On half-loading trains... the physics

I don't think you're listening. How do you know what the park does or doesn't want? Have you asked them? Are you Monty's right-hand man? A Swiss engineer?

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

Correct me if im wrong, but I think the most logical thing to do is to put a kicker wheel or two at the top.

Let's just hope they don't have to contemplate whether or not to half load this Friday....what happened to the smooth operation I saw during BW?
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HW 2K3: 1

Kicker wheels move trains on level track... they aren't going to pull a train over the top.

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

Jeff, your way of trying to prove someone wrong is to ask how they know what the park wants. You resort to it in pretty much any debate, and that's why I stopped posting so long ago. No, I am not affiliated with CP. No, I don't know Monty. No, I am not a Swiss engineer. But that has nothing to do with what I am asking. I am a smart person using basic knowledge of physics and common sense and I am not even stating anything as fact. In fact, my entire post was based on a question. Do you know the answer to that question Jeff? Is the launch force fixed at a certain value no matter what the outdoor conditions are? If so, it would be nice if you told me. If not, as I suspect, continue to ask me how I know what the park wants and feel like you've "gotten me." Either way I've got too much work to do than continue a debate with you.

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CWRU '07

Acctually Jeff, Kickers wheels would help prevent rollbacks on TTD or prevent the trains from stalling. In fact, Dodonpa in Fuji-Q Highlands has a kicker wheel ontop at the crest of the tophat. Its highly affective in preventing rollbacks or stallouts. Here is a pic....

http://www.rcdb.com/installationgallery1423.htm?Picture=6

Kicker wheels dont just work on level track, They can be used on top of the top hat. I think with TTD, This would be very useful and we would see alot less rollbacks or slow moving trains over the top.

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- Dennis
When I die, They'll read this And say a genius wrote it.
2003 Count - TTD: 3 MF:18 WT: 30+
http://drinkduff.com/

Stalling is one thing, but stalling or even slow passes over the top don't happen frequently enough to make a difference.

Allan: Yeah, you're right, I do use that point all of the time. You know why? Because too frequently people talk about what they "know" when in reality it's just guessing or wishing something to be true. It has been going on ever since AOL started offering Internet access.

You've said twice now that, "Yeah, the ride does have a capacity greater than what is being used and CP does not want to reach it because it would stress the system." Again... how do you know this? Sure sounds like you're trying to state a fact to me.

If I had the answers, I wouldn't have started this topic. The one thing I do know is that the park has a greater emphasis on capacity than any other park in the world (with the possible exception of the Orlando Disney properties). All in one statement, you say that they don't want to reach higher capacity, and that doing so would "stress the system." The first point is ludicrous and the second you're not qualified to make.

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

Jeff, I think when Allan uses the word 'capacity' he's talking about the capablilties of the launch system, not rider capacity.

All I know is that a week ago, the line moved much faster with half loaded trains than it did when every other train was rolling back. I'm curious to see what happens tonight. Gonna be cold again. If it runs the same as last Friday, I think we may have all learned something here.

Of course the line moved. Taking 16 people out of line every two minutes is better than taking 24 out of line every ten.

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

Thanks Scott for pointing out that Jeff did not realize I was referring to the capacity of the launch system. My post focused on a potentially fixed launch force which was not even close to the system's capacity. It had nothing to do with rider capacity. I just assumed that was obvious. Sorry for the confusion.

So, back to my original question. Is the ride set to launch with equal force every day regardless of conditions? Because if it is, adding new, uncontrollable resisting forces such as stiff wheel bearings due to cold weather may cause it to roll back unless a controllable resisting force (passenger weight) is partially removed. If the launch force is varied according to conditions, this point is moot.

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CWRU '07

I don't think front loading the train will help it when it crests. Presumably the amount of energy imparted on the train in launch will get the CoM up to a certian height. It will hit this height on the way up rather than the way down, regardless of whether you frontload or backload the train. If this height is > 415' (wherever the CoM is when the train is equally loaded and perfectly balanced on the top) you won't rollback. If it's less than that, it will.

I think.....

One thing I have noticed with my K'nex is a lightly loaded train will often travel faster than a heavily loaded train. I have a feeling it has to do with the normal force exerted on the wheel bearings creating more friction. It may also have to do with the heavier train causing more sway in the structure, but I don't really know that analysis.

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A rollercoaster? What's that? Is it fun?

As Gilman mentioned on CB, Monty Jasper apparently said at CoasterMania that launch speed is determined by the speed at which the previous train crested the top, starting at a certain base speed, so it's not an "equal force" for every launch.

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

Exactly, Jeff.
No, it's not an equal force each time. The system adjusts itself, apparently, based on the speeds of previous trains. When there hasn't been a previous train for a while the system will reset to a default speed. While the default speed can be changed (and has been tweaked through the early days of the season and I'm sure is still being played with) it is not adjusted automatically.

