Boeing Fuel Cell Plane Flies At Last!

....And now for a slight thread-hijack:

OK, so no one here is arguing against the end-product: An
electrically-powered propeller or ducted fan.

Can I stop for a minute and say "WTF?" to the recent article about
how jet engines are the future of self-launch?
(I think this was in SOARING magazine, IIRC)

Jets are wonderful devices for specific missions (especially sustained
thrust at higher speeds, where props become less efficient). But in a
glider, at low speed and for short periods of time?

The article talks about how the jets are improving and becoming more
and more suited to use in a sailplane... But:
1) You still have to carry a dangerous, liquid, flammable fuel. Oh,
and that fuel can turn to vapor that might incapacitate the pilot if
breathed, and the fuel can EAT your aircraft's core materials in some
cases, if it seeps into the structure - yipes!

2) Despite being reliable and simple compared to an internal-
combustion engine, jet engines still have as much or more complexity
than a simple electric motor. The heat and stress on bearings and
other parts has got to be higher than an electric motor, right?

3) Jets put out a LOT more HEAT than an electric motor. Can anyone
tell me how resins that cure at ambient-temperature levels are
supposed to hold up well when a jet engine retracts inside the
fuselage while its still hot? I've heard that they can cool down
efficiently in as little as 30 - 45 seconds; but what about operator
error? What about the distance / altitude lost during that wait
period? I know the drag of a turbine is less than a big ol' prop; but
still...

4) With a jet, you already need electrical equipment, for the starters
and igniters and such. Why add a whole second fuel/energy-delivery
system (i.e. Jet-A) when you can stick with a single source and a
single output?

OK, OK, I'll quit ranting... :-P

--Noel

Weight and size. (you did ask)

noel.wade wrote:
...And now for a slight thread-hijack:

OK, so no one here is arguing against the end-product: An
electrically-powered propeller or ducted fan.

Can I stop for a minute and say "WTF?" to the recent article about
how jet engines are the future of self-launch?
(I think this was in SOARING magazine, IIRC)

Jets are wonderful devices for specific missions (especially sustained
thrust at higher speeds, where props become less efficient). But in a
glider, at low speed and for short periods of time?

The article talks about how the jets are improving and becoming more
and more suited to use in a sailplane... But:
1) You still have to carry a dangerous, liquid, flammable fuel. Oh,
and that fuel can turn to vapor that might incapacitate the pilot if
breathed, and the fuel can EAT your aircraft's core materials in some
cases, if it seeps into the structure - yipes!

2) Despite being reliable and simple compared to an internal-
combustion engine, jet engines still have as much or more complexity
than a simple electric motor. The heat and stress on bearings and
other parts has got to be higher than an electric motor, right?

3) Jets put out a LOT more HEAT than an electric motor. Can anyone
tell me how resins that cure at ambient-temperature levels are
supposed to hold up well when a jet engine retracts inside the
fuselage while its still hot? I've heard that they can cool down
efficiently in as little as 30 - 45 seconds; but what about operator
error? What about the distance / altitude lost during that wait
period? I know the drag of a turbine is less than a big ol' prop; but
still...

4) With a jet, you already need electrical equipment, for the starters
and igniters and such. Why add a whole second fuel/energy-delivery
system (i.e. Jet-A) when you can stick with a single source and a
single output?

OK, OK, I'll quit ranting... :-P

--Noel

On Apr 10, 10:52 pm, Bruce wrote:
Weight and size. (you did ask)

I did. :-)

Weight: Hopefully Cui's battery improvements (or some similar change)
will alleviate the need to carry many pounds of batteries.

Size: Have you seen how small a powerful brushless electric motor is
these days? The prop has a large dimension in one direction; but at
least it can lie parallel to the mast and not take up much total
volume. I'm surprised there hasn't been more work on a ducted fan
solution - maybe the blades would just have to be too short to be
efficient, and still fit inside the aft fuselage... *shrug*

Take care,

--Noel

Hi Noel

This has exercised my little brain for some time.
The brushless DC motor is a perfect motive unit. Small, relatively light, simple
and reliable, and its performance is perfect for the job. It produces almost
flat torque, and will swing an efficient propeller with the same torque at the
high density altitudes I fly at.
The batteries are getting smaal enough that it could be done - Existing
improvements like the A123 Lithium batteries are not only safe but have much
better energy densities.
However - the batteries size comes with shape constraints as well, whereas you
can put that smelly dino stuff into just about any shape you want.
And the other part is also a problem, the propeller demands a large hole in the
structural strength determining skin of the boom. So you need to add lots of
heavy strengthening as well as doors etc.

If I ever work out how to do it and stay under the "non-lifting" limits my Std
Cirrus will be an experimental self launcher...

Bruce

noel.wade wrote:
On Apr 10, 10:52 pm, Bruce wrote:
Weight and size. (you did ask)

I did. :-)

Weight: Hopefully Cui's battery improvements (or some similar change)
will alleviate the need to carry many pounds of batteries.

Size: Have you seen how small a powerful brushless electric motor is
these days? The prop has a large dimension in one direction; but at
least it can lie parallel to the mast and not take up much total
volume. I'm surprised there hasn't been more work on a ducted fan
solution - maybe the blades would just have to be too short to be
efficient, and still fit inside the aft fuselage... *shrug*

Take care,

--Noel

On Apr 8, 10:01 pm, sisu1a wrote:
Here is a link to an article about the first manned fuel cell flight.
It has been in the works for some time, and wonderful to see it coming
to fruition:http://www.gizmag.com/first-manned-f...e-flight/9117/
For those who don't know, Boeing converted a Dimona motorglider to
have an electric motor, and on board proton exchange membrane (PEM)
hydrogen fuel cells (integrated with L-ions) that generate enough
juice to power the aircraft during powered level flight. Neat stuff!

Paul

Now if they could only get the 787 into the air.
http://news.google.com/news?hl=en&ta...nG=Search+News