"When reading “To the stars!” I was dismayed to see the discussion on Roger Shawyer’s EM Drive.
We read that “Tajmar hopes to have a device that can prove or disprove the EM Drive by the end of the year”. The statement betrays a misunderstanding of the scientific method.
In science and engineering, we deal with uncertainty and confidence intervals. It is only from pure mathematics that we arrive at the concept of proof. If you wanted an ‘experimental proof of zero thrust,’ then supposedly you would need an infinitesimally precise and perfectly infallible measurement device (and supposedly one which also accounts for the Heisenberg uncertainty principle). Such an experimental set-up would be, to say the least, problematic.
Not only is there no statistically significant data to support the claim of any such reactionless engine, but there’s also no physical explanation for the existence of such an engine. The data we have received from this engine also looks suspiciously like the transients one might expect from thermal processes, and so far the only torque demonstrated has fallen within the range of experimental uncertainty.
I’ve seen this story before in discussions on perpetual motion machines which make their way into newspapers and Facebook. In this age of disinformation, I find it a shame that Professional Engineering would present what should be considered pseudoscience until shown otherwise. I suggest we should spend more time discussing proposals for interstellar travel which operate within the known laws, or at least consider more of the impressive recent developments in electric propulsion technology.
Don’t get me wrong; I would enjoy a new issue looking at the crossover from sci-fi to reality. Although in our regular issue I would prefer we didn’t muddy the water and instead show healthy criticism and restraint with regards to features on any such device claiming to break the known laws of physics."
Jay Smith, Derby
Light on the brakes
"I wonder how many “electric cars are bad for you” articles have been written by people who do not own such a vehicle.
Your article describes the dust from tyres and brakes from electric vehicles as being equivalent to that from fossil-fuel vehicles (“Why electric cars won’t stop air pollution”). Not so! When driving an electric car, because of regenerative braking, we barely use our brake pedal, but learn quickly when to lift our foot off the pedal so we stop at the right place without using the brakes at all. And therefore braking is less harsh, reducing tyre wear.
As engineers, we should be careful not to draw conclusions on important issues like airborne pollution from vehicles without thorough consideration of the facts."
Andy Brown, Gloucester
Safety on track?
"There is one aspect of the HS2 proposal that does not seem to have been discussed to a significant degree but is very important – that’s the issue of safety.
A transport system designed for high speed is safer in terms of deaths per passenger mile. Is that not the case with motorways?
The superb French TGV rail system was primarily a project to engineer the track rather than the train, with smooth variations in both horizontal direction and vertical undulations that avoid damaging forces at high speed. On less-smooth track the greater the speed the greater the potential rolling-stock damage or risk of leaving the track.
Rail track these days is welded and avoids shock loads on rolling stock at rail joints. However, there can be minor undulations in the track; a lift of 10mm in 10m (0.1%) can produce quite a shock loading at speed. At 240km/h, 10m is covered in 0.15 seconds. That 10mm lift is quite an impact load on the unsprung part of a train. Very high impacts when encountered on a bend could cause derailment.
I am unable to fully calculate the impact or load which might cause a real problem but I believe the possibility is clear and depends on the geometry of the track.
High-specification track smoothness would not cause these problems. Is there a specification for safe very high-speed track in terms of smoothness in both vertical and horizontal planes which would safely accommodate say 500km/h?
The combination of even a moderately tight curve and a fast train can cause derailment as we saw a few years ago when a driver in Spain took a bend at a higher than recommended speed and derailed.
I have no doubt that current trains on current tracks have the power to travel almost as fast as HS2 but the issue I have is the margin of safety.
There was a successful attempt on the train speed record in France in 2007 when 574.8km/h was achieved. The YouTube video is gripping.
I am not suggesting that would be a wise normal speed but one could feel pretty safe on a TGV at its normal speed of half that rate.
How near to the safe limit is our current track, not upgraded to the proposed HS2 standards?
I understand the TGV train on the record run needed some mechanical attention after the attempt. However, the point is HS2 is primarily a high-speed track which fast trains can use well within safety parameters, with a future lower risk of death. How do you cost that?
Modernisation of high-speed road started in Germany in 1941. We caught up in 1959 with the M1. France introduced high-speed rail in 1981 – we need to catch up now. The high-speed Channel tunnel line to London is an extension of the TGV system and not a significant part of our national infrastructure.
Modernisation of rail transport in the US seems to be disappointing, reportedly influenced by the oil lobby favouring road and air travel. Can there be a better place for an environmentally friendly high-speed rail system? Vast distances in a rich country."
Carl Stalker, Canewdon, Essex
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.