CAFE Electric Aircraft Symposium Set For May 1

On Tue, 28 Apr 2015 08:40:43 +1200, george152 wrote:

On 28/04/2015 4:23 a.m., Larry Dighera wrote:
On Mon, 27 Apr 2015 08:25:02 +1200, george152 wrote:

On 27/04/2015 1:58 a.m., Larry Dighera wrote:

Glaring omission: SOLAR IMPULSE
http://us3.campaign-archive2.com/?u=553e7fdb79a7f1570622b070d&id=5e3b071d05&e=2b92d 60fc6
Round the world flight with the Sun as sole fuel source!



Thanks for that Larry.
At present I'm extracting the urine (taking the ****) out of some-one
who thinks the Solar Impulse is a breakthrough.
Pointed out that that last leg took them 17 hours.
Most of the Cessnas and Pipers I fly would do it with 4-6 SOB in 4 hours


You are correct, George. Eric Raymond was flying solely on solar power many
years before the Solar Impulse project began. That said, I know of no other
solar powered aircraft that has succeeded, indeed embarked upon, a
round-the-world flight fueled solely by sunlight as the Solar Impulse has.

Comparing today's electrically powered aircraft to Cessnas and Pipers is a bit
like comparing the Wright Flyer to them; electrically powered aircraft are
still in their infancy of development.

What I found interesting about the symposium was the big names on the roster of
speakers: Airbus, Northrop-Grumman, NASA, Carnegie Mellon University ... It
would seem that electrically powered aircraft are making steady advances in
performance and credibility as they are continuing to be developed and
technology improves.

Personally, I believe that one day the world will look back on the
petroleum-based era of motive power as the "Model T" era, and be thankful for
the development of far more efficient and cleaner electrical power. But then,
as being a "card carrying" IBEW member for over 50 years, and having benefit of
the schooling they provided for four years, I may be a bit biased. :-)


There was an electric aircraft in the 30s.
Had an endurance of 2 hours.

First I've heard of it. Are you able to provide any more information about it?


I checked through some of the current machines.
Apart from the self launched sailplanes most are two seaters with a two
hour endurance.
Any cross country would be limited by the reserve requirement. Don't
know what it is in the US but here minimum is 15 minutes.
Not a great range and the recharge will really stuff your day

Yeah. Current electric aeronautical technology is still a bit nascent. Given
the comparatively high energy density of petroleum-based aviation fuels, it's
going to be difficult to achieve comparable endurance with any electric
technology other than perhaps highly pressurized hydrogen feeding a remarkably
efficient fuel cell generator.

The way I see it currently, is that a lighter than air craft, that doesn't
relies on power to maintain altitude, and could possibly be covered in
photovoltaic "fabric" (such technology is still pretty new.) is a reasonable
starting place with a far better probability of success than winged aircraft.

The high efficiency of electric power is somewhat enabling in potentially
replacing internal combustion power plants be they piston or turbine.

Larry Dighera wrote in
:

Yeah. Current electric aeronautical technology is still a bit nascent.
Given the comparatively high energy density of petroleum-based aviation
fuels, it's going to be difficult to achieve comparable endurance with
any electric technology other than perhaps highly pressurized hydrogen
feeding a remarkably efficient fuel cell generator.

Liquid H: 2,600 WattHours/Liter 39,000 WattHours/Kilogram
Gasoline: 9,000 WattHours/Liter 13,500 WattHours/Kilogram

Gasoline has nearly 3.5 times more energy per volume.

Although liquid hydrogen has nearly 3 times more energy per
unit weight, that does not take into account the mass of the
containment vessel. A liquid hydrogen tank is going to more
than 3 times as massive as a gasoline tank or fuel bladder,
thus resulting in a net loss of energy per unit weight of the
fuel plus it's container.

Brian
--
http://www.earthwaves.org/forum/index.php - Earth Sciences discussion
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Sed quis custodiet ipsos Custodes?

