Glider power systems

[Bill Daniels]

After reading the annual installment of the 12V vs.14V soap opera and the
"We can't power any more electronics" whine, I took a little time to read
the Maxwell Electronics information on their Ultracaps.

See: http://www.maxwell.com/index.html

Maxwell makes a pretty good case for combining a small ultracapcitor with a
NiMH or Lithium-ion battery for use in typical consumer electronics like
computers and cellphones. It seems to me that the devices in our gliders
could use the Maxwell approach. Transmitters place a high demand on the
batteries for short periods and the varios and flight computers place a low
demand for long hours.

The Sealed Lead Acid batteries most of us use are great for short, heavy
amperage demands but not so hot for powering electronics for long hours.
The typical NiMH or increasingly common lithium-Ion are great for low
current devices but not good at high current demands. Maxwell's solution is
to combine a low amperage power source with an Ultracap so the Ultracap
handles the high-current short-duration, demands like transmitters and the
main lithium-ion battery handles the low-current, long-duration demand.

Of course, you still need the same AH's to go the distance but your
transmitter will get the voltage it needs at the end of a long day. We need
our EE's to quit arguing about 14V vs. 12V and whip up a nice circuit for an
Ultracap + Lithium-ion battery.

Bill Daniels

[Stephen Haley]

I thought that some LIon are actually quite good at high current draw
applications. They are certainly making inroads into the model plane market
now their price is dropping. The main problem with them is their pontential
to explode if shorted out through thermal runaway and they require
specialised charging requirements. A secondary problem is that you cannot
measure the battery state through voltage.
The main advantages of lion are the light weight per amphour BUT they are
bulkier than lead acid by about a factor of 2.
At my level (Rank beginner using club equipment) the main problem is
normally that the battery is either getting old or is not charged. Going
back to my sailing days we converted to using NiFe batteries as we could
charge them at over 300 amps, 30mins motering gave us full batteries,, the
voltage was almost constant until completely discharged and they could be
badly abused (completely flattened) and still recover. I know that they
are/were used in aviation for engine starting but not sure if they were ever
used in flight.

For real usable results in battery technology I suspect we should look to
the new Hybrid Petrol/Electric cars being developed by Toyota but as with
all things it wil take time for them to be affordable/usable.

I suspect a real driver in Glider battieries will be the requirement in
Europe for Mode S transponders with some countries adopting them before
discrete iterrogation is switched on meaning that in some areas transponders
may be interrogated many times a min. This will require some real
improvement in battery technology for existing gliders where retrofitting
with solar charging would be difficult .

rgds
stephen

"Bill Daniels" > wrote in message
news:fK5mc.27410$TD4.3881262@attbi_s01...
> After reading the annual installment of the 12V vs.14V soap opera and the
> "We can't power any more electronics" whine, I took a little time to read
> the Maxwell Electronics information on their Ultracaps.
>
> See: http://www.maxwell.com/index.html
>
> Maxwell makes a pretty good case for combining a small ultracapcitor with
a
> NiMH or Lithium-ion battery for use in typical consumer electronics like
> computers and cellphones. It seems to me that the devices in our gliders
> could use the Maxwell approach. Transmitters place a high demand on the
> batteries for short periods and the varios and flight computers place a
low
> demand for long hours.
>
> The Sealed Lead Acid batteries most of us use are great for short, heavy
> amperage demands but not so hot for powering electronics for long hours.
> The typical NiMH or increasingly common lithium-Ion are great for low
> current devices but not good at high current demands. Maxwell's solution
is
> to combine a low amperage power source with an Ultracap so the Ultracap
> handles the high-current short-duration, demands like transmitters and the
> main lithium-ion battery handles the low-current, long-duration demand.
>
> Of course, you still need the same AH's to go the distance but your
> transmitter will get the voltage it needs at the end of a long day. We
need
> our EE's to quit arguing about 14V vs. 12V and whip up a nice circuit for
an
> Ultracap + Lithium-ion battery.
>
> Bill Daniels
>
>

[Bill Daniels]

"Stephen Haley" > wrote in message
...
> I thought that some LIon are actually quite good at high current draw
> applications. They are certainly making inroads into the model plane
market
> now their price is dropping. The main problem with them is their
pontential
> to explode if shorted out through thermal runaway and they require
> specialised charging requirements. A secondary problem is that you cannot
> measure the battery state through voltage.
> The main advantages of lion are the light weight per amphour BUT they are
> bulkier than lead acid by about a factor of 2.

