Smoke Deflectors

[jopsuk]

Surely not a loading gauge thing? Many large continental steam locomotives had huge smoke deflectors!

 

[70014IronDuke]

If you say so.

A film was made with 7018 hauling. The guard is shown checking the stock and tells us the weight for that day. Perhaps you can find it.

I have taken note.

...
When the Warships replaced steam, speeds definitely were above 90mph and occasionally above 100mph until limited to 90mph max.

I would not question that, but now we are talking diesels, not steam. I know Castles could reach 90 - 100 mph, certainly at some favoured points downhill, but that is not the issue here.
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Surely not a loading gauge thing? Many large continental steam locomotives had huge smoke deflectors!

Indeed, and in some cases, much use may it have done them! I don't question the German-style jobs (as fitted to the A3s), as one can well believe the shape does give extra upward draught to the exhaust smoke - as noted by MarkyT.

Fitting big deflectors francais-style to the express locomotives of the SNCF may have worked too, I have no idea yea or nay. But I do wonder today if the flat sided ones as fitted, eg to the Spanish mixed traffic 4-8-2s or the Portuguese 4-6-0s produced any noticeable effect. Same with those fitted to the SR 2-6-0s (primarily the Us and Ns) - did any of these locomotives ever go above 60 mph in normal service? In which case, did these deflectors do anything? Ditto those fitted to 9F 2-10-0s.

I believe even on rebuilt Royal Scots there was no clear evidence that the curved deflectors (carried by all but 46106) actually made any difference.

but to get back to your point - it was loading gauge per se

EDIT Meant to write: "it was not loading gauge per se" ....

that has been cited as the problem - it was the differences between the loading gauges that led to shorter chimneys on non-GWR locomotives.

So, if the continental locos had proportionally larger someboxes, it's possible that the loco chimneys were also restricted in height, even by the more generous continental loading gauge.

 

[edwin_m]

But I do wonder today if the flat sided ones as fitted, eg to the Spanish mixed traffic 4-8-2s or the Portuguese 4-6-0s produced any noticeable effect. Same with those fitted to the SR 2-6-0s (primarily the Us and Ns) - did any of these locomotives ever go above 60 mph in normal service? In which case, did these deflectors do anything? Ditto those fitted to 9F 2-10-0s.

I think that rather than creating an up-draught, flat smoke detectors were intended to change the airflow in the boundary layer and create a smoke-free area between the deflector and the side of the smokebox. The driver would then have a view through this area from the cab front windows.

The deflectors fitted to HSTs had a similar effect. Originally the cab roof dome (painted yellow at the time) would collect soot when running as the rear power car. Fitting a plate parallel to the roof but slightly higher, with a hole for the exhaust itself, created a boundary layer of clean air which flowed back to separate the roof dome from the smoky layer above it.

 

[70014IronDuke]

I think that rather than creating an up-draught, flat smoke detectors were intended to change the airflow in the boundary layer and create a smoke-free area between the deflector and the side of the smokebox. The driver would then have a view through this area from the cab front windows.

The deflectors fitted to HSTs had a similar effect. Originally the cab roof dome (painted yellow at the time) would collect soot when running as the rear power car. Fitting a plate parallel to the roof but slightly higher, with a hole for the exhaust itself, created a boundary layer of clean air which flowed back to separate the roof dome from the smoky layer above it.

Aha! That's different altogether, of course. Good point. I wonder if it worked, however?

 

[MarkyT]

Indeed, and in some cases, much use may it have done them! I don't question the German-style jobs (as fitted to the A3s), as one can well believe the shape does give extra upward draught to the exhaust smoke - as noted by MarkyT.

The style also became popular in post-war Czechoslovakia (along with double Kylchap exhausts), Victoria (Australia) and was certainly known about in nations across Europe where thousands of 3rd Reich Kriegsloks were distributed and remained in use for many years after the war. That was certainly not a particularly fast design, yet most were fitted with the same small deflector design.

So, if the continental locos had proportionally larger someboxes, it's possible that the loco chimneys were also restricted in height, even by the more generous continental loading gauge.

The larger loading gauge available in mainland Europe and USA simply allowed larger boilers on the biggest engines, the main reason they could build more powerful locos than were possible in the UK. With the boiler built out as far as possible, the space remaining for the chimney was limited just the same as in the UK.

 

[coppercapped]

I think that rather than creating an up-draught, flat smoke detectors were intended to change the airflow in the boundary layer and create a smoke-free area between the deflector and the side of the smokebox. The driver would then have a view through this area from the cab front windows.