On Mon, 4 May 2015 02:10:28 +0000 (UTC), Skywise
wrote:

Larry Dighera wrote in
:

Yeah. Current electric aeronautical technology is still a bit nascent.
Given the comparatively high energy density of petroleum-based aviation
fuels, it's going to be difficult to achieve comparable endurance with
any electric technology other than perhaps highly pressurized hydrogen
feeding a remarkably efficient fuel cell generator.

Liquid H: 2,600 WattHours/Liter 39,000 WattHours/Kilogram
Gasoline: 9,000 WattHours/Liter 13,500 WattHours/Kilogram

Gasoline has nearly 3.5 times more energy per volume.

Although liquid hydrogen has nearly 3 times more energy per
unit weight, that does not take into account the mass of the
containment vessel. A liquid hydrogen tank is going to more
than 3 times as massive as a gasoline tank or fuel bladder,
thus resulting in a net loss of energy per unit weight of the
fuel plus it's container.

Brian


Thank you for that information. I hadn't seen it before.

I'll agree that a liquid H2 tank will likely be more massive than today's
gasoline tanks, but couldn't liquid H2 be stored in a Styrofoam containing
vessel?

Aren't the relative efficiencies of electrical propulsion vs internal
combustion powerplants being overlooked here?

Larry Dighera wrote in
:

I'll agree that a liquid H2 tank will likely be more massive than
today's gasoline tanks, but couldn't liquid H2 be stored in a Styrofoam
containing vessel?

The problem is either temperature or pressure, or both.

Liquid H2 is cryogenic. It doesn't exert pressure any more than
water does in a tank. But it has to be kept at -423F or -253C.

Styorofoam would just take up space.

If the idea is to avoid the crygenic temperatures, you then
need to fight the pressure. If I did my math right, and read
the phase diagram for hydrogen right, then liquid H2 at room
temperature has a pressure of about 2.5 million atmospheres.
There's no tank in the world that can hold that back.

Pressurized hydrogen at room temperature is just compressed
gaseous hydrogen. So a vehicle with that is like carrying around
a bunch of scuba tanks, which IIRC are only 3000-4000 psi or
about 200 to 270 atmospheres pressure, and look at how heavy
those are!!

I have heard about efforts to store hydrogen in metallic foams
but don't know the state of that work.

The problem is, the energy is in the hydrogen atoms. The more
atoms you have, the more energy you have. So if you want a lot
of energy, you have to cram a bunch of hydrogen atoms together
in a small space.

Now here's the killer. The properties of hydrocarbon molecules
is such that gasoline has a higher density of hydrogen atoms
than even liquid hydrogen!!! There's more hydrogen atoms per
unit volume. That's why gasoline has a 3x higher energy/density
value than liquid hydrogen. There are simply more hydrogen atoms
and therefore more energy.



Aren't the relative efficiencies of electrical propulsion vs internal
combustion powerplants being overlooked here?

My thought on electrical propulsion is, how is the electricity
produced in the first place? One rule of reality is that every
time you convert one form of energy to another, there are losses,
eventually ending up as heat. Basic Laws of Thermodynamics stuff.

Internal combustion (or turbine) engines burn the fuel and directly
convert it to mechanical work. That's bascially only one stage of
conversion to have any conversion losses.

Or, burn the fuel to drive a generator (loss 1), which generates
electricity (loss 2), which is then stored in a battery (loss 3),
which then is drawn from the battery (loss 4) to power an electic
motor (loss 5).

All those conversion losses add up. That's why gasoline is so hard
to beat. Doesn't matter if you like fossil fuels or hate it, it's
a simple fact that right now and in the forseable future, it's the
most efficient energy storage mechanism around.

The only alternative I see is to use elctricity from batteries
but generate the electricity by some other means than fossil fuels.
After all, isn't the whole point of this? to stop burning oil and
polluting the atmosphere? Burning the fossil fuels to generate
electricity to run cars and busses and planes only changes the
location of where it's burned. All these people driving their
electric cars feeling smug about themselves are not realizing that
the electricity is most likely coming from a coal fired generating
plant. And due to conversion losses, there's a good chance they
are actually increasing their "carbon footprint" than decreasing it.

