Or a few questions regarding tractive effort and how it's figured. Jerry, One thing I don't know if you've touched on, during your classes, is locomotive tractive effort. How is it figured for a locomotive? And how is tractive effort affected by things like rain, snow, extreme heat/cold? What about the use of sand? I know it helps increase traction, but can it hinder operations just as it helps? Copyright 2008 Jerry DeBene
Jerry will be able to explain more about how tractive effort is calculated but as a basic it has to do with the weight of the locomotive which is displaced onto the powered axles. therefore in certain weather conditions tractive effort will be reduced due to increased slippage esp wet weather. sand dropped onto the rail head allows the slipping axle to regain traction allowing the train to move. you may have of heard of sand blowers placed behind the axles on locomotives, this has become a requirement on most railways (at least in the western world) as the sand can form an isolation between the wheel tread and the rail head and if the line has a track circuited based signalling and train detection system it can loose detection. There was an incident north of Sydney Australia at a place called Cowan Bank where a Steam train excursion had stalled on a steep grade, it had dropped sand to regain traction, the sand interferred with the trackcircuits and an Intercity passenger service ran into the back of the stalled steam train. 7 people were killed. alot of tests were done as part of the enquiry into the accident and the sand forming an isolation between the wheel and the railhead was given as the cause Copyright 2008 Jerry DeBene
Whoa! I can't say I had heard that before... US locomotives have traction motor blowers that cool the TM's, and also keep a positive air pressure inside the TM case. The excess air is blown out, causing the small 'sand clouds' near the trucks. This is especially prevalent on heavy grades. Now, my Q to Jerry: does this air pressue blow the crushed sand duct from the rails? Does the track circuitry for signalling require the railheads be clean enough to maintain electrical wheel/rail contact? Copyright 2008 Jerry DeBene
don't know about the US, but I have heard stories (esp in the UK) where wet leaves have caused almost a total detection blackout, GATS and Colonel should be experts on that subject, as for sand blowers, the US might not have them, it'll be a small tube located on the other side of the wheel from the sanding tube, I usually dont get that close to freight locos overhere to have a lok but I know after that Cowan bank Incident, they made it law Copyright 2008 Jerry DeBene
Sten is correct about the TE being figured by the weight of the locomotive on the axles. When you have wet rails/leaves, etc. what you lose is 'adhesion'. Or the ability to hold the rail. Applying sand to the rail helps slipping. I haven't heard about the sand affecting the signals in the states.....interesting. I do remember that when I was operating with 765 we had a 'track washer' pipe that we would operate when sanding. It was behind the trailing truck, and basically blew the crushed sand off the rail. I was told it was so you wouldn't be dragging a heavy passenger train across the sand, creating more drag then if the wheels were rolling on a smooth rail. (On a side note....765 had a tractive effort of 69,000lbs.) Mathematicians please step forward if you know an easy way to figure the weight/TE/adhesion of a locomotive. (I usually look at the charts posted for the section of RR I am running on, which shows the ratings of each different type of locomotive.)
Here's a link to a class we did on Trainboard about sanding..... http://www.trainboard.com/cgi-bin/ultimatebb.cgi/ubb/get_topic/f/108/t/000004.html?
Here's some EXCELLENT info on tractive effort, and some applications of it: http://www.alkrug.vcn.com/rrfacts/hp_te.htm Copyright 2008 Jerry DeBene
Considering that the contact patch area between a locomotive wheel and the rail is about the size of a DIME; its amazing they get any adhesion at all! IMHO Copyright 2008 Jerry DeBene
that in a way is why they get so much adhesion, a Dash 9 weights around 205t and sits on the equivalent of 12 dimes - that's 17t per wheel Copyright 2008 Jerry DeBene
Its still amazing to me!!! I guess you can go back to the old theory that when a woman wearing high heels steps down heel first, there more pounds per square inch being "applied" in that small area than when an elephant steps down. Copyright 2008 Jerry DeBene
Sten is correct in terms of sand causing electrical isolation to track circuits. Sand is a natural insulator therefore enough sand placed on rails will electrically insulate the wheels from the rail. I have seen it occur on several occassions. To prevent this occurance locomotives have blowers to remove excessive sand from the rails. Copyright 2008 Jerry DeBene
In the UK, leaves not only may cause loss of train detection but also loss of power supply in third rail areas in the UK. The leaves act as an insulator between the pick-up rail and the collector shoe eventually stalling the train. The end result of the Cowan accident was testing done using the same grade of sand at the same rate of application crushed under the same weight. The electrical properties of such that it required over 300V AC to break down the insulative qualities, much higher than any currently used track circuit voltage. Copyright 2008 Jerry DeBene
Don't know if you've ever seen this or if it'd help. http://www.alkrug.vcn.com/rrfacts/traincalc.htm Copyright 2008 Jerry DeBene
Thanks hope to have need for one somedday but as for now it's all forgein and mind bogling to me. Hope it's something that's useful to engineers since it was devolped by one. Copyright 2008 Jerry DeBene
