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Why no pre-drops on B&M's anymore?


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I've noticed that more and more new B&M's no longer have the pre-drop. I thought that it was so that the chain didn't have as much tension as it crest the top of the lift. I'm just wondering as to why not do this anymore I thought it looked cool. But the real reason I ask this is to try to explain to my little brother (I'm just now getting him into coasters (he's 11) ), we live in Charlotte and out two B&M's Top Gun (I mean After Burn) and VORTEX have pre-drops and I told him thats how he can tell a B&M coaster out (besides the box middle rail) but when I showed him Led Zeppelin and Behemoth, he told "Those aren't B&M's". Show I showed he the stats on RCDB, he gets it now. But its a question I would like to be able to answer for him (and myself now).

 

Thanks in Advance

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I'm guessing, but I'm sure B&M has better technology now, and therefore does not need the pre-drop to relieve tension on the chain. I actually like the pre-drop, especially on Mantis with the turnaround.

 

From Wiki

 

One feature of Bolliger and Mabillard coasters that is almost universal throughout their product line, and almost exclusive to B&M, is an element known as a "pre-drop" (which is known in the industry as a "Kicker"). This is a short drop after the top of the lift hill and before the start of the first drop, designed to reduce tension on the lift chain. The flat section between the pre-drop and the first drop serves as a shelf to carry the weight of the train, reducing related stresses on the chain. By comparison, on most coasters without a pre-drop, the weight of the train as it begins its descent tends to pull on the lift chain, as the latter half of the train is still being lifted by the chain at this point. More recently, the pre-drop is only used on coasters with curved drops, whereas coaster with straight drops, such as Goliath at Six Flags over Georgia, Hydra at Dorney Park, Behemoth at Canada's Wonderland, and Led Zeppelin: The Ride at Hard Rock Park do not have a pre-drop.
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This is a short drop after the top of the lift hill and before the start of the first drop, designed to reduce tension on the lift chain.

 

Is there any real proof to this statement? Is there a published statement from B or M in a reliable publication? From a mechanical standpoint, I find this hard to believe. (Don't ask me to explain my theory, I don't want to bore you. hehehe) Just seems a lot of times, people just make stuff up to sound knowledgable, and this sounds like one of those things. Not that it's REALLY important, it could be just a matter of an initial design that always worked for them, and for all we know, to pump out coatser designs, that was made the default lift template in their CAD in the beginning.

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Not that it's REALLY important, it could be just a matter of an initial design that always worked for them, and for all we know, to pump out coatser designs, that was made the default lift template in their CAD in the beginning.

 

 

They don't design their own coasters, Stengel does most of the layout/forces calculations. It does reduce lift chain stress, since th chain is gently disengaged instead of the train ripping itself off. This can be heard on a lot of older steel coasters (Arrow and Vekoma), when the train makes a huge clunking noise when disengaging from the chain (Ninja at SFoG is a good example).

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IMO it's quite logical. If the train is on the middle of the lift, the weight of the train is held up by all the chain dogs. Then, when the train goes over the top, chaindog after chaindog disengages and the more weight is put on fewer chaindogs, thuss meaning that the weight of the train is not evenly spread anymore.

 

now, i don't have a PhD so if anybody can prove me wrong, please do.

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Not that it's REALLY important, it could be just a matter of an initial design that always worked for them, and for all we know, to pump out coatser designs, that was made the default lift template in their CAD in the beginning.

 

 

It does reduce lift chain stress, since th chain is gently disengaged instead of the train ripping itself off.

 

You just answered my question! It's not tention it relieves, it's stress, there is a difference here.

 

Once you used the word "stress", and everyone's explanation after it, it fits.

 

Someone needs to change that Wiki!

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I genuinely thought Stengel changed the design because it was cheaper and more efficient maintenance-wise to just increase the speed of the lift chain as the train left the crest of the lift hill?

 

Perhaps I am wrong, but I would be 95% percent sure that from the quote I read from B&M at one point suggested that it was simply wiser from a design stand point that as the weight decreased on the lift chain they simply sped up the motor to balance the tension?

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^ So if they did speed the lift motor up, why is it that Six Flags coasters still do the whole slow down to a crawl thing at the top?

 

I can't stand up for every single Six Flags roller-coaster in the chain and neither can you. Different parks, different maintenance teams, different parts used to run different coaters. Simple as that. However, I went to the extreme effort of using the search on TPR and found this for you:

 

http://www.themeparkreview.com/forum/viewtopic.php?t=38592&postdays=0&postorder=asc&highlight=lift+hill+start+drop&start=20

 

I asked this same question to a gentleman that had worked with constructing a a couple B&Ms in the US, and this is what he had to say. There were two main factors in the origin of the B&M pre-drop:

 

1. Evacuations. Supposing a train crested the hill and balanced prior to going over because the chain stopped, getting people out of those first few cars really is quite inconvenient. If you have a flat area with a catwalk under it, getting those first two rows unloaded becomes much easier, than with the modern straight drops.

