Design Features

Woodies and Steelies

Things can get even messier when riders take their stomachs, ears, and bursas from a wooden coaster to a state-of-the-art metal model. Roller coaster enthusiasts debate the relative merits of "woodies" and "steelies" with the same vociferousness that hunting enthusiasts use to debate the relative merits of shotguns and assault weapons ­ though coaster enthusiasts typically have opposable thumbs and upright posture.

Among the advantages of woodies, the clickety-clack sound created by the interplay of metal wheels, metal tracks, and an underlying wood framework. This can be more exciting than the relatively silent steelies, which use neoprene coatings on the wheels to keep down the noise that would be created by steel on steel on steel. The most dramatic difference, however, is the comparative lack of variety that wood provides in track design. Since metal is much more flexible than wood, only the metal coasters have the loop-the-loops, corkscrews, and other features generally frowned upon by representatives of Amnesty International.

A high speed coaster does not necessarily produce a better ride than a low speed 'twister'. Our bodies are relatively insensitive to speed as such - we are much more responsive to acceleration and fluctuations of acceleration ('jerk'). Airline passengers may be flying at a steady 500 mph. but experience littleÝsensation of this when confined to a mid-row seat in the main cabin - we rely so much on peripheral vision for our sense of absolute speed so robbed of this our brains cannot interpolate the speed at which we are travelling.

Hypercoasters

Hypercoasters are about twice as tall as regular roller coasters. This larger scale adds new design challenges. Going down a 200-foot hill, a car has more time to accelerate and gains more speed. If while going at this fast speed the car experiences a sudden change in direction or speed, the car's acceleration changes. A big or sudden change in speed or direction can make a bigger acceleration. Since the force acting on the car (and you) is equal to its mass times its acceleration, the bigger the change in direction or speed and the less time that change takes, the greater the acceleration and the bigger the force you'll feel.

To keep these forces at safe levels, the designer has to stretch out the time and the distance it takes to navigate the curve at the bottom of the hill. This spreads the change out over time, decreasing the force you feel. The top of the next hill has to be high enough to slow the coaster down, or stretched out to a gentler or banked curve, so the car doesn't fly off the track.

Space is a problem. Coasters go forward two feet for every foot they climb. If the highest hill is 100 feet, it takes about 200 horizontal feet to get the car that high. If the highest hill is 200 feet, it takes 400 feet. Since land is expensive, the designers have to be creative about the use of space. A track shaped into a curve takes up less space than one left in a straight line.

In the quest for speed coasters larger than the current +200 ft mega coasters will no doubt continue to be built but perhaps it is worth concluding this section by considering their potential limitations.

• Speed Height Relationship
  For a gravity coaster we get a poor trade off between height and speed. Doubling the height only achieves a further 40 percent increase in theoretical maximum speed and from a practical point of view a gravity powered coaster would have to have a potential height of around 350 to 400 ft. to consistently achieve the holy grail of a 100 mph train speed.

• Size and Cost
  The quantity of materials for the structure of the ride becomes disproportionately larger as the height of the structure increases as do the problems of maintenance and inspection. This adds considerably to both the cost of construction and operation. Large coasters take up a great area of land which many parks cannot provide or allocate for a single ride. In many locations planning permission may not be granted for the erection of structures above a reasonable height.

• Centripetal acceleration and G forces
  Centripetal acceleration occurs whenever the train changes direction. This acceleration is proportional to the square of the speed of the coaster cars and inversely proportional to track radius. Doubling the train speed quadruples the centripetal forces generated unless the radius of the curve is also quadrupled. G forces must be kept reasonably low for the comfort of the riders and to minimise damage to the structure. This in turn implies even shallower curves than those found on our current mega coasters. The size of the riders stays the same, of course, and generally so does the train length at around 30/36 passengers. The consequence of this is that the coaster starts to feel more like a high speed elevated railway.

• Wind and Weather In many locations the prevailing wind strength is greater above 200 feet than at ground level - this can adversly affect the operation of a mega-coaster and could be an even greater problem at +400 feet.

• Mega Looping Coasters
  G forces may also limit the maximum diameter of a vertically looping mega-coaster. The entry speed will typically create around 6/7 G's which is tolerable for a couple of seconds but will lead to potential blackouts if sustained for several seconds. The train and passengers will be subject to the high G entry phase for a longer period in a large loop than a small one even though the train speeds are greater (doubling the speed implies quadrupling the radius hence actually doubling the transition time round the loop). A solution here might be to use a magnetic booster for the upper part of the loop thus allowing lower entry speeds and hence lower positive G forces.

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