P2 Locomotive Company and related matters

As Tuplin (no doubt among others) pointed out, a steam locomotive can deliver much more power for a short time (while the steam pressure, the water level in the boiler and the amount of coal on the grate are all decreasing) than it can sustain for a long time. Sustained power output depends on how fast the fireman can shovel.

Other things being equal, however, the relative power outputs of different locomotives will be roughly proportional to their grate areas -- and a Peppercorn A1 (and therefore the new P2 with more or less the same boiler) and a Stanier Duchess just happen to have the same 50 square feet. If there's another set of comparative trials up Shap (or anywhere else) some time, the respective performances will depend on several factors besides the differences in design. The most significant design difference may be the valves.

 

Don't say that or they'll bore out the cylinders to prove you wrong.

 

To pull in the crowds we need high speed parallel running. Now that the "slow" lines on the WCML north of Stafford are passed for 100mph they could thrash all the way to Crewe. Of course the Duchess would run better through the kinky crossover at Crewe.

 

No Brainer really...

 

Wouldn't that be something!

 

Remind me not to order the soup...

 

You mean the West Countries? In Scotland, wasn't it? They were the only class that got above 2000 dbhp in the trials.

@2968 mentioned dynamometer cars. I actually think that would be fairly easy to obtain these days if somebody had the will and the money (and I don't think it would be that expensive either). Take one buckeye coupled coach. Fit electronic force transducer in line with coupling hook spring. Replace buffer extension sleeves with two incorporating additional transducers. Feed into datalogger with GPS for speed. Much cheaper than overhauling a surviving dynamometer car, and probably just as accurate. I don't have actual components in mind, I hasten to add, but if I needed a dynamometer car that'd be what I'd look at first.

 

Don't know that GPS would really cut the mustard when it came to serious accuracy, not that speed recording is difficult at all on a rail vehicle. However seems to me that the dynanometer car is almost the easy bit. What you're going to test, where you're going to test it, how you're going to get permission to deliberately run the machinery to its limits. All those seem like really big organisational problems to me. And then what exactly are you going to test. Outright power, economy, efficiency... The 1948 trial data seems pretty unsatisfactory because of all the variables, and it seems to me that if it were straightforward to make realistic comparisons we'd have the information anyway.

I do remain highly suspicious of comparisons based on published numbers. If it were as simple as that there would't be all that effort expended on valve gear, superheater design, front end, all the rest of it. Like trying to compare IC engines based solely on cylinder capacity, carburetor and valve sizes. Sure it tells you something, but not remotely enough. It certainly doesn't tell you which engine is well designed and which isn't.

 

If possible, it would be interesting to couple it to a Pendolino, and the use the regenerative braking to load it up!

 

Now there's a thought! " Er, Mr Branson, could we just borrow one of your..." No, I can't see it really.

There remains the question: should we really be pushing such old machinery to the limits? I have doubts.

 

At the end of the day given similar cylinder efficiencies at turning the steam into work; at the very limit of boiler steam production and cylinder output (which the A1/P2 may just have the edge in terms of lbs/hour per sq ft ) these machines are capable of using more steam than they can generate, in which case the Duchess will win out because it has a bigger boiler and a bigger reserve of steam once usage outstrips output. I wouldn't expect that 2007 will outperform BluePeter by much other than in its surefootedness and whatever benefits its unique valve gear brings to the Party
Reckon that DoG still takes them all in terms of sustained Dbhp.

Perhaps they could sort a kylchap or similar for the streamlined Duchess... no one can see it...

 

It already happens on the RH&DR. I was present on the very first occasion, in the mid1980s. Bags of fun

 

There is no point in producing more power than your adhesion can absorb. Boiler size alone is no accurate indicator of steaming capacity. In an ideal design the boiler needs only to be able to continuously meet the maximum power obtainable from the cylinders, providing, of course, that the adhesion can cope with this.
The thermal storage capacity of a boiler is irrelevant when you compare it with the amount of energy being liberated in the firebox to meet the requirement of steam generation.
So the P2 is better able to deliver a higher power output because it has superior adhesive weight but this assumes that the cylinders can produce sufficient to be able to make use of that adhesion. The cylinder volume of the proposed P2 is less than that of the Princess Coronation but the overall performance of that volume can easily be far greater than that of the Pacific. The impact of back pressure alone can be enough to do this - there are so many factors.
So far as maximum speed is concerned, driving wheel diameter is no true indicator of potential.

 

I can well understand the theoretical argument for larger diameter driving wheels but I'd question if in practice this made any difference. The V2s, Thompson B1s, Thompson A2 Pacifics and Peppercorn A2s all very capable machines with high speeds recorded and all had 6ft 2in wheels.

Same size as the P2. I think on the main line it'll be clear that the P2 will be capable of some very good work.

 

In South Africa during the early 1980s, David Wardale proposed a high speed test of 3450 with an 8 coach train after the rebuild of the locomotive, his conservative estimate was 16o kmph (approx. 100 mph). Unfortunately, the test was vetoed, a pity, as this would have been quite an achievement for a Cape Gauge loco with a coupled wheel diameter of just 5'-00".

However, in 1991 3450 did achieve 125 kmph (approx. 78 mph) on a service train of 21 coaches - 870 tons gross, a speed record for a steam loco in regular service in South Africa. As related above, coupled wheel diameter is no pointer to what can be achieved, I wonder how fast 2007 could go if not restricted to 75 mph?

Cheers,

Alan

 

In New Zealand, members of the 4-8-2 JA class were accurately timed up to 73mph. With 4'6" wheels and 26" stroke pistons, that is equivalent wheel rpm to a Gresley A4 doing about 108mph.

Tom

 

Indeed Tom, the Ja class were, shall we say, modern locomotives not unlike the 25NCs in South African, with a related North British heritage. IIRC, I once read that the Jas had reached over 80 mph in service and that on a railway with a speed limit at just above 60 mph!! I would dearly have liked to hear that train approaching!!

Cheers,

Alan

 

Apparently the racing stretch was along the Canterbury plains approaching Christchurch. My father-in-law, growing up on South Island in the 1950s, was of the opinion that they would be going way in excess of what you could do by car on the parallel main road. Supposedly the Ja class was restricted to 50mph, but drivers often went quicker if trying to recover lost time. 73mph was the highest properly timed speed, but stories up to 80-odd mph are certainly talked about.

I had a footplate ride on one once - impressive bit of kit. Though double headed Ja's on a five coach train of vintage carriages may have been overkill!

JA 1250

by Tom James, on Flickr

Tom

 

An outrageous thread swerve, but just for you Tom and any others if you are interested:

http://www.internationalsteam.co.uk/tales/lythgoe118.htm

Wilson Lythgoe has some wonderful stories here covering the last years of New Zealand steam - plus other Global adventures - great commentary and photos, hope you enjoy.

Cheers,

Alan

 

I know that stretch. It is very straight.......and absolutely stuffed with level crossings!