Brian
--
http://www.earthwaves.org/forum/index.php - Earth Sciences discussion
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Sed quis custodiet ipsos Custodes?

Hello Brian,

You seem to have firm grasp of the physics involved. Are you able to suggest
how efficient an electric power system powered by LH2 would have to be to
offset the power density difference from gasoline/kerosene?

Larry


On Mon, 4 May 2015 22:27:45 +0000 (UTC), Skywise
wrote:

Larry Dighera wrote in
:

I'll agree that a liquid H2 tank will likely be more massive than
today's gasoline tanks, but couldn't liquid H2 be stored in a Styrofoam
containing vessel?

The problem is either temperature or pressure, or both.

Liquid H2 is cryogenic. It doesn't exert pressure any more than
water does in a tank. But it has to be kept at -423F or -253C.

Styorofoam would just take up space.

If the idea is to avoid the crygenic temperatures, you then
need to fight the pressure. If I did my math right, and read
the phase diagram for hydrogen right, then liquid H2 at room
temperature has a pressure of about 2.5 million atmospheres.
There's no tank in the world that can hold that back.

Pressurized hydrogen at room temperature is just compressed
gaseous hydrogen. So a vehicle with that is like carrying around
a bunch of scuba tanks, which IIRC are only 3000-4000 psi or
about 200 to 270 atmospheres pressure, and look at how heavy
those are!!

I have heard about efforts to store hydrogen in metallic foams
but don't know the state of that work.

The problem is, the energy is in the hydrogen atoms. The more
atoms you have, the more energy you have. So if you want a lot
of energy, you have to cram a bunch of hydrogen atoms together
in a small space.

Now here's the killer. The properties of hydrocarbon molecules
is such that gasoline has a higher density of hydrogen atoms
than even liquid hydrogen!!! There's more hydrogen atoms per
unit volume. That's why gasoline has a 3x higher energy/density
value than liquid hydrogen. There are simply more hydrogen atoms
and therefore more energy.



Aren't the relative efficiencies of electrical propulsion vs internal
combustion powerplants being overlooked here?

My thought on electrical propulsion is, how is the electricity
produced in the first place? One rule of reality is that every
time you convert one form of energy to another, there are losses,
eventually ending up as heat. Basic Laws of Thermodynamics stuff.

Internal combustion (or turbine) engines burn the fuel and directly
convert it to mechanical work. That's bascially only one stage of
conversion to have any conversion losses.

Or, burn the fuel to drive a generator (loss 1), which generates
electricity (loss 2), which is then stored in a battery (loss 3),
which then is drawn from the battery (loss 4) to power an electic
motor (loss 5).

All those conversion losses add up. That's why gasoline is so hard
to beat. Doesn't matter if you like fossil fuels or hate it, it's
a simple fact that right now and in the forseable future, it's the
most efficient energy storage mechanism around.

The only alternative I see is to use elctricity from batteries
but generate the electricity by some other means than fossil fuels.
After all, isn't the whole point of this? to stop burning oil and
polluting the atmosphere? Burning the fossil fuels to generate
electricity to run cars and busses and planes only changes the
location of where it's burned. All these people driving their
electric cars feeling smug about themselves are not realizing that
the electricity is most likely coming from a coal fired generating
plant. And due to conversion losses, there's a good chance they
are actually increasing their "carbon footprint" than decreasing it.

Brian

Larry Dighera wrote in
:

Hello Brian,

You seem to have firm grasp of the physics involved. Are you able to
suggest how efficient an electric power system powered by LH2 would have
to be to offset the power density difference from gasoline/kerosene?

A quick disclaimer.... I don't have any degrees in this stuff or
work with it. I just happen to be very interested in the sciences
in general and have taught myself a few things over the years.
Having said that, I try very hard to check my facts and figures
before I say anything. I have an allergy to foot-in-mouth disease.

