On half-loading trains... the physics

I don't take it as evidence that it is the right decision---I was just trying to explain why half-loading could make a difference.

Edit: technically, I was taking a Wild-A$$ed-Guess as to why it might make a difference

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It's not war, famine, or pestilence; it's only downtime.

*** This post was edited by Brian Noble 9/23/2003 3:41:27 PM ***

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SteelMonsters said:
The odd part about friday night was half full trains where making it over more consistantly than empty or full trains.

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Right there is the evidence. It's not an issue of weight. Empty trains and full trains have the same center of gravity.

The reason half full trains made it over, like I suggested above, is that the center of gravity is forward. That is the trick to make it work. Equal energy means the full, empty or half full trains will make it to about the same point. Since the trains that were forward loaded require less distance to reach the point of no return, they make it over the top. The other loading configurations don't.

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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.
*** This post was edited by Pete 9/23/2003 3:45:51 PM ***

I see the whole thing with the center of gravity too, but like Jeff said, that is only going to take affect when the trains are extremely close. Physics would tell me that a heavier train would make it over easier. Since mass has nothing to do with the -9.8 m/s/s that the train is accelerating at while traveling upward, the fully-loaded train isn't going to go up any less farther than a half-loaded one. Well, when the train turns horizontal for that moment in time, the acceleration will only be equivalent to the friction coefficent times -9.8 m/s/s. Well, I don't think the friction added with 8 more people is really going to make that much of a difference unless, with all factors included, a very small change would result in a rollback. The heavier train as it turns horizontal would have more inertia making it harder for friction and air resistance to slow down. So, physics would tell me, unless the added friction makes that much of a difference when the train turns vertical, a heavier train would be more likely to make it over the apex. All the rollbacks I have ever seen were of the first train launched and/or empty trains, so I would think that this would be somewhat true. The wind must have an interesting affect on the physics of this monster.

OK, so empty trains and full trains have the same center of gravity... and when they sent up test shots eventually they got one over empty. So again, what's the difference? The fact that you send a train three times empty and it makes it over the last time tells me that it's an issue of cold wheels and bearings. You know how they solved that on MF, they put heaters under the station.

In fact, of the rollbacks I saw on Friday, only one was even close to the apex in the first place. The others didn't get far enough to make the weight distribution of the train matter one bit. I think Sparty says his rollback barely got much past the twist. Half-loading the train will make no difference.

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

Maybe the park should just do adults in front and kids in back? ;)

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AKA Cobraroller on Cbuzz

Okay, here it goes -

Basically from what I understand this 10,000 HP motor, bascially puts out the same amount of force for each launch, since there isn't any type of system in place to weigh the trains or anything along those lines.

The simple formula F = MA (Force = Mass*Acceleration) gives a brief scenario of the launch, with the force being that constant 10,000 HP tug, if you will.

If you were to solve for acceleration here, since that's what we're looking for, then we have F/M = A. In this case, when mass is greater, then amount of Accereration is decreased.

This doesn't even take in to account, that when you have more fatties on the train, there will be a greater amount of friction, since gravity has the greatest effect when the train is parallel to the ground during the launch portion of the ride.

In conclusion, basically the engineers took all the elements such as wind, temperature, mass, etc. and added a degree of contingency, but when all the above occurs, along with a margin of error due to this never being done before, well that's when we get the problem houston. It looks to me like they should have went for the 11,000 HP motor that was included with the SE edition :-)

Hope that makes sense to someone out here.

Later,

Jazz

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

But there not using the full 10K horses of that motor, there not even using 7500 horses. I say that because at the winter tour Monty stated the motor at Knotts farm was enough to get the trains up to 120MPH. Knotts Motor is 7500 HP. (Or something close to that)

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"This second hill is my favorite part of the ride. It is so Cool!"
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"Hey Werewolf lady"
*** This post was edited by Hooper 9/23/2003 9:41:53 PM ***

It probably can, but with all the variables they're facing such as wind, temperature, mass, etc., shouldn't there be a system in place to adjust the force of the launch? I'm sure when it's nice and warm, with a half loaded train and 0-5 mph winds, the trains just fly over. Unfortuneatly, that won't always happen at CP.

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

Assuming the average rider's weight is around 170 pounds, there'll be approximately a 10% weight difference between a full and half loaded train. I think this difference is a little more than most think and could easily alter the launch speed by several mph, giving that extra boost to fight the wind. Normally I'd discredit this theory beacause the launch is supposed to shut down after a certain speed is reached, but how are the sometimes 2-3 mph differences on the radar clock accounted for if this is true? I think the extra mph or so that you gain from the launch combined with the center of gravity idea could help your chances of making it over quite a bit. I'm more than likely putting too much faith in a not so accurate radar gun and common knowledge of TTD, but it does seem that a 10% load difference would have to have an effect on something.

Edit: A couple people posted before I finished, and I'd like to add something. I do agree with the fact that all 10,000 horses aren't being used, but I still think it's probably set at a constant force, which would mean when the train's load changes, something else has to change too.

