Tractive effort

[Alan Wright 5Participant @alanwright5]

I remember many years ago that a formula or ratio was given for weight of loco and lbs it could pull. I realize that there are many variables such as wheel configuration and track material but the formula seemed to be fairly reliable.

[Alan Wright 5Participant @alanwright5]

Ratio of loco weight to weight pulled

[SillyOldDufferModerator @sillyoldduffer]

Are you thinking of the coefficient of friction between the wheels and the rail? It's about 0.30 for a heavily loaded wheel and a dry rail, meaning a driving wheel won't slip as long as the weight on the wheel is not less than 3.33 times the rotational force.

Dave

[mark costello 1Participant @markcostello1]

So a train weight of 6000 tons will require how much traction? I realize the engine needs to only start the first car, but how about pulling up a steep grade?

[duncan webster 1Participant @duncanwebster1]

The loco has to start all the trucks, well something has to. If it is loose coupled it doesn't have to start them all at once, but if they are on roller bearings it doesn't make a lot of difference as static and dynamic friction of the bearings are much the same. For full size rolling resistance work on about 10lbs per ton rolling resistance, pull needed to go up gradient is load * gradient.

For your 6000 ton train on a 1 in 100 gradient this comes to 6000*10 + 6000*2240*1/100 = 194400 lbf

With a 6000 ton train you probably need to add a bit for curvature unless the railway is very straight.

[SillyOldDufferModerator @sillyoldduffer]

Getting a heavy weight to slide on water or rolling on rails requires much less effort than pushing it up a slope, let alone lifting it vertically.

To put a sense of scale on rolling resistance, despite me being an out of condition pensioner I was able to move a 15 ton canal narrow boat on my own.

The hard part was getting the boat moving, after that I reckon about 50W of duffer power was enough to keep it moving on still water. Ideal towing conditions – no wind, weeds or incompetent steering to make it difficult. After about 30 yards I'd had more than enough, but I reckon a couple of fit men could tow a narrow boat several miles. Any canal experts able to confirm? A horse could pull one for hours on end.

Dave

[not done it yetParticipant @notdoneityet]

One can practically forget any gradient on a canal, so in simple physics terms f = ma.

In words: force equals mass multiplied by acceleration. Apart from the boat’s inertia, friction and moving aside the water is the problem of getting decent acceleration while manually pulling a narrow boat. Once moving one only need to overcome the retarding forces, which are not particularly great – try stopping the boat when it is already moving! Not quite the same if there is a current, mind, which there can be around locks and overflows.

‘Legging’ through tunnels was commonplace. Locks would need human intervention and some poor souls may have been reduced to manpower rather than horsepower at times. However horse, pony, or donkey power has been used at least since Roman times. Apparently 50 times the towing capacity on water, compared to roadways.

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