Energy economy of launched coasters vs. chain lifts

Hi,
when I was at SFMM the last time, I was serioulsy impressed with the launch of Superman the Escape - and I also heard that they had problems supplying enough electrical power to drive the launch mechanism.
Of course, a lot of Watts are used in a very short amount of time for a LIM launch like STE. The newer hydraulic launch mechanisms overcome this problem by "accumulating" the electrical energy in an intermadiate format before releasing it on the train during the launch.

At first I thought: Launches - what a waste of energy! But when I reconsidered it, to launch a coaster doesn't necessarily use more energy than to pull the train up to the highest point with a chain lift. The work done: Moving the train to the highest position of the coaster at which it stands almost still -
is actually the same overall. So in theory, if the wheels are well lubricated, a coaster launch should use about the same amount of energy overall as a cable lift.

?

*** Edited 3/3/2004 9:45:32 AM UTC by superman***

In theory the same work must be done, but in practice, it's not the case I'm sure. Isn't there some rule regarding friction and speed? I don't actually remember from physics, that's why I'm asking.

My guess is that launches require far more energy judging only by the amount of heat (wasted energy) generated. A chain lift idles while not lifting, but even when it does, the heat generated by a motor is significantly less. I've been in those motor rooms, and while warm, they don't get that hot.

Now compare that to standing under any Impulse while loading, or compare it to the gigantic air conditioners for Dragster, which by the way still don't get the room to a balmy temperature. Both of these launched rides are putting out a whole lot of heat compared to a chain lift, and therefore wasting a lot of energy.

Drag usually increases exponentially with increased speed.

I always thought there was a component that was linear and a component that was more or less static, but I wasn't a mechanics major, so...

I guess I'm thinking more about friction with moving parts than drag. *** Edited 3/3/2004 6:11:31 PM UTC by ApolloAndy***

exponentially? That doesn't seem right, but I'm too lazy to look it up. But, there are darn few natural processes that proceed exponentially (c^n, where n is the free variable). I am prepared to believe "more than linearly".

In any event, Jeff's on the mark. Wasted energy in terms of heat/noise is the difference maker.

Then again, a LIM launch has no friction...

"Drag usually increases exponentially with increased speed."

That explains the fact that the faster I drive the more I feel like wearing a dress!

mOOSH [sorry...couldn't help it. Back on topic now]

*** Edited 3/3/2004 9:11:06 PM UTC by Mamoosh***

I dont think it increases expedentally with speed but it increases enough, lifts definatly take less energy.

LIM launches are not frictionless, for one thing there is air drag witch increases with velocity and there is friction between the wheels and the track.

I vaguely recall reading somewhere that the launch on Tower of Terror (Dreamworld), while in progress, temporarily doubles the power consumption of the entire park. Keeping a chain going isn't going to require anything like that amount of power.

In practice, if LIMs were that cheap to run, why did Intamin move to Hydraulics for their newer rides? After all, if LIMs can do 0-72 in 2 seconds or so, I think it's a reasonable assumption that they can go on to 120 in the four second window.

Regards,
Richard

Aerodynamic drag does indeed increase exponentially with speed;

F = 1/2CdDAV^2

Where:
F - Aerodynamic drag force
Cd - Coefficient of drag
D - Density of air
A - Frontal area
V - Velocity of object

The entire equation to figure the force required to drive a wheeled vehicle (known as Tractive Effort) is;

TE > GR + RR + WR

Where:
TE - Tractive Effort
GR - Grade Resistance
RR - Rolling Resistance
WR - Wind Resistance (or Aerodynamic drag force, F, above)

Thus, to power your vehicle (or coaster) through the air you have to overcome the aero component, the grade component (obviously it's easier to go downhill than uphill) and the rotating components' rolling resistance, which includes your wheel-to-track and internal wheel bearing friction losses.

Therefore, I would expect that a chain lift would require less energy input to lift a train to a given height, as it does not face nearly the amount of wind resistance that a launch creates.

Later,
EV

Not sure how much of a difference it would make, but the launched ride, in addition to the already stated reasons, seems like it'd take more energy because the train is actually travelling a farther distance to reach its maximum height than a chain/cable lift would. It's just like a simple right triangle, a launched ride like TTD has to travel the base of the triangle and the height of the triangle, where a standard lift would only have to travel along the hypotenuse, which is shorter than the sum of the other two distances.

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ApolloAndy said:
Then again, a LIM launch has no friction...

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You mean besides the wheels on the track, the wheels on bearings and axels and air resistance?

EV: hate to break it to you, but if F ~ V^2, that's quadratic, not exponential. There is a *big* difference.

Edit: to clarify, if it were exponential, then F would be ~ [some constant]^V.

This message brought to you by your friendly neighborhood engineering professor.

*** Edited 3/3/2004 11:43:36 PM UTC by Brian Noble***

A LIM uses very high electrical current to launch the train. The high current combined with the resistance of the windings in the linear motors is what makes all of the heat. Don't forget, with a chain lift, you usually only have one motor that has no trouble remaining cool where as a launched coaster has several linear motors that each need a blower motor to keep them cool. And the blowers use more power. Then you have the motor controllers that also get hot. All around a launched coaster will use a lot more energy than a regular lift coaster. Cedar Point installed a dedicated 20,000 volt line just for WT and have since added TTD to the circuit. That’s a lot of energy for two rides. Also, I'm not sure if the rides store up power for a launch or not, but if the don't, power companies usually charge a surge charge for large demands of power. Mills have to pay these charges when they start large motors and such. I don't know if the parks get around this or not.

I just wonder what an electric bill is for an entire park for a regular day. You figure all the rides, air conditioning, lights, games, and food prep things running for 12 hours a day.

i believe that Launches use more power because, if i remember my physical science class correctly,

Power=work/time

launches and lifts to the same work, but in a much quicker time.

Bwizzle: But launches only have to operate once every few minutes whereas lifts are doing work about half the time. If the train exits with the same energy, in a ideal world, energy would be exactly the same.

Jeff: What I mean is that a LIM launch doesn't have to deal with its own motor friction, chain friction, or any other frictions associated with the moving parts of the lift mecahanism. Obviously the train will have the same types friction...

.. you'd be surprised how inexpensive a LIM launch coaster is compared to some lift systems energy wise..

The LIMS are VERY energy efficient vs. your standard 3-phase coil motor. *** Edited 3/4/2004 5:54:46 AM UTC by Red Garter Rob***

But LIMs are essentially that 3-phase motor spread out linearally. How can it really be all that different?

Spread out is an understatement. That's a lot more coils. Moving something with LIM's at lower speeds I'm sure is more efficient, but with all that heat at high speed I have a hard time seeing them as cheap to operate.

The hydraulic motor you can bet is low on the efficiency scale, considering the pumps are almost in continuous motion. Not to mention the power used for the air conditioners!