and W1, to be pedantic.  One might include certain incarnations of the P2 as well, perhaps.

[rob D2]

So at what speed does drag become worth sorting out ?

The slab fronted EMUs are only a bit slower than a pendolino which is much more streamlined .

 

they are both a lot slower then the TGV or bullet trains , which are clearly built to punch a hole in the air - or are they ? Is it just for aesthetics ?

[Zomboid]

I think it's about 80mph where aerodynamic drag becomes a real big deal, but I'm not sure where I'm pulling that from so it's probably wrong.

 

Pendolinos were designed for 140, and the 350s were initially specified for 100. If enough power is available then you can bludgeon your way to just about any speed, but for a given weight and rolling resistance you'll use more energy in a flat fronted EMU at 110mph than a 390 at 110.

[Nearholmer]

The basic formula is the Davis (without an ‘e’) equation, but that is full of train-specific coefficients, and it is they that tell you the answer, and for the sorts of trains you are talking about, they are discussed here https://journals.sagepub.com/doi/pdf/10.1243/0954409001531306 (which is possibly behind a pay wall). One of the authors is Felix Schmid, now an emeritus Prof at Birmingham, and he probably has the best knowledge of the topic in the U.K.

 

If you Google about, there are online tutorials about train resistance, including air resistance, which do give coefficients, but most are from the US, looking at freight trains. SNCF material is in the public domain on-line, but I can’t find it at the moment.

 

 

Edited November 25, 2021 by Nearholmer

[Nearholmer]

While looking for the SNCF stuff, which I still can’t find, I bumped into this, which looks really good, even if I do have to chew slowly because my French isn’t great. It’s effectively a technical history of streamlining.

 

https://www.google.co.uk/amp/s/trainconsultant.com/2021/01/19/laerodynamisme-seulement-pour-la-beaute/amp/

 

The author, Clive Laming, is both a retired railway engineer and a mega railway enthusiast, and he speaks good English and loves an e-chat, so if you have further questions, he’s your man.

[Nearholmer]

Here is a paper that isn’t behind a pay wall, and does include relevant coefficients: https://www.imeko.org/publications/wc-2012/IMEKO-WC-2012-TC3-P20.pdf

[rob D2]

There's not enough time in my life to read it - what's the abridged version ?

 

all this CO2 stuff surely would be better served by streamlining 

[Nearholmer]

All other things being equal, if you make a train with a front like a brick, and lots of sticking-out bits and recesses that create turbulence, air resistance becomes a significant factor in overall resistance at a lower speed than if you “fair” it and, as speed increases above 100mph it begins to be worth thinking about what we’d recognise as streamlining.

 

Most of the US work on freight trains, especially “double stacks” and “intermodals”, both of which they crank up to passenger train type speeds, is indeed about emissions reduction (actually, it’s really about reducing fuel consumption, but talking about emissions sounds better).

[njee20]

3 hours ago, Zomboid said:

I think it's about 80mph where aerodynamic drag becomes a real big deal, but I'm not sure where I'm pulling that from so it's probably wrong.

 

Pendolinos were designed for 140, and the 350s were initially specified for 100. If enough power is available then you can bludgeon your way to just about any speed, but for a given weight and rolling resistance you'll use more energy in a flat fronted EMU at 110mph than a 390 at 110.

Aerodynamics in cycling is material at speeds above ~18mph, so it’s always a factor! Air resistance increases by the square of the speed, so yes, more material on a TGV than a suburban DMU, but you could still improve fuel consumption on the DMU with some aerodynamic improvements.