I don't think you are right about the comparison with SLA's. Li-Ion has a
much greater power per unit volume and weight than Lead. The thermal
runaway has been solved with imbedded safety circuitry. (BTW, a shorted,
fully charged SLA isn't too nice to be around either but main fuses take
care of this.)

I don't need to monitor battery state if I know it will last twice as long
as I need it to. Cell phones with Li-ion batteries work just fine if
charged regularly. (A five-day battery charged daily is a no-problemo.)

BTW, I have no financial interest in Maxwell Technologies or Ultracaps, they
just have a nice web site that explains the technology well. Their point is
that batteries designed for low discharge rates will last a lot longer than
those designed for fast discharge. Ultracaps can supply short bursts of
high current for transmissions and recharge from the low discharge rate
Li-ion's. For a given size and weight, a Li-ion + Ultracap should be able
to power a lot more electronics than an equivalent SLA.

Bill Daniels

[Robert Ehrlich]

Bill Daniels wrote:
> ...
> Cell phones with Li-ion batteries work just fine if
> charged regularly.
> ...

No. Most lead-acid batteries in my club are much older than
my cell phone and are still working, while the battery of my
cell phone is dead.

[Martin Gregorie]

On Wed, 5 May 2004 16:21:59 +0000 (UTC), "Stephen Haley"
> wrote:

>I thought that some LIon are actually quite good at high current draw
>applications. They are certainly making inroads into the model plane market
>now their price is dropping. The main problem with them is their pontential
>to explode if shorted out through thermal runaway and they require
>specialised charging requirements. A secondary problem is that you cannot
>measure the battery state through voltage.
>The main advantages of lion are the light weight per amphour BUT they are
>bulkier than lead acid by about a factor of 2.
>
Are you sure? I made some calculations of Li-poly vs NiCd, comparing
two Kokam 145 mAh Li-poly cells delivering 5 v through a 7805 v.reg
with a five cell pack of Sanyo N50-AAA (50 mAh) cells. The Kokam pack
gives three times the capacity for 1/2 the weight and 2/3 the volume
of the NiCd pack. It's power/wt ratio is about 4.5 times better and
its power/volume ratio is 4 times better than the NiCds.

On a quick and dirty comparison using a Kobe 12v 7 Ah gel cell and
5500 mAh D-size NiCds an equivalent NiCd pack (10 x D cells) would be
very similar in power/volume ratio to the gel cell - certainly within
+/- 10%. A cross check for Sanyo 7Ah F-size cells gives the same
answer, but the super-F (10 Ah, F-size) will have a 30% better
power/volume ratio than a gel cell. I've no idea about power/weight
ratios: I haven't got anything to hand that can weigh the 12v gel
cell.

Li-poly cells are better and safer than Li-ion cells: the Li-poly seem
to be more popular with the indoor RC crowd than Li-ion. I think both
will spontaneously combust if the thin plastic cover is pierced.

As others have pointed out, you MUST have a special (and relatively
expensive) charger for Li-Poly cells.

>For real usable results in battery technology I suspect we should look to
>the new Hybrid Petrol/Electric cars being developed by Toyota but as with
>all things it wil take time for them to be affordable/usable.
>
What sort of battery technology do these use?

>I suspect a real driver in Glider battieries will be the requirement in
>Europe for Mode S transponders with some countries adopting them before
>discrete iterrogation is switched on meaning that in some areas transponders
>may be interrogated many times a min. This will require some real
>improvement in battery technology for existing gliders where retrofitting
>with solar charging would be difficult .
>
Although available NiMH cells of AA cell size or smaller have double
the power density of NiCd there's nothing in Maplins or RS catalogues
bigger than 2.3 Ah C and D-size cells while NiCds go to 10 Ah per
cell. Has anybody spotted an NiMH with a capacity of 5 Ah or bigger?

So, it looks like the answer will be Li-poly, then. Expensive, and
requiring crash-proof containers to prevent the outer membrane being
pierced in a crash and causing a fire.


--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

[Bill Daniels]

"Robert Ehrlich" > wrote in message
...
> Bill Daniels wrote:
> > ...
> > Cell phones with Li-ion batteries work just fine if
> > charged regularly.
> > ...
>
> No. Most lead-acid batteries in my club are much older than
> my cell phone and are still working, while the battery of my
> cell phone is dead.

My cell phone Li-ion battery was still working fine after five years when
the service provider went bad.

