On Electric Aircraft

Martin Gregorie wrote on 2/10/2020 5:52 PM:

That was an interesting read.

For fun, I dug up the numbers on a 7.2 AH SLA, Gasoline, and a SAFT Li-
ion cell and lobbed the lot into a spreadsheet. I picked on SAFT cells
because they made the cylindrical Li-ion cells used in the Antares, and
used the numbers for their highest capacity cell.

Here's what it showed:

Parameter Yuasa NP7-12 Petrol (1 litre) SAFT LS133600

Chemistry SLA Hydrocarbon Li-ion
Voltage (V) 12 3.67
Capacity (AH) 7 17
(w.hr) 84 9600 62.39

Weight (Kg) 2.200 0.755 0.090
Volume (litres) 0.739 1.000 0.323
Density 0.976 0.755 0.278

To hold equal amounts of energy, we need
Units installed 114.286 1.000 153.871
Weight (kg) 251.429 0.755 13.848
Volume (litres) 84.497 1.000 49.728

I hope the formatting doesn't get too mangled by the wonders of NNTP.

Its interesting that petrol (gasolene) is lighter than SAFT cells by a
factor of over 10 and takes up around 50 times the space - and this is an
underestimate because its the total volume of the cells and doesn't count
either the extra space needed because cylindrical cells can't be packed
without leaving air gaps or the space needed to cooling air to circulate
round the batteries, which are quite widely spaced inside the Antares
wing.

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.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1