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14 July 2016


Why wheel is more efficient than magnetic levitation

30 years ago, the author of SkyWay transport studied all possible options of suspension for the string transport system: magnetic and air cushions, a steel wheel, a pneumatic tyre, an electric field. A thorough preliminary analysis showed that the most optimal variant for a high-speed traffic is a steel wheel.

It is widely accepted in the world practice to do things in contrast to a logical plan of actions ("first think - then do"). So, Elon Musk admitted in a recent interview: "What would I change in the initial project? If someone re-started the implementation of the Hyperloop project, I would advocate starting with the simplest useful system. I would probably advocate wheels." The author of the SkyWay string technologies Anatoly Yunitskiy commented on the statement of the Hyperloop's "father" Elon Musk.

In this new release you will also find out how the use of a magnetic cushion would affect the cost of construction and rolling stock operation, as the use of a magnetic field would affect the efficiency and cost of a route itself, as well as much more.

Translation of the video:

Good day! Here is Mikhail Kirichenko. You are watching SkyWay news, where we tell you about the developments and implementation of breakthrough transport technologies.

Views of future cities have long been agitating human minds. However, the thing is that real changes in city planning are introduced only when a vital and extreme need for them appears. Such moment has come now. Kinds of traffic jams in cities are such that we are confident a bright future awaits our project.

Firstly, because no progress is possible with the existing transport problems. Secondly, the number of the developed future transport technologies is such that, according to all the laws of dialectics, it will inevitably transform into new quality. And, thirdly, we repeatedly spoke about the advantages of the rolling stock and the whole SkyWay transport system over the competitors and we are convinced there is no alternative to SkyWay.

Nevertheless, sometimes there appear opinions, questions or suggestions: wouldn't the unibus be better if it moved not on steel wheels but, say, on an air or magnetic cushion? I also decided to make a suggestion. I think it is ingenious. I invented a chair on magnetic suspension. However, is it necessary? And how much will it cost? It would be better to ask a specialist first.

— Anatoly, it seems to some supporters of our project that it lacks some spicy or exotic feature like levitation in a magnetic field. Could you tell us if you considered such solutions. What would be the unibus like on a magnetic cushion? What would be its difference from the adopted version on steel wheels?

— Certainly, I considered it. I analyzed it long ago. Perhaps, some 35 or 40 years ago. When the idea came, I looked for a way how to suspend a vehicle relatively to the track structure. Naturally, I examined all the possible suspension systems: a magnetic cushion, an air cushion, a steel wheel, a pneumatic tyre, an electric field (it is also possible for suspension). I even considered the exotica - anti-gravity. Perhaps, one day it will be discovered. The studies showed the most optimal version is a steel wheel. By the way, later I published an article. There is such a Russian journal "Problems of engineering and automation". This is the main scientific journal in the field of machine building. There are five academicians of the Russian Academy of Sciences in its editorial board. Here there is my article "Optimization of a ground-level transport system", where I showed how, based on the laws of physics, a transport system can be optimized. I analyzed here all the transport systems I mentioned above. It has the diagrams showing advantages of various systems including financial differences, their cost, etc. Long ago, more than 30 years ago, I came to the conclusion that the optimal solution for high-speed motion in land conditions is a steel wheel.

— And how would the use of a magnetic cushion affect the cost of rolling stock operation?

— A magnetic cushion increases energy consumption for motion tenfold and even more, strange as it may sound.

— That is above ten times.

— Yes above ten times. I can show it by a diagram. If I draw it, everything will be clear. Now I am going to draw a diagram of a train operating on a magnetic cushion. This is a beam, a heavyweight beam. A magnetic cushion train runs on it. I'll draw the Transrapid design developed by Siemens. This is a "skirt". I draw it conditionally. The proportions are approximately correct. This is a "skirt" and this is a compartment. In fact, this part is parasitic because it gives additional resistance. It has a substantial surface, therefore it produces not only frontal, but also lateral drag. And the gap is small, only 10 mm, in which air is inhausted. Naturally, it creates drag. To suspend a train relatively to the track structure, operating coils are located on the underside, not atop, because they use ordinary electric magnets. And an electric magnet only attracts, it does not repel. Therefore, a carriage should be lifted to provide a gap. To have an anti-derailment system and to avoid collisions, the coils are added here. You should understand that these coils are not small; they are large bobbins of copper wire. Each of them is connected to a cable, because each coil operates individually. To make this whole system work at small speed, it also has wheels. Therefore, generally speaking, it is also a wheeled transport. Later the wheels are retracted inside, like a chassis in an airplane. You didn't know it?

— No.

— And this is so. Now I am going to draw a unibus that does not have this "beauty". Instead of this beam, I draw our string rails.

— They say, beauty is the ultimate functionality. Well, here is the real beauty.