OTOH, I replace my glider SLA at every two years or sooner to be sure I have
full capacity. It makes me wonder how many complaints about $3000+ flight
computers and varios are due to the owner being too cheap to buy a new $30
battery. Flaky lead acid batteries make most electronics flaky too.

Bill Daniels

[Mihael]

If you are interested in lithium batteries there is tons of information's on
address:

http://www.saftbatteries.com/120-Techno/20-10_Lithium_system.asp

Michael

"Robert Ehrlich" > wrote in message
...
> Bill Daniels wrote:
> > ...
> > Cell phones with Li-ion batteries work just fine if
> > charged regularly.
> > ...
>
> No. Most lead-acid batteries in my club are much older than
> my cell phone and are still working, while the battery of my
> cell phone is dead.

[Mike Borgelt]

On Wed, 05 May 2004 13:11:39 GMT, "Bill Daniels" >
wrote:

>After reading the annual installment of the 12V vs.14V soap opera and the
>"We can't power any more electronics" whine, I took a little time to read
>the Maxwell Electronics information on their Ultracaps.
>
>See: http://www.maxwell.com/index.html
>
>Maxwell makes a pretty good case for combining a small ultracapcitor with a
>NiMH or Lithium-ion battery for use in typical consumer electronics like
>computers and cellphones. It seems to me that the devices in our gliders
>could use the Maxwell approach. Transmitters place a high demand on the
>batteries for short periods and the varios and flight computers place a low
>demand for long hours.
>
>The Sealed Lead Acid batteries most of us use are great for short, heavy
>amperage demands but not so hot for powering electronics for long hours.
>The typical NiMH or increasingly common lithium-Ion are great for low
>current devices but not good at high current demands. Maxwell's solution is
>to combine a low amperage power source with an Ultracap so the Ultracap
>handles the high-current short-duration, demands like transmitters and the
>main lithium-ion battery handles the low-current, long-duration demand.
>
>Of course, you still need the same AH's to go the distance but your
>transmitter will get the voltage it needs at the end of a long day. We need
>our EE's to quit arguing about 14V vs. 12V and whip up a nice circuit for an
>Ultracap + Lithium-ion battery.
>
>Bill Daniels
>


Do we really have a problem that requires this if we use 2 x 7 A-h
sealed lead acid batteries? I use one routinely, keep the other
charged and when #1 dies, switch to # 2 which doesn't have any
charge/discharge cycles on it (you might like to do one to confirm it
is a good battery). After the flight put #2 in the #1 position and put
a new battery in #2.

Automatic chargers for lead acid are cheap and available. Li-ion
batteries are *very* fussy about charging and can be dangerous if this
is done incorrectly.

In many respects our power requirements are lower nowadays. We aren't
running old 360 channel radios full of TTL logic that drew up to 800mA
on standby receive.

Modern radios have standby receive currents of 25 to 100mA.
A B50 vario draws about 100mA
A B40 18mA until you turn the volume up.
GPS receivers are now available that will draw as little as 30Ma from
a 12 volt source.
Our B2000 glide computer draws 50mA.

Allow about 300mA for continuous load and the 7 A-h battery has plenty
of capacity for the whole day even allowing for some reduction with
age and receive/transmit loads.

Add a transponder and you get about another 400mA continuous.

Still likely OK for normal use and you have the other battery at the
end of the day.

What you should do is actually measure what your systems consume. You
may get a surprise.

Also check that you aren't losing volts between the battery and the
systems. Measure the voltage at the battery and at the system. You may
have some unwanted resistance in the circuit.

Use good mil- spec aircraft wire to do your installation. Put a fuse
right on the battery terminal.

We may get a reduction of a few pounds of weight by going to Li
batteries and supercaps and /or some increase in capacity. The
question becomes - how much do you want to pay for this?

Mike Borgelt

[Tim Ward]

"Stephen Haley" > wrote in message
...
> I thought that some LIon are actually quite good at high current draw
> applications. They are certainly making inroads into the model plane
market
> now their price is dropping. The main problem with them is their
pontential
> to explode if shorted out through thermal runaway and they require
> specialised charging requirements. A secondary problem is that you cannot
> measure the battery state through voltage.
> The main advantages of lion are the light weight per amphour BUT they are
> bulkier than lead acid by about a factor of 2.

The other advantage is that they work much better at low temperatures --
which is significant if you're flying in, say, wave.

