EVEN MORE THOUGHTS ON GUIDED PERSONAL TRANSIT
William G. Turnbull
A few days ago, I set forth several observations/opinions as seen from the viewpoint of a relative newcomer to this debate. In a gracious reply, I think it a fair description that while Mr. Jensen (More Thoughts on Guided Personal Transit . . . , 29 August) did not embrace everything I had to say, neither did he find anything he violently disagreed with - something totally wrong.
Of my comments, I believe that by far the most important was the observations that there seemed to be "An emphasis on advancing a specific hardware concept before a comprehensive evaluation of the problem from a system viewpoint." Jensen suggested that although there had been intense debate on the control issue earlier, it might be time to update the debate, and that ". . . not all problems are solved."
I was heartened. Perhaps I am too impatient, but the subsequent three papers, including one by Jensen, basically returned to justifying the choice of specific hardware. I was less heartened.
While I find much to agree with in Mr. Goltermann's (Pros and Cons, 30 August) discussion, I am disappointed that he seems to have adopted the prevalent view that once one adopts an LSM the operation and control problem is forever resolved. I am not opposed to LSM's per se, only the view that they solve all problems. An LSM can be an excellent means to control velocity; but, in an of itself, it does not provide information on position. It is apparently true that at least one manufacturer (MagneMotion) can supply auxiliary apparatus that can provide this. However, Goltermann provides no information on how this information is to be used or how it might be distributed to the various sites that require it. If one is to launch a vehicle of any type onto the guideway, there must be positive information that a vacancy exists, with adequate room to safely insert, and precisely where it is.
Goltermann also seems to believe that once an LSM is provided, there is no further need to consider friction with the guideway. The braking action of an LSM is limited to essentially the same force that can be provided in acceleration. Safety considerations will undoubtedly require more. Moreover, there is the question of affective braking in the event of a power failure. I am not suggesting that these concerns can not be satisfied; only that he did not mention them, and thus are apparently not high on his priority list.
I do not wish to single out Goltermann for particular criticism, from what I can tell he represents the majority view. And as I said at the outset, I find most of what he has to say very useful. He provides a particularly insightful observation at the end of his paper when he points out the importance of the switching function, and how it is to be controlled. I could not agree more.
Then we come the reply by MegaRail's Henderson (Response to Kim Gothermann's Comments, 31 August). Although not directly related to the control issue, I find it appalling that Henderson felt the need to defend against the charge of being "cheap". If their approach can not do the job, then by all means challenge it. If the only objection is that it is not sufficiently "high-tech" - that is ludicrous.
Henderson defends the use of pneumatic tires and an onboard electric motor primarily on the basis of reduced cost, although technical arguments are also advanced. My prejudice is that on the cost issue, Henderson is probably correct. But that is precisely the problem, it is a pre-judgement. It seems to me that the advocates of LSM's need to provide a credible cost analyses, and the onboard people need to do the same. Only then can an engineering judgment be made as to the cost effectiveness of each. As I remarked earlier, engineering is a business of numbers, not religious conviction. As an aside, I should point out that if the issue of sufficient traction is resolved (as apparently Henderson believes), the advantages claimed for linear synchronous motors are also available in rotary motors.
We are assured that " . . . multiple redundant, voting electronic control systems can provide the needed control with the necessary degree of safety and reliability." So far, so good. But it would be nice if we had some hint of the control philosophy - how this is to be effected. We are further assured that "fly-by-wire aircraft flight control systems can be adopted for this use." These were designed to manage the control surfaces, and thus to maneuver the aircraft; not to keep them from flying into one another. To extend the aircraft analogy one step further; one of the most serious problems facing civil aviation is runway encroachment. That problem has not been adequately solved. It is the same problem; keeping airplanes or dualmode vehicles from smashing into one another.
It is interesting to note that Henderson re-interpreted Goltermann's general comment on switching (at least I interpreted it as applying generally) to one applying principally to maglev. We are again assured, but not informed as to details, that the MegaRail switch is relatively simple.
Again, I do not wish to single out Henderson for particular criticism. It apparently represents the norm. I concede that once a string of vehicles is formed, an LSM or other system can maintain the string. The problem is that the string is continually forming and reforming, and it is in this area that control is critical. The MegaRail people have obviously done considerable work, and I have no reason to believe that they have not considered and solved the control issues. I would suggest, however, that a discourse on these rises at least to the level of the relative importance of steel wheels and pneumatic tires.
Then we come to Jensen's latest paper (Pros and Cons for RUF Dualmode, 3 September). In spite of his previous suggestion that control needs revisiting, he ignores the question completely. Well not quite; he acknowledges that the system must be automated. No one can argue with that.
I don't mean to be a fishwife about this, and I apologize if the style of my presentation causes offense - but I do think it is a serious problem that, judging from current discussion, is not getting the attention it deserves. Whether a system is government or industry supported, both state and federal regulators will still have to be convinced that it is completely safe before any revenue service can begin. It is not too early to address this.
Last modified: May 27, 2001