TTD: A Techincal Intro Questions

This is particularly directed at Rideman since he wrote the TTD: A Technical Introduction article, but I'm sure others may be able to contribute because I'm sure it's probably come at some time or another. 1) What happens when a train rolls back? More specifically, with the pusher assembly. The idea of the launch pusher is that it can't allow the train to pass over it in reverse, otherwise it couldn't push the train during launch? 2) TTD works on the incompressibilty of fluid. If I remember correctly, at high speeds (N/A because this ones on the order of .5 MACH or something) or high temperatures, incompressible fluids become compressible. Any idea how hot this stuff would have to get for that to happen? I know the whole system is under a lot of pressure and with pressure comes a rise in temperature. 3) Concerning the hydraulics, do you know if they are affected by weather? I don't know if the building has any of climate control, but if it did not, the performance of TTD would vary as the temperature does (from day to day, day to night, etc) right? 4) Does the crew have any control over how fast the train launches? When a rollback occurs, you assume that the train didn't have enough 'umph' to get over. Do they crank it up more or do they cross their fingers and try again? If they can adjust the speed, do you have any idea what type of mechanism they use to control that? Whew..that's it.

Why didn't you wirte him a private message?

TTD does not use a pusher. Instead the trains have a "pin" on the bottom that is lowered before launch and then engages the sled. Once the train reaches the launch speed, the sled begins to slow down and the train outruns it. Once that happens the pin is retracted and therefore it will not hit the sled in case of a rollback. I also remember someone on here saying that the computer monitors the speed and if a train rolls back it increases the speed automaticlly.

timbers01, because if I got a private message it might be a week or more before I ever noticed the notification on the forum screen. :) (sorry, a jab at Jeff; see here for details)

Well, I'll answer what I can...

Q1: What happens with the launch sled during a roll-back?

The launch sled is little more than a big piece of steel with a hole in it, tied to three great big wire ropes. On the underside of the train, just ahead of the fourth axle, a hinged rod drops down from above the car spine. There isn't any position where you can see this, because the only time the rod is down is when it is fitting into the launch sled, and at that point there is a brake fin in the way. But when the train is in the staging area you can see the slot under the car. Some mechanism is used to hold that pin in a raised position. Those two silver canisters on either side of the slot have electrical contacts on the bottom which make contact with an electrical bus located on either side of the launch sled at the launching point. You can see the contacts...on the raised black pads on either side of the sled...in this photo. For the launch, the train is brought up to the launching point, the launch sled is reset if it isn't already in place, and power is applied to the electrical contacts. This causes the pin to drop, and you can hear it drop if you are standing next to it. Next, the advancing wheels behind the train are dropped, and gravity pulls the train backward (since the track slopes uphill) until the pin jams against the back of the slot in the sled. The contact is de-energized, but the pin stays down because it is tight against the back of the slot in the sled. The train is launched by dragging the sled forward at an increasing rate of speed. At some point, the train reaches its target speed, and the launch system is disengaged. At this point, the train will simply over-run the launch sled, and the pin will retract back into the bottom of the train. If the train doesn't make it over the top of the hill, it will come back down and roll backward...but because the pin is disengaged, it won't catch on the launch sled, so it doesn't matter where the launch sled is when the train comes back...there is no need for the sled to beat the train back to the launch point, and there is no need for the sled to wait for the train to clear the tower before rewinding.

If you sit in the fifth row of the train, you can hear, perhaps even feel, the pin disengage from the sled and bang against the floorboard as it swings up into its cavity at the end of the launch.

Q2: At what temperature does hydraulic oil become compressible?

Sorry, I'm afraid I don't know that much about hydraulic oil.

Q3: Hydraulics affected by the weather?

I'm not sure what effect the weather has on Dragster's hydraulic system. The hydraulic system would be affected by temperature at the very least, if only because the expansion of the gas in the accumulators has to obey those laws about temperature and pressure. That said, I suspect that the ride probably generates enough heat that compared with the environmental range the system is asked to operate in, the effect is probably minimal. Part of that, though, is related to the fact that there is not only air conditioning in the hydraulic building, but also a system of oil coolers. Rumor has it that some of the system heat is being dumped into the lagoon, which would be a pretty effective heat sink, but I have not been able to confirm or deny that statement. I think environmental issues probably have a more significant effect on the launch sled track, the train wheels, and wind effects on the train, as those are areas where there is less control over environmental factors than in the hydraulic building...and likewise, where there is probably more variation in the various factors, particularly heat. After all, the hydraulic system will heat up quickly and stay hot; the temperature of the plastic runner in the launch sled track will be more dependent on the weather conditions.

Q4: Can the crew control the speed?
I am not familiar with the ride's control system, but I suspect that the crew has little if any direct control over the launch speed. The control system is designed to monitor the train progress on every launch, and to make fine adjustments to the launch acceleration on every run. At CoasterMania last year, Monty Jasper explained that this continuous adjustment process combined with a "timeout" when there is a long delay between launches is responsible for many of the rollbacks we see, including the one he was talking about which was captured on CBS television.

I don't know how the launch rate is adjusted; I'm guessing it's a variable rate regulator in the plumbing...probably in the return lines...coming from the motors. That, or perhaps some of the motors (there are 32 separate motors in a planetary arrangement around the main drive shaft) are switched out to vary the launch force.

Hope that helps! Perhaps some of this ought to be added to that article...

--Dave Althoff, Jr.

Thanks, Dave. That post actually helped me clearify some things. I'm glad it was on a thread and not private, so I could figure out what was going on.

-Eagle-

Well, I started a thread because I thought someone else may be interested. Apparently Sean got somethin out of it ;). Thanks Dave. Regarding the pin disengaging, I've only had one ride on TTD but I distinctly remember that I could actually feel the sled disengaging. I thought that was wierd that I noticed something so small on my one and only ride.

---

timbers01 said:
Why didn't you wirte him a private message?

---

If he wants to ask Dave on a date, ask him for money, or if he likes pancakes, then he can "wirte" him a PM. Otherwise, don't you think it's something that perhaps everyone might be interested in?

Thank you Dave, I appreciate the time you give to this website. Your posts are always very entertaining and educational....
I have studied and rode this ride from the beginning and I still can't figure it all out. You are a huge help.