There can be 6 inches of slack per car in a train. This can help you start a train rolling as you stretch out the accordion one car at a time. Remember the locomotives only weigh so much and the coefficient of friction of steel wheels on steel rail is only .03 or so (even if you're sanding the rail). Getting going can be tough. And being in the 100th car back can give you a bad case of whiplash as the momentum of 99 cars moving at 1/2 mile per hour accelerate you to 1/2 mile per hour instantly! But the slack can also play havoc with the train over the road. Imagine a slight grade, followed by a dip, followed by another grade and a 100 car train of loaded coal hoppers. The engines strain to take you over the first grade and you stretch out all the slack on the way up. But on the way down, you compress the slack out of the train and then play 'crack the whip' on the way up, pulling the slack back out. If you're lucky, you don't break a coupler and make 2 train segments. Regards, Bob S.
On Tue, May 26, 2009 at 8:08 PM, Adam Maas <[email protected]> wrote: > On Tue, May 26, 2009 at 8:03 PM, Joseph McAllister <[email protected]> wrote: >> On May 26, 2009, at 07:18 , Graydon wrote: >> >>> The fundamental limits on train size are engine traction and drawbar >>> strength. >>> >>> Remember that when starting the train, at some point the engine to first >>> car drawbar has the entire mass of the train on it; this turns out to be >>> more of an issue than engine traction. Past a certain size, you get an >>> awful ping noise as a drawbar breaks, and then you have *two* trains. >> >> Isn't the drawbar heavily spring loaded, so as to allow the engine to at >> least get it's wheels turning a tiny bit before the weight of the train is >> slowly, but quickly, pressed upon it? I'm talking only a few inches of >> spring compression with a heavy load, but it does change the math a bit. >> >> Am unable to find any drawings or descriptions in cursory search, so I may >> be mistaken, confusing model railroad engines to line engines. Anyone know >> fer certain? >> >> >> Joseph McAllister > > Yes, and before starting a large train they push it together to take > up the slack, which allows the train to get teh front cars moving > before the rear cars, reducing the total force required as you only > have to overcome one cars coefficient of static friction at a time. > -- > M. Adam Maas > http://www.mawz.ca > Explorations of the City Around Us. > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and follow > the directions. > -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
