Tractive force of a loco

playmofire said:
I thought of that one, Mick, and tried to find the book in which I'd read about it to confirm date and place but couldn't. If I remember rightly, the driver had expressed concerns about the length of the train but had been over-ruled by the local manager and told to run the train as it was, The driver was right and the train had to be split. The accident led to new regulations on braking systems I believe.
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The accident you refer to was at Armagh, June 12th, 1889. (Source: Red for Danger by LTC Rolt, my favourite train book)
 
And I'll echo that!
 
Yes, thanks Greg - A bit of background to it here
http://en.wikipedia.org/wiki/Armagh.../commons/d/d9/Armagh_ILN1.jpg[/IMG] Rik
 
I hooked a luggage weigh scale to Playmobil 5258 loco on table top.

It recorded 0.35 kg max pull.
 
Sounds like a good typical number.
Try some more weight if you want to increase it.

Now you can try measureing the force needed to pull a few wagons along the track with the scale. When you get enough wagons to read 350g, that's how many you can pull on level track.
 
The international unit of mass is the kilogramme.
The international unit of force is the newton.

The international unit of length is the metre
The international unit of time is the second.

force is define as mass x accelleration

1 newton = 1 kg x 1 m/s

Gravity on earth is usually around 9.81 m/s2

Any body on earth is therefore accelerating towards the earth at 9.81 m/s2

Weight is the measure reaction to the mass of an object being accelrated by gravity.

Weight is therefore a force. The international unit of force is the newton so the international unit of weight must be the newton ???

So to measure tractive effort of a loco, the technical term for the pulling force, have a length of track high up, attach a string over a pulley at the end and see what load it lifts. If the weight is measure in kg then to get it into the right unit multiply by 9.81, or 10 for a quick guide.

if you can measure it pulling over a measured distance you could also calculate the power.
 
Got called for lunch - so continuing.

power (in watts) = force (newtons) x distance ( metres )/time (seconds)

and believe me, compared with using the old imperial units these calculations using SI are a doddle.

While the SI system uses metric measures, ie metre, kilogramme etc. the newton was only established in the 1960s and should have been used as the unit of weight - but, as usual, the politicians bottled it. So we have a system where the legal unit of weight is not the technical unit of weight, but the unit of mass. Using the unit of mass for products will only make sense when products are sold in multi-gravity environment. So untill Tesco et al are on the Moon, Mars etc. we have the anomaly of the unit of mass being the legal unit of weight, but actually it isn't.

A weight of 1 newton, or 1N is around the weight of your average apple. So when anyone tells you that the metric system is foreign, unlike the pound, foot set up then point them towards the true unit of weight (newton), the unit of power ( watt), unit of energy ( joule ) and the correct unit of temperature the kelvin where the freezing point of water is 273K. Celcius or centigrade is just a sub-set with the same spacing but does not work with many heat calculations.

And for those who hark back to the foot/pound days remember that the pound is the unit of force/weight so for the unit of mass had to be divided by 32 and no one really named the unit of mass. Many were applied including poundal and slug!

OK - I now get off my hobby horse. ;)
 
Roundhouse has confirmed that pulling power for Little John is 15 lb or 7 kg appx. Motor is of 19 Watt.
 
And ..... just note this. The "yardstick" Kilo weight, from which all kilo weights are neasured, was made in Britain for the French. Vive l'angleterre (don't know if I've spelt that right) ;D
 
trammayo said:
And ..... just note this. The "yardstick" Kilo weight, from which all kilo weights are neasured, was made in Britain for the French. Vive l'angleterre (don't know if I've spelt that right) ;D
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and the standard hosepower is kept in a stables in Paris somewhere????? ;)
 
gregh said:
pretty hard to believe 7kg, unless it has traction tyres. I would think that the loco would have to weigh something like 30 kg to get that TE.
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Could be that it will pull a train of 7Kg rather than pulling at 7kg force.
 
What interesting topic lots of theory and some of the equations used on the railways to calculate Tractive effort very good ! Now comes the bomb What is more important Tractive effort or :- wait for it ! Draw Bar Pull ie.How much exertion is exerted on the drawbar to over come static friction and to increase inertia! Any of you here who are railway mechanical and electrical engineers should know that Tractive effort is a theoretical force derived from the wheel diameter boiler pressure(Steam Loco)or engine size on diesel loco or power output amount on electric loco current etc (Not my field). But the true figure of power is what is exerted on the drawbar using the spring gauge on the coupling between the loco and the train should be given as far more accurate term as to the power the loco is exerting. Tractive effort is the theoretical value of what should be developed wheel to rail contact in perfect conditions ( A vacuum) ;D. So I do hope you find the above not too much waffle !! At the end of the day in model form if it pulls what you require over your railway its a good performer !!! ;D So the endeth the lesson !! ???
 
Sorry Gareth, I don't agree with you that Tractive effort and drawbar pull are different things.
Sure you can calculate a theoretical value for tractive effort, but the way to measure it is using the pull on the drawbar. And if your equations are not too far wrong, then you get the same number by calculation and measurement.

Maybe the only difference is that the drawbar pull excludes the force being used to move the mass of the loco itself.

I will continue to use the term 'tractive effort' to signify how much force a loco can exert on a train.
 
Sorry wrong Tractive effort is calculated as stated above on a set equation and therefore theoretical Its very rare for a loco too develop the actual figure the reason for this is there are many factors to take into consideration ! Believe me the list is long and takes in many factors from rail condition to ambient temperature and even atmospheric pressure ! Hence most CME & E prefer drawbar forces as a more accurate result of power as this takes in most of the factors that Tractive effort does not take in !! Suggest you read Dave wardales book Red Devil and also read Porters Work and also Chapeleon and Bullied and Gresley as well yes Tractive effort is quoted , but much more reliance is placed on Drawbar effort as a more accurate measment . But everyone is entitled to there own opinion !! And aslo these are only models and are supposed to be fun .
 
I tested LGB 78400 Stainz. Drawbar pull varies fro 0.28 to 0.35. So more or less same as Playmobil 5258. I expected Stainz to be s better hauler. :-\
 
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