🚀 go-pugleaf

I would just like to chime in that while I beleive that the problems
of catastrophic failure is a real problem with flywheels, I also feel
that the problem might be solvable.

As was discussed, all the energy of the flywheel will be dumped in
a accident and methods must be developed to insure a explosion does 
not result.   Here are some possibilities

1) Slow down the rate of energy dumping.  Good design should allow that
  even under conditions of a crash the flywheel will remain intact and
  contained.  Thus instead of blowing apart what we want is for the
  wheel to bang around inside a housing, loosing energy as it colides
  with the housing.  Thus instead of dumping all its energy in under
  a second, it will release it over the period of many seconds (the
  longer the better)  This reduces the problem tremendously.

2) Avoid or control the explosion.  If the materials in the housing 
  vaporize only a VERY high temperatures, then even in the flywheel
  dumps its energy, no GASES will be generated, and thus no explosion.
  Alternately, you can use gas creation to absorb the enery and design
  methods of savely venting it.

3) Absorb the energy.  There is no reason why some of the energy could
  be converted to something besides heat.  If the housing was lined with
  some chemical that underwent fast, a heavily endothermic reaction, much
  of the energy could be absorbed as chemical potential energy.  (High
  heat of melting or vaporization?) If such chemicals can't be found, as 
  a worst case, the housing could be made out of something with a high heat 
  capacity and high melting point.  

Finally, if all of these fail, a flywheel will still be possible simply
by scaling it down.    As was mentioned, the large POWER density of
a flywheel make it ideal for regenerative breaking.  It may be desirable
to have a small flywheel for this purpose.  Since it holds far less 
energy, make int safe should be easy.

I believe a road worthy flywheel can be made.  The only question is 
is it worth it.  It might be too heavy or too expensive, or there simply
might be better ways of storing energy for vehicular applications.

Vance