On to your question....

Per numbers in http://www.tinaja.com/glib/energfun.pdf

Liquid H2 has an energy density of 2600 Watt-hours/liter.
Gasoline is 9000 Watt-hours/liter.

[I used energy density per volume rather than per mass
because that's the limiting factor in any vehicle, the
volume of the 'gas tank']

If we make an assumption for discussion's sake that an LH2
powered system were 100% efficient, then the gasoline system
would only need to be 2600/9000 = 29% efficient to reach
parity with LH2. But note that nothing is ever 100% efficient.
There are _always_ conversion losses. It's a matter of how
much.

Per:
http://en.wikipedia.org/wiki/Interna...rgy_efficiency

Engine efficiency is limited by thermodynamic laws. "Most steel
engines have a thermodynamic limit of 37%." Further, "most engines
retain an average efficiency of about 18%-20%."

Right away we see it's at least potentially possible for gasoline
to still beat out 100% efficient LH2. But let's go on the low
side and assume a gasoline engine is 18% efficient. Then we need
to figure out the efficiency required of an LH2 system to beat
gasoline:

9000 * 18% = 1620
1620 / 2600 = 62%

Therefore an LH2 system would have to be 62% efficient overall to
beat a typical gasoline engine.

Per the same Wikipedia article, "Electric motors are better still,
at around 85%-90% efficiency or more, but they rely on an external
power source (often another heat engine at a power plant subject to
similar thermodynamic efficiency limits)."

OK. So an electric motor _by itself_ is more than efficient, but
as stated it has to get it's electricity from somewhere else. We
are assuming an LH2 powered source.

Let's go with the high side of 90% on the electric motor. So we
have to now figure out what efficiency is required in converting
LH2 to electrity so a 90% efficient electric motor produces
1620 Wh/l of LH2...

1620/.90/2600 = 69%

Now that leaves us with finding out how efficiently LH2 can be
converted to electricity.

Per: http://energy.gov/eere/fuelcells/fuel-cells

"Fuel cells can operate at higher efficiencies than combustion
engines, and can convert the chemical energy in the fuel to
electrical energy with efficiencies of up to 60%."

So we may be coming up a bit short.

However, all my pondering here is surely a gross oversimplification.
And it's possible I goofed on my math or went astray with my logic.
And I imagine different sources will give different numbers. But I
hope it gives you some idea. There are surely other factors that
need to be taken into account. Some may make things work out better,
others may make things worse.

Brian
--
http://www.earthwaves.org/forum/index.php - Earth Sciences discussion
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Sed quis custodiet ipsos Custodes?

Skywise wrote:
Larry Dighera wrote in
:

Hello Brian,

You seem to have firm grasp of the physics involved. Are you able to
suggest how efficient an electric power system powered by LH2 would have
to be to offset the power density difference from gasoline/kerosene?

A quick disclaimer.... I don't have any degrees in this stuff or
work with it. I just happen to be very interested in the sciences
in general and have taught myself a few things over the years.
Having said that, I try very hard to check my facts and figures
before I say anything. I have an allergy to foot-in-mouth disease.

On to your question....

Per numbers in http://www.tinaja.com/glib/energfun.pdf

Liquid H2 has an energy density of 2600 Watt-hours/liter.
Gasoline is 9000 Watt-hours/liter.

[I used energy density per volume rather than per mass
because that's the limiting factor in any vehicle, the
volume of the 'gas tank']

If we make an assumption for discussion's sake that an LH2
powered system were 100% efficient, then the gasoline system
would only need to be 2600/9000 = 29% efficient to reach
parity with LH2. But note that nothing is ever 100% efficient.
There are _always_ conversion losses. It's a matter of how
much.

Per:
http://en.wikipedia.org/wiki/Interna...rgy_efficiency

Engine efficiency is limited by thermodynamic laws. "Most steel
engines have a thermodynamic limit of 37%." Further, "most engines
retain an average efficiency of about 18%-20%."