<snippage>

Tim Ward

[Bill Daniels]

"Mike Borgelt" > wrote in message
...
> On Wed, 05 May 2004 13:11:39 GMT, "Bill Daniels" >
> wrote:
>
> >After reading the annual installment of the 12V vs.14V soap opera and the
> >"We can't power any more electronics" whine, I took a little time to read
> >the Maxwell Electronics information on their Ultracaps.
> >
> >See: http://www.maxwell.com/index.html
> >
> >Maxwell makes a pretty good case for combining a small ultracapcitor with
a
> >NiMH or Lithium-ion battery for use in typical consumer electronics like
> >computers and cellphones. It seems to me that the devices in our gliders
> >could use the Maxwell approach. Transmitters place a high demand on the
> >batteries for short periods and the varios and flight computers place a
low
> >demand for long hours.
> >
> >The Sealed Lead Acid batteries most of us use are great for short, heavy
> >amperage demands but not so hot for powering electronics for long hours.
> >The typical NiMH or increasingly common lithium-Ion are great for low
> >current devices but not good at high current demands. Maxwell's solution
is
> >to combine a low amperage power source with an Ultracap so the Ultracap
> >handles the high-current short-duration, demands like transmitters and
the
> >main lithium-ion battery handles the low-current, long-duration demand.
> >
> >Of course, you still need the same AH's to go the distance but your
> >transmitter will get the voltage it needs at the end of a long day. We
need
> >our EE's to quit arguing about 14V vs. 12V and whip up a nice circuit for
an
> >Ultracap + Lithium-ion battery.
> >
> >Bill Daniels
> >
>
>
> Do we really have a problem that requires this if we use 2 x 7 A-h
> sealed lead acid batteries? I use one routinely, keep the other
> charged and when #1 dies, switch to # 2 which doesn't have any
> charge/discharge cycles on it (you might like to do one to confirm it
> is a good battery). After the flight put #2 in the #1 position and put
> a new battery in #2.
>
> Automatic chargers for lead acid are cheap and available. Li-ion
> batteries are *very* fussy about charging and can be dangerous if this
> is done incorrectly.
>
> In many respects our power requirements are lower nowadays. We aren't
> running old 360 channel radios full of TTL logic that drew up to 800mA
> on standby receive.
>
> Modern radios have standby receive currents of 25 to 100mA.
> A B50 vario draws about 100mA
> A B40 18mA until you turn the volume up.
> GPS receivers are now available that will draw as little as 30Ma from
> a 12 volt source.
> Our B2000 glide computer draws 50mA.
>
> Allow about 300mA for continuous load and the 7 A-h battery has plenty
> of capacity for the whole day even allowing for some reduction with
> age and receive/transmit loads.
>
> Add a transponder and you get about another 400mA continuous.
>
> Still likely OK for normal use and you have the other battery at the
> end of the day.
>
> What you should do is actually measure what your systems consume. You
> may get a surprise.
>
> Also check that you aren't losing volts between the battery and the
> systems. Measure the voltage at the battery and at the system. You may
> have some unwanted resistance in the circuit.
>
> Use good mil- spec aircraft wire to do your installation. Put a fuse
> right on the battery terminal.
>
> We may get a reduction of a few pounds of weight by going to Li
> batteries and supercaps and /or some increase in capacity. The
> question becomes - how much do you want to pay for this?
>
> Mike Borgelt

With what's in my glider now, one 7.5AH 12V SLA is good enough. I was just
answering the question, "Are we running out of power to run all these
electronic gadgets". The answer is no, there are plenty of options for the
future even if that future means full glass cockpits, transponders and
situational awareness aids.

Better battery options are available now and they will get better in the
future. As you point out, Mike, electronics makers are constantly lowering
power demand. Taken together, the two trends insure that we can add a lot
of avionics if we choose to.

Your point about wiring is very true. We tend to put the batteries behind
the pilot and the electronics forward. A much lighter battery could go
right in the panel without affecting the CG much and the wiring runs would
be much shorter.

I have a friend who mixes his metaphors. He says that lead batteries in
gliders makes as much sense as an air-cooled submarine.

Bill Daniels

[DGManley]

>Li-poly cells are better and safer than Li-ion cells:

Before you become convinced of their safety, take a gander at this warning
issued by the Academy of Model Aeronautics.