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HW 2K3: 1

*** This post was edited by mantis_man 9/23/2003 10:05:11 PM ***

The amount of power output from the motors is controled by the pressure that the accumulators are charged to. The amount of pressure involved is over 4000 PSI. I have a feeling that the PLC that controls the launch resets every time a train rolls back. Normaly it might take the information from the last launch to adjust for the next launch but if they have to reset the system, then the PLC might lose that information. Building the pressure more than now will make the train go over, but it's not safe. I think the hydraulic motor is less sensitive to load than most launches. An empty train weighs 5.3 tons, a fully loaded train might very from 6.5 to 7 tons. Usually the first loaded train of the day makes it over dispite the huge increase of weight

The train I watched roll back three times almost made it the first time, the second time it wasn't even close, the third time it was somewhat better than the second time and then it finaly made it over. The speed of the launch doesn't vary much but it makes a huge difference of the speed at the top. Also the speed at the top changes constantly. One train barily makes it over while the next goes over fairly quickly. As long as the train makes it over and doesn't overspeed there is no problem. When the system resets, the pressure changes to a known safe value.

Simply physics only involves one problem and a small number of variables. Top Thrill Dragster has a large number of contributing physics involved and a substantial number of variables. It's not one thing that makes the ride run, many things must happen and accommodate for other variables to make the trains go down the right side.

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Eddy the retard is awesome.

What's all of this talk about hydraulic pressure? You fill the tanks and release by a valve, close the valve when you reach the speed you need. Remember... that motor system allegedly has power to spare.

I don't think most of this discussion is even relevant. Like I said, when the ride is operating normally, a full train launches riders over the top. The motor is the same, the trains are the same, the riders are, for all practical purposes, the same. The only thing different that night was that it was somewhat cooler.

I'm still searching for a reasonable explanation for half-loading trains on the same ride that can operate with full trains. You might argue wind, but at that point in the evening you could see in the midway flags and far less choppy water that the wind had died down to average, or even below average, by 8pm.

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

Were these trains half-loaded with relatively even weight-distribution or was it loaded more to one end of the train?

Well, that may not be important. I know the motor is 10,000 hp and is capable of doing much more than it is asked to do, but CP also does not want to put extra load on this system. Especially given its complexity and propensity to break down. Say they fix the launch power to X, which is a value determined to be enough to make the train barely clear the hill every time in decent operating conditions. Decent operating conditions should include a train full of riders, but the launch force still is partially negated by a larger resisting force when this is the case. Although this extra weight is usually not enough of a factor to make it roll back, it may be when the trains have cold wheel bearings. When the bearings get cold, it creates yet another resisting force during the launch. Since the resisting forces (extra weight to pull + "tight" wheel bearings) take away enough of the pulling force to make it roll back, it is necessary to remove one of the resisting forces. There isn't much one can do to eliminate the cold, so it is best to eliminate some of the riders. Does this make sense?

Much of this discussion assumes that the only options for the hydraulic valves are fully opened or fully closed. I would have thought that "servo" valves would have been used. With a servo valve, the PLC would constantly adjust the oil flow to achieve the desired speed profile. The high pitch “whine” which is heard during launch is characteristic of a servo valve. Does anyone know if servo valves were used?

Like I said, the discussion about the motor's capabilities isn't relevant. And "MagnumAllen," how do you know what CP does or doesn't want to do? The only thing any of us can say we know the park wants is to put as many people over the top of that hill as they can.

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

I think you're missing my point. I am asking if the force of the launch is fixed at a certain value. I know the power of the motor is way beyond what is necessary. That doesn't matter. What does matter is that the force it is set on *may* be what CP believes is ideal (powerful enough to get it over the top, not so powerful that it stresses the system). If it is fixed at a certain value, then that value may not be high enough to get it over the top when a full train combines with cold weather conditions to create an unusually high opposing force during the launch. If CP does in fact change the force of the launch to compensate for colder conditions, then call this point moot.

Wait... you said you "know" they don't want to "stress" the system, then you say you know it has extra capacity. Isn't that a contradiction?

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

This is just off the top of my head but I belive losses due to friction and wind are the big factors here. When they design such a system there has to be an operational range for example "60F-80F". Also things like humidity are accounted for. And of course the wind factor.

Take these 3 things for example and then skew them say even 10% below or above the design specs. What hapens to the coefficient of friction for your system if the temp drops to 50F? What kind of negative velocity impact does a 5mph wind apply from a given direction. In theory by shifting the center of gravity by running 1/2 cars they are simply using a quick fix to a problem they cant control. Perhaps cold weather leads to colder steel and wheels thus alot more frictional drag than expected. The velocity, momentum, etc are drasticly changed by these variables as soon as you start to climb up that 420 foot monster.

As far as a complex math formula goes for this I dont think you can get one because stuff like the *exact* effects of friction on a given coaster and stresses and tolerances etc are things that only Intamin would know, because of course they are the ones who built it. I hope this helps or at least gets us pointed towards a suitable answer.

One thing I just thought of too - Lets look at the obvious. The launch height is fixed. And I belive here is the key - the launch speed is fixed to a tight window. they might have a 100,000 hp motor and it would be irellevent because it is being used to achieve a launch velocity. If any of the variables are just being a pain on a particular day they cant just up the velocity to over 130mph or whatever. At least not without risking riders passing out or something. Again Intamin has got to have all these numbers crunched on calculators.

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. Capacity does not mean maximum available power WITHOUT stress. If CP were operating an automobile, would they want to run it at redline all day? Sure, the car's capacity is whatever the end of the redline is, but can you hold a car at redline and not stress it?