Right away we see it's at least potentially possible for gasoline
to still beat out 100% efficient LH2. But let's go on the low
side and assume a gasoline engine is 18% efficient. Then we need
to figure out the efficiency required of an LH2 system to beat
gasoline:

9000 * 18% = 1620
1620 / 2600 = 62%

Therefore an LH2 system would have to be 62% efficient overall to
beat a typical gasoline engine.

Per the same Wikipedia article, "Electric motors are better still,
at around 85%-90% efficiency or more, but they rely on an external
power source (often another heat engine at a power plant subject to
similar thermodynamic efficiency limits)."

OK. So an electric motor _by itself_ is more than efficient, but
as stated it has to get it's electricity from somewhere else. We
are assuming an LH2 powered source.

Let's go with the high side of 90% on the electric motor. So we
have to now figure out what efficiency is required in converting
LH2 to electrity so a 90% efficient electric motor produces
1620 Wh/l of LH2...

1620/.90/2600 = 69%

Now that leaves us with finding out how efficiently LH2 can be
converted to electricity.

Per: http://energy.gov/eere/fuelcells/fuel-cells

"Fuel cells can operate at higher efficiencies than combustion
engines, and can convert the chemical energy in the fuel to
electrical energy with efficiencies of up to 60%."

So we may be coming up a bit short.

However, all my pondering here is surely a gross oversimplification.
And it's possible I goofed on my math or went astray with my logic.
And I imagine different sources will give different numbers. But I
hope it gives you some idea. There are surely other factors that
need to be taken into account. Some may make things work out better,
others may make things worse.

Brian

The efficiency numbers look to me to be back of an envelope correct.

The real world, however, has very little interest in the energy efficiency
of things like airplanes.

Some numbers that people care about are endurance, operating cost. initial
cost, and life time maintenance cost.

Given some reference platform, such as a C-172, what would be the enduraance
of a LH2 system for that platform versus gas?

How much does 1 hour of LH2 cost versus gas?

In what column do we put the typical 1%/day evaporation loss of LH2 and
the venting equipment you would have to have in a hanger to get rid of
it?

We can swag what a LH2 system would cost from commercial stuff, but how
much of an adder will aircraft certification cost?

LH2 tanks have limited life; inspection and replacement costs?

Energy efficiency is nice to talk about, but it is dollars that make
things happen.


--
Jim Pennino

On Wed, 3 Jun 2015 21:57:44 +0000 (UTC), Skywise
wrote:

Larry Dighera wrote in
:

Hello Brian,

You seem to have firm grasp of the physics involved. Are you able to
suggest how efficient an electric power system powered by LH2 would have
to be to offset the power density difference from gasoline/kerosene?

A quick disclaimer.... I don't have any degrees in this stuff or
work with it. I just happen to be very interested in the sciences
in general and have taught myself a few things over the years.
Having said that, I try very hard to check my facts and figures
before I say anything. I have an allergy to foot-in-mouth disease.

On to your question....

Per numbers in http://www.tinaja.com/glib/energfun.pdf

Liquid H2 has an energy density of 2600 Watt-hours/liter.
Gasoline is 9000 Watt-hours/liter.

[I used energy density per volume rather than per mass
because that's the limiting factor in any vehicle, the
volume of the 'gas tank']

If we make an assumption for discussion's sake that an LH2
powered system were 100% efficient, then the gasoline system
would only need to be 2600/9000 = 29% efficient to reach
parity with LH2. But note that nothing is ever 100% efficient.
There are _always_ conversion losses. It's a matter of how
much.

Per:
http://en.wikipedia.org/wiki/Interna...rgy_efficiency

Engine efficiency is limited by thermodynamic laws. "Most steel
engines have a thermodynamic limit of 37%." Further, "most engines
retain an average efficiency of about 18%-20%."

