Train weight and pulling power

[gregc]

Lithonia Operator

Now the train is stopped on the ruling grade, with no slack. Can the engineer get the train going?

my understanding is that max horsepower in a diesel locomotive is available at any speed.   Horsepower is work / time.    work is force multipled by distance

at least on level grade, the force applied needs to overcome the friction of the bearings which is dependent on speed.   But consider, for a moment that the friction, hence force is constant at any speed.   Then the horsepower required depends on the work being done and is proportioinal to the distance the force is applied over

this means half the horsepower it required at half the speed, or that twice the force is available at half the speed.

when going up a grade, when force must also overcome a percentage of the weight of the train, the available horsepower will limit the distance the train can move at the higher force.

so when facing a steep grade, the distance traveled per unit time may be small, but not zero.

of course this is not true for a steam locomotive where horsepower is not constant and depends on speed. 

[Overmod]

gregc

my understanding is that max horsepower in a diesel locomotive is available at any speed.   Horsepower is work / time.    work is force multipled by distance

Maximum 'horsepower' in a diesel locomotive is imposed by the characteristics of the prime mover.  But the curve close to zero road speed is nowhere near as extreme as often drawn (especially in early EMD 'propaganda') as the effective instantaneous 'tractive force' (which is the only thing that matters when calculating resultant with train resistance) is both adhesion- and traction-motor limited.

Even with AC drives there are some limitations on the practical near-locked-rotor torque that can be produced from "maximum horsepower for traction" at the motors (e.g. from the combustion engine through the generator, inverter system, and cabling losses).  If you look at how AC motors generate torque off synchronous speed you will understand the electrical 'slip' involved; modern synthesis drives can maximize the effective torque at a given speed.

Of course, you're familiar with DC motor limitations, which are far more severe, and dramatically limit both applicable torque and effective duty cycle below about 11-12mph road speed.

There are ways to overcome much of the low-speed disadvantage of the reciprocating steam locomotive -- some of which are nominally wasteful of steam mass flow and 'associated considerations' but which can be made efficient with the correct forms of traction control and valve gear.

[timz]

No diesel locomotive can generate full horsepower at its wheelrims at 1 mph. At 30 mph today's 4400 hp locomotives can produce maybe 3800 hp at the wheelrims; at 1 mph, 3800 hp would be 1,400,000 pounds of TE.

[gregc]

i agree

my point is that the drawbar force is not proportional to horsepower.   it's inversely proportional to speed. 

so maximum force is at the lowest speed and of course limited by max tractive effort (i.e. weight on drivers)

[tree68]

I've heard that a 5 HP Briggs and Stratton could move a sizeable train (on flat ground) given the traction and suitable gearing.  Not fast, but it could move it.

I've also heard that HP=speed.  This is where the HP/ton factor comes into play.  If you want to get the load over the road quickly, pile on the HP.  If you just want to get the load over the road, put on just enough power to do so.

[BaltACD]

tree68

I've heard that a 5 HP Briggs and Stratton could move a sizeable train (on flat ground) given the traction and suitable gearing.  Not fast, but it could move it.

I've also heard that HP=speed.  This is where the HP/ton factor comes into play.  If you want to get the load over the road quickly, pile on the HP.  If you just want to get the load over the road, put on just enough power to do so.

Watched a B&O SW-1 with all of 600 HP and 30 years service move 8700 tons of cement out of Clark Ave. Yard in Cleveland to Brooklyn - of course it took 3 hours to go that 5.7 miles.

[timz]

No need for 5 horsepower -- a 0.1-horsepower person can move a train if his winch rope runs around a sufficient number of pulleys.

Power is force times speed -- in other words, force is power divided by speed. If you can accept the necessary low speed, you can produce any needed force from any power source. As long as power remains constant,  you can double the force by halving the speed, and you can keep doing that forever.

[SD70Dude]

What is the HP rating of a typical car-moving winch?

[Northtowne]

SD70Dude, right about the SD40-2. A yard that I watched for a long time had a SD40-2 switcher, then changed to an SD60, now have to ease starts to move the same amount of cars.

[monon99]

With the train stretched on a grade it can be tough to restart a train. Sometimes sand, a little independent brake to keep the wheels from hopping, will get the job done.

If your power just doesn’t have the grunt(let’s say an emd), you can set a little air, shove back gently to bunch the train, set full service when the eot beeps and says movement.

Now take a deep breath, let everything settle down. Go to suppresion on the air brake, wait for that to settle, no hissing. You will get a “slow release” like from a minimum set. Brakes will now release one car at a time from the head end to the back(assuming no dp). Now you can throttle out and start moving a few cars at a time. You better have a good feel of your train. Gradually you can move the whole thing.

I’ve used this a lot on the hilly Monon subdivision, thankfully the skilled hoggers who worked that line taught me well.

[MMLDelete]

monon99

With the train stretched on a grade it can be tough to restart a train. Sometimes sand, a little independent brake to keep the wheels from hopping, will get the job done.

If your power just doesn’t have the grunt(let’s say an emd), you can set a little air, shove back gently to bunch the train, set full service when the eot beeps and says movement.

Now take a deep breath, let everything settle down. Go to suppresion on the air brake, wait for that to settle, no hissing. You will get a “slow release” like from a minimum set. Brakes will now release one car at a time from the head end to the back(assuming no dp). Now you can throttle out and start moving a few cars at a time. You better have a good feel of your train. Gradually you can move the whole thing.

I’ve used this a lot on the hilly Monon subdivision, thankfully the skilled hoggers who worked that line taught me well.

 

Thanks. I was wondering if that sort of thing was ever done.

[BigJim]

tree68

I've also heard that HP=speed.  This is where the HP/ton factor comes into play.  If you want to get the load over the road quickly, pile on the HP.  If you just want to get the load over the road, put on just enough power to do so.

Quite true. In times of poor rail adhesion, it was not uncommon to be able to take my tonnage train over the mountain in the sixth notch in order to keep from losing traction. But, that was what was needed, it was just slow as all get out!