On Tue, 15 Apr 2008 22:35:03 GMT, wrote in
:

Larry Dighera wrote:
On Tue, 15 Apr 2008 17:45:04 GMT, wrote in
:

Another limitation is that for something the size of a C-172, your
battery has to deliver around 120 kW to get off the ground and
climb to altitude.


I don't see that fact as being too limiting. Why do you feel that's
an issue?

Big wires your battery has to deliver that much power without going
up in flames, yet be light enough to carry on an airplane.


If the electric motor, controller, battery, and fuel-cell are sited in
close proximity to each other (al la Sonex), the connecting bus can be
kept reasonably short. As in IC engine powered aircraft, there is the
necessity to dump waste heat to the atmosphere. The electric motor,
controller, and Li-ion battery are quite efficient, but they do
generate considerable heat at the power level you chose as an example
(C-172; ~166 HP). Here's John Monnett describing the system:

http://www.youtube.com/watch?v=P8Pb_psj1A8
Sonex Electric Powered Flight, EAA AirVenture Oshkosh 2007
John Monnett

Of course there is always the potential for fire when dealing with
volatile or reactive fuels as we've been discussing. Engineers have
been reasonably successful in designing systems that minimize the
probability of that hazard. That would, of course, part of the
development goal.

As a "back of the envelope" hack at the practicability of an hydrogen
(/oxygen) fuel-cell powered electric aircraft employing present day
technology, I'd say it looks worth an effort if for no other reason
than to be ready to exploit future technical discoveries as they are
made.

[snip]

However according to the articles below, hydrogen embrittlement
doesn't seem to be an issue with carbon fiber composite cylinders:

http://en.wikipedia.org/wiki/Hydrogen_tank
A Hydrogen tank (other names- cartridge or canister) is used for
hydrogen storage, most tanks are made of composite material
because of hydrogen embrittlement. Some tanks are used for fixed
storage others are exchangeable for refueling at a hydrogen
station[1].


http://www1.eere.energy.gov/hydrogen...s/32405b27.pdf
The 5,000 and 10,000 psi tanks developed by QUANTUM Technologies
have been validated to meet the requirements of DOT FMVSS304,
NGV2-2000 (both modified for 10,000 psi hydrogen) and draft
E.I.H.P standard. Typical safety tests completed, in order to
ensure safety and reliability in an automotive service environment
included: Burst Tests (2.35 safety margin), Fatigue, Extreme
Temperature, Hydrogen Cycling, Bonfire, Severe Drop Impact Test,
Flaw Tolerance, Acid Environment, Gunfire Penetration, Accelerated
Stress, Permeation and Material Tests.

And nowhere does it say anything about the actual tank weight.


It was the best information I could find quickly. Over the course of
our discussion, I believe I've provided enough information to show
that the weight of the electrical equipment would be at least in the
same order of magnitude as that it would be replacing if not
reasonably close to equaling it, not only in weight, but power and
runtime. There will be differences to be sure.

The very last thing you would want to do is put it in a wing spar.

Why do you believe that is true?

Hydrogen embrittlement.


Not that I'm sincerely proposing it, but if spar/cylinder of a carbon
fiber composite tube could be successfully developed, it might be
feasible, as it appears the that material is not affected by hydrogen
embrittlement. At least that's what the information I found implies.
Personally, I don't see why it would be, as it would seem that
hydrogen could as easily migrate through composite as metal.

Of course these rough theoretical calculations are predicated on
existing technologies, and don't consider the inevitable future
technical advancements.

Which are no better than a wish and a hope in the real world.


You've got to start somewhere, right?

Why?


At this time in the history of civilization, with the planet's finite
petroleum reserves being pumped at ever higher volume, and the onset
of climate change, it would seem prudent to have the power to produce
a non-polluting, renewable-energy powered aircraft (in the event
anti-gravity technology doesn't become practicable BG) before the
use of our present fuel becomes impractical.

Diesel airplanes sound like a lot better idea than electric or hydrogen
airplanes to me, plus the technology to do it exists now.


It not only exists, you can currently purchase diesel converted
Cessnas. I'm not considering becoming involved in an electric
project, but it does look like electric may actually be achievable.

Diesel airplanes need some refinement to be generally usefull.

Electric and hydrogen airplanes need new and major basic science
breakthroughs which may not ever occur and right now are nothing
more than a pipe dream.

I believe Boeing's recent effort has demonstrated that electric fuel
cell aircraft motive power is achievable with current technology.
Hopefully Boeing's demonstration will provide some impetus toward
improvement and refinement.