Right away we see it's at least potentially possible for gasoline
to still beat out 100% efficient LH2. But let's go on the low
side and assume a gasoline engine is 18% efficient. Then we need
to figure out the efficiency required of an LH2 system to beat
gasoline:

9000 * 18% = 1620
1620 / 2600 = 62%

Therefore an LH2 system would have to be 62% efficient overall to
beat a typical gasoline engine.

Per the same Wikipedia article, "Electric motors are better still,
at around 85%-90% efficiency or more, but they rely on an external
power source (often another heat engine at a power plant subject to
similar thermodynamic efficiency limits)."

OK. So an electric motor _by itself_ is more than efficient, but
as stated it has to get it's electricity from somewhere else. We
are assuming an LH2 powered source.

Let's go with the high side of 90% on the electric motor. So we
have to now figure out what efficiency is required in converting
LH2 to electrity so a 90% efficient electric motor produces
1620 Wh/l of LH2...

1620/.90/2600 = 69%

Now that leaves us with finding out how efficiently LH2 can be
converted to electricity.

Per: http://energy.gov/eere/fuelcells/fuel-cells

"Fuel cells can operate at higher efficiencies than combustion
engines, and can convert the chemical energy in the fuel to
electrical energy with efficiencies of up to 60%."

So we may be coming up a bit short.

However, all my pondering here is surely a gross oversimplification.
And it's possible I goofed on my math or went astray with my logic.
And I imagine different sources will give different numbers. But I
hope it gives you some idea. There are surely other factors that
need to be taken into account. Some may make things work out better,
others may make things worse.

Brian


Hello Brian,

Thank you for your fair and conservative analysis. Very much appreciated.

So generally on a theoretical basis, it is within the realm of possibility that
using LH2 to generate electric power with a fuel-cell to power an electric
motor might be completive in terms of performance with today's General Aviation
internal combustion powered aircraft, because the efficiency of the
electrically powered system is potentially so much greater than the IC
technology, that it compensates for the reduced power density of the LH2 fuel
compared to petroleum. The laws of physics don't prohibit it.

Of course, for this to be realized, significant engineering remains to be
accomplished, but the path to electrically powered aircraft isn't a dead end
due to the laws of physics.

Larry

On 5/3/2015 10:10 PM, Skywise wrote:
Although liquid hydrogen has nearly 3 times more energy per
unit weight, that does not take into account the mass of the
containment vessel. A liquid hydrogen tank is going to more
than 3 times as massive as a gasoline tank or fuel bladder,
thus resulting in a net loss of energy per unit weight of the
fuel plus it's container.

I'm not sure where you got that information from, but it's wrong.
Compressed hydrogen takes a heavy tank because of the pressure.

On the other hand, liquid hydrogen need not be under pressure, so it
does not need a massive tank. However, cryogenic fuels have their own
issues! What a cryogenic fuel tank needs that is different from other
liquid fuels is insulation. That insulation need not be heavy, but it
will take up valuable volume in your airframe. Also, cryogenic tanks
are always venting unless you have heavy, expensive power-hungry
refrigeration equipment aboard. So that means that your liquid
hydrogen-fueled airplane could be assumed to be sitting in a cloud of
flammable gaseous fuel whenever it is fueled and sitting on the ground.
No thanks!

Vaughn wrote in :

On 5/3/2015 10:10 PM, Skywise wrote:
Although liquid hydrogen has nearly 3 times more energy per
unit weight, that does not take into account the mass of the
containment vessel. A liquid hydrogen tank is going to more
than 3 times as massive as a gasoline tank or fuel bladder,
thus resulting in a net loss of energy per unit weight of the
fuel plus it's container.

I'm not sure where you got that information from, but it's wrong.

http://www.tinaja.com/glib/energfun.pdf

The numbers can be confirmed by other sources.

But I think you misread what I wrote.

Brian
--
http://www.earthwaves.org/forum/index.php - Earth Sciences discussion
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Sed quis custodiet ipsos Custodes?