Question: Forces in helixes

The helix:  possibly my favorite coaster element.  I have noticed that they pull two kinds of forces, positive (Raptor, X-Flight) and lateral (The Beast, Shivering Timbers) g's, and I have a question about how.

First off, I understand how a coaster designer creates lateral g's in the helix, that is, by underbanking the curve for the speed the train will travel through it.  As for how designers create helixes that feel like they are going to rip your face off, I don't quite get. 

When I look at the Raptor's final helix, I see that the track is banked pretty heavily, reducing lateral g's which would probably be pretty uncomfortable in an inverted coaster train, anyway.  I don't understand what causes the positive g's though.  I guess I don't see how a curving motion can plaster a rider down in his/her seat.  Are there any Physics geeks (I use the term respectfully :) ) out there who can help me out?

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It's a simple equation: CCI + CP = #1 Wooden Coaster!

Okay, let's see...Depending on speed and banking, either the positive or lateral G forces will be felt more prominently, which you've already stated. As to why: As the train moves around the helix, the force on the train is always moving out from the center of the helix. When the track is banked less, that force is felt more laterally. When the track is banked heavily, as in Goliath or Raptor, that force is felt more positively. This results in the feeling of being glued to your seat.

In two helices of equal diameter, one with track that is barely banked and one with track that is extremely banked (around 60 - 90 degrees), the general motions of the forces are the same. The force always moves outward, but when you're in the non-banked helix, you feel the forces on the side of your body instead of on your posterior.

So essentially, you're moving in the same direction, just in a different position. Hope this helps.

And I take 'Physics Geek' as a compliment! :)
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If bees make honey, then do earwigs make chutney?

*** This post was edited by dmb-crush on 8/22/2001. ***

Real simple, with the banking think of the proverbial bucket of water you swung around as a kid. Did the water stay in the bucket? Yes. Why? Centrifgal force and enertia. The water, or in this case the coaster train wants to continue in a straight line, but the track, or your body, keeps them moving in a circular motion. If you take the banking away, or hold the bucket of water on its side, the forces are in the same direction, but the reaction of your body, or the bucket of water will be different. With no banking the water flies out of the bucket to the side because there is nothing to force it to do otherwise. Same thing with the coaster, with no banking your body want to continue in a straight line and the only thing keeping it from doing so is the side of the coaster car. I hope this didn't confuse you any more, but it's hard to compose your thoughts at midnight when your tired! :)
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Just a couple of G-force junkies!

Another trick designers use is to wrap the helix in tighter as the train circles it. As in, the radius of the helix slowly decreases over it's extent. The force felt is equal to the following equation:

F = (m * v^2) / r

where m is your mass, v is the velocity of the train, and r is the radius of the curve. As the radius decreases, that fraction grows larger...thus creating a larger force. This is also why downward helices produce a force that grows with time and upward helices decrease in force (as that changes the velocity).

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James Draeger
http://draegs.tripod.com/
"Legend is a wooden Jesus"

*** This post was edited by ACEerCG on 8/22/2001. ***

simple answer: high positive g's result from a properly banked, small radius helix.  if you would make the helix larger then you wouldn't get all of those positive g's.  and just for the record there is no such thing as centrifugal force.
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Knott's Berry Farm Cuba ~South Park

I see how it works now.  In any helix, a lateral g force and a positive g force are really the same force, but depending on how the track is banked (and at what angle the rider is positioned relative to the force) the rider will experience the force by either being pushed to the side (lateral) or down (positive).  I guess it's not too difficult to understand at all. 

Thanks everyone!

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It's a simple equation: CCI + CP = #1 Wooden Coaster!

Its all in the banking

Another way to think of it is this.  Inertia causes your body wants to continue to travel in a straight line.  Changing direction requires a force to change your direction, otherwise you would just go straight.  The resultant equation as previously mentioned is F=m*v^2/r.