Electric Motorglider Flies

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?


However, hydrogen gas compressed to a pressure of ~10,500 psi [700 bar] (143
MJ/kg) would only weigh ~1/3 as much as the equivalent gasoline energy
it replaces. If that hydrogen were used along with atmospheric oxygen
to produce electricity by a fuel-cell with a typical efficiency of
~36% http://en.wikipedia.org/wiki/Fuel_cell#Efficiency, and the
efficiency of the electrical motor, wiring, and controller were 90%,
and the weights of the total systems were roughly equivalent, it would
appear that there would be a close approximation of performance of
today's aircraft including waste heat, but not noxious emissions nor
noise. I'm not sure exactly how the overall efficiency would be
affected by the use of pressurized oxygen, or if both the hydrogen and
oxygen were produced by the electrolysis of water by photovoltaics.
(Now, if the compressed hydrogen were carried in a tubular wing spar,
imagine it's rigidity... /dream mode)

You are forgetting about the enormous weight of a tank capable of
containing hydrogen at 10,500 psi

Of course gasoline also requires tanks, but they are often just sealed
parts of the wing structure, so their weight isn't really significant.
I don't know the strength of carbon-fiber or Kevlar composite, but
pressure cylinders constructed of them are about 60% lighter than
comparable Al cylinders
http://www.mhoxygen.com/images/Cylinder-dimensions.pdf. It would
appear that carbon fiber or Kevlar composite pressure cylinders may be
strong enough to contain the high pressure.

There's a tensile strength chart he


http://en.wikipedia.org/wiki/Tensile...sile_strengths

Material Ultimate strength (MPa) Density (g/cm³)
================================================== =========
Steel,
high strength alloy
(ASTM A514) 760 7.8
Carbon Fiber 5650 1.75


as well as the problem of hydrogen emb[r]ittlement at those pressures.


From the information at the link below it's not clear if carbon
composite materials are subject to hydrogen embrittlement.

http://en.wikipedia.org/wiki/Hydrogen_embrittlement
Process
The mechanism begins with lone hydrogen atoms diffusing through
the metal. When these hydrogen atoms re-combine in minuscule voids
of the metal matrix to form hydrogen molecules, they create
pressure from inside the cavity they are in. This pressure can
increase to levels where the metal has reduced ductility and
tensile strength, up to the point where it cracks open ("Hydrogen
Induced Cracking", or HIC). High-strength and low-alloy steels,
aluminum, and titanium alloys are most susceptible. Steel with a
ultimate tensile strength of less than 1000 MPa or hardness of
less than 30 HRC are not generally considered susceptible to
hydrogen embrittlement.



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.


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

Why do you believe that is true?


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?

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.

However, hydrogen gas compressed to a pressure of ~10,500 psi [700 bar] (143
MJ/kg) would only weigh ~1/3 as much as the equivalent gasoline energy
it replaces. If that hydrogen were used along with atmospheric oxygen
to produce electricity by a fuel-cell with a typical efficiency of
~36% http://en.wikipedia.org/wiki/Fuel_cell#Efficiency, and the
efficiency of the electrical motor, wiring, and controller were 90%,
and the weights of the total systems were roughly equivalent, it would
appear that there would be a close approximation of performance of
today's aircraft including waste heat, but not noxious emissions nor
noise. I'm not sure exactly how the overall efficiency would be
affected by the use of pressurized oxygen, or if both the hydrogen and
oxygen were produced by the electrolysis of water by photovoltaics.
(Now, if the compressed hydrogen were carried in a tubular wing spar,
imagine it's rigidity... /dream mode)

You are forgetting about the enormous weight of a tank capable of
containing hydrogen at 10,500 psi

Of course gasoline also requires tanks, but they are often just sealed
parts of the wing structure, so their weight isn't really significant.
I don't know the strength of carbon-fiber or Kevlar composite, but
pressure cylinders constructed of them are about 60% lighter than
comparable Al cylinders
http://www.mhoxygen.com/images/Cylinder-dimensions.pdf. It would
appear that carbon fiber or Kevlar composite pressure cylinders may be
strong enough to contain the high pressure.

