Can Aircraft Be Far Behind?

wrote)
If a Cri-Cri were to be set up with electric motors and a battery, how
big (heavy) would the battery need to be to allow the pilot to: Take-off,
fly around for 15 minutes at 100 kts, and land?

Altair has a graph on their Web site that seems to show that their
batteries will give 90 Wh/kg at a 15-minute discharge rate. On the other
hand, that graph also has "Altair's Disruptive Technology" written on it,
which means it was probably produced by salesmen and not engineers. If you
take the 90 Wh/kg at face value, you'd need about 169 lb (77 kg) of
batteries.


This is why I love these groups!!

Thanks for the answer.

Ok, so 170 lbs worth of batteries it is! :-)

I have 50 lbs 'to give' swapping over to electric. So now all I need to do
is find 120 remaining lbs (55 kg) of weight, and shave THAT off the Empty
Weight of the Cri-Cri.

Gotta start somewhere! g


Montblack

http://www.technologyreview.com/Energy/18054/

describes GM's plans to build car with A123 System Li Ion batteries

James Robinson wrote:

You are correct that the hydrogen itself is very light for each unit of
energy. The problem is the weight of the container necessary to hold
that energy.

Hydrogen molecules are the smallest in nature, and as such, they will
more easily pass through container walls than other types of energy
source. That means any containers have to be more complicated than a
simple tank that holds fuel like avgas. They are typically built with a
number of layers to not only resist impact and rupture, but they also
have to be thick enough to keep hydrogen leakage to a minimum.

If made with steel, they have to be extra thick because hydrogen affects
the physical properties of steel over time, making the steel more
brittle. This hydrogen embrittlement means that any steel vessels have
to be extra thick to retain their ability to resist impacts. Layers of
other materials can help, but not eliminate the problem.

These requirements mean that the containers will necessarily be heavy.
Further, the containers typically have to be cylindrical in shape,
because of the pressures involved. Finding convenient places to put
cylinders in an aircraft would be a challenge.

I was aware of the difficulties in containing the hydrogen, but I was of
the impression that the weight of the container was more than
compensated by the energy to weight ratio of the liquid hydrogen. If
not, why would they use it on the space shuttle? That's not to say that
what works on the space shuttle will work well in an airplane. The
shuttle can be fulled shortly before it is launched, and then burns off
all of it's fuel in just a few minutes. I assume that would allow for
the tank to be lighter than it would have to be if it need to store the
hydrogen for a long period. I also know that things that work on a
large scale often don't work very well on a smaller scale.


--
Chris W
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On 11 Jan 2007 08:38:33 -0800, "JD" wrote in
.com:

http://www.technologyreview.com/Energy/18054/

describes GM's plans to build car with A123 System Li Ion batteries

Here's another link to information about GM's 'Volt prototype hybrid
automobile dated Jan. 7, 2007.


http://www.canada.com/topics/finance...aa&k=45978&p=2
Lutz said the engineering development of the car itself is 18
months from being completed. The batteries are about 18 months
behind the rest of the car.

How many years would that put GM's product behind the Japanese? :-(

Chris W wrote:
I was aware of the difficulties in containing the hydrogen, but I was
of the impression that the weight of the container was more than
compensated by the energy to weight ratio of the liquid hydrogen. If
not, why would they use it on the space shuttle?

Actually there was (and still is) considerable debate on the value of using
liquid hydrogen for rockets - with a fair number of people who consider the
decision to use liquid hydrogen for the shuttle as a design mistake. If you
Google past discussions on groups like sci.space.policy or sci.space.tech
you'll find long-running debates on this issue.

Montblack wrote:
Thanks for the answer.

You're welcome.

Ok, so 170 lbs worth of batteries it is! :-)

If you believe Altair. One rule of thumb for rechargeable batteries
is to apply a correction factor of 0.5 to the numbers the salesman
emits, which puts you up to 340 lbs. Also, call them up and see if they
can sell you some of their batteries if you give them a credit card
number. If they can't, then as far as you're concerned, their batteries
don't really exist.

I have 50 lbs 'to give' swapping over to electric. So now all I need
to do is find 120 remaining lbs (55 kg) of weight, and shave THAT off
the Empty Weight of the Cri-Cri.

Say the Battery Fairy gave you some batteries with an energy density
equal to gasoline. Then, going electric would let you lose the carbs,
cylinders, and exhaust pipes, which would probably help the drag a
little. The shape of an electric motor would make it easy to have a
nice smooth fairing over it, right behind the prop hub. Unfortunately
I've been putting dead D cells under my pillow for years and the Battery
Fairy has never shown up for me.

I wonder what a G1000 weighs, compared to steam gauges.

Matt Roberds

Larry Dighera wrote:
On Tue, 09 Jan 2007 22:54:18 -0600, James Robinson
wrote in :

Considering that a C150 has a usable capacity of only 370 lb. or so
with full fuel, The electically-powered aircraft would already be
more than 200 lb. overloaded, and we haven't even considered the
pilot, passenger, or baggage. Doesn't sound too practical, does it?

Now that you put it that way, reality is beginning to dawn on me.

It's almost like all those engineers working at Cessna and Boeing and
all the rest really _do_ know what they're doing when they pick internal
combustion engines fueled by liquid hydrocarbons.

