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This is a technical discussion about Hyperloop, getting behind all the media hype, and looking at how it could actually work. Are the researchers heading in the right direction?
We look at Air skis, Maglev, and Wheels, and see which is the most suitable for high speed transportation. Which technology will be most achievable and give the best results?
Video snippets courtesy of Virgin Hyperloop One, Hyperloop Transportation Technologies, Ohio State Engineering, Luke Starkenburg
My comments about the progress of the commercial companies is my assessment, based on the limited technical information they publish.
My figures about maglev performance is a best estimate, after extensive research. It’s difficult because they have never published any technical data. If they were proud of their energy efficiency, they would let us know!
There are three choices of levitation for Hyperloop; Air skis, maglev, and wheels.
In this video I’m going to discuss the merits of each, look at what’s been done so far, and suggest a better way to make progress.
The air ski proposal would never produce enough air flow to lift the pod. This is a simple calculation, backed up by failed experiments by various teams. With air skis failing, Hyperloop researchers have now decided to use maglev. Once again, they have committed to one technology without really looking at the alternatives. Are they making the same mistake again?
So we’ll compare maglev and wheels to see which one is most suitable for Hyperloop.
Speed. The Blue Flame rocket car, in 1970 achieved an amazing 1014 km an hour using Goodyear pneumatic tyres. The fastest is Thrust SST at 1228 km, their ultimate speed was limited by the sound barrier, not their metal wheels.
We can see that wheels can perform reliably at double the maximum speed of the fastest maglev.
Modern car tyres are very efficient, with a 300:1 lift/drag ratio, and racing bicycle tyres are better at 500:1.
Traction efficiency. Traction is not often discussed, but it is very important as it’s the major cause of maglev’s high energy consumption. A high-speed pod will use a lot of energy to reach full speed, we need good efficiency to recover most of it on braking.
Maglev uses linear motors, the circular ring around the motor is rolled out along the full length of the track, which could be hundreds of kilometres long. Traction efficiency is compromised, because it’s too expensive to use the exotic materials and precision construction of a normal motor. Linear motors are 70% efficient, or less, compared to conventional motors driving wheels which are 90% efficient. So linear motors waste three times as much traction energy.
Mechanical wear is the one feature where maglev has the advantage. This is an important challenge for wheels, and the main focus for research. It’s inevitable that there will be running expenses due to wear of the wheels, but we need to minimise the effect on the overall operating expenses. Hyperloop is the most extraordinary project, why would anyone choose air skis and maglev, instead of the obvious choice of wheels? Maybe the attraction of hyper technology! Air cushion and maglev are not novel, futuristic concepts, they have both been researched for a very long time. The reason you don’t see them operating is because they don’t work very well and are too expensive.
So now we’ll look at how to develop wheels that are suitable for high speed transportation.
How do we keep the passengers comfortable when cornering? Aircraft do it by banking to the correct angle so the passengers feel upright but with some extra g-force. Wheels can do the same, the pod can run up the side of the tube at exactly the right angle, so that high speeds can be maintained in curves. This would be very difficult with maglev.
Surprisingly, pneumatic tyres are the best solution. The tyre is an incredibly strong structure, it can run at 1,000 kph, using the normal construction of polyester fibres, steel, but with very thin rubber.
With Kevlar and carbon fibre, the tyre would be structurally capable of running at 2,000 kph.
The pneumatic tyre is ideal for smoothing out bumps, it has good grip, and low rolling resistance.
We don’t need any dramatic new inventions, just a combination of existing technology to suit the purpose. We can reduce the rotational stress, and increase the speed with a large diameter tyre, 1.5 m (5ft) or larger.We need hard rubber to reduce wear, of course we don’t need wet grip like road tyres. The structure needs to be quite thin and flexible, using modern materials like Kevlar or carbon carbon fibre.There is a support ring for run-flat security, this also helps internal cooling because of the lack of outside air flow to keep the tyres cool. The running surface is important, the polished steel tube wall might be ideal, but we can research better options.It’s possible that a thin film of special lubricant on the tube would reduce tyre wear and still allow adequate grip.