The deflectors fitted to HSTs had a similar effect. Originally the cab roof dome (painted yellow at the time) would collect soot when running as the rear power car. Fitting a plate parallel to the roof but slightly higher, with a hole for the exhaust itself, created a boundary layer of clean air which flowed back to separate the roof dome from the smoky layer above it.

This is certainly getting closer! When a bluff-fronted body is exposed to an air stream there is a sort of 'bow wave' effect, the air is pushed outwards from the body at the front and immediately behind it will be a low pressure zone. In the case of the round steam locomotive smokebox there will be a low pressure zone immediately behind the front plate as the air flow separates on the sharp edge of the smoke box. This means that any exhaust which is vented into the low pressure zone at low velocity will stay trapped in the low pressure area.

Smoke deflectors work by being projected forward of the front of the smoke box and therefore constraining an air flow to fill the low pressure area around the the smoke box. Tweaks like shaping the lower edge as in the A3 deflectors obviously help lift the exhaust.

Another approach is to ensure the exhaust is vented above the low pressure area which is where the relatively tall chimneys of the GWR locomotives helped. Obviously as the train goes faster the low pressure area increases in size so this solution becomes less effective. Having a high velocity exhaust is also of advantage as it is more likely to punch through the low pressure area.

The GWR rarely required its locomotives to run at much more than 80mph in day to day service so it's solution was adequate. If faster day-to-day running were found to be necessary then, aerodynamics being the same for all railways, a Gresley A4-type front would have become unavoidable as the size of the low pressure area was reduced and the exhaust vented outside the boundary layer.

 

[MarkyT]

I think that rather than creating an up-draught, flat smoke detectors were intended to change the airflow in the boundary layer and create a smoke-free area between the deflector and the side of the smokebox. The driver would then have a view through this area from the cab front windows.

The deflectors fitted to HSTs had a similar effect. Originally the cab roof dome (painted yellow at the time) would collect soot when running as the rear power car. Fitting a plate parallel to the roof but slightly higher, with a hole for the exhaust itself, created a boundary layer of clean air which flowed back to separate the roof dome from the smoky layer above it.

Interesting. The streamlined casing of the A4 was considered to be a very effective smoke lifting device and there was no problem at all with the softer exhaust of the Kylchap on A4s. During development of the shape in the 1930s, wind tunnel tests were conducted using a small model. The first attempts were found to be very poor for visibility with smoke closely hugging the casing, but a later iteration lowered the casing slightly immediately behind the chimney and this was found to be most effective, no doubt by creating a similar boundary layer. Anecdotally, the feature was first introduced accidentally by a tester's thumb indentation in the soft clay model on replacing it in the wind tunnel!

 

[70014IronDuke]

The style also became popular in post-war Czechoslovakia (along with double Kylchap exhausts), Victoria (Australia) and was certainly known about in nations across Europe where thousands of 3rd Reich Kriegsloks were distributed and remained in use for many years after the war. That was certainly not a particularly fast design, yet most were fitted with the same small deflector design.

Yes, I thought about the Czech locos after I'd posted. Had completely overlooked the Kriegsloks though.

The larger loading gauge available in mainland Europe and USA simply allowed larger boilers on the biggest engines, the main reason they could build more powerful locos than were possible in the UK. With the boiler built out as far as possible, the space remaining for the chimney was limited just the same as in the UK.

Yes, that is what I was saying (obviously no clearly enough - didn't help that I missed out a 'not' I suppose )

 

[edwin_m]

Interesting. The streamlined casing of the A4 was considered to be a very effective smoke lifting device and there was no problem at all with the softer exhaust of the Kylchap on A4s. During development of the shape in the 1930s, wind tunnel tests were conducted using a small model. The first attempts were found to be very poor for visibility with smoke closely hugging the casing, but a later iteration lowered the casing slightly immediately behind the chimney and this was found to be most effective, no doubt by creating a similar boundary layer. Anecdotally, the feature was first introduced accidentally by a tester's thumb indentation in the soft clay model on replacing it in the wind tunnel!

I think this is working on a different principle. The wedge front of the A4 means that much of the air it has to push out of the way is pushed upwards, creating an updraught around the chimney which should lift the smoke clear. As the chimney itself is in the sloping section it is presumably clear of the low pressure zone mentioned by Coppercapped. With a more conventional front end shape the air is going more to the sides and here the traditional smoke deflector is both more necessary and more effective. I believe the bathtub shape on the LMS Pacifics was less effective in this respect - it would have pushed some air upwards but the chimney was behind the end slope. However the smooth end profile would probably have created less of a "bow wave" and therefore less of a pressure drop behind it than the front of an unstreamlined loco.