Let's see if I can come up with a hypothetical example. Now, these are just numbers I'm pulling out of my butt to illustrate what I got out of Monty's explanation at Coastermania. I could be way off base, or I could be right on. Now, mind you that the computer probably has a complex mathamatical forumla that it uses to calculate the adjusted speed... this example is in no way scientific. On to the example:

Let's say the goal speed at the top is 3MPH.

Train 1 launches at the (hypothetical) default speed of 117MPH and rolls back after almost reaching the point of no return.

The system adjusts the launch speed to 118 and Train 1 launches at 118MPH. The train clears the tophat at 1MPH. That's not fast enough.

The system adjusts the launch speed again to 120MPH. Train 2 launches at 120 and clears the tophat at 5MPH (this could be a change in the mass of the train affecting the kinetic and potential energy and other physics garbage... but that's not what this example is about). That's too fast, so the system drops the launch speed to 119MPH.

Train 3 has a different total mass, so when it launches at 119MPH it clears the tophat at 2.5MPH. That's getting pretty close, so the system adjusts back to 120MPH.

Train 4 launches at 120MPH and crests at exactly 3MPH.

Train 5 launches at 120MPH and crests at 1MPH so the system continues to adjust.

Get the picture?

Top Thrill Dragster's launch is speed based, not force based, so get the idea of being dependant on weight out of your head, folks. Given the fact that the launch speed is dynamic I can't find a single, logical reason for front-loading the trains other than a last ditch effort to solve a problem that really shouldn't exist in the first place.

It seems to me that front loading is basically a "hey, let's try it and see if it works" kind of thing. I'm not convinced that it's helping and that it's not coincidence. Sure, it'll help the train fall forward instead of back when it stalls at the very top, but I really can't see how a lighter train would affect your average rollbacks.
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- John
*** This post was edited by Michael Darling 9/26/2003 11:52:01 PM ***

Heavier train => greater normal force in wheel bearings => more friction.

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A rollercoaster? What's that? Is it fun?

That difference in bearing friction would be negligable. The bearings aren't exactly a spool on a stick- they're engineered so that there is little difference between the friction in the bearings between a full train and an empty train.

When was the last time you saw a coaster train slow down because it was heavier? The loaded train will have more kinetic energy than the empty train, overcoming the difference in bearing friction. Yes, there will be a difference in friction, but the difference in kinetic energy will be greater than the friction.

You're using words that make it sound like you know what you're talking about (even though I'm sure you do having an @mit.edu e-mail and all ;) )when you aren't really putting all the thought into what you're saying, aren't you?;)

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- John
I Snap Flyers
*** This post was edited by Michael Darling 9/26/2003 11:59:31 PM ***

Umm....just because I have an idea that you don't agree with/understand, doesn't mean I'm talking out of my ass.

Regardless, in a frictionless environment, equal speed would result in equal height. Yes, the train has more kinetic energy, but it has to use more kinetic energy to reach the same height. (You'll notice that m drops out of the equation). Thus, bearing (and other friction) would probably make the difference. Especially at 120MPH. Granted, I don't really know how much of a factor bearing friction is compared to other frictions.

Re: When was the last time....

As I mentioned above, my k'nex coaster definitely travels significantly faster when empty. This is obviously a completely different system, but it is a model of a real coaster and I still have yet to explain why it travels faster empty.

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A rollercoaster? What's that? Is it fun?
*** This post was edited by ApolloAndy 9/27/2003 10:16:46 AM ***

All I'm saying is that your idea that the change in friction in the bearings of a coaster will slow the ride down is bunk. Your K'nex coaster is an entirely different thing. I would wager to say that since it's such a completely different device that comparing the two would be trivial.

Think about this: when you load your K'nex train how much weight are you adding? 50% of the train's weight? 200% of the train's weight? Now, think about a real coaster full of people. What percentage of the total weight of the train is people? I'd wager a guess that it's a much smaller percentage than when you load up your K'nex train, hence making the difference in bearing and rail frictions not quite as dramatic.

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- John
I Snap Flyers

Wait, wheel bearings are intended to minimize friction? Say it ain't so, John! ;)

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

The K'nex argument has no relevency not only because of what John said, but if you think the quality of your toy's wheels is the same as Intamin's wheels you're out to lunch.

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HW 2K3: 2

Let me clarify. I'm not saying that the k'nex train is an accurate model of an Intamin train. I am saying that the reason a lightly loaded knex train travels faster MAY provide insight into why the Intamin train travels faster. I then proposed an idea about why it may be so (bearing friction). Whether or not you buy my specific idea, I think my general train of thought is still useful.

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A rollercoaster? What's that? Is it fun?