Electriflying

On 2011-06-25, Orval Fairbairn wrote:
Well, Vaughn, all you have to do is a simple back-of-the-envelope
calculation to see it.

First, calculate the fuel and air consumed in an internal combstion
engine:
1. fuel, at 6 lb/gal
2. air, at f/a ratio of 1:15.

This means that, for every pound of fuel, you consume 15 pounds of air.
You may use kilograms, if you please.

Not correct, you don't consume the nitrogen which is around 80% of air.

If you are using batteries, you now have to carry the equivalent of both
the fuel and the consumable air to do the same job, or almost a ton of
consumables.

But you're comparing apples and oranges! Batteries do NOT work on oxidation.
The thing that charges the battery may indeed work by oxidising the
fuel (but equally it may not, it may be a nuclear power plant, a wind
turbine, a solar panel or whatever). You cannot compare how a battery
works to how fuel is burned. They just aren't the same thing at all.

Additionally your calculation on the air consumed is quite significantly
wrong. Not just because you forgot about the nitrogen, but when calculating
how something burns you must consider how many moles of a substance
is reacting, i.e. its molecular mass.

Gasoline is a mix of quite a lot of chemicals, but mostly things like
C6H12 and these numbers will come out the same for any alkane.

To burn one mole of C6H12, we need 12 moles of O2
1 C6H12 x 12 O2 = 6 CO2 + 6 H2O

6 of the O2 molecules coming in make 6 carbon dioxide molecules,
the remaining 6 O2 molecules are used to make the 6 water molecules.

So we use 12 moles of O2 per one mole C6H12.

One mole of O2 is 32 grams.
One mole of C6H12 is 84.2 grams.

So for every 84.2g of fuel we need 320g of oxygen. This means the ratio
by mass of oxidiser to fuel is around 3.8 parts oxidiser to each part
of fuel -- NOT 15 parts oxidiser to each part fuel.

On 2011-06-27, Dylan Smith wrote:
But you're comparing apples and oranges! Batteries do NOT work on oxidation.

Actually, I already stand (sit) corrected on that one looking a bit
closer at the chemistry. But that still doesn't mean a battery must
carry all of its reaction chemicals. Indeed, there is a type of lithium
rechargable battery that uses oxygen from the air (just as burning
avgas uses oxygen from the air). Still in research stages, and it
still remains to be seen what the maximum C rating of this kind
of battery would be.

Dylan Smith wrote:
On 2011-06-25, Orval Fairbairn wrote:
pretty good empirical evidence, though! If we weren't near the limits of
battery chemistry, we would have had an order of magnitude of change in
battery performance over the last century, since there have been major
needs for such performance: submarines, spacecraft, aircraft,
automobiles, laptop computers.

Well, we have had an order of magnitude change. The first long life
rechargable battery (as in lasts many charge cycles), the lead acid
battery, has an energy density of 41 watt hours per kilogram.

The latest long life rechargable battery, the lithium polymer,
has an energy density of 128 watt hours per kilogram. That's pretty
close to an order of magnitude. (You could nit-pick and say the
lithium battery was invented a long time ago, but that lithium
battery was not rechargable and is a far cry from a modern Li-Poly).

That's close to an order of magnitude for those that feel 3.1 is close to
10.

Also the performance just within lithium polymer batteries has increased
enormously. Ten years ago, the maximum discharge rate of any kind
of rechargable lithium battery didn't exceed 1 to 2 C (1C = a current
equal to the amp hour capacity of the battery, so if you had a 10aH
Li-Ion with a maximum discharge of 1C, it would mean it could
give at most a current of 10 amps). I have a LiPoly battery here
that has a maximum discharge rate of 60C continuous, 120C peak.
It's the size of a cigar packet and can start a car engine. This just
wasn't possible even 10 years ago.

Additionally, UC San Diego is working on a battery that is expected
to give an energy density of around 1kWh per kilogram (an order of
magnitude better than current lithium rechargable batteries). It
remains to be seen what C rating it will have, which is enormously
important for anything that moves. Lithium cobalt oxide batteries
in the lab have a 500 watt hour/kg energy density. From past performance
it typically is about 10 years from being a "yeah it works in the lab"
to a commercial product.


1kWh per kilogram is 3.6 MJ/kg.

100LL Avgas is 44 MJ/kg.

Batteries need to be able to produce better than 20 MJ/kg to be generally
usefull for transportation.


-
Jim Pennino

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In article , Dylan Smith
wrote:

On 2011-06-25, Orval Fairbairn wrote:
Well, Vaughn, all you have to do is a simple back-of-the-envelope
calculation to see it.

First, calculate the fuel and air consumed in an internal combstion
engine:
1. fuel, at 6 lb/gal
2. air, at f/a ratio of 1:15.

This means that, for every pound of fuel, you consume 15 pounds of air.
You may use kilograms, if you please.

Not correct, you don't consume the nitrogen which is around 80% of air.

If you are using batteries, you now have to carry the equivalent of both
the fuel and the consumable air to do the same job, or almost a ton of
consumables.

But you're comparing apples and oranges! Batteries do NOT work on oxidation.
The thing that charges the battery may indeed work by oxidising the
fuel (but equally it may not, it may be a nuclear power plant, a wind
turbine, a solar panel or whatever). You cannot compare how a battery
works to how fuel is burned. They just aren't the same thing at all.

They still work on chemical reaction -- the point being that you have to
carry ALL of the chemicals with you, rather than getting the majority of
them from the air. In addition, your landing weight will be the same as
your takeoff weight, since nothing is dumped overboard as a result of
flying.



