On Mon, 10 Feb 2020 19:12:42 -0800, Eric Greenwell wrote:

Your chart doesn't account for the efficiencies in converting energy to
propulsion. An electric motor will deliver about 95% of the electrical
energy to the propeller, but only about 40% of the gasoline energy will
be delivered to the propeller.

Since it is propulsion we desire, not just stored energy, you should
reduce the lead acid and lithium battery sizes by 55% to account for
their greater energy to propulsion efficiency.

Fair point, but SLA still shows as a non-starter while SAFT cells are
still six times the weight of hydrocarbon and occupy at least 25 times
the volume.

The one thing we both missed, though is that a good brushless motor plus
its controller will be a lighter and smaller than the equivalent ICE
piston engine driving a propeller. Has anybody got numbers for this? IOW,
is motor+controller+prop+Li-ion battery still heavier than petrol+piston
engine+prop? It will almost certainly be heavier than a Jet-A+turboprop
engine+propeller.

And, or course, empty fuel tanks are a lot lighter than full ones but a
flat battery weighs the same as a fully charged one.


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Martin | martin at
Gregorie | gregorie dot org