— What is functional, is beautiful. These are the wheels instead of coils. Of course, it is less costly. Vehicles run at 1 km distance from each other, therefore wheels are also at 1 km distance. And here a lot of coils are fixed in every 1 meter. Finally, there is an anti-derailment system. Now let's compare energy losses. I would start with electric energy losses. Electric energy is generated at power stations. To supply it to this transport system, voltage at a power station should be raised to 1 million volts or 500 kilovolts. Naturally, with some loss in a transformer. Then it should be transmitted by thousands kilometers to the place of the route. With inevitable energy loss. Then it should be reduced losing energy again. Then it should be supplied to cables with energy loss. Therefore, if we take the energy efficiency factor for Transrapid, the first losses will be in energy transmission and transformation. Minimum 50% is lost. As a result, the energy efficiency factor is 0.5 at best. Next, I speak about the linear electric motor. The gaps here are large, not tenths of millimeter. Energy is also lost in coils that are part of the linear electric motor, because it would get down and stop without a cushion. Therefore, these losses due to large gaps and a great number of coils will make the efficiency factor also 0.5 in this part. We multiply it by 0.5. And there remain some more losses that many do not know about. To move a carriage or a train on the Transrapid system, current frequency has to be changed in coils. We are used to changing voltage, it is easy. A transformer raises or reduces voltage. And here current frequency should be changed, it is a more complicated task. Depending on the speed, this frequency must be different. Commutation switches and frequency convertors are needed to monitor the speed of a carriage and to provide certain frequency on a coil in a certain place. Therefore, they almost became insane while designing it. They have been doing it for about 50 years.

— They had to calculate frequency at each coil.

— Yes, just this controls the speed. A running magnetic field is needed. The efficiency factor there is also 0.5 at best. When we multiply it, we get 0.125. This is 12.5%. A modern locomotive has 15% of this factor. It is for an electric locomotive. The old steam locomotive had 5%. This is for a modern locomotive.

— This new generation transport is worse than the previous generation locomotive.

— Now let's consider our transport, a unibus. I speak about the electric part. Here we have a motor-wheel with the energy efficiency factor equal to 96%. We have designed and developed such wheels. We have them. The difference from Transrapid seems not large 12.5% to 96%, though actually it is large. It should be compared differently. Losses should be compared. What is the correlation (delta) equal to? We have to deduct the efficiency factor from 100%. 12.5%, right? So as to determine losses. And to deduct 96 from 100%. We get here 87.5 divided by 4 and as a result - approximately 22. So it is "only" by 22 times. A steel wheel is better by 22 times from the energetic point of view. However, this is not sufficient for comparison. There are some more losses. They are also substantial, this is not all, because the main thing is not this one - how to suspend relatively to the rails. Aerodynamic drag turned out to be the main thing. I realized it long ago, too. There is a simple formula. It is from the physics course at school. Wattage is equal to force multiplied by velocity. Therefore, if the speed is the same but the drag force is different, then different wattage is needed for motion. So if we consider the magnetic cushion train, there is a rail track, there is a carriage and there is a "skirt" embracing the track. In addition to the air screen, much energy is spent for the "skirt". Therefore, the aerodynamic drag factor Cx here is 0.5 at best. If we take a unibus, which actually moves in the air and has a special shape, its Cx is 0.05. In fact, experimentally we received 0.04. Even a little bit less. I'll disclose the secret - 0.03. However, there are wheels, wheel arches, splits in the doors, an air intake, etc. There are also narrow rails that create some small air screen.

— A current collector, too.

— No, we do not have protuberances. We do not have current collectors, though we have a current-collecting unit. It is electrified, but there is no overhead contact system. Therefore, we have some small change for the worse. So, look here, if we take this formula, it becomes obvious that, all other things being equal, when the cross-section is equal, the difference is by 10 times. Since the resistance force depends on Cx, in our version the force of aerodynamic drag will be 10 times less compared to Transrapid magnetic cushion train. 10 times. In addition, we spend 22 times less energy. Therefore, to compare the efficiency, we should multiply 22 by 10. The difference is by two orders of magnitude. Therefore, Elon Mask realized something in this connection. Perhaps, his engineers have calculated something and explained. That's why he made such speech.

— [ Speech of Elon Mask ]

— I repeat I realized it more than 30 years ago after doing such analysis.

— Anatoly, how would creation of a magnetic field affect the cost of route construction?

— Well, a magnetic field can be created only on a flyover. Its cost would increase tenfold, even by 15 times. By dozens of times. There is a simple explanation for it, because in addition to a heavyweight beam, a conventional bridge beam along which the rolling stock moves, high-voltage cables should be laid. Coils should be arranged for the carriage suspension. And the coils are placed rather densely, in every meter. They are large. Then various switches, commutators, etc. Just imagine, a 1,000 km route will have about 1 million coils. Large copper coils. Naturally, it is very expensive.

— Then why such reputable companies that you have mentioned, in particular, Transrapid creators, educated, clever and laborious nations, like Germans and Japanese, spend time on such things, if it is so inefficient and expensive?

— The term is very nice. Magnetic cushion. They fall for the words. It's lyrics. But beside lyrics there is physics. Engineers are human, too. They also want to do something beautiful and interesting. And this opinions that a magnetic cushion reduces energy consumption, derives from lack of experience. It's easy! Suspend it, push it and it goes by itself! But this is not so.

— Do you really need a chair on a magnetic cushion? A chair with wheels copes with its duties perfectly, too.

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