From Newsgroup: rec.aviation.piloting

Jim Pennino <jimp@gonzo.specsol.net> wrote:

Larry Dighera <LDighera@att.net> wrote:

On Sat, 28 Dec 2024 20:56:20 -0800, Jim Pennino <jimp@gonzo.specsol.net> wrote:

Larry Dighera <LDighera@att.net> wrote:

On Sat, 28 Dec 2024 15:22:37 -0800, Jim Pennino <jimp@gonzo.specsol.net> >>>> wrote:

<snip old crap>

Energy density by any any metric.

I'd prefer to see a complete sentence, at least.

Are you referring to the comparative energy density of petroleum and Lithium
batteries?

If so, when you factor in system efficiency, they're not so far apart. >>>>

Even if you factor in efficiency, the best REAL sources of electrical >>>energy all have energy densities in J/kg and J/m^3 that are far less than >>>an order of magnitude than that of either gasoline or jet-a.

That has NOT changed in all the years you have been posting.

Jim,

From your response, I infer that I failed to state my view clearly enough to convey my meaning to you.

Unlike you, I am not a credentialed engineer, and I most assuredly do not have the mathematical skills of one. So, I posed this issue to ChatGPT:

You are aware, are you not, that AIs are known to lie and make stuff up?

I asked ChatGPT when the lithium battery was invented as that should
be an easy question about a factual historical event. The AI went on
and on about the first rechargeable lithium battery made in 1970 and
then bloviated at length about battery development in the 1980's. The
correct answer to the question I asked is 1912, i.e. the date when
the first lithium battery was made.

AI doesn't ever say WTF are you talking about and will make up answers, sometimes just wrong and sometimes out of whole cloth.

If a vehicle requires 100 hp for operation and its engine/motor is 25% efficient for vehicle A and 98% efficient for vehicle B, solve for J/kg and J/m^3 for each A and B.

Bzzzt, wrong question to ask.

The energy densities of fuels and electrical sources are well known
quanties and are a trivial lookup.

The energy efficiencies of engines are well known quanties and are about
30 - 35% for piston engines, 30 - 40% for turbine engines and 85 - 95%
for electric engines.

The horsepower for aircraft is also a trivial lookup. For example, a
Cessna 182 ranges from 230 to 300 horsepower or 172 to 224 kilowatts.

Note that this is the actual power produced by the engine and the energy efficiency of the engine is irrelevant to the problem because we are
using actual engine power.

For a 182 with a 230 HP engine and 75 gallon tanks and an altitude of
5000 feet, the endurance is 3.4 hours at 75% power and 3.9 hours at 65%
power with a 45 minute reserve.

Therefore a 182 carries 520 - 535 kWh of real, actual energy on board in
the form of 205 kg of 100LL.

The question to ask is, for the various real sources of electricity that
can actually be purchased, what is the weight and volume for 520 - 535
kWh of energy?

When I asked that question for lithium-ion batteries I got an answer of
1962 - 2600 kg. 1962/205 = 9.6 which is basically an order of magnitude
more weight and 207 - 275 gallons which in the best case is 2.8 times
the volume.

<snip huge pile based on not understanding the actual problem>

After going over the numbers, I have some corrections. I misread the
endurance graph and forgot to account for start, taxi, takeoff and climb
fuel.

At 5000' and 65% power the range of a 182P is 725 nm and the endurance
is 5.5 h and a speed of about 134 KTAS.

The tanks hold 75 gal usefull and 1.8 gal are used for start, taxi and
takeoff, 2.9 gal for a normal climb from S.L. to 5000' with 6.5 gal for reserve.

Fuel used for these is thus 11.2 gal or 30.6 kg leaving 63.8 gal or
174.2 kg.

172 kW x 65% x 5.5 h = 614.9 kWh of real energy.

614.9 kWh / 174.2 kg = 3.5 kWh/kg actual energy density.

The current energy density for lithium-ion batteries is about 0.3
kWh/kg.

The theoretical maximum energy density for lithium-ion batteries is
about 0.6 kWh/kg. Theoretical maximums for anything are very rarely ever achievable but irrelevant as 0.6 kWh/kg is still too low to be practical.

The one and only hope that there ever will be a practical GA aircraft is
the lithium-air, or more properly, the lithium-oxygen battery which has
a theoretical energy density of 5 to 10 kWh/kg.

There is just one little problem. Research into this battery has been
intense for about 30 years now and to date nobody has been able to come
up with a practical implentation of this chemistry and many doubt that
it will ever happen.

There is no other element on the periodic table that can exceed the
electric generation potential of lithium.


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