Weighing the trains does make sense...
With a conventional coaster, the mass doesn't matter because the force provided by gravity to propel the train varies proportionally with mass at a ratio of about 32 pounds per slug. The practical upshot of all this is that regardless of the train's mass, its top speed will be the same.
With a launched ride, you're not using gravity to provide the force, but you still need to have enough energy to overcome gravitational force (which, again, amounts to 32 pounds per slug) if you plan to make it over the first hill. Since the force of gravity varies with mass, the amount of energy you need to climb the tower will be different for every train. Consider a 100' tower...To coast to the top you need an initial velocity of about 80 feet/second. If the train mass is 187.5 slugs (weighs 6,000 pounds) empty, you'll need an initial force of about 480,000 pounds to get it moving fast enough to go over the top. Fill that full of riders, and the train mass goes up to about 468.75 slugs (weighs 15,000 pounds), which means now your launch has to be 1,200,000 pounds.
But if you launch the empty 6,000-pound train at 1.2 million pounds, you'll end up shooting it off at 200 feet/second (136 mph). So you can see there's a certain advantage to knowing the vehicle mass when you fire it off with a launch. And furthermore, you can see why the cars on
Superman: The Escape at SFMM don't always go the same distance up the tower!
--Dave Althoff, Jr.
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*** This post was edited by RideMan on 1/30/2001. ***