Tractive force of a loco
- Thread starter Mobi
- Start date
ge_rik
British narrow gauge (esp. Southwold and W&LLR)
I've not tried it but I'd imagine the simplest approach would be to attach a Newton meter (a bit like a spring balance) to the back of a loco, and then the other end of the balance to an immovable object and then drive the loco forwards until the wheels slipped. I assume the reading on the Newton meter would be the loco's tractive effort.
Rik
Rik
For real locomotives this was a calculated figure, taking the piston area, position of the crank, an 'accepted' figure for the coefficient of friction between steel wheel and steel rail (dry), and usually calculated at 85% full boiler pressure. I think adhesion weight comes into it somewhere as well!
For diesel and diesel electrics something similar would be used, but using the torque output of the traction motors (etc.).
A spring balance as suggested would be fine to give a comparison figure between various G scale locomotives.
For diesel and diesel electrics something similar would be used, but using the torque output of the traction motors (etc.).
A spring balance as suggested would be fine to give a comparison figure between various G scale locomotives.
playmofire
Registered
I'm not sure how meaningful it would be bearing in mind that it is, say, a 1:22.5 loco dealing with the forces of the full scale world. One test which might give some guidance would surely just to attach trucks to the loco on a level line until wheel spin set in. Presumably the weight of the trucks pulled give you some measure of the locos pulling force and allows comparison with other locos.
I think this could be interesting, do you mean to compare locos like for like or against their full scale counterparts?
Don't forget it is all physics, many things such as adhesion and inertia will also affect this, Hence how full scale locos produce possibly 6 times more K/N ( kilo Newtons) when starting of, this then drops as the inertia drops off. You could simply get a weighing scale used to measure fish it'd be cheaper and then do the math.
Don't forget it is all physics, many things such as adhesion and inertia will also affect this, Hence how full scale locos produce possibly 6 times more K/N ( kilo Newtons) when starting of, this then drops as the inertia drops off. You could simply get a weighing scale used to measure fish it'd be cheaper and then do the math.
spike
It's me
Some where on the forum I did this with a few of my locos.ge_rik said:I've not tried it but I'd imagine the simplest approach would be to attach a Newton meter (a bit like a spring balance) to the back of a loco, and then the other end of the balance to an immovable object and then drive the loco forwards until the wheels slipped. I assume the reading on the Newton meter would be the loco's tractive effort.
Rik
CoggesRailway
Registered
I have done this with a fishing scale to compare tractive effort. Coupler hooked to the fishing scale (similar to that one above) and other end attached to a screw through a sleeper (slightly raised for the purpose from its normal position).
LGB 2095 and Alco White Pass where the heavy hitters.
LGB 2095 and Alco White Pass where the heavy hitters.
spoz
What do I do? What I'm told by SWMBO
Well, from Wikipedia for real steam locomotives the formula is:
? where t is tractive effort, c is a constant representing losses in pressure and friction (normally 0.85 is used), P is the boiler pressure, d is the piston bore, s is the piston stroke and D is the driving wheel diameter.
That would work for G scale live steamers as well I would think.
There was a way whereby the steam nuts of the past could work out the horsepower being exerted by the loco using the speed gain or loss and the gradient up which the train was running and that should be able to be used to calculate the power being exerted by a non steam loco. I can't remember, if I ever knew, how to do that and I can't find a reference; but there must be somebody out there who still knows, or who can work it out from first principles.
The starting position would however have to be to know the rolling resistance of the train, and you'd have to calculate that for each vehicle individually (including the loco) and then add them up. I think rolling resistance r = CW where C is the coefficient of rolling resistance appropriate to the two surfaces and W the weight of the body bearing on the resisting surface. C is about .002 for steel on steel wheels I think, although I'm pretty sure it varies somewhat with wheel diameter although that shouldn't be significant in G scale. I should be able to get from rolling resistance of the train to the horsepower being exerted to overcome gravity in a climb, but I can't remember how! (Senior's moment I hope or my engineering professors will never forgive me!!)(on the other hand I imagine they are all dead so i don't suppose they care)
Alternatively, I suppose, you could just do as previously suggested and use a pull against a spring balance. After all, that's the principle of a dynanometer car, which the real railways also used.
