Did this improve performance? Streamlined King + Castle

I don't think that's a very realistic assumption though.

We are used in heritage line running (and to a certain extent in mainline steam) to locomotives running at constant speed (either 25mph or 60/75mph) but with power output varying considerably with gradients etc. However, that is a far from optimum way to drive: it is more difficult for the fireman, places a considerable thermal strain on the firebox, requires the driver to be constantly adjusting controls, risks much blowing off if the fireman is not on top of their game etc. So it was far more common in days past to try to try to drive at a more or less constant power, and allow speed to vary somewhat according to the conditions, gradient etc. Ideally, the power setting would be what the fireman could reliably cope with in terms of firing rate, allowing also for the capacity of the grate to burn coal. Clearly there was a certain amount of running a bit harder up hill and then moderating on the descents, but nothing like the amount that is required today. So if, for example, a class 8 pacific can run at about 2000hp near-constantly (and the fireman can cope), then the schedule would be built around that level of power output, rather than a 3000hp dash up hill and then a period at 500hp or less while the fireman was scooped up from a crumpled heap on the floor and the boiler was refilled.

Somewhere on YouTube there is an LMS training video on "controlled firing", extolling the efficiency benefits of trying to keep firing at a steady rate throughout the journey. The corollary of a steady rate of firing at the power-production end of the locomotive is the need for a steady rate of consumption at the power-usage end! So no mad dashes uphill or away from stations ... A bit of extra effort maybe, but certainly not the difference between a 3000hp start followed by a 500hp "cruise".

Tom

 

Might have been "preferable" (? Really?) but Gresley's shape is undoubtedly the best that was produced in this country for streamlining on a steam locomotive as it worked across a number of factors including smoke deflection.

I can't speak for locomotives designed abroad though.

 

A google search brings up a number of streamlined designs. Some "bullet nosed" a la Manorbier Castle and others with a full casing a la Duchess/A4. Would appear to be in roughly equal quantities
so like you, I would question Jimc's statement.

 

If there aren't any wind tunnel/water channel test results proving a particular design, ignore it. A bit like speed records without dynamometer cars....

 

Models of the A4 were tested in wind tunnels.

 

Exactly....

 

When Chris Boardman was commentating on the World Track Championships he said that the important aspects in overcoming wind resistance were firstly, body shape and position, secondly kit and thirdly the machine. Modern racing cycles have some parallels with the A4s. Great effort is put into aerodynamic structures but the transmission is lumpy, angular and threshing about in the airstream.

 

I was sorely tempted but prefer the fresh air. I'm pleased that I can reach Wiggins' speed at the Derby Velodrome and hold it for ....... one lap!

 

Yes, but that's because the rules heavily restrict what can be done with the machine. Otherwise the race cycles would look about as much like a street cycle as an A4 looks like a Stirling single

 

I think I remember reading that the LMS did the same with the Princess Coronation, and that they claimed it was "more efficient" than the A4 (I presume in reducing the drag coefficient).
Surely someone on here knows someone with access to a wind tunnel and we could borrow some 00 locos...?

 

According to a book I read one problem with the LMS casing was the flat top to it caused a lee in a crosswind and the lower pressure drew the exhaust down

 

I can't particularly see how that would be different with e.g. The A4 casing, which also very bluff to cross winds. But one thing I learned after over a decade in fluid dynamics is that sometimes small changes have big effects, e.g. if it means the flow separates at a different point.

 

The one main difference with the A4 casing design was the "thumb print" behind the chimney, apparently this had a favourable effect on smoke lifting.

Cheers,

Alan

 

I am suitably impressed

 

Its more difficult than that I fear. There are all sorts of - ironically - scaling effects that need to be considered. The larger the models the better. And then I think it very likely that the exhaust has a significant effect on what's going on. I think you'd want the largest models you could get and ideally be steaming them on a rolling road. And don't forget the train as well... Its a decidedly non-trivial exercise.

 

So how many models did Collett test in a wind tunnel?

 

Oh look. I now know how Mr Martin feels about Thompson.

All I am saying is that the approach Collett took to streamlining has also been taken by a good number of other designers, some of them very well respected and mostly, but not all, after Collett. That suggests the general concept wasn't fundamentally flawed. That in turn suggests that mocking Collett for that choice of streamlining principle isn't actually particularly logical or fact based, and even maybe a little insular. That's it really.

Maybe further, I'm not aware that anyone has done any serious *comparitive* testing of all the forms of streamlining adopted on all the world's railways, and in the absence of such testing I think its a bit odd to claim that implementation A was obviously better than implementation B, other than on the grounds of aesthetics. And yes, if you say that Gresley wins on that category I'd probably agree with you, although some of the US implementations have a certain massive dominance that also has its appeal.

On the other side of aesthetics, Collet's were sure as hell not pretty (unusually for him), but I think he's beaten by the
Deutsche Reichsbahn 4-6-4 Baureihe 05, http://www.germansteam.co.uk/german-steam/FastestLoco/fastloco-04.jpg, which one really should admit was the fastest steam locomotive ever built, even if it didn't clock up the fastest recorded speed.

The 5AT site is relatively quiet on the subject of streamlining, which is a shame, but I did find this in http://5at.co.uk/index.php/faqs-2/questions-about-tech-specification.html

 

That depends on the level of detail you want! I have been told of windtunnel tests of commercial OO (1:76) models of an air smoothed Bulleid vs the rebuild version, the difference was measurable. I myself have put a 1:43.5 (O-gauge) model in front a a table ventilator and a wire test showed all the local vacua that cause misery with the exhaust.
As for the 5AT the streamlining and the low exit velocity of the Lempor exhaust may be mutually exclusive for exhaust lifting, however the chimney is high enough above the low pressure area on the boiler.
Kind regards
Jos Koopmans

 

Oh for sure you'll get measurable differences. But the differences won't be at all the same as the differences at full size. Unfortunately I only really know enough about the topic to know how little I know, but windtunnel testing produces enormous problems with scaling, which is why they tend to test large if they can.

 

I'd love to see the wind tunnel where they tested a full size Airbus 380.