There's a tensile strength chart he


http://en.wikipedia.org/wiki/Tensile...sile_strengths

Material Ultimate strength (MPa) Density (g/cm?)
================================================== =========
Steel,
high strength alloy
(ASTM A514) 760 7.8
Carbon Fiber 5650 1.75


as well as the problem of hydrogen emb[r]ittlement at those pressures.


From the information at the link below it's not clear if carbon
composite materials are subject to hydrogen embrittlement.

http://en.wikipedia.org/wiki/Hydrogen_embrittlement
Process
The mechanism begins with lone hydrogen atoms diffusing through
the metal. When these hydrogen atoms re-combine in minuscule voids
of the metal matrix to form hydrogen molecules, they create
pressure from inside the cavity they are in. This pressure can
increase to levels where the metal has reduced ductility and
tensile strength, up to the point where it cracks open ("Hydrogen
Induced Cracking", or HIC). High-strength and low-alloy steels,
aluminum, and titanium alloys are most susceptible. Steel with a
ultimate tensile strength of less than 1000 MPa or hardness of
less than 30 HRC are not generally considered susceptible to
hydrogen embrittlement.



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.

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.

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?

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

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.


--
Jim Pennino

Remove .spam.sux to reply.

On 2008-04-15, Larry Dighera wrote:
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?

120kW, or about 160 horsepower, at any sane voltage is going to be a
tremendous amount of current. If your supply voltage to the motor was
600 volts, you'd need to deliver 200 amps. This requires a serious piece
of cable to do efficiently (i.e. without getting insanely hot). It also
needs batteries or a power source with a very low resistance to not also
get very hot. With typical high current motive applications like trains
or cars you can just add more metal to the conductors to the motors. You
have a weight issue with aircraft, though, with both the control
circuitry and the high voltage, high current wiring.

Of course gasoline also requires tanks, but they are often just sealed
parts of the wing structure, so their weight isn't really significant.
I don't know the strength of carbon-fiber or Kevlar composite, but
pressure cylinders constructed of them are about 60% lighter than
comparable Al cylinders

It's not just the tanks - you also have to make an idiot proof fuelling
system that can be operated by the typical 17 year old line boy, but is
capable of handling *five tonnes* per square inch of pressure.

To put that into perspective, that's like two SUVs sitting on each
square inch of pipe, connector and tank. Without even considering the
energy content of the actual fuel, the potential energy of even an
inert gas at those sorts of pressure would result in very bad stuff
happening if someone got careless with the fuelling equipment.

While the engineering challenges can be solved, it's never going to be
anything remotely resembling low cost due to the enormous pressures
involved, and the safety issues with handling anything at those enormous
pressures.

--
From the sunny Isle of Man.
Yes, the Reply-To email address is valid.

On Wed, 16 Apr 2008 11:07:53 +0000 (UTC), Dylan Smith
wrote in
:

On 2008-04-15, Larry Dighera wrote:
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?

120kW, or about 160 horsepower, at any sane voltage is going to be a
tremendous amount of current. If your supply voltage to the motor was
600 volts, you'd need to deliver 200 amps. This requires a serious piece
of cable to do efficiently (i.e. without getting insanely hot).

I would use bus bar instead of cable. Here's a chart showing the
ampacity for copper bus bar:
http://www.stormcopper.com/design/Am...uick-Chart.htm
It indicates that 1/4" X 1" copper would conduct 400 amps with a 30 °C
temperature rise.

It also needs batteries or a power source with a very low resistance to not also
get very hot.

Internal resistance is a serious issue, and deserves serious
consideration. The battery internal resistance is considerably better
than that of the fuel cell. From the battery specification sheet here
http://a123systems.textdriven.com/product/pdf/1/ANR26650M1_Datasheet_MARCH_2008.pdf
it would appear that it's not impossible (10 m0hms typical). The fuel
cell internal resistance is considerably higher, but I took that into
consideration in my previous rough calculations.

With typical high current motive applications like trains
or cars you can just add more metal to the conductors to the motors. You
have a weight issue with aircraft, though, with both the control
circuitry and the high voltage, high current wiring.

That is true. To decrease conductor weight silver might be
substituted for copper, but it would only provide about a 10%
improvement.

It seems fuel-cells have a rather high internal resistance at high
currents. That's where most of the losses will be.