Emergency Safety Alert: Lithium Battery Fires
(Added 4/23/04)

Lithium batteries are becoming very popular for powering the control and power
systems in our models. This is true because of their very high energy density
(amp-hrs/wt. ratio) compared to Nickel Cadmium (Ni-Cds) or other batteries.
With high energy comes increased risk in their use.
The principal risk is fire which can result from improper charging, crash
damage, or shorting the batteries. All vendors of these batteries warn their
customers of this danger and recommend extreme caution in their use.

In spite of this many fires have occurred as a result of the use of Lithium
Polymer (Li-Poly) batteries, resulting in loss of models, automobiles, and
other property. Homes and garages and workshops have also burned.

A lithium battery fire is very hot (several thousand degrees) and is an
excellent initiator for ancillary (resulting) fires. Fire occurs due to contact
between lithium and oxygen in the air. It does not need any other source of
ignition or fuel to start, and burns almost explosively.

These batteries must be used in a manner that precludes ancillary fire. The
following is recommended:

Store and charge in a fireproof container, never in your model.
Charge in a protected area devoid of combustibles. Always stand watch over the
charging process. Never leave the charging process unattended.
In the event of damage from crashes, etc., carefully remove to a safe place for
at least a half hour to observe. Physically damaged cells could erupt into
flame. After sufficient time to ensure safety, damaged cells should be
discarded in accordance with the instructions which came with the batteries.
Never attempt to charge a cell with physical damage regardless of how slight.
Always use chargers designed for the specific purpose, preferably having a
fixed setting for your particular pack. Many fires occur in using
selectable/adjustable chargers improperly set. Never attempt to charge lithium
cells with a charger that is not specifically designed for charging lithium
cells. Never use chargers designed for Ni-Cd batteries.
Use charging systems that monitor and control the charge state of each cell in
the pack. Unbalanced cells can lead to disaster if it permits overcharge of a
single cell in the pack. If the batteries show any sign of swelling,
discontinue charging and remove them to a safe place—outside—as they could
erupt into flames.
Most important: NEVER PLUG IN A BATTERY AND LEAVE IT TO CHARGE UNATTENDED
OVERNIGHT. Serious fires have resulted from this practice.
Do not attempt to make your own battery packs from individual cells.
These batteries cannot be handled and charged casually such as has been the
practice for years with other types of batteries. The consequence of this
practice can be very serious and result in major property damage and/ or
personal harm.

—AMA Safety Committee

[Martin Gregorie]

On 06 May 2004 16:41:36 GMT, (DGManley) wrote:

>>Li-poly cells are better and safer than Li-ion cells:
>
>Before you become convinced of their safety, take a gander at this warning
>issued by the Academy of Model Aeronautics.
>
I didn't say "safe", merely safer, but I was wrong. See below.

Here's an account with pictures of what happens when a fully charged
Li-poly cell is charged for an hour at 1 amp and twice its rated
voltage...

http://www.rcgroups.com/forums/showthread.php?s=&threadid=151687&perpage=15&pagenumber=1

I've seen it said that Li-poly cells are more stable than Li-ion but
no supporting evidence as to why this should be so. Now here's a
statement from the manufacturer of "Thunder Plus" Li-poly and Li-ion
cells. Makes interesting reading.

"The “Lithium Polymer battery” used in the hobby and in most
commercial applications is really a Lithium-ion battery that has had
the internal power generating materials folded to a flat matrix
instead of rolled up to fit in the cylindrical can, it is then
installed in a light aluminium container that was original designed
for food storage but works great. The good news is that the “lithium
Polymer battery” is a bit lighter and has the ability to support
higher loads because of it’s ability to dissipate heat under higher
loads. This is the good part; the other side of the coin is that under
the charging process the “Lithium Polymer cells” don’t include any of
the safety systems that are part of a Lithium-ion cylindrical cell, so
the cell has no way of protecting itself. This then requires control
of the charging cycle imperative. There was/is a false presentation in
the hobby that the “Lithium Polymer Battery” is completely safe and
won’t create an unhappy experience. The electrolyte used in these
cells is liquid and flammable. If the cell or pack is overcharge
(voltage) for any reason the first indication is that the cell will
start to puff up like a balloon. If you are lucky the cell pops (gas
release vent) and you cut off the charge before further problems. I
will say that lithium doesn’t like exposure to oxygen."

I guess that answers me. Li-poly are no safer than Li-ion. I've only
looked at the Kokam website in detail, but did notice that most of the
cells they sell have protection circuitry attached to them though all
are flat and contained in just a plastic membrane.

