On Mon, 14 Apr 2008 12:47:38 -0700 (PDT), Andrew Sarangan
wrote in
:


Boeing also recently flew a fuel cell + battery powered airplane.
http://www.avweb.com/avwebflash/news..._197531-1.html

This is a necessary step if GA is to survive past this century. The
technology is just getting started so things can only get better. With
piston engines, the good days are behind us.

Agreed.

With the ever increasing torrent of discoveries being made in physics,
I fully expect advancements in anti-gravity (not to mention quantum
computing) to occur before the end of the century. But I'm an
optimist. Just as likely, some fool will unleash the nuclear dogs of
war, and sterilize our planet.

That said, electrical propulsion does have the potential for three to
four times the efficiency (~90%) of internal combustion engines (~20%
to 30%). Unlike petroleum, sunlight is (for all practical purposes)
not a finite resource, and no nation or region has a monopoly on it.
Imagine a solar powered photovoltaic system on the ground that quietly
electrolyzes water into its constituent parts, hydrogen and oxygen,
percolating away all day long generating the fuel to run a fuel-cell
electric generator (with its exhaust consisting of only pure water).
Photo-cell technology (Spectralab) is currently approaching 40%
efficiency, and electric motors and controllers are =90% efficient,
so clean and quiet electric propulsion is clearly the future.

The application of electric propulsion for aviation today is in its
infancy, and only possible at all because of the technical
breakthrough provided by light Li-ion batteries enabling it. I look
for Li-Ion technology to steadily improve over time. As it is, the
individual cells used today are only approximately the size of common
AA batteries. Imagine the weight savings possible if larger cells
were produced; there would be significantly less steel jacketing
necessary. That said, it's difficult to imagine a battery with the
energy/power density of gasoline, so there will certainly be
tradeoffs.

Despite the fact that electric motors must use iron/steel in their
construction, they are significantly lighter (50%) than their
internal combustion counterparts. But when the wiring, controls,
batteries and perhaps fuel-cells are considered, I would guess the
weight of an electrically powered aircraft would be roughly comparable
to one powered by an internal combustion engine. So, with
significantly less power/energy density than gasoline, batteries will
not provide the same range/duration until they are improved further.
But it is encouraging to see progress being made at last.