UK 12 wheeled, 8coupled tank engines

[Mod6]

Never confuse the starting tractive effort estimate with 'power'. Power output in steam locos requires consideration of factors such as grate and superheater area; in addition to boiler pressure, cylinder volume and wheel diameter, that are used to generate the starting tractive effort estimate. These small wheeled eight coupled types were probably good for around 1,000 hp sustained output. Express passenger types with much larger firegrates and superheaters and TE estimates in the same 30 - 40,000lb range were capable of more like 2,000hp.

 

The GER Decapod had 43,000lb TE, and 42 sq ft of grate, no superheater. Probably good for circa 1,700hp in bursts.

 

Glad to see somebody questioning the use of tractive effort as a measure of how powerful a locomotive was. I have quoted this before but when the GWR announced that the King was the most powerful express passenger loco in the UK because it had the highest tractive effort, somebody answered with something along these lines........

 

"If you remove the coupling rods from a King, the theoretical tractive effort would remain the same. If you took the boiler off and replaced it with a Sentinel vertcal boiler, it probably wouldn't move itself but you would have increased the tractive effort because of the higher boiler pressure."

 

Its all very well getting all high and mighty about TE excetera, but when thats the only available information at hand you have to use what you can. Be my guest and spend several hundred quid on books to find out measurements of DBHP etc. just for one thread. Peronally I'm really not that bothered about it. Several posters on this forum seem to take great pleasure in attempting to belittle people at any oppotunity.

 

For the record, ACTUAL Tractive Effort is the force that the loco exerts on the track to move itself and its train in a given direction. With a steam loco, it starts at the maximum at zero mph and falls exponentially as speed rises, the rate of fall depending on several factors, driving wheel diameter not the least but valve events also come into it. Adhesion also plays a part. NOMINAL Tractive Effort, as quoted in the ABCs, is a purly theoretical value with little relevance to actual conditions or ability to grip the rails.

 

Power is the loco's ability to keep a train moving at a speed, and is largely a function of the boiler's ability to generate steam in sufficient quantities over time, while tractive effort derives from an instantaneos boiler pressure, allied to cylinder dimensions and wheel diameter.

 

It does get more complicated than this, but I'm trying to avoid getting bogged down in the technology!

 

I don't really see how passing on a slightly humerous anecdote to illustrate why tractive effort does not equal power represents being "high and mighty" or "taking great pleasure in attempting to belittle people at any opportunity".

 

It's fashionable to rubbish people with actual knowledge. Please don't do it. You don't need to spend several hundred quid to know that lbs is a measure of weight or force and power is measured in horsepower or watts - having a pulse whilst at school should have been sufficient. "Using the only information at hand" is like saying Chelsea beat Liverpool 2-0 when asked what the score in the Man Utd vs Arsenal game was.

 

Two points to make here:

 

What I've seen is an attempt to add value to the topic by clarifying what TE actually means, followed by a rather petulant response from D605Eagle as if learning something new wasn't of value or interest.

 

It does seem though that Ian Allan's ABCs have done generations of trainspotters and steam enthusiasts no real favours by quoting TE values for every class - it's hardly surprising they are often taken as the only indicator of power with which to compare.

 

But let's cool it down now please.

[keefer]

i remembered this page from al krug's website:

 

http://www.alkrug.vcn.com/rrfacts/hp_te.htm

 

i must admit i'm not used to using this much brain-power, but hope it's useful!

[melmerby]

 

It does seem though that Ian Allan's ABCs have done generations of trainspotters and steam enthusiasts no real favours by quoting TE values for every class - it's hardly surprising they are often taken as the only indicator of power with which to compare.

 

Not just the ABCs but drawings from the railway companies themselves often quoted the TE. (not just the GWR going for the 40000lb barrier!)

The TE is a useful comparison of potential power of a locomotive. IMHO The Sentinel boiler on a King chassis is hardly a relevant comparison.

 

I, and not doubt most others, realise that other factors have to be taken into account and the power is only generated when some work is being done. E.g moving something in a given time. (basic physics).

 

Enlarging a 2-8-2T to a 2-10-2T and using a larger boiler, firebox and cylinders (in similar proportions) should produce a proportional increase in power available to do useful work, of which the new TE would be a useful indicator.

 

Keith

[62613]

If you use the formula most used in the UK, the tractive effort of a steam loco. would only increase if either of the cylinder dimensions, or the boiler pressure were increased, or the driving wheel diameter was decreased. The wheel arrangement has nothing to do with it if the same boiler, engine and driving wheels are used. hence the Sentinel boiler on a King chassis.

 

Strictly speaking, when a body is moved by a force, you do work on that body, and expend energy when doing the work. Power is the rate of doing work, and is (was?) measured in horsepower, or nowadays kiloWatts

[t-b-g]

i remembered this page from al krug's website:

 

http://www.alkrug.vc...facts/hp_te.htm

 

i must admit i'm not used to using this much brain-power, but hope it's useful!

 

Wow! My brain hurts!

 

That is a very interesting read for anybody into more technical/engineering/physics type stuff.

 

What it does explain is why the railways quoted and used the tractive effort figure, by putting it into other calculations to come up with loco's potential power output, which was new to me. Of course we have to assume that it is all accurate and represents the correct version of such matters but it looks highly convincing to me. If it was a load of made up waffle I wouldn't be any the wiser.

 

Going back to the (supposedly humourous but obviously cage rattling) example of the Sentinel boilered King, using the formula that Tractive effort times speed equals power, then the fact that the thing would hardly move would mean that it has lots of TE and sod all power, which seems about right!

 

All this technical stuff is of course, way off topic so I apologise if my initial posting caused some wandering about.

 

Going back to the subject of 12 wheeled 8 coupled tanks, I do have some etches for a GCR tank (LNER S1) so one day I may get around to putting them together but quite where I shall run it is another matter. A model of Wath yard, or indeed any huge marshalling yard, is certainly not on the agenda!

 

What a brute of a loco that one was.