On half-loading trains... the physics

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?

Up until Friday I was with you Jeff, but now I'm not convinced. Yes the train has less momentum with fewer riders. But I think it's more of a balance issue. When the train is right on the edge of making it, the extra weight at the front of the train might just be enough to help it over.

There is less drag with less riders... that would be my guess as to why it has less rollbacks with less riders.

Front load the train, and you have the train's center of mass past the center of the tower when it stalls. If its center of mass is past the center of the tower it will go on down the down side instead of rolling back down the upside.

There is still something wrong with that analysis, I think, but at this hour of the night, it's a good starting point. :)

--Dave Althoff, Jr.

Also the extra weight of the train creates a greater friction force. I have never witnessed a rollback nor a half-loaded train in my visits, and I really find it hard to believe that half-loading a train makes a huge difference. However, I guess since successful trains barely make it over the top, any slight different could cause a rollback. I would attribute rollbacks with full trains to greater friction force and a potentially greater distribution of weight towards the back. Otherwise, it is most likely wind, imperfect motor function, etc. One interesting thing is that I notice they strongly emphasize keeping your arms down. Is this just to state safety rules for the sake of maybe insurance or is this an attempt to reduce wind resistence by minimizing the surface area of the train and its riders?

Not sure how much water this will carry, but fewer riders means less weight in the trains which means less load on the launch which means you can crank it up a bit more to fight the wind. Add in moving the center of gravity forward in the train and you've got somewhat reliable operation.

Based on what I saw Friday night, dare I say that TTD might have "winter rules"? We all know that Intamins don't like the cold. They might just have to half load trains for the last few weekends of the season.

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

After what I experienced last Friday night half loaded trains are the answer.

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Dan Haverlock
TTD Rollbacks 0 For 26
"get a job man!"

But why? Give me some science here. You half-load a train and sure, the train's center of mass is forward which may help it on a close call. But how much help does it really offer? I want math, because I don't believe it's significant enough of a difference to warrant cutting the ride's capacity in half.

In fact, if it's the right thing to do, why is it then that every loaded rollback I saw was half-full? Call me a skeptic, but at that point I'd question what the point is when you rollback anyway.

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

Skeptic.

Sorry, Jeff, I don't have any math for you, but I will chime in to agree that moving the center of mass a bit forward will (theoretically) help with a close call or two.

But then wonder if the reduced capacity would be less than launching full trains and having to wait for a train to reset after a rollback. Are you going to move more people through the ride if you just take your chances? Is it really worth it in the end?

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- John
I Snap Flyers

When you move the center of gravity forward, the train has less distance to cover before it reaches equilibrium and starts downhill again. It may only be 10 feet or so, but that may be enough to prevent a rollback.

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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.

The answer is probably very complex and can't be solved with just college physics. However, another possibility is that the hydraulic system is able to launch a lighter train faster. This of course makes perfect sense since it has less load. One would think the launch is adjusted to account for differences in train weight, but this may not be the case. Please can someone give a definitive answer on that? If it is not adjusted for weight, then I'm sure it can launch a half-loaded train just a bit faster. Add that to a reduced friction force and a moved center of mass, and the train makes it over easier. I think it is really a combination of very slight advantages that make it appealing enough to reduce capacity by half.

As its been stated here many times, the ride aims for a certain speed. It does not weigh trains.

A 10,000 hp motor is not even a factor in adding a few hundred pounds worth of people to the ride.

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

Did I miss something, or are they now only loading the trains half full? Is this for the remaining season, or just when the winds are up?

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Life is too short...go ride a coaster!!

Friday also convinced me that half empty trains make a huge difference. Just two people were the difference between a rollback and a complete circut on friday night. Eight people per train cleared the tower but ten people was a guaranteed rollback. One particular group of people got three concecutive rollbacks before two people were removed from the train and then they cleared the tower. It was a very windy day so hopefully this isn't a friday night ritual for the remainder of the sesaon!
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C.P. Visits in 2003: 14
Dragster Rides: 9 (2 Front Row)

A small change in balance might significantly change the odds because the window of tolerance for launch speeds is so narrow.

I recall from RideMan's transcript of CoasterMania that there is a 2-3mph window between rollback and excessive negative G's.

Think of it as a ratio; the numerator is the balance, and divisor is the launch speed variance. Since the divisor is small, small changes in the numerator have a greater impact on the overall ratio.
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It's not war, famine, or pestilence; it's only downtime.

To answer your question Jazzman I was there on this past Sunday and they were launching fully loaded trains. It must just be when the winds are high.

Edit: typo

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CP2K3: Visits: 34 Drag races won: 17
*** This post was edited by Scott Cameron 9/23/2003 5:01:38 PM ***

The odd part about friday night was half full trains where making it over more consistantly than empty or full trains. The problem that rollbacks cause it more idle time for the whole system to cool down. When they do get it going it keeps going but getting it there is the hard part. The point of balance is one factor but it certainly isn't the only. Another factor could be less weight means less kinetic energy but more weight changes the amount of pressure that needs the be built up in the accumulators. The intersection of the two factors might end up somewhere between a fully loaded and empty train.

There is likely more factors involved. After the system starts running consistantly more rows can be phased in. I remember back in july they eventually shut down because they couldn't get it over most of the time. I think they may have stumbled over this idea one of those nights.

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Eddy the retard is awesome.

I agree... trains sitting idle no doubt does more to cause the rollbacks. We've all seen how sluggish Millennium Force is when it's cold, no doubt Dragster is no different.

What I take issue with here is that many of you consider seeing a half-loaded train make it as "evidence" that it's the right decision. Well, why? Think about it... if they manage to make it over fully loaded on any other day then the problem isn't how many people are on the train. That's not logical.

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

Obviously the cold weather and the wind were major factors that night. I wonder if those factors combined with the fact that the ride hadn't run for four days might have caused the problems. I don't think that half-loading is always going to be the solution, but Friday night it worked.

Seeing 3 rollbacks in a row, then watching the ride run flawlessly with 8 riders is "evidence" to me that it was the right decision for that particular set of circumstances.