West Somerset Railway General Discussion

No, energy (ie work done in moving the train) does not vary with the square of speed. (You are thinking of kinetic energy. Kinetic energy is the energy the train possesses due to its motion. You are also wrong to be dismissive of my EDHP calculations)

However clearly if a train travels faster it is doing more work as seen in the previous typical calculation to determine power requirements at 25mph and 40mph. i.e. more coal of a given calorific value will be burnt to evaporate more water. (this will be if operating within the locos middle power range a linear increase, if it involves pushing the loco close to the limit it will be greater).

As a matter of note in the previous example the EDHP of c.900 at 40mph on the 1/92 is right at the limit for a GWR large 'Prairie'. Observations suggest that when 4160 operated at 225psi the EDHP with RFO and 40% was in the range 850-900. The overall thermal efficiency would have been less than with a shorter cut off.

Michael Rowe

 

It's this sort of discussion that I really appreciate when browsing the forum. Personally I am not technically minded but the insights of those who are so blessed are always most welcome.

Recent postings made me think back to an article in a long-lost Railway Magazine (circa 1960) entitled "Engine driving. Is it an art or a science?" The conclusion reached by the writer was a combination of both. The ideal footplate man is therefore presumably an experienced driver/fireman with an aptitude for mathematics, or a mathematician who knows what to do with a shovel.

 

During our Thomas event we shuttle trains in and out of the platforms at Ropley. The "game" is to stop so the step on the platform that gives access to the brakevan (~90ft away) doesnt have to be moved each time. Means stopping within +/-6". I get it about 9 times in 10. I dont suppose for a second that my skill as a driver is greater than that of the WSR drivers. Stopping for water wouldnt tax them too greatly I feel.

 

Not much of all this theory actually finds its way onto the footplate. Mathematics is certainly never mentioned beyond steam pressure figures, how many buckets of coal are required and how many minutes late we are. Things are too fast changing for any other concern over theory.

Crewing steam locos is much more about taking notice of what the engine is telling you (yes really), using your own experience and knowledge of the route.

 

I knew there had ro be a reason why those grubby footplate types aren't seen around nice clean drawing offices too often!!

 

I think that 99.9999% (one in a million?) is a slight exaggeration since I have been to various WSR Galas and experienced delays due to various (tank) locos suffering lack of water, mainly due to being held up by a delay in the train in the opposite direction. At least one had to take on water via a hose at Williton.
I was also on the service hauled by the "Pacific that got to Blue Anchor".... It was 34053 Sir Keith Park. Not only did the crew "forget" to take on up to 4,000 gallons of water at MH following a crew change, but after the locomotive was attached to the rear of the down service (double headed) they "forgot" to release the brakes. The loco having been "dragged" back to MH suffered wheel flats.
Robin L.

 

The loco didn't get dragged very far with the brakes on as I've seen a video on YouTube of it on the back of the train having just left Blue Anchor and the wheels are turning. Any wheel flats couldn't have been serious because, after refilling, it went straight back into service.

 

I guess it's a balance.

I would concede that having multiple water sources may be a loco operating benefit. There is, also, a heritage benefit in having the water columns at either end of Williton reinstated, in that it recreates the look we can see in the 'Then and Now' photos I have been posting.

But all that comes at a cost, both capital and maintenance, and there may be greater priorities. I, for one, would like to see the loco facilities at Bishops Lydeard move forward from a collection of portacabins to something more 'GWR'.

Might that be a higher priority?

Robin

 

I'm sort of glad the old lattice footbridge didn't survive. The current one looks much better, and being covered provides photographers (like me) with shelter from the rain.

 

I took a video from beside the level crossing, which clearly show the motion bars were not moving. I do not know how long the brake remained on, but apparently wheel flats were "polished out" by the SVR.
Robin L.

 

Under BR auspices, post the various Rugby and Swindon testing initiatives, much more "of all this theory" found its way into MICs. Particularly wrt fuel efficiency and a preference towards full Regulator and shorter cut off working. However yes the driver/fireman 'feel' was/is arguably the key element.

The demands of much current mainline steam scheduling mitigates against such niceties I think, the 70mph uphill and down dale requirement. However on Heritage lines there are IMHO many oppurtunities.