Of course gasoline also requires tanks, but they are often just sealed
parts of the wing structure, so their weight isn't really significant.
I don't know the strength of carbon-fiber or Kevlar composite, but
pressure cylinders constructed of them are about 60% lighter than
comparable Al cylinders

It's not just the tanks - you also have to make an idiot proof fuelling
system that can be operated by the typical 17 year old line boy, but is
capable of handling *five tonnes* per square inch of pressure.


It would appear that has already been done:
http://www.fuelcells.org/info/charts...ngstations.pdf
http://www.sciencedirect.com/science...1eb7fca01a8c1d
http://biz.yahoo.com/prnews/080331/lam082.html?.v=101
http://www.ieahia.org/pdfs/honda.pdf

To put that into perspective, that's like two SUVs sitting on each
square inch of pipe, connector and tank. Without even considering the
energy content of the actual fuel, the potential energy of even an
inert gas at those sorts of pressure would result in very bad stuff
happening if someone got careless with the fuelling equipment.


It's currently being done, so evidently the technology exists.

While the engineering challenges can be solved, it's never going to be
anything remotely resembling low cost due to the enormous pressures
involved, and the safety issues with handling anything at those enormous
pressures.

It appears that it's currently cost effective enough to be viable in
the marketplace. Perhaps you are able to provide some information
that supports your assertion.

Thanks for your input, Dylan.

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.

Larry Dighera wrote:
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:

Why in the world would you have a battery and a fuel cell, ignoring
for the moment that neither is practical for aircraft use?

Any waste heat just makes the problem worse. Neither batteries nor
fuel cells have the energy density required with 100% efficiency,
much less with energy ****ed away as heat.

The big wires have to be IN the battery. You think nano wires are
going to carry 120 kW?

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.

A lab toy and press release fodder, nothing else for the forseeable
future.

snip

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.

Why?

It makes more sense to put the effort into producing cheap electricity
on the ground, which has a much better chance of sucess, then synthesize
engine fuel with it.


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.

Not a chance. The electric airplane, not the diesel.

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.

Well, sure, if you goal is to spend a huge pile of money to get a
motor glider up 3000 feet.

The Boeing demo was PR for military products, pure and simple.


--
Jim Pennino

Remove .spam.sux to reply.

There is an electric motorglider that has been in series production
for over a year now, with others entering the market this year. 57 HP
motor running at 190 - 288V and pulling up to 160A. The Li-ion
battery pack delivers 10,000 feet of climb before depletion. In the
absence of soaring conditions, this translates to roughly 100 miles of
range. Certainly these are not figures that meet airplane
requirements, but they do very nicely for a motorglider, and I think
they go along way toward proving the feasibility of electric powered
aircraft for certain applications.

http://lange-flugzeugbau.com/htm/eng...tares_20E.html



On Apr 16, 5:07 am, Dylan Smith wrote:
On 2008-04-15, Larry Dighera wrote:

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?

120kW, or about 160 horsepower, at any sane voltage is going to be a
tremendous amount of current. If your supply voltage to the motor was
600 volts, you'd need to deliver 200 amps. This requires a serious piece
of cable to do efficiently (i.e. without getting insanely hot). It also
needs batteries or a power source with a very low resistance to not also
get very hot. With typical high current motive applications like trains
or cars you can just add more metal to the conductors to the motors. You
have a weight issue with aircraft, though, with both the control
circuitry and the high voltage, high current wiring.

Of course gasoline also requires tanks, but they are often just sealed
parts of the wing structure, so their weight isn't really significant.
I don't know the strength of carbon-fiber or Kevlar composite, but
pressure cylinders constructed of them are about 60% lighter than
comparable Al cylinders

It's not just the tanks - you also have to make an idiot proof fuelling
system that can be operated by the typical 17 year old line boy, but is
capable of handling *five tonnes* per square inch of pressure.

To put that into perspective, that's like two SUVs sitting on each
square inch of pipe, connector and tank. Without even considering the
energy content of the actual fuel, the potential energy of even an
inert gas at those sorts of pressure would result in very bad stuff
happening if someone got careless with the fuelling equipment.

While the engineering challenges can be solved, it's never going to be
anything remotely resembling low cost due to the enormous pressures
involved, and the safety issues with handling anything at those enormous
pressures.

--
From the sunny Isle of Man.
Yes, the Reply-To email address is valid.

There