Did this improve performance? Streamlined King + Castle

Statistically you will find that locomotives without the chimney cap do have more problems with smoke abatement. It separates the flow in one upwards and one downwards instead of a stagnation in front of the chimney and a severe low pressure volume behind it.
Btw Holcroft in his article in the Engineer, 26 sept 1941, states that PLM had found that the side plates absorbed 35 hp at 60 mph, so streamlining and smoke abatement cancel each other out!
Kind regards
Jos Koopmans

 

I wonder if what we'd now call corporate image came into it. I've been doing a bit of sketching, and given a more complete integrated cylinder/steam pipe/splashers fairing and plain casings for the chimney and safety valves/top feed what you rapidly get is something that looks somewhat like Porta's Argentina, but not much like a GWR locomotive.

 

For what gain ,really? In all this you have to remember the conditions & the times of the 30s on the railways . Though I agree the A4s were good streamlined, and as someone said ,the internal 'streamlining' in the cylinders was just as important, a lot of it ,on both sides of the country was good for publicity as for anything else.
And someone said why didnt they carry on with new streamlined locos after the war , well it was a very changed world then!

 

Indeed. I think that in the public perception streamlining would have been regarded as frippery.

 

Any comparison with the 5AT design is not really valid, except on grounds of appearance.

The 5AT was designed to run in everyday service and as a matter of routine at speeds over 100 mph (indeed up to 112 mph), in order to make pathing of steam specials easier on the modern railway. For that kind of speed, some streamlining is well worth doing as reducing air resistance adds significantly to performance (or saves fuel, if you prefer to look at it from that perspective).

Back in the 1930s however, streamlining (except for the special case of the A4s on lightweight expresses) was almost all about marketing and looking modern. At normal in-service train speeds of that period (normally not much over 70-80 mph, and averaging much less) there is very little gain to performance from streamlining, so one can understand why most steam loco engineers were not keen on it.

 

I'm not sure what to make of this thread. Surely an A4 would have spent a fair proportion of its working time at speeds of around 80 mph, and using Jimc's figures the saving due to the streamlined casing would have been approximately 100 hp. Although capable of 1500 hp or more, I would have thought that even by 60 mph the power would be starting to fall away, so would the power available at 80 mph be much, if anything, greater than 1300 hp? I don't have figures to support this, by the way, perhaps someone on the forum has some real information? A saving of 100 hp would therefore seem very worthwhile, and at 90 mph even more so.

How relevant this is to the thread topic is another matter, as I have no idea what the typical speeds of Manorbier Castle and King Henry VII would have been, or how effective the streamlining. It certainly looks clumsy and unattractive. Did it ever go near a wind tunnel? It looks as though the streamlining is only applied to about 30% of the cross sectional area of the locomotive, unlike an A4. Was it successful even as a PR exercise?

I can understand the decision not to streamline the A1s though. In the post-war era of austerity and rationing it would probably not have sat well with public opinion. No point in de-streamlining the locomotives you already have though - hold the gains!

One final thought, I couldn't read the comments that streamlining is not effective above 90 mph or even 60 mph, without remembering riding my bicycle to school (and later work) into a head wind. I really, really knew about it, and I can assure you I was going nowhere near 60 mph, let alone 90 mph.

Dave

 

The big pacifics - Stanier Coronations, Gresley A4s, Bulleid Merchant Navies - were capable of churning out about 3,000 ihp and sometimes quite a bit more for short periods, so 100 ihp becomes far less a proportion of that available. What's more, the power output needed to reach a given speed rises exponentially with the rise in speed: it takes about four times the power needed at 80 mph as it did at 40, not double, so the extra 100 ihp becomes less effective at higher speeds.

Another point not mentioned, I think, is that the aerodynamic resistance rise with the length of the train, and also with the number of vehicles as each one has its own length and frontal area. The streamlining of the loco alone isn't really much use unless action is taken elsewhere also.

This greater resistance at speed, by the way, is why earlier railways computed the loads in this way, i.e. equal to a number of base units, both for goods and passenger, rather than tonnage. The LNWR eventually instigated the notorious 'Equal to 17 Rule'; any train conveying more that the equivalent of 17 four-wheels had to have an assistant engine.

 

It should be remembered that the A4 streamlining was as much about smoke deflection as it was about streamlining. It was applied to the P2s for this reason (and their average speeds were much lower than the A4s on their original work).

Thompson applied to the board for the A1/1 to be streamlined from the outside (and there's a line drawing of this somewhere I seem to recall), but this was rejected on cost grounds. The A1/1 with the traditional Gresley streamlining would have been a rather handsome locomotive in my opinion, and probably would have placated people more than the austere lines of the locomotive as rebuilt.

Both Peppercorn's A1 and A2 classes had plans for streamlining, and models of these locomotives do exist (or have existed - there are photographs of these models in a few publications). They were somewhere between the Gresley Bugatti nose and the high shouldered running plates of the P2s and Thompson's Pacifics in look.

It remains interesting to me that more of an attempt to standardise the A4 style across the board wasn't made by the LNER, given how successful the shape was on the A4s. One suspects the funds simply weren't there during or either post war to justify changing the existing Pacifics to streamlined form. One suspects the ostentatious look of the A4s might have been looked upon rather unfavourably by the general public still in the height of austerity and rationing.

But the point stands: it was not just for publicity, it had a very specific purpose and that was streamlining and more importantly, smoke deflection. There was no better shape for this.

 

I'm sure the GW streamlining was at the instigation of the publicity department who wanted to get in on the current fad. I'm sure the way it was done was Collett taking the p**s
As for your cycle ride the question is how much energy would you have saved if you had been streamlined and the answer is it's probably to small to measure.