Steve
That would work for G scale live steamers as well I would think.
There was a way whereby the steam nuts of the past could work out the horsepower being exerted by the loco using the speed gain or loss and the gradient up which the train was running and that should be able to be used to calculate the power being exerted by a non steam loco. I can't remember, if I ever knew, how to do that and I can't find a reference; but there must be somebody out there who still knows, or who can work it out from first principles.
The starting position would however have to be to know the rolling resistance of the train, and you'd have to calculate that for each vehicle individually (including the loco) and then add them up. I think rolling resistance r = CW where C is the coefficient of rolling resistance appropriate to the two surfaces and W the weight of the body bearing on the resisting surface. C is about .002 for steel on steel wheels I think, although I'm pretty sure it varies somewhat with wheel diameter although that shouldn't be significant in G scale. I should be able to get from rolling resistance of the train to the horsepower being exerted to overcome gravity in a climb, but I can't remember how! (Senior's moment I hope or my engineering professors will never forgive me!!)(on the other hand I imagine they are all dead so i don't suppose they care)
Alternatively, I suppose, you could just do as previously suggested and use a pull against a spring balance. After all, that's the principle of a dynanometer car, which the real railways also used.
Steve
maxi-model
UK/US/ROW steam narrow gauge railways 1:1
There was a video on YouTube of an Accucraft live steam K-28 pulling a 250 lb man but I can't find it right now. K-28 on 45 mm the flat car with man on 5" laid outside the 45 mm. No tricks with inclines.
Fun as it may be to work these things out I don't see it as a major buying criteria. I rekon most go for the subject matter rather than its capabilities. And what manufacturer would want to put the kybosh on sales on what is already a calculated gamble by telling the buyer it wouldn't pull the skin off a rice pudding however nice it looked.
I work on the basis the more driven axles with a good bit of weight over them the better. So why is my Roundhouse Darj' 0-4-0 one of the most capable up an inline with a load on my line ? Bit like the prototype.
Max.
Fun as it may be to work these things out I don't see it as a major buying criteria. I rekon most go for the subject matter rather than its capabilities. And what manufacturer would want to put the kybosh on sales on what is already a calculated gamble by telling the buyer it wouldn't pull the skin off a rice pudding however nice it looked.
I work on the basis the more driven axles with a good bit of weight over them the better. So why is my Roundhouse Darj' 0-4-0 one of the most capable up an inline with a load on my line ? Bit like the prototype.
Max.
maxi said:
One reason of course is that it's an all adhesion loco. The worst thing you can do on a loco you need to pull hard, especially up inclines, is put on a rear pony truck or bogie. I know that the yanks did this with the huge articulateds, but it gets a bit different with that sort of size, however for UK sizes, then you're better off without it
Hence why Bulleid pacifics, the big atlantics, and even to a lesser extent Gresley pacifics were not good starters from rest, and one reason why the GWR stuck to 4-6-0s and the main reason why the Andean railways evolved the Andes Class as 2-8-0s.
Because of the height of the loco drawbar above the axle line, when starting there is a considerable weight transfer effect, with a rear pony truck, this actually tends to unload the drivers, making them more likely to slip. Without the rear truck, the effect just loads up the rear drivers, increasing adhesion..
Regarding train resistance, there is a formula for this, the Johansen formula, which I can't remember, but which could probably be found on the net somewhere. I can't see it applying to G Scale trains though!
PaulRhB
This Way Up
Publishing reactive effort for models is fairly pointless unless people have accurately measured their gradients and usual trains. Traction tyres skew the figures badly too as does the fact many LGB locos of different sizes use the same motor so the figures won't be in line with the prototypes. Especially for followers of rule 8 isn't it more fun to see what they're capable of on your line and rate them by standard stock as real railways do? 
