On half-loading trains... the physics

I'm still going with drag.. people aren't aerodynamic.. but what do I know...

Neither are the giant headrests which mostly negate the exposure of humans anyway.

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Jeff - Webmaster - GTTP - My Blog
Blogs, photo albums - CampusFish
What time does the water show start?

I've never seen a rollback..where does usually make it on the tower during these rollbacks?

It usually makes it to the point where the front few cars are past the middle of the crest. I hadn't seen a rollback until one day I went and saw seven. They happen a lot in the morning, after it rains, or if it has been sitting for a while.

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Phillip Studans said:
They happen a lot in the morning, after it rains, or if it has been sitting for a while.

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Yes, or if it's daytime, nighttime, a day of the week ending in "-y," hot, cold, or dry.

;)

The rollback I saw yesterday was exactly as Phillip has described, the train made it to the top but just short of the point of no return. In a situation like that, having the back of the train empty would make to train go over the top.

Could they just make the train go faster to get the same results? Maybe, but they have to pay attention to positive Gs in the pull up to the tower. When I rode yesterday night, the last three rows were empty and a glance at the speedometer on the hydraulic building showed 124mph. Could they ramp it up to 126mph or more? Probably, but would the G force still be in the range CP wants them to be? Who knows.

Empty rows is a solution for marginal conditions when they don't want the trains to run unusually fast. I have to believe the people at CP know the ride well, and they are making a choice between increased speed or a forward center of gravity, based on what is best for the riders and the equipment.

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I'd rather be in my boat with a drink on the rocks,
than in the drink with a boat on the rocks.

I think the number of times as a percentage that having the train's center of mass more forward by half-loading the trains would help is remarkably small. I haven't collected data, mind you, but that's from casual observation. Based on that, it's not a remedy, it's just a capacity killer.

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Jeff - Webmaster - GTTP - My Blog
Blogs, photo albums - CampusFish
What time does the water show start?
*** This post was edited by Jeff 9/29/2003 12:06:29 PM ***

Front loading does move the point of no return (tm) down the tower a little bit, but I don't see how it's really that signifigant of a distance. The trains weigh 5 tons, how is a difference of losing 500 or 600 pounds in the rear going to affect it a noticable amount?

Pete- It never occured to me that a reason for not cranking up the speed a little more (since we all know the ride is easily capable of 130MPH +) might be the Gs on the pull-up. Also, another consideration might be the wheel-less catch car who enjoys getting really hot. Although, I can't see how that'd be a problem on a day like yesterday.

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- John
I Snap Flyers

Edit: punctuation
*** This post was edited by Michael Darling 9/29/2003 1:41:17 PM ***

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Jeff said:
OK physics whizfolk... explain to me why half-loading a train will prevent a rollback, because I'm not convinced.

Would not a heavier train tend to stay in motion longer than one that is empty? Maybe I'm just a grumpy skeptic, but I would really like to know the physics behind the decision, if any physics were considered at all.

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Jeff - Webmaster - GTTP - My Blog
Blogs, photo albums - CampusFish
What time does the water show start?

On HP's Lightning Racer, the heaviest train always wins regardless of conditions, so you indeed are correct.

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I was super before Superstew was cool!

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As an engineering college student, here's the way I see it. If the train is going the same speed at theend of the launch, which I am assuming is true by what Jeff said and the sign at the bottom, it will (under ideal circumstances) go to the same height regardless of weight (er, mass that is). It's a conservation of energy problem. Kinetic energy -> Potential energy.

1/2 * m * v^2 = m * g * h

where m = mass, v = velocity, g = gravity, and h = height reached. The mass cancels out. What it comes down to is that a bowling ball going 120mph and a fully loaded dragster train going 120mph will, in theory, reach the same height. At least their center of mass will. That's what matters, center of mass. Regardless of where it is in the train, it will try to reach that height. Oh, and path doesn't matter. The height can be either straight up or over a 100 mile hill. It's the height above the starting point.

*but*

The world isn't perfect, which makes an extremely simple problem infinitely complex. The fact of the matter is that the train (center of mass) just won't reach the height given from the forumlas above. Probably not the bowling ball either. The biggest complexities would be air resistance and wheel friction. People tend to be more aerodynamic than flat seats, so that probably will actually help matters. This is where the guess-work begins. But my gut instinct is friction. The friction won't be a whole big problem on the way up, since it is in "freefall" then, but at the top when it starts to level out. Since path doesn't matter, it will still try it's hardest to level out, but the heavier the train the more frictional force there is slowing it down.
Friction = µ * m * g (µ being coefficient of friction - a constant unique to each material). So even a small amount change in weight can greatly effect the force of friction between the wheels and the track. The is also an issue (perhaps moreso) with the upstop wheels. An object moving doesn't like to change directions. The massive airtime on the top is putting a large force on the bottom wheels as well as the riders.

Now please remember that, while the top part is fact, the bottom part may or may not be the reason why it matters. That was just a best-guess. I would tend to believe that it wouldn't matter enough to change things. Hope this helps though Jeff.

--James

*** This post was edited by jdoty 9/29/2003 8:21:52 PM ***
*** This post was edited by jdoty 9/29/2003 8:23:54 PM ***

A perfectly logial explanation, but I still contest the the difference in friction between a loaded and unloaded train would be so minute that it can be ignored. There are just so many variables that would be changed that I refuse to believe that friction from a loaded train is the problem.

You get bonus points for actually including a Mu in your equation, though!
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- John
I Snap Flyers

I agree... I just can't imagine the difference in friction is that important in this case. Now that I see the science, I in fact am even more confident that half-loading a train is not a solution.

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Jeff - Webmaster - GTTP - My Blog
Blogs, photo albums - CampusFish
What time does the water show start?

I don't want to sound like a wiseguy here, but what do People Who Know(tm) say about this??

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Scott W. Short
mailto:scott@midwestcoastercentral.com
http://www.midwestcoastercentral.com

They(TM) say it probably has something to do with saving money or some perceived means of saving money. The word on the street this year is "cheap," as in, "We're being so cheap this year that it's negatively affecting operations just so we can meet that cash distribution goal."

Although as a serious unit holder, I don't mind that last part.

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Jeff - Webmaster - GTTP - My Blog
Blogs, photo albums - CampusFish
What time does the water show start?

Sunday a half-loaded train rolled back (which in turn made someone in my party vow never to ride). They fired a few more half-loaded trains and then went to fully loaded, both making it over in the same fashion.

I am definately not an expert but is weight factored into the system? Meaning if they factored weight and track temperature into the situation would it maybe help getting the trains over? Say maybe a sensor that detects the weight of the train when it rolls into launch area and a track temperature sensor.Then say if there was a train which is 10 lbs. heavier than the last train that successfully made it over. Plus we have seen as it gets colder more and more trains roll back as noted previously about Millie. I am surprised by now that Intamin has not incorporated track heaters into their loading areas of the track. Obviously you can throw a turbo heater or two under there but you would think radiant heat would be more efficient and effective at keeping the wheels and bearings at optimal operating temperatures when trains are idle waiting to load. Earlier in the season we know the hydraulic system was to blame for rollbacks. Now it seems as those problems were ironed out. Looks to me like a temperature issue at this point. You said they sent one train 3 times which did not make it. On the 4th time it did. Seems te wheels would have been far warmer on the 4th launch than the first three. Just my 2 cents.
*** This post was edited by GetOverIt 10/2/2003 6:48:25 AM ***

No, the trains are not weighed.

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Jeff - Webmaster - GTTP - My Blog
Blogs, photo albums - CampusFish
What time does the water show start?