Streamlined steam locos and Garratts

[rue_d_etropal]

Whilst doing some research on Bulleid for a project I was working on, I wonderd if any of his design were based on French design. I searched for French streeamlined steam locos, and found a few.

Now it is well known that Bulleid and Gresley based the LNER A4 loco on the wedge shape of the Bugatti railcar, and no surprises, both the railcar and the A4 proved they were the fastest in their class, so why did French steam designers not follow the same wedge shape design . From certain angles some of the French streamlined steam loos resemble an A4, but when you look at front end, they have bullet shaped fronts to the boilers and shaped smoke deflectirs whicg mimick the wedge shape. Now as far as I know, the A4 were never fitted with additional smoke deflectors, so the wedge shape must have also fixed the problem of smoke getting in field of vision of the driver.

I was also looking for info on French Garratt locos and discovered there were some French built ones for the railway in Algeria. Not for freight but for passenger use, and apparently they were the fastest Garratts poduced. The shape of the front and rear driving units is partly streamline, but I think it could have gone further.The drive units could have been made more like that of an A4, and the boiler and heels could have been covered up. The extra smoke deflectors on this loco suggest this is one area tan could have been looked at more.

The locos were tested on French mainlines, and one photo looks like a French loco shed area. Not much info online, possibly because the locos were scrapped in 1951, after poor maintenance during WW2 and poor water quality not helping. I think there might be parts available to build a model in HO(3D printed?), but have not found any scale drawings.

I found a couple of websites including these ones

https://petervandermark.home.blog/2019/01/10/a-french-built-beyer-garratt-locomotive/

 

https://www.mylargescale.com/threads/streamlined-garratt-build-log.46450/

 

 

 

[sncf231e]

About French streamlined locomotives (not Garrets). In France, unlike some other countries, most streamlining was done on existing locomotives and in general only with one copy. So the streamlined body was build on an existing boiler and smoke box; a Bugatti type of front end was then not possible. Streamlining however was very popular in French toy trains as can be seen in my e-book on the subject of streamlined locomotives ; it shows correct models and toy type "steamliners" of France (and Germany and Britain and...). The book can be read or downloaded for free: http://sncf231e.nl/steamliners/

 

Regards

Fred

[Gordonwis]

I'm not an expert but it is my understanding that French engineers used smoke deflectors and 'arrowhead' features (as on PLM pacifics) to do the job of 'streamlining', although there were of course the 232R, S and U in the later SNCF era 

[Pacific231G]

Hi Simon

There was a fairly detailed article about French streamlining of steam locos by Leslie Coombs in  the June 2020 French Railways Society Journal. The general conclusion, after all the work on streamlining done in the 1930s seems to have been that any efficiency savings were far less than suggested by wind tunnel modelling and, though the loco itself might be more aerodynamically efficient, its total aerodynamic drag was only about 4-6% of that of a typical express train. Far more drag comes from the form and skin friction drag of the rest of the train. A typical railway carriage generates a lot of turbulence in the air passing it from wheels, brake gear etc. etc. but if you try to reduce that by adding skirts you also increase the total surface area and that increases drag.

There was a wide range of "carénage" tried by the French main line railways during the 1930s, some of them incorporating smoke deflectors (which increase drag though not by enough to obviate the advantage of having them). I though the air smoothed casing of the Bulleid Pacfics was more about lifting smoke clear of the cab than as an attempt at aerodynamic drag reduction but was probably also about creatinmg a clean moderns looking design.

The PLM did fit a number of its express locos with "Prandtl"  streamlined smokebox doors, the ones shaped like bullets and these were probably the most familiar. The GWR also tried these with a King and a Castle but didn't find them worthwhile.  If you think about it, there's something slightly absurd about a loco with a streamlined smokebox followed by a dozen or more fourgons and rivetted coaches covered in turbulence generating features from roof ventilators and large gaps between them to steps and all the paraphenalia  dangling under the chassis.  

Locomotive hauled trains in France were also limited by law to fairly modest speeds of 130 then 140km/h which is below the speeds where streamlining might actually be of any real significance.

The Bugatti autorails were allowed to travel at up to 160km/h and, as integrated single, double or treble sets not hauling coaches, may have got some benefit from their streamlined shape. I suspect though that a light weight monocoque construction and plenty of power from up to four 12.7 litre petrol/ethanol  engines (designed for a luxury car whose market had disappeared with the great depression)  had more to do with their speed.  If you look at the trains used for the 1955 Speed record runs on the dead straight track between Lamothe and Labouheyre on the Bordeaux-Dax main line you'll notice that BB9004 is very flat fronted while CC7107 (which probably didn't get to quite the same 331km/h speed) is not much better. More useful was filling the gaps between loco and coaches with rubber diaphragms and fitting the  last coach with a streamlined end.

https://www.youtube.com/watch?v=1KRM1jAlpB0

 

With the exception of Mallard's record breaking run, steam locos didn't really travel at the sort of speeds where frontal resistance was all that significant and André Chapelon was certainly convinced that far more benefit could be got by focussing on streamlining the flow of steam within the loco than adding assorted casings to its exterior.  However, it's arguable that the main reason for streamlining express steam locos and even whole trains (like the PLM's "Train Aerodynamique") was to make them appear look sleek and modern in a world where aircraft and automobiles were making railways seem like yesterday's technology. "Streamline Moderne" was a definite style and applied to everything from ocean liners and buildings to table lamps. 

 

 

Edited March 17, 2021 by Pacific231G

[rue_d_etropal]

Thanks for that David, I suspect one of the main reasons full streamlining was not used in France was the limited top speed. Just seems odd that Gresley and Bulleid designed the A4  shape based on the Bugatti railcar, and they also designed specially streamlined coaches to run with it. I think they were impressed by the aerodynamics of the Bugatti railcar, but not so enthused by the petrol engine.

Having said that many modern trains have wedge type front ends suggesting that does work. I wonder if the speed record locos in 1955 had been built with a wedged front end , would they have gone faster, or at least used less power to do so.

[Edge]

From an aerodynamics point of view, a bullet shaped snub-nose front can actually be a significant advantage.
 

A Bugatti story front end will tend to cut through the air and consequently there is normally regular pressure air pressing down on the whole of the loco and train, this creating more drag. A snub nose creates a far greater initial resistance but actually sets up a shock front of high pressure air which actually acts as a shield for a low pressure bubble behind it. This has the effect of actually lowering drag overall.

 

now, that being said, I actually agree with the idea that the streamlining on the vast majority of steam locos is style over substance. In practice, they almost never worked at the speeds necessary to see any sort of return on the whole idea, and the aerodynamics never actually seem take in to account things like the wheels and protruding items from carriage rooves etc. 
 

streamliners (yes, even the GWR examples) are a wonderful bit of railway history. But I do think that they are examples of railway PR rather than practical methods for making the engines go faster

[DCB]

It would be interesting to compare the  A4, Streamlined Duchess, MN, WC, B17 streamliners, and GW Castle and King streamliners for drag in a wind tunnel.     I reckon A4,B17, Caste, King, Duchess, MN, WC in descending order.   

[sncf231e]

A very complete and in depth overview of streamlined locomotives from around the world, including of course France, can be found in a recent book by Anton von Hornstein. He spend 30 years researching for this book, so you might go for a course in German, it is worth it. 

 

 

 

Regards

Fred