Posted Tuesday, August 21, 2001 4:33 AM | Contributed by Jeff
Now that Six Flags New England has released its findings as to why two trains collided on its Superman roller coaster, many members have more questions than answers. Intamin's magnetic braking system should be fault tolerant.
What happened? CoasterBuzz member and keeper of the Roller Coaster Rollback(TM) Dave Althoff, Jr., a student of ride safety systems, has analyzed the braking system of these Intamin coasters so you can decide for yourself.
Very, very nice, Dave, and educational! I can see where this system is supposed to be fail safe, but we now know it is not.
If it was a "simple" blown air supply hose, why was it not caught by the daily inspection by the SF mechanics? I have always assumed those daily ride checks do occur in parks all over, and not just on the rails and rolling stock. Seems to me the air hose that was about to break would have had some tell-tale sign. Like looking at your garden hose that has a weak spot...you would probably fix it if you saw it. But of course, you have to look for a trouble spot. I would hope SFNE will now always actually look for potential trouble. Again, tho, this assumes the actual truth to this accident is a blown air hose. As you imply, Dave, there could be more to the story.
The air hoses in that system are...or at least were...plastic hoses. They're nice and flexible, they're rugged, long-lasting, UV resistant, impervious to the lubrication oils used, can handle high pressure, and as I understand it, can easily fail without warning. I'm not willing to fault Six Flags for failing to spot a pending failure of the air hose. I'm reasonably certain that the daily inspection would include a look at the hoses and fittings; it would only take a few moments to look them over. But the inspection would be looking for things like loose fittings, kinked hoses, or mechanical chafing. With no evidence of any obvious problems (the hose probably wasn't bulging or anything like that) the ride would be good to go. Then midway through the operating day, the hose blows. Sometimes that's the way parts fail.
Does anybody know off-hand how many calipers there are on the brake run? Could it be that the loss of two calipers (one on each side) is enough to keep the train from stopping?
Got it, Dave, I concur that sometimes there is no advance evidence of a pending failure.
I do not know how many calipers are on the brake run. On my next visit to SFNE (sometime in September), you can bet I am going to count them! From your excellent pictures it looks to me like 7 or 8 per side (14 or 16 total) because the first caliper is shown at almost the last car of the train, the another at the next car. I believe the S:ROS trains are 9 cars. Looks like that averages out to 1 or 2 less calipers per side than cars in the train.
----------------- I know you rider Gonna miss me when I'm gone
*** This post was edited by MABrider on 8/21/2001. ***
*** This post was edited by MABrider on 8/21/2001. ***
wat happens if we have an accident on MF like this, with the train cruising at 60 mph at the end. Thank god it happened on this ride.....I hope CP looks at this and does something about it too. -----------------
Millennium Force has a slightly different design for its braking system. First of all, there is a long run of fixed calipers which are, of course, impervious to air system failure. Second, it looks like Millennium Force has a different type of actuating cylinder; it looks like it might be a single-acting cylinder instead of the double-acting cylinders on the Superman rides. With a single-acting cylinder, air is used to move the rod in one direction, and some external force...gravity, a spring, another cylinder, whatever...is used to move it in the other direction. A good example of a single-acting cylinder is the multi-stage lifting cylinder on an Enterprise. Fluid is pumped into the bottom of the cylinder to extend the rod, and gravity is used to bring it back down again.
One correction I would make to the article is that while SFA's Ride of Steel did stay open for a few days with two trains, it did close shortly after for an extended period. I noticed a clanking sound in the brake run Sunday after the train stops that sounds like a modification.
Actually Jeff on the S;ROS rides there are four calipers on each side for a total of 8. Also Dave I want to point out that the valve in use is most likely a 4 way valve, and there are many variations of these. The type I would imagine they would use would be of a nature so that when it's energized a piston in the valve is pulled to one side thus allowing air to flow to the top of the cylinder and open the brakes. Upon power being removed the piston in the cylinder would move to the other side, most likely under the force of an internal spring, thus causing air to flow to the bottom of the cylinder and closing the brakes. Additionally as the piston in the valve is moving back and forth it will always be in a postion to vent the air from the side of the cylinder not being supplied. Thus the reason I am still confused as to how the accident could of occurred. If a supply hose going to the top of the cylinder had blown this would not have caused the brake to open. In fact it would have prevented it from opening. If the hose going to the bottom of the cylinder had blown, while it's true air is probably being supplied to the cylinder to hold it closed, the counter weight should have held it closed. Remember yesterday that I said I had wittnessed a braket securing a piston to a brake caliper break. The brake still stayed closed and functioned properly even with no force other than the counter weight holding it closed. Not trying to muddy anyone here I just want to understand this as much as everyone else. Also being that the state was invloved there most likely was a report written by them. It probably could be obtained through the FOI act. While I don't have time to do it maybe someone would like to take the time to try and get the report and we could get the confusion cleared up once and for all.
phil... I was thinking about that valve last night. Let's assume for the moment that the valve has a single supply line, two output ports, and two vent ports. For our convenience, let's call the left port, which feeds the top of the cylinder, "A"; the right port, which feeds the bottom of the cylinder, then would be "B". Let's also assume that under spring bias, with no power applied, the solenoid reverts to feeding port "B". That way, if electrical power is lost, the valve will reset to the "B" position and close the brake if it isn't already closed, provided that air pressure still exists.
So if we cut the white hose (the supply hose), while the valve is in the "B" position, the "A" side of the cylinder should already be empty, and set to vent through the solenoid valve. Of course, with no air supply, the "B" side of the cylinder will also vent, this time through the supply port rather than through the vent port. That shouldn't cause the cylinder to move, but it would remove the usual resistance to motion. So anything that would serve to push the caliper open would be able to do so with little or no resistance.
That leaves the question of the counterweight. You say you've seen the counterweight hold the brake closed with the cylinder disconnected from the caliper (and I have no reason to doubt you!) which suggests that there isn't any force there during braking that would tend to kick the caliper open. So we are left with the original question: Why did the caliper open when the airline failed?
Jeff, any other tricks for getting that photo to come up? All I get is the damned Angelfire logo...and the page takes forever to load if I go in the front door...
--Dave Althoff, Jr.
*** This post was edited by RideMan on 8/21/2001. ***
A thought here on how to get that link to work (it was the only way that worked for me) is to click the link and let the angelfire logo come up, then remove the http:// that is at the beginning of the address, finally hit enter. All I can say is that method worked for me. Good luck and thanks for your wonderfully insightful knowledge you bestow upon us know and then. I know I greatly appreciate any information that you bring to the table.
I figured it out. I had to clear the cache. Even though Netscape is set to check documents "every time" it was still pulling that one from the cache for some reason.
BTW: I've updated The Page with some of the additional information that has come up here and in email; also SFNE sent me a copy of the official press release relating to the results of the official investigation, which I also reproduced on the page. The updates will continue.
Wow. Keep going, Dave. I believe the solution is there, and probably quite simple.
One thing I might add: engineers do make mistakes. I know, I'm one of them (not for rollercoasters :( ). They have a tendancy to put more trust in thier "parts", be it hardware or software, then they should sometimes; and then trying to get one to admit the mistake is next to impossible. This reeks of such a mistake...