Additionally your calculation on the air consumed is quite significantly
wrong. Not just because you forgot about the nitrogen, but when calculating
how something burns you must consider how many moles of a substance
is reacting, i.e. its molecular mass.

Gasoline is a mix of quite a lot of chemicals, but mostly things like
C6H12 and these numbers will come out the same for any alkane.

To burn one mole of C6H12, we need 12 moles of O2
1 C6H12 x 12 O2 = 6 CO2 + 6 H2O

6 of the O2 molecules coming in make 6 carbon dioxide molecules,
the remaining 6 O2 molecules are used to make the 6 water molecules.

So we use 12 moles of O2 per one mole C6H12.

One mole of O2 is 32 grams.
One mole of C6H12 is 84.2 grams.

Hextane? I don't think so! Don't you mean octane (C8H18)?

So for every 84.2g of fuel we need 320g of oxygen. This means the ratio
by mass of oxidiser to fuel is around 3.8 parts oxidiser to each part
of fuel -- NOT 15 parts oxidiser to each part fuel.

I stand by my analogy in that, even though the nitrogen does not
participate in the chemical reaction, it still plays an important role
in the propulsion equation, by providing a working medium to receive
heat and expand to push pistons or to turn turbines.

Batteries still require at least an order of magnitude improvement to be
practical for transportation. And we still haven't talked about the
weight of the batteries themselves!

wrote in message
...

100LL Avgas is 44 MJ/kg.

When burned in an IC airplane engine, most of those MJs are turned into waste
heat, not propulsion.

Batteries need to be able to produce better than 20 MJ/kg to be generally
usefull for transportation.

How many light planes are actually used for transportation?

Vaughn

vaughn wrote:

wrote in message
...

100LL Avgas is 44 MJ/kg.

When burned in an IC airplane engine, most of those MJs are turned into waste
heat, not propulsion.

That is why I said batteries need to be able to produce better than 20 MJ/kg
to be generally usefull instead of better than 40 MJ/kg.

This takes into account the compartive real world energy efficiencies of
electric versus gasoline motors.

All of this neglects cost issues; even if batteries somehow get there,
they won't be economically practical if it turns out the cost of a battery
pack for something like a 172 costs a million bucks and has to be replaced
every 5 years.

Batteries need to be able to produce better than 20 MJ/kg to be generally
usefull for transportation.

How many light planes are actually used for transportation?

All of them that fly unless they are remotely controlled.

The trip may be as short as 3 turns around the pattern to maintain currency,
but a person is still being moved.


--
Jim Pennino

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wrote in message
...
How many light planes are actually used for transportation?

All of them that fly unless they are remotely controlled.

The trip may be as short as 3 turns around the pattern to maintain currency,
but a person is still being moved.

Sorry, but that's stretching a point beyond nonsense. You could also argue
that a pogo stick is a transportation device, but few would take you seriously.
"Three turns around the pattern" may actually be either recreation or training,
but hardly transportation. Most light planes are used for training and
recreation, not transportation. Regardless of the owner's intentions when they
buy them, few light planes are actually used for serious transportation.

This thread started with a post about a 2-place training aircraft with a 90-
minute endurance. Fact is, that plane (if it really exists) could handle many,
(possibly most) of the missions I see flown out of my local airport. If
available as a rental, it could handle about 70% of my own flights.

Vaughn

vaughn wrote:

wrote in message
...
How many light planes are actually used for transportation?

All of them that fly unless they are remotely controlled.

The trip may be as short as 3 turns around the pattern to maintain currency,
but a person is still being moved.

Sorry, but that's stretching a point beyond nonsense. You could also argue
that a pogo stick is a transportation device, but few would take you seriously.
"Three turns around the pattern" may actually be either recreation or training,
but hardly transportation. Most light planes are used for training and
recreation, not transportation. Regardless of the owner's intentions when they
buy them, few light planes are actually used for serious transportation.

This thread started with a post about a 2-place training aircraft with a 90-
minute endurance. Fact is, that plane (if it really exists) could handle many,
(possibly most) of the missions I see flown out of my local airport. If
available as a rental, it could handle about 70% of my own flights.

Vaughn

transportation, Noun

1. The action of transporting someone or something or the process of
being transported.

transport, Verb

1. To carry from one place to another; convey.


The word "transportation" implies nothing about either the purpose or the
distance of the movement. It just means movement.

If I fly 25 miles to get a hamburger, the airplane provided the
transportation.



--
Jim Pennino

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wrote in message
...

transportation, Noun

1. The action of transporting someone or something or the process of
being transported.

transport, Verb

1. To carry from one place to another; convey.


The word "transportation" implies nothing about either the purpose or the
distance of the movement. It just means movement.

If I fly 25 miles to get a hamburger, the airplane provided the
transportation.



OK. This conversation has descended to idiocy.

See you next thread perhaps.

Vaughn

vaughn wrote:

wrote in message
...

transportation, Noun

1. The action of transporting someone or something or the process of
being transported.

transport, Verb

1. To carry from one place to another; convey.


The word "transportation" implies nothing about either the purpose or the
distance of the movement. It just means movement.

If I fly 25 miles to get a hamburger, the airplane provided the
transportation.



OK. This conversation has descended to idiocy.

See you next thread perhaps.

Vaughn

Sorry if my use of English words as defined by the dictionary offends
you somehow.



--
Jim Pennino

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