Michael Rowe

 

I'm afraid it is essentially right. It is a fundamental law of physics that energy can neither be created nor destroyed but its state can be changed. If you had a frictionless flat railway then the energy required to accelerate to a speed does indeed increase with the square of the speed. however, once up to speed there is no further input of energy and the train will continue at that speed for ever and a day until you apply the brakes. The kinetic energy is then changed to heat energy. However, that is not the reality. On our real railway we have friction and we have gradients.
What happens in reality is that we start off with our coal, which contains chemical energy. We convert this chemical energy into heat energy, which we then convert into a combination of kinetic energy, potential energy (increase in height) and heat energy (friction). If we go from A to B and B is higher then the gain in potential energy is a constant no matter what speed we run at. Friction does vary with speed but this is not significant at low speeds. The rolling resistance of a Mk.1 coach is 3.8 lbf/ton at 20 mph and 6 lbf/ton at 40 mph,, nothing like a quadrupling. So, once up to speed, the only steam (water) required is that to overcome friction and gradient. If we are going faster, the train will run further up a gradient or further along the level before coming to a stand.
My statement that you use the same amount of water to go from A to B whatever the speed may not be perfectly correct, largely because of changes in friction but it is essentially so.

 

Every couple of years I do a training session on the NYMR which includes a section essentially showing how the theory stacks up with reality. This goes from working out the energy required to get a train from Grosmont to Goathland and translating this into the actual amount of coal that is shovelled through the firehole door. The theory and practice actually work out to be quite close if you take a trip where the fireman is not producing huge amounts of black smoke or sending lots of the heat up the chimney with too much air.

 

We missed each other last time you were in Somerset, but if I provide the refreshments and the chalk and blackboard, happy to invite you to Station House, Stogumber to continue this discussion......

Robin

 

Happy to do that next time I'm in Somerset and free to do so. When that will be, I've no idea. I'll be on the M5 next week but if I divert from it SWMBO will probably end my life there and then. You could always venture up north. Grosmont Crossing box is always worth a day out.

 

Consider it a fixture for next year.

I was privileged to spend a shift in Grosmont last year with one of your signalmen who is a main line bobby somewhere like Middlesborough, IIRC. Nothing derailed that day!

Robin

 

I did a back of an envelope calculation, as follows

- Assume a Manor (109 tons) and 6 * 35 ton carriages (210 tons)
- Loco resistance 12lbf / ton
- Carriage resistance 3.8lbf / ton @ 20mph, 6lb/f ton @ 40mph, as given by @Steve
- 10km rising gradient of 1 in 100, which is fairly close to the actual figure from Williton to Crowcombe Heathfield
- Assume the train spends 1km to accelerate to 20mph and then 9km at steady speed; or else 2km to accelerate to 40mph and then 8km at steady speed
- Assume the carriage resistance averages half the stated figure during the acceleration phase and then achieves a steady figure
- Convert everything to metric!

So in each case, the train (weighing 319 tons gross) starts at rest, then accelerates to speed, climbing 100metres in the process. It starts with zero KE and PE; ends up with both and an amount has been absorbed in rolling resistance. (The KE and PE gained are then wasted uselessly in brake heat when the train slows for a station).

At 20mph:

KE = 12.6MJ
Rolling resistance absorbed = 86.5MJ
PE gained against gravity = 312.6MJ
Total energy used = 412MJ

At 40mph

KE = 50.4MJ
Rolling resistance absorbed = 100.9MJ
PE gained = 312.6MJ
Total energy used = 472MJ

So running at double the speed only uses about 14% more energy - about 1 extra shovel full of coal in every 7. (And equivalent extra water consumption - 1 gallon in 7).

It is the gradient that is the killer in energy use, not the speed.

Note however that the 10km journey takes 1240s at 20mph - nearly 21 minutes - but only 675s at 40mph - about 11 minutes. So the average power output is 0.7MW at 40mph; 0.33MW at 20mph. So you need twice the power for the quicker journey, but as @Steve said, don't use much more energy because the travelling time is correspondingly reduced.

Tom

 

I'm not a fan of eating when travelling on a heritage railway but a breakfast on the QB I have broken my unwritten rule in the past and very good it was too .

Paul .K

 

Note that it seems the menu has been trimmed to an all day breakfast rather than a different menu for lunch. An excellent idea that should make it much easier for the staff.