On the national network they rate locos by tonnage they will pull which can then be divided by the set weights of stock to provide a figure in average conditions. The problem comes when they overload one time and make it but the conditions are less than ideal the next. Non standard couplings to rescue it then rear their head and unlike G you can't just use a paper clip to join a knuckle and loop
On the national network they rate locos by tonnage they will pull which can then be divided by the set weights of stock to provide a figure in average conditions. The problem comes when they overload one time and make it but the conditions are less than ideal the next. Non standard couplings to rescue it then rear their head and unlike G you can't just use a paper clip to join a knuckle and loop
spike
It's me
1:1 scale tractive effort from the Republic Locomotive website.
TE required to move a train on straight and level......2>5pounds/ton
For curvature add 0.8pounds/ton/degree of curvature
For grade add 20pounds/ton/every 1% of grade
To accelerate to 6mph in 1minute.....10pounds/ton
If you want to scale any of these divide by the cube of the scale.
For 1:29 divide by 24389
For 1:22 divide by 10648
For 1:20 divide by 8000
TE required to move a train on straight and level......2>5pounds/ton
For curvature add 0.8pounds/ton/degree of curvature
For grade add 20pounds/ton/every 1% of grade
To accelerate to 6mph in 1minute.....10pounds/ton
If you want to scale any of these divide by the cube of the scale.
For 1:29 divide by 24389
For 1:22 divide by 10648
For 1:20 divide by 8000
playmofire
Registered
I'm not sure that simply dividing by the scale will give an accurate answer. There have been a number of cases where scaling up from successful test models have produced a 1:1 product that doesn't work because physical laws don't seem to work that way.
James Day
Guano Corner Rly - Runs weekly - Guano permitting
I seem to recall that some years ago Model Railway Constructor conducted meter tests when reviewing new models. I no longer have my back issues, but I recall them being highly critical of the lack of pulling power that many 00 models had back then (late 80s?). I also recall how impressed they were with the 'Super Strong Pulling Power' chassis that was fitted to the Hornby Thomas, which featured a separately sprung axle and traction tyres. This beat all the other models they had ever tested.
I am a great fan of traction tyres, as they allow models to effectively apply the weight that they have to the rail. On a real loco the metal wheel actually deforms slightly as it rolls round and makes contact with the rail, although the contact surface is incredibly small. Our models are too small for that to work, so long live the traction tyre!
My own examples of this are my three beloved LGB Steeple Cabs. One came with a tyre fitted from new (mid 70s), two didn't but had this added to them.
Without a traction tyre, without extra weight a loco could not manage more than one LGB coach on my graded branch line. Extra weight was added, but this made no difference at all. With a traction tyre, but no extra weight, it could manage two coaches, but with the extra weight it can do three. I seem to recall once working out that the branch is graded at around 1:30 throughout, but has an LGB second radius curved approach. That is the real killer, as mentioned in the posts above!
I also tried tests with these locos on the level many yeas ago, and found that the extra weight coupled with the tyre allowed them to haul much longer trains on the flat, but sadly cannot find the figures now.
James
I am a great fan of traction tyres, as they allow models to effectively apply the weight that they have to the rail. On a real loco the metal wheel actually deforms slightly as it rolls round and makes contact with the rail, although the contact surface is incredibly small. Our models are too small for that to work, so long live the traction tyre!
My own examples of this are my three beloved LGB Steeple Cabs. One came with a tyre fitted from new (mid 70s), two didn't but had this added to them.
Without a traction tyre, without extra weight a loco could not manage more than one LGB coach on my graded branch line. Extra weight was added, but this made no difference at all. With a traction tyre, but no extra weight, it could manage two coaches, but with the extra weight it can do three. I seem to recall once working out that the branch is graded at around 1:30 throughout, but has an LGB second radius curved approach. That is the real killer, as mentioned in the posts above!
I also tried tests with these locos on the level many yeas ago, and found that the extra weight coupled with the tyre allowed them to haul much longer trains on the flat, but sadly cannot find the figures now.
James