Given:

http://en.wikipedia.org/wiki/Lithium_ion_battery
Lithium ion battery
Specific energy density: 150 to 200 W?h/kg (540 to 720 kJ/kg)
Volumetric energy density: 250 to 530 W?h/L (900 to 1900 J/cm3)
Specific power density: 300 to 1500 W/kg (@ 20 seconds [2] and 285
W?h/L)

http://en.wikipedia.org/wiki/Gasoline
Gasoline
Energy content
Fuel type Megajoules/L MJ/kg BTU/US gal
Premium Gasoline 32.84 43.50 131,200

Can you quantify the prospect of replacing Avgas with LiIon batteries?

The numbers are there, you just have to deal with metric prefixes a
little bit. Li-ion at 540-720 kJ/kg is 0.540-0.720 MJ/kg. Therefore,
the energy in a kilogram of premium gasoline is equal to the energy in
(43.50/0.720) to (43.50/0.540) or about 60 to 80 kg of Li-ion batteries.

If you consider the whole system, you can get away with fewer batteries,
because electric motors in general are better at converting electrical
to mechanical energy than internal combustion engines are at converting
chemical to mechanical energy. If your engine is 30% efficient, you
only get (43.5 * 0.3) or 13.1 MJ of mechanical energy for every kilogram
of gasoline you burn. If your motor is 90% efficient, then to get that
same 13.1 MJ of mechanical energy, you need to put in about (13.1/0.9)
or 14.5 MJ of electrical energy. This would require (14.5/0.720) to
(14.5/0.540) or about 20 to 27 kg of Li-ion batteries.

Matt Roberds

Don't forget about the volume of the hydrogen tank. An LH2 tank is much
larger in volume than almost any other fuel.

Danny Deger

On Wed, 10 Jan 2007 15:39:17 -0000, Dylan Smith
wrote in
:

On 2007-01-09, Larry Dighera wrote:
Charge time for the Altair batteries is only a few minutes as I
recall.

I'm extremely skeptical - if these batteries are not snake oil, consider
this. Let's call "a few minutes" 10 minutes, and let's say the battery
pack stores 70kWh (enough to run a motor producing 94 hp for 1 hour).

To put 70kWh's worth into a battery pack in 10 minutes would require a
charger capable of putting out 420kW.

At 120 volts, 420kW would require a current of 3500 amps. Look at the
massive thick wire coming into your house (which maybe is rated at 80
amps).

Now let's say these batteries give three hours worth at 70kWh, and
charge in 10 minutes - now you're up to 10,500 amps at 120 volts. YOU
CANNOT AVOID high voltage, high amperage controls in a vehicle like the
Tesla, regardless of the battery technology. You are moving around
tremendous amounts of current. If this mythical charger was 99%
efficient, the 1% emitted as heat could heat an entire office building
in the dead of winter in central Canada. To consider this new battery
technology a silver bullet is to ignore the well established laws of
physics. Now imagine if *everyone* is charging their mythical car. No
practicable electricity distribution network that's feasable in the near
term could cope.

It would be totally and utterly impractical to charge these batteries at
this rate. I'll let you do the calculations for the equivalent in
electricity that filling a Cessna 150 with avgas in 4 minutes (the
typical time to do it at a self serve pump) would be.


The issue of high charging current is true, of course.

After studying the information available on the Altair web site
http://www.altairnano.com/markets_amps.html, it has become apparent
that their battery technology trades energy density for low internal
resistance. So their product is probably not the best choice for
aircraft due to weight considerations.

On 10 Jan 2007 11:59:02 -0800, wrote in
. com:


Larry Dighera wrote (rather quoted a comment from wired.com):
http://www.wired.com/news/wiredmag/0...l?tw=rss.index
The Tesla as it stands is obsolete if it doesn't use the new type
batteries from Altair[**]. It will be the laughingstock of the
business world if it delivers its current overly-complicated
battery system, with its computers and sensors and HVAC system.

Larry, just BTW, the Altair Nano batteries this guy is going on
don't pass the sniff test very well...

Tesla isn't using them because Tesla wants to ship cars
sometime this decade.

Altair claims that WRT conventional graphite electrode lithium-ion
batteries, their TiO nano-granule electrode lithium-ion batteries
have 3X the energy density, 60X the max charge rate, and 10X
the charge-cycle lifetime.

I must have overlooked that "3X energy density" claim. I did see this
marketing claim however:

"Three times the power of existing batteries".

The way I read the chart on the Altair web site
http://www.altairnano.com/markets_amps.html, it looks like Altair's
product's Specific Energy (is that similar to energy density) is about
half of that of conventional LiIon cells.

If these batteries actually existed in a form that would allow
Tesla to ship 200 cars this year, you would think that every
single cell phone and laptop in the universe would be running
on them, wouldn't you? I mean, *I* want my cell phone charge
to last 2 weeks instead of 5 days, *I* want to be able to charge
my laptop in 1 minute, and then have it last through an entire
8-hour flight, *I* want my cell phone battery to
last longer than the phone instead of having to replace the
battery after 18 months.

If you can trust The Motley Fool:
http://www.fool.com/investing/high-g...at-altair.aspx
it looks like it will be Toshiba delivering this technology.

But yet I can't go to batteries.com and buy one of these
wonderful batteries that Tesla is so stupid for not using.
I think there *might* be a reason for that. :-)

Agreed.

BTW, this press release:
http://www.autobloggreen.com/2006/12...-phoenix-moto/

seems to indicate that Altair's entire production volume of batteries
to date is 10 35kWh battery packs for $750,000. It apparently
took 30 days (well, that includes Christmas) to deliver all 10 battery
packs.

I hope Altair and Phoenix are fabulously successful, but there is
good reason for skepticism.

-Jay-

So it would seem.