Current and Proposed New-Builds

What? The self-appointed unofficial Secretary of State for Heritage Railways out of his depth? Surely not!

 

Sorry for being

Personally I don`t care about a locomotive is "under powered" for mainline or "over powered" for heritage lines. I choose to donate money to new build locomotives (and restoration projects) which I like the design of and attracts me. Also important is that the team behind it seems well organized and with great progress.

kind regards

Knut

 

More "vital" than merely "important" IMO.

Sorry if this seems like nit-picking Knut, but I'd say A1SLT showed us exactly the difference between those two adjectives!

 

No harm my friend. It`s just me and my english/norwegian dictionary

 

Ignoring the subsequent "Oh yes they are", "Oh no they're not" spats, large wheels do have one disadvantage; you can't fit in so many of them for the same size of frames and boiler, so you get less adhesion weight. Compare for example Stanier 5MT and 8F, GW Hall and 2800, or all those early 20th century 4-4-0s and 0-6-0s.

 

I don’t know much Paul, but if I was a betting man I’d say the gentleman with experience in driving large wheeled Pacifics at low speeds probably has the edge in this debate over your small chuffer experience.

Matter of opinion my foot. Does knowledge and experience count for nothing anymore? “Sorry it’s my opinion, prove me wrong”.

Utterly nonsensical.

 

But these big wheels chuffers were built for passenger trains. 8 Mk1's weigh in at about 272tons tare, and that's about typical on most of the bigger preserved lines. A4's used to manage to start and accelerate 360 tons through 25mph and keep on going to 80-90mph and for 400 miles. They are capable of doing the job asked of them.
The 8f's and 2800's etc were built for hauling 40-odd 16t mineral trucks, a gross weight of 950tons. Hence the requirement for lots of small wheels. Typically these trains ran at rather less than 25mph, with plenty of time sitting waiting for faster trains to pass. These locomotives will truly come into their own when the NYMR is routinely running trains of 25+ coaches

 

I don't deny that. You design a locomotive to do the job that you want it to do. Most reciprocating steam engines (not just locomotives) of the type we are familiar with are designed about a maximum working speed of 360 rpm so, if you want it to go fast, you fit bigger wheels; if you don't want fast speeds you can take advantage of smaller wheels and the advantages that this usually brings. What gets my back up is people saying a big wheeled loco is unsuitable for slow speed running purely because it has big wheels.

 

Perhaps not unsuitable, but perhaps the small wheeled engine is better...?

 

I'm sure I remember a very informative topic about this being on the forum some time ago, I can't find it now mind!

Chris

 

Better for what, though? A small wheeled loco will probably be cheaper to build so it is better in that respect. It will wear out faster, though!

 

For the same tractive effort, a small wheeled locomotive will have smaller forces in the frames. It's good if you don't want to go fast.

 

Running at those speeds, Steve. All machinery is designed for an optimum speed / rpm range, and on a steam locomotive this is largely dependent on wheel diameter. Yes, the big -wheeled engines will run at this speed, but it isn't what was intended: 25mph was transient as they accelerated their trains to a higher speed range. The phrase, "Having to hold it back'" comes up often, and I know the SVR crews aren't over-enamoured with the Bulleid Pacifics, especially when climbing Highley Bank.

Slightly different but on a similar theme, I recall a documentary many years ago on the Fort William - Mallaig trains, one of the drivers referring the Black Fives. "Good engines, but a bit big in the wheel."

 

That is not entirely true though is it?

Are we forgetting wheel balancing? Maybe something as simple as whether the class has axle box shims or not? What type of valve gear employed?

Whenever we get this cyclical debate of small versus large steam locomotive I feel like shouting to the heavens. It doesn’t matter!

Our preserved railways have to play the hands they are dealt and short of melting everything bigger than an Ivatt tank down and building austerities for the rest of our days, can do nothing about it.

This debate has been done in so many different forms and it’s always by the same people trying a new tack each time to try and convince us all of the right way to do steam railways. How about small chufferitis be small chufferitis and we can be big chufferitis and we agree to disageee?

Because this debate absolutely takes the proverbial every single time and is utterly wearying to take part in, read or experience.

Lord knows if we had this kind of in depth discussion about how we attract younger generations to railways all of the above might be moot as we might have enough manpower to overhaul everything in the first place!

 

A very valid point, but there are also a lot of people around who are intereseted in the technicalities.

 

If I was designing a locomotive to run on heritage railways it wouldn't have big wheels. if I was offered a locomotive for use on a heritage railway that had big wheels, I wouldn't say it was unsuitable and turn it down because of this. Similarly, if someone wanted to recreate a long lost class of locomotive that had big wheels I wouldn't ridicule the project because it would only ever run at 25 mph. I think that is the main point of the argument.

 

And that is fine, I have no issue with the genuine debate on the technicalities of locomotive engineering.

I can’t help but feel that here it was mutton dressed as lamb...!

 

This particular thread is about new builds. All sorts of considerations can have some relevance to choosing one potential design over another, but wheel size will be well down the list unless use on the main line is envisaged, in which case the advantage of large wheels becomes significant. I think Tom listed the crucial considerations way up thread. Far and away the most important is whether any suggested project can attract enough cash and manpower to get built in a reasonable time.

 

Indeed ..... it does tend to help!