Thursday, 1 September 2011

Judit Nadal, Inquest Findings

This link is to the Daily Mail report on the inquest into the death of Judit Nadal, a researcher at Imperial College, London.
It seems that she did make a mistake of some kind, shortly before her electric car was hit by a much heavier Skoda. The Gee Whiz Electric car was turning across the path of the Skoda and the broadside impact tore the Gee Whiz in half. Which makes argument as to whether Judit Nadal was wearing a seat-belt or not a little academic.

The Coronor and Investigating Officer make some comments as to the lightness of the Gee Whiz.
Actually, it's more to do with strength and weight distribution. The cockpit of a Formula One racing car weighs less than a Gee Whiz, but if a driver stays in it, he can survive enormous impacts which send the cockpit safety cell spinning through the air.

The Gee Whiz is very light, but within that light weight, is a very heavy battery pack, which concentrates nearly all of the vehicle's mass under the back seat behind the driver. The photograph of the wreckage clearly shows that the structure failed, almost neatly, along the front of the battery. Had the light structure not contained the battery, the heavier Skoda might simply have knocked it spinning across the junction. This wouldn't necessarily be survivable; that would depend on the nature of subsequent impacts, especially if this involved a still larger vehicle which might ride over the Gee Whiz. But still, surviving the first impact would in most cases leave the occupant facing smaller second and subsequent impacts, so it would be a worthwhile improvement of the odds. Especially as a structure which survives the initial massive impact, can also be made to shed kinetic energy in s series of glancing impacts as it bounces around. This is why the crash of a modern Formula One car looks terrible, but is survivable. It's meant to spin around the landscape, so that it loses energy, with glancing impacts on a different bit of structure each time.

There is not just a need for the structure of lightweight electric vehicles to be made stronger and "smarter" (more thought given to where the strength is), but also for the mass of the power source to be spread over the vehicle. It appears the Nadal's car was hit at a position and angle which ideally exploited the mass and strength of the battery to shear the vehicle in half. If the front of the Gee Whiz had shared more of the mass, it might not have been cut in half.

This is an argument for electric vehicle development to centre on super-capacitors rather than environmentally questionable lithium batteries, let along nickel-based batteries which are proven environmental disasters.

Super capacitors are more efficient, in that pretty well all the electricity put in can be got out, and they can absorb massive surges of power, allowing much more effective use of regenerative braking. They are also much lighter for any given amount of energy stored, which would allow more of the car's weight to be structure than battery. And they do not suffer from such a rapid loss of storage capacity as chemical batteries.

But the prime virtue of super-capacitors is that they are made of carbon nano-fibres and they are themselves very strong structural components. This, coupled with the fact that they can last the economic life of the car, means that they can be used throughout the structure, making everything stronger and avoiding any single concentration of weight that concentrates the force of an impact on what becomes a line of failure.

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