I'm not sure whether the fire/explosion problem is due to:

1) the high energy density
2) ease of electrical damage at high discharge rates
3) ease of electrical damage with improper charging
4) using a thin plastic membrane to contain an assembly
that is spontaneously flammable in air and explosive in the
presence of water.

My guess (and that's all it is) is that (3) and (4) are the most
significant causes of Li-poly fires.

There's already a direct bearing on cockpit fires because the
batteries in iPAQ PDAs (certainly in the 36xx series and probably the
others too) are Li-poly cells. They are flat, encased in a silvered
plastic membrane and don't appear to contain cell protection circuits.
The cell is stuck to the plastic backplate of the iPAQ with nothing
separating it from the PCB except its membrane. I replaced one
recently in my iPAQ 3630: that's how I know this.

BTW, I would not want to be in a closed cockpit with a lithium cell
that had even vented without burning: the 'white smoke' is almost
certainly LiOH (lithium hydroxide) and that's at least as corrosive as
caustic soda.

From the Academy of Model Aeronautics:

>Emergency Safety Alert: Lithium Battery Fires
>(Added 4/23/04)
>
>Lithium batteries are becoming very popular for powering the control and power
>systems in our models. This is true because of their very high energy density
>(amp-hrs/wt. ratio) compared to Nickel Cadmium (Ni-Cds) or other batteries.
>With high energy comes increased risk in their use.
>The principal risk is fire which can result from improper charging, crash
>damage, or shorting the batteries. All vendors of these batteries warn their
>customers of this danger and recommend extreme caution in their use.
>
>In spite of this many fires have occurred as a result of the use of Lithium
>Polymer (Li-Poly) batteries, resulting in loss of models, automobiles, and
>other property. Homes and garages and workshops have also burned.
>
>A lithium battery fire is very hot (several thousand degrees) and is an
>excellent initiator for ancillary (resulting) fires. Fire occurs due to contact
>between lithium and oxygen in the air. It does not need any other source of
>ignition or fuel to start, and burns almost explosively.
>
>These batteries must be used in a manner that precludes ancillary fire. The
>following is recommended:
>
>Store and charge in a fireproof container, never in your model.
>Charge in a protected area devoid of combustibles. Always stand watch over the
>charging process. Never leave the charging process unattended.
>In the event of damage from crashes, etc., carefully remove to a safe place for
>at least a half hour to observe. Physically damaged cells could erupt into
>flame. After sufficient time to ensure safety, damaged cells should be
>discarded in accordance with the instructions which came with the batteries.
>Never attempt to charge a cell with physical damage regardless of how slight.
>Always use chargers designed for the specific purpose, preferably having a
>fixed setting for your particular pack. Many fires occur in using
>selectable/adjustable chargers improperly set. Never attempt to charge lithium
>cells with a charger that is not specifically designed for charging lithium
>cells. Never use chargers designed for Ni-Cd batteries.
>Use charging systems that monitor and control the charge state of each cell in
>the pack. Unbalanced cells can lead to disaster if it permits overcharge of a
>single cell in the pack. If the batteries show any sign of swelling,
>discontinue charging and remove them to a safe place—outside—as they could
>erupt into flames.
>Most important: NEVER PLUG IN A BATTERY AND LEAVE IT TO CHARGE UNATTENDED
>OVERNIGHT. Serious fires have resulted from this practice.
>Do not attempt to make your own battery packs from individual cells.
>These batteries cannot be handled and charged casually such as has been the
>practice for years with other types of batteries. The consequence of this
>practice can be very serious and result in major property damage and/ or
>personal harm.
>
>—AMA Safety Committee
>
>

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

[kotka]

I saw a small fuel cell system (2 lbs and about the size
of a beer can) designed to power a Pro Video camera.
The kind that you normally see used in remote news
trucks. I don't remember the specs that they were
quoting but it was much better than the normal batteries.
Not that I would want to fly with a fuel cell yet but they
are working on it.....
Rob

[Mike Borgelt]

On Thu, 06 May 2004 02:31:35 GMT, "Bill Daniels" >
wrote:

>
>I have a friend who mixes his metaphors. He says that lead batteries in
>gliders makes as much sense as an air-cooled submarine.
>
>Bill Daniels


Ever noticed the strange looks you get from power pilots or members of
the public when you tell them your glider carries hundreds of pounds
or water?

The safety stuff about lithium batteries looks interesting doesn't it?

Mike