 

2. Perhaps the biggest reason was having to do with chain wear and tear. You'll notice B&Ms all have "feeder" wheels at the base of their lift. This is designed to match the speed of the train with the speed of the lift chain, so that when they engage, it is one fluid motion. The result is less stress on the chain. The pre-drop was implemented at the top of the ride to once again reduce tension and wear on the chain when the train began to disengage. After the first chain dog on the train has disengaged, there still may be one or two more still lodged in place, and the pre-drop made it so that for the most part, all of the chain dogs release from the chain at the same speed. These two features significantly reduce the amount of strain placed on the chain, and as such increases reliability.

 

(By contrast, I might point out, that most all other coaster companies do not have these design features on their lift hills. Whereas on most coasters, a cracked chain is not unheard of, B&Ms have a stellar reputation- their chains hardly ever break.)

 

Ok, anyway so why did they get rid of the Pre-Drop?

 

From what I understand, there is a simple, "duh", solution that solves both of the problems stated above, that was simply looked over in the design of the first B&Ms: Speed up the chain as the train starts to crest over the hill! A proximity sensor detects when the first car has reached just slightly passed the apex of the lift, and signals the lift motor to speed up. The end result is that the dogs release from the chain because the lift hill speeds up to match the speed of the train cresting and falling down the first drop. A keen eye will see on Nitro and Hydra that the chain speeds up as the train starts rolling off the top of the ride.

 

And because the chain motor is speeding up, it gives that extra little "nudge" to the back cars just in case the power were to suddenly kick out, so that there is enough momentum to push the train all the way over the lift hill, thus preventing any chance of the train balancing before the first drop.

 

Simply speeding up the lift chain at the right time relieves the necessity of a catwalk for evacuations, and unneeded stress on the chain. So I hope this solves your mystery!

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You just answered my question! It's not tention it relieves, it's stress, there is a difference here.

 

Once you used the word "stress", and everyone's explanation after it, it fits.

 

Get that physics book back out. Tension = a type of stress, aka tensile stress.

 

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Actually, not quite.

 

In engineer speak, Tension is a force, the stress is that force divided by the area it is acting over. Strain is that stress divided by the modulus of elasticity of the material it is made from.

 

That's what I get for taking a year of physics in 8 weeks. And I took Physics for girls, aka no calc.

 

But back to the original issue, it's tensile stress the pre-drop is trying to relieve. N'est pas?

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Actually, not quite.

 

In engineer speak, Tension is a force, the stress is that force divided by the area it is acting over. Strain is that stress divided by the modulus of elasticity of the material it is made from.

 

That's what I get for taking a year of physics in 8 weeks. And I took Physics for girls, aka no calc.

 

But back to the original issue, it's tensile stress the pre-drop is trying to relieve. N'est pas?

 

Yes yes. I agree with you there completely. Releaving tension in also reilves the stress, and vice versa.

 

The important thing about limiting the stress (or tension) is not about the total amount, but the changes in stress the chain sees. Each change in stress reduces the life of the chain so anything that can be done do make it as constant as possible will make it last longer.

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I told him thats how he can tell a B&M coaster out (besides the box middle rail) but when I showed him Led Zeppelin and Behemoth, he told "Those aren't B&M's". Show I showed he the stats on RCDB, he gets it now. But its a question I would like to be able to answer for him (and myself now).

 

The nice thing about the pre-drop though, is that if you see it, at least you know its a B&M!

 

^ So if they did speed the lift motor up, why is it that Six Flags coasters still do the whole slow down to a crawl thing at the top?

 

This is only on certain rides, one of which you're probably thinking about is Goliath. The reason behind doing that on Goliath is the ride just moves too darn fast. They can't seem to keep its speed down, so slowing the lift slows down the pace of the ride. Otherwise the force at the bottom of the first couple drops would be much more forceful.

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Pre-drops are not a B&M-only thing. Arrow's do have pre-drops too. The Viper at Darien Lake has a pre-drop as well. It's all to releive stress, and wear and tear on the chain as the train transistions from one chain dog to the next. If you have noticed, the sprocket at the top of the lift hill appears to end at the bottom of the pre-drop as well. This is so that by the time the first chain dog disengages, most of the train has already crested the lift and gravity starts to take over. It's almost like the 2nd chain dog isn't necessary but they put it there for one of those "what-if" situations.

 

I think B&M is eliminating pre-drops to keep costs down and save space. Pre-drops take up space and uses more steel work than those that don't have one.

 

There are also other designs where a pre-drop IS necessary, but not used. One fine example would be the Vekoma Whirlwind coaster, formerly at Knoebels. At the top of the lift, there's a flat section of track before it starts to drop. When the first chain dog near the front of the train disengages at the top, there's still a gap between the second chain dog near the back of the train and the chain link. What ensues is a very loud bang and jolt at the top of the lift. Robb has consistently made fun of this fact while the coaster stood at Knoebels. (Just check out the fifth photo from the top of this page: http://www.themeparkreview.com/pa2004/knoebels/knoebels2.htm )

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