I see from Wikipedia that the Japanese attempts at streamlining a steam loco were mainly intended to deflect smoke, since speeds were too low to offer any significant reduction in resistance to motion. The resulting loco has two fins on the front which resemble classic smoke deflectors but in reality will be collecting the air and forcing it upwards past the chimney. Other than that the profile is very A4-like.

https://en.wikipedia.org/wiki/Streamliner

 

[deltic08]

I have taken note.



I would not question that, but now we are talking diesels, not steam. I know Castles could reach 90 - 100 mph, certainly at some favoured points downhill, but that is not the issue here.

No. Steam was used at short notice on diesel timings right up to the introduction of the D1000s in 1962 on both the Bristolian and Red Dragon. Not difficult on the Red Dragon as it was timed for D7000 Hymeks + 10 initially.

 

[6Gman]

the GWR engines didn't need smoke deflectors as they didn't go fast enough

And wouldn't the fact that there's a bend every 20 yards disperse the exhaust?

 

[MarkyT]

I see from Wikipedia that the Japanese attempts at streamlining a steam loco were mainly intended to deflect smoke, since speeds were too low to offer any significant reduction in resistance to motion. The resulting loco has two fins on the front which resemble classic smoke deflectors but in reality will be collecting the air and forcing it upwards past the chimney. Other than that the profile is very A4-like.

https://en.wikipedia.org/wiki/Streamliner

Quite similar in appearance to the original P2 front end on "Cock of the North" although a little more raked back and smoother. Also 10000 "Hush hush" as originally built. Those were both rebuilt later with A4 style noses and subsequent P2s were all built new with that style.

 

[DarloRich]

If this comment is directed at me, although not sure what you mean, I am GWR through and through but still contributed the equivalent of 'a pint a week' (I am teetotal) towards Tornado built in Darlington.

Did you?

I did indeed - it was built at the end of my street! I have the certificates somewhere and was on the first train. A good locomotive. Built in Darlo you see

As for City of Truro I guess the GWR didnt get round to chucking it out! They set aside quite a few potentially interesting locos ( 2 early broad gauge ones in particular) but ran out of space at Swindon so chopped them up. In fairness the movement to create a national railway museum at that time failed and they obviously couldn't see a point in keeping the locomotives

The NER set up their own museum around the same time hence why so much of the NRM collection is of NER heritage.

 

[Oxfordblues]

I remember as a young trainspotter in Preston in the early-1960s we called them "windshields" and thought they were "go-faster" devices. Pats, Scots, Semis, Brits, Clans and 9Fs: they all looked more powerful with windshields!

 

[Phil.]

LNER A1, A2 and A3 classes all had taper boilers as did the Maunsell 2-6-0 classes as well as the Britannias and the Clans. In fact most locos fitted with smoke deflectors had taper boilers.
As for the Kings being more powerful than the Dichesses - nonsense. Highest ever horsepower recorded by a UK steam loco was a Duchess. As for the KIng worrying the Americans, you do realise that they had locos capable of cursing along at 100 mph with a 1000 tons on the drawbar?

One hesitates to use the word "nonsense" but that's nonsense. The "King" didn't worry the American railroad engineers, it impressed them with it's clean exhaust and high power for it's size.

 

[Spamcan81]

One hesitates to use the word "nonsense" but that's nonsense. The "King" didn't worry the American railroad engineers, it impressed them with it's clean exhaust and high power for it's size.

I think you've quoted the wrong post. I was quoting and disagreeing with an earlier post that had claimed the Kings had worried the Americans. I'm also intrigued why you highlighted the bit about American locos running at 100 mph with 100 tons on the drawbar.

 

[Phil.]

I think you've quoted the wrong post. I was quoting and disagreeing with an earlier post that had claimed the Kings had worried the Americans. I'm also intrigued why you highlighted the bit about American locos running at 100 mph with 100 tons on the drawbar.

Well either I mis-read it or the original post was edited but I read it as 100 mph with 1000 tons on the drawbar. That was the nonsense bit.

edit. Yep, definately quoted 1000 tons at 100 mph. Yes, I was trying to quote that the "King" hadn't worried the American railroaders, it had impressed them.