Why Lightning Rod is late

May 19, 2016, 1:56 PM

We all know of the launch issues that Lightning Rod is having, however; Screamscape reports that the coaster is running at 80 mph, not the intended 73 mph. Should make for an even wilder ride! Also, a Dollywood employee said that the ride is begining training and has finished the testing phase. Expect to ride Lightning Rod in mid to late June!

Replies (4)

May 19, 2016, 7:59 PM

Uh, rides running faster than trains and tracks were designed for doesn't strike me as a good thing.

May 19, 2016, 10:18 PM

WARNING! Engineering Content Below! Read at your own risk.

This particularly rumor has been circulating around the internet for about a week or so, and it is one of those that really gets on my nerves because I'm 99.9999999999% confident it is incorrect. Some sites have been reporting that the ride is running as fast as 90 MPH, and while the launch system may be able to propel a train fast enough to reach that speed I'm doubtful it has.

First, let's take a look at the exact text from Screamscape:

"According to a reader who visited Dollywood, they were told that Lightning Rod has entered the final testing phase and is set to begin employee training as soon as they finish checking off all the safety and operational procedure documentation. Best guess right now is that it may be ready to open in early to mid June.
I don't know how true this last part is, but hearding an interesting rumor that Lightning Rod is running a lot faster than originally intended. Instead of maxing out at 73mph, Lightning Rod has been clocked blazing through the hillside at over 80mph. Nothing was said about adding trims to the experience, so Lightning Rod may really be a wild experience when it opens."

That first part of the rumor I think is true. Lightning Rod began testing with water dummies today, and assuming there are no problems usually rides need 2-4 weeks of testing from that point before they are ready to go. I'm sure Dollywood wants to get the coaster open ASAP, and at this point I'm going to guess June 11th is a probable date (coincidentally, that's the same day GhostRider reopens at Knott's Berry Farm). The second part of the rumor, however, is what I believe is bogus. First off, Screamscape themselves are not confident in the rumor, and given that their accuracy is about 75% if they doubt a rumor it probably isn't true. While I will say that most of the stuff they post with confidence is accurate, they have been wrong enough that I never take anything I see there at at face value until other sources provide evidence or confirmation.

Now, let's see if this could be true. Today, we'll be applying a concept called conservation of energy. This concept states that, in the absence of non-conservative forces, the total energy at two points is conserved. Now, in this case there are a couple of non-conservative force involved, namely friction and drag. However, for simplicity we will ignore these because they are relatively small and would only subtract energy. For this case, that leaves us with potential energy (represented as mgh) and kinetic energy (represented as 0.5mv^2), where m is the mass of the train, g is the acceleration due to gravity (32.2 ft/s^2), h is the height, and v is the velocity. The equation will be using, therefore is:

mgh1 + 0.5mv1^2 = mgh2 + 0.5mv2^2

where 1 and 2 represent two points. To simplify this, we can ignore mass because it shouldn't change, and we can use a height difference (designated H) instead of two individual heights. Therefore, we get:

0.5v1^2 = 0.5v2^2 + gH

Now, let's do some calculations. First, since it is safe to assume the maximum speed will occur at the bottom of the drop we'll find the required speed at the top (v1). Rearranging the equation gives us:

v1 = sqrt(v2^2 + 2gH)

From roller coaster database, the maximum speed of Lightning Rod is 73 MPH and the drop size is 165 ft. Therefore:

v2 = 73 MPH = 107.1 ft/s
H = -165 ft
v1 = 28.9 ft/s = 19.7 MPH

Now, let's assume the ride is actually hitting 80 MPH at the bottom of the drop. Therefore:

v2 = 80 MPH = 117.3 ft/s
v1 = 56 ft/s = 38.2 MPH

While it doesn't quite double, that is a significant increase in speed. Let's see what launch speed is required to reach that. Reportedly, Lightning Rod's LSMs will launch riders at 45 MPH. As can be seen in pictures, the LSMs do not reach the peak of the first hill, so let's determine approximately how far below they stop. For this, the equation will be rearranged to:

H = 0.5(v1^2 - v2^2)/g

From previous information:

v1 = 45 MPH = 66 ft/s
v2 = 19.7 MPH = 28.9 ft/s
H = 54.7 ft

Now, let's find v1 for the 80 MPH max speed case. Using the original rearranged equation:

v2 = 38.2 MPH = 56 ft/s
v1 = 81.6 ft/s = 55.6 MPH

So, in order for the ride to be running at 80 MPH the coaster needs to be launching over 10 MPH faster than it is designed to. That is a HUGE margin of error. Now, LSM launches are one of the most technically complicated systems and require very precise computer control, so if the ride is not programmed for this launch speed it absolutely would not be launching at that speed. In fact, no coaster is going to operate that far off base without the computer downing the ride. While higher speeds do result in a more intense ride, they can also result in an unsafe or uncomfortable ride and they put more wear and tear on the attraction. Even if a ride can run faster no park would ever do so. For example, Xcelerator at Knott's Berry Farm is designed to launch at 82 MPH. However, the launch system is capable of accelerating a train to over 100 MPH and the ride has been tested at this speed. However, there is a sensor installed at the end of the launch track that measures the train's speed to help with calibration of the hydraulic system. While I don't know the exact number, I know that the margin for error is +/- 1-2 MPH (it's 2% from what I've heard). If the train launches outside of this range, the computer will down the ride and maintenance has to come to repair it. There is no way that any manfacturer would ever certify a ride to operate over 20% outside of design parameters, and if this happened just once when it wasn't supposed to it would likely send testing back to square one.

While I have no inside knowledge on this project, my gut feeling is that the problems with Lightning Rod have been related to reliability. The LSM system was designed by Velocity Magnetics, a company well known for magnetic braking systems but that has never done an LSM launch before. Due to the fact that there have been successful test runs, it is obvious that the system works. However, it may have been registering too many faults and/or having other issues, such as overheating or short shooting the train too frequently. While nothing works perfectly every single time, a ride is no good if it cannot perform at a reasonable standard. Ever wonder why Intamin hasn't been able to land any US contracts lately? It's because their rides are not reliable enough more than anything else.

Lastly, Jaiden, please note that I am not trying to attack you, I just would like to prevent the spread of highly dubious information. Rumors can be fun, but they tend to become fact all too quickly in today's world and there is a ton of misinformation out there.

May 25, 2016, 8:30 AM

My guess is Disney has given up all thogther in fixing Rocket Rods... Oh sorry, wrong ride.

May 25, 2016, 12:31 PM

Ha ha ha ha

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