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[quote]QUOTE: Originally posted by GP40-2 [quote]QUOTE: Originally posted by trainjunky29 Dear GP40-2, maybe you have established it, but wait one minute: If torque vs. rpm is Gaussian, wouldn't that mean that at 0 rpm's, you would have no torque? And if you have no torque when stopped, then how does a steam locomotive get things moving? Quite the contrary, a steamer's torque is at a maximum at speeds near 0, and only goes down from there. I admit that I may not have the benefit of college mechanical engineering classes, but I can still read a graph. Secondly, wikipedia is an open source document. That makes it MORE reliable--any malicious or ignorant falacies on the sight would soon be corrected by others either well-meaning or more knowledgeable. If you don't want to use wikipedia, then be my guest to pick some other reference. Without a reference, we could very easily end up arguing over two completely different subjects. Finally, why are we dealing with the largest of the large in terms of random numbers? You can model the Big Boy in Monte Carlo routines if you so desire. I personally prefer brass [:)]! And has anybody noticed that we are arguing about stuff completely different than what this topic started about [8D]? Sincerely, Daniel Parks [/quote] Torque always has to start at zero. You just can't instantly have say 10,000 lbs ft torque out of no where-it has to start somewhere-and that starting point is zero. Now, we are getting into the idea of limits. If you graph the starting torque of any locomotive in small enough increments you will see a ramp up from a zero starting point, a maximum, and a fall back to zero. Second, as you are aware, power is torque X speed. It is possible to have a large torque reading while having zero power. Example: You are pressing hard on a wrench to remove a stuck bolt. When you first place the wrench on the bolt, you don't instantly have maximum force. Your force starts at zero, then your muscles apply all the force they have. If you are applying all your strength, and the bolt still is not turning, you have created maximum torque BUT zero power. Now, the bolt slowly starts to free itself and turn. The torque reading on the wrench will go down, but the power you have produced will go up. Anyway, we were talking about a locomotives power at certain speeds, not it's tractive effort.. I said to graph the Big Boy's Power vs. Speed. I never said for you to graph a locomotives tractive effort curve (which is nothing more than a linear reading of the torque produced by the locomotive's wheels). P.S. Here's a tip for the future: You can say what you want about the Wikipedia, but I guarantee you if you use that thing for a college level paper you will get a nice big fat F on it. [/quote] I agree with most of this post. I do not, however, agree with your earlier post. Here's why: You said that torque vs. rpm was Gaussian. Certainly torque cannot go from 0 to whatever instantaneously. However, using your bolt example, you could put on, say, 150 foot-pounds, and the bolt would still be stuck. You would have 0 rpm's, but plenty of torque (not Gaussian). Similarly, with a Big Boy, you could have full steam pressure in the cylinders, with full torque, but not be moving (say the train you're coupled to has the hand-brakes applied, and you are on a "cog Big Boy" so the wheel's won't slip) (not Gaussian). Additionally, you said, "Trainjunky, we already established that the locomotive's job is to apply torque to the rails, and torque curves are gaussian in nature. Therefore, it is impossible for a steam locomotives power curve NOT to be gaussian in nature." There are three things here I hold issue with: 1.) A locomotive's job is to apply a force through the coupler to the train. Torque really isn't the issue here, it's the mechanical advantage between the crankpin and the tire on the locomotive's driving wheels (wheel and axle, so to speak) (Galileo once described the wheel as the "perpetual lever"). Then of course you have to figure in the friction between the wheel and the rail. Basically, torque isn't as important as force--the piston puts a linear force on the main rod, which creates torque, which is made into a "rectified" linear force by the wheels. 2.) We've already gotten into torque vs. rpm (or speed) curves, but just to summarize my argument: At zero rpm's (or zero mph), torque can vary from zero to whatever maximum the locomotive can produce. A gaussian torque vs. rpm curve would mean no or practically now torque at 0 rpm's. 3.) You assert that since torque curves are Gaussian in nature, horsepower curves are by default. I deny that torque curves are Gaussian in nature, but let's do a little math: For the sake of arugment, let's ignore the force fluctuations throughout a locomotive wheel's revolution (so that a constant force acts on the wheel all the time). Torque equals the perpendicular force times the radius from which it acts. Therefore, the perpendicular force = torque/radius. The force exerted to the rail is the aforementioned "torquing force" times the crankpin radius devided by the wheel's radius, or F = f x r / R (r/R is a mechanical advantage less than one). Finally, Power = Force x velocity. Now let's do some substitution, and you'll end up with Power = torque x velocity / wheel radius (or because there are 550 foot-pounds in a horsepower, Horsepower = torque x velocity / 550 x wheel radius). But let's just stick with Power = torque x velocity / a constant. We are graphing power vs. speed. Obviously, velocity vs. speed will be a linear graph. Even if torque vs. rpm were Gaussian (which I deny), a Gaussian graph times a linear graph would not be Guassian any more than a sinusoidal graph times a parabolic graph would be sinusoidal. Sincerely, Daniel Parks
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