 

It is also worth remembering that any saving of power from streamlining is not pure gain. Adding streamlining to an existing design costs money; adds some weight; and makes servicing more difficult, as parts that need lubrication, cleaning, or inspection are less accessible (and indeed faults may be missed because things are out of sight).

 

An interesting point but a friend of mine recalls his first sighting of a Bulleid Pacific at Chatham in 1946/7, all bright green and air smoothed. Created quite an impression and a pleasant change from the gloom and austerity still prevalent from war time. Maybe some more streamlined Pacifics on the LNER/BR(E) would have had a similar effect. Sadlyw e'll never know.

 

Really? I would have thought that this would make it even more important to free up an additional 100 hp, not less important, especially as the available hp will be falling away as the speed rises.

True, each vehicle will also have an aerodynamic effect, but as regards frontal area, remember that each one will, to borrow a motor racing term, be slipstreaming the one in front. However, nobody has suggested that action shouldn't also be taken elsewhere.

You should have asked me that as I got off the bike. The second word you heard would have have been "off".

Seriously though, although the gains would be relatively small (though not immeasurable), remember I was travelling at around 5 mph, not 60 or 90 mph. The point still stands.

Dave

 

The point I was making was that 100 ihp is less a proportion of 3,000 ihp than it is of 1,500 ihp, so its effect is less significant. This, coupled with the exponential increase in required power required to reach progressively higher speed, makes the 100 ihp even less so.

Which is the point: the physics still apply. The human being on a bike isn't the most aerodynamic of vehicles, but if you are travelling at 5 mph into a 5 mph headwind, you have doubled your speed through the air so quadrupled the energy needed to do this. How much this would be reduced with 'streamlining' is debatable when balanced against the energy needed to carry the extra weight.

 

This debate seems to be going along the lines of "not invented here so not worth it." As has been pointed out in previous posts, the A4 streamlining not only produced worthwhile power savings at higher speeds, it was an effective exhaust lifter and the latter reason is quite probably why they are not defrocked before withdrawal.

 

I'm not sure that's true, Spamcan. To me the debate is:

1) was the purpose of streamlining publicity?
2) was the purpose of streamlining higher speed?
3) was the purpose of streamlining to lift the exhaust?

It was certainly a fad before WWII, so a fashion accessory is a viable explanation. As far as exhaust lifting goes, this appears to have been applicable to A4s only; it was not claimed for Stanier's Big Lizzies and Bulleid's engines struggled with smoke drifting on introduction. Granted that in this last case, 'streamlining' as such wasn't the intention.

 

I don't think there is much debate. The current 1 hour cycling record for a man on a (more or less) conventional bike is held by a certain Bradley Wiggins at 54.5km. The record on an HPV (effectively anything goes with regards streamlining) is about 91.5km. That looks like a pretty clear benefit.

Whether it is a train or a bike, the power requirement can be modelled as a polynomial along the lines of:

P = A.v + B.v^2 + C.v^3 ...

where A, B, C are constants. Broadly that means there is a linear requirement of power against speed, which is largely due to the force needed to overcome gravity on a gradient (so A tends to zero on flat track, and goes negative when running downhill); a square component of power to overcome the mechanical and rolling resistance; and a cube component to overcome wind resistance. (Note that the forces are F = A' + B'.v + C'.v^2, but the power required then multiplies each term by the speed; hence air resistance is proportional to the square of the speed, and therefore the power required to overcome drag is proportional to the cube, etc. Similarly the force required to overcome gravity on a gradient is a constant, so the power required is proportional to the speed).

The big difference between a bike and a train is the relative size of the constants. A train is relatively massive, which means the linear component (A) starts to become significant at even modest gradients. Which is why a gradient of 1% (1 in 100) starts to make a big impact on the maximum sustained speed of a train of given power output, whereas elite cyclists can ride at high speed on such gradients, and only really start to slow down when the gradient reaches 3 - 4% (i.e. 1 in 33 - 1 in 25). For a cyclist, 1 in 10 is a slog; for a train, 1 in 60 is a slog.

The other big difference is that the rolling and mechanical resistance of a train is relatively high compared with the drag; whereas for a cyclist drag trumps everything and mechanical and rolling resistance are, at most realistic speeds, somewhat negligible - at least for a racing cyclist with modern tyres etc. So the physics is the same, but the different relative values of the constants explains why for a cyclist, overcoming drag is paramount, whereas for a train, as a proportion of the total available power, the gradients and mechanical resistance tend to mean that wind resistance doesn't come into play until quite high speeds. (Of course, for modern railways where speeds are routinely double or more what was common in steam days, wind resistance becomes a very significant part of the equation).

Tom

 

Or

4) Was it to enable the locos to be driven through carriage washing plants

Tom

 

In the case of the A4s, 1, 2 and 3 all apply.

 

Whilst that's true, they were not actually run consistently at those power output levels. So even if you needed all 3,000 hp to accelerate away from rest and get up steep banks, if the timetable only required 500HP output when "cruising" on the majority of the trip then the fuel saving from lowered drag equivalent to 100HP might still look attractive.

The weights diagram for Manorbier Castle with the fairings, BTW, shows no increase over the standard Castle. We may not believe this of course. I'm not sure I do, although it may not have been very great.

The reason I brought up the comparison with 5AT etc earlier, is that the commonly held proposition "Collett was an idiot/didn't care about streamlining and it was a waste of time" logically needs to be extended to every other designer who used a similar treatment on their locomotives, which includes the likes of Porta and Wardale. Globally it appears to me that the Collett style streamlining was applied more often than the Gresley style streamlining, so a good number of designers felt it was a worthwhile proposition and preferable to the dustbin approach.

 

Ah yes, I recall all these locos dashing around at speeds in excess of 100 mph.