Can Aircraft Be Far Behind?

Larry Dighera wrote:

I would think that the LiIon cells could be made lighter if
specifically designed for aviation use. Currently they are steel
jacketed AA sized. Steel might be replaced with Titanium (atomic
number 22). Lithium (atomic number 3) is a light metal as is the
carbon (atomic number 6) anode.

The problem is not how the chemicals are contained, the problem is the
weight of the chemicals themselves. There could be some minor
improvement in the overall weight of the batteries, but not enough to
overtake the high energy density of liquid fuels.

You seem to have a firm grasp of the issue. Given:

http://en.wikipedia.org/wiki/Lithium_ion_battery
Lithium ion battery
Specific energy density: 150 to 200 W·h/kg (540 to 720 kJ/kg)
Volumetric energy density: 250 to 530 W·h/L (900 to 1900 J/cm3)
Specific power density: 300 to 1500 W/kg (@ 20 seconds [2] and 285
W·h/L)


http://en.wikipedia.org/wiki/Gasoline
Gasoline
Energy content
Fuel type Megajoules/L MJ/kg BTU/US gal
Premium Gasoline 32.84 43.50 131,200

Can you quantify the prospect of replacing Avgas with LiIon batteries?

The key comparison is the specific energy density, since that would tell
you how far you could fly, and with what load. If batteries are going to
be competitive, they would have to have a weigh about the same as the
liquid fuel to be competitive in aviation use. Otherwise, either useful
load would drop, the range would be limited, or the aircraft would be
completely impractical.

To end up with a similar weight, they would need similar energy
densities, multiplied by the efficiency of the prime mover.

From the table provided above, the energy density of gasoline is 45
MJ/kg, and lithium batteries are 0.72, at best. A gasoline engine is
perhaps 25% efficient in an aircraft, and an electric motor, with its
control, would be about 90% efficient.

Multiplying the two to get the required useable energy density gives:
For gasoline engines: 43.5 X 0.25 = 10.88 MJ/kg
For batteries: 0.72 X 0.9 = 0.65 MJ/kg

Therefore, you would need a battery pack that weighed about 15 times as
much as the gasoline fuel and tank to be able to perform the same amount
of work. That isn't even close.

Given the huge difference in weight, the prospect of using lithium ion
batteries to power conventional aircraft is almost nil. Battery
designers don't need a breakthrough, they would need a miracle to get the
energy density to a point where it would be competitive with liquid fuel.