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

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.


--
Martin | martin at
Gregorie | gregorie dot org

At 12:33 11 February 2020, Martin Gregorie wrote:
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.

Not Quite True.
Since a charged battery contains a greater total amount of energy than a
dead battery, the earth's gravity will pull more strongly on it.
But you will have trouble measuring the difference ;¬))

On Tuesday, February 11, 2020 at 5:15:04 AM UTC-8, Tim Newport-Peace wrote:

Not Quite True.
Since a charged battery contains a greater total amount of energy than a
dead battery, the earth's gravity will pull more strongly on it.
But you will have trouble measuring the difference ;¬))

But seriously, no. Energy in and of itself has no mass. A an old-time watch or windup toy has the same mass regardless of whether it is wound or unwound.

On Tue, 11 Feb 2020 10:09:18 -0800, Bob Kuykendall wrote:

On Tuesday, February 11, 2020 at 5:15:04 AM UTC-8, Tim Newport-Peace
wrote:

Not Quite True.
Since a charged battery contains a greater total amount of energy than
a dead battery, the earth's gravity will pull more strongly on it.
But you will have trouble measuring the difference ;¬))

But seriously, no. Energy in and of itself has no mass. A an old-time
watch or windup toy has the same mass regardless of whether it is wound
or unwound.

....but an electron does have mass, just not very much:
9.1093837015 × 10^-31 kg

Not that it matters, because as many electrons flow into a discharging
battery as flow out.


--
Martin | martin at
Gregorie | gregorie dot org

Martin Gregorie wrote on 2/11/2020 4:33 AM:
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.

We are all agreed that short powered range favors electric power, while long range
favors fossil fuel power. The details, such as overall weight, become very
interesting in the design of a self-launching sailplane, because the desired power
range is much smaller than for an airplane.

Schleicher's ASH 26E and AS-34 are 18M span gliders with similar gliding and power
performance. That would be a good start for comparing propulsion systems. My
impression is the propulsion systems have similar weights. Note the fuel weight is
not significant for powered ranges less than 250 miles: the 26E holds 4 gallons,
only 25 pounds in a 1020 pound glider (including pilot).

High density altitude favors the electric systems, because the motor power does
not decrease with altitude, unlike the normally aspirated Wankel or two-stroke
engines.

The smaller, lighter, but powerful electric motors give electrics an advantage
unmatched by IC engines: they make the FES system practical.

For us, all this talk about electric powered seaplanes, passenger carrying
airplanes, and alleged fraud is irrelevant: electric powered gliders are available
from all the major manufacturers and some of the smaller ones. They will only get
better and more numerous.

--
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

On Tuesday, February 11, 2020 at 4:33:26 AM UTC-8, Martin Gregorie wrote:

..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...

Not only that, but it delivers smoother power with less vibration, delivers it the moment it is started, requires less service infrastructure (starting, lubrication, cooling, exhaust, etc), and can easily be positioned for stowage. It runs cleaner and cooler and more predictably under a wider range of conditions, and is more easily monitored for performance and troubleshooting.

--Bob K.

On Tue, 11 Feb 2020 10:16:45 -0800, Bob Kuykendall wrote:

On Tuesday, February 11, 2020 at 4:33:26 AM UTC-8, Martin Gregorie
wrote:

..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...

Not only that, but it delivers smoother power with less vibration,
delivers it the moment it is started, requires less service
infrastructure (starting, lubrication, cooling, exhaust, etc), and can
easily be positioned for stowage. It runs cleaner and cooler and more
predictably under a wider range of conditions, and is more easily
monitored for performance and troubleshooting.

Another thing, but this probably doesn't affect us much: a brushless
motor, which all these units are, has its rpm set primarily by the rate
at which the controller switches power round its (static) field coils
and, when driving a propeller, isn't much affected by the load its
working against. Its one reason electric brushless motors are popular
with the RC and CL aerobatic crowd - the nearly constant RPM causes
airspeed on uplines and downlines to be more constant than it ever was
with IC engines.


--
Martin | martin at
Gregorie | gregorie dot org

What a wonderful way to spend a snowy morning, discussing the weight of
a full versus an empty battery!

What if we talked in terms of mass instead of weight? :-D

Seriously, I got a lot of entertainment after the thread went off topic
as is so normal with RASicrucians.Â* I especially liked the comparison
that Bob made of a wound versus unwound watch or toy. I've been banging
my head against the wall trying to see that in the context of the Laws
of Conservation of Matter and Energy.

More coffee is in order...

On 2/11/2020 11:34 AM, Martin Gregorie wrote:
On Tue, 11 Feb 2020 10:16:45 -0800, Bob Kuykendall wrote:

On Tuesday, February 11, 2020 at 4:33:26 AM UTC-8, Martin Gregorie
wrote:

..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...
Not only that, but it delivers smoother power with less vibration,
delivers it the moment it is started, requires less service
infrastructure (starting, lubrication, cooling, exhaust, etc), and can
easily be positioned for stowage. It runs cleaner and cooler and more
predictably under a wider range of conditions, and is more easily
monitored for performance and troubleshooting.

Another thing, but this probably doesn't affect us much: a brushless
motor, which all these units are, has its rpm set primarily by the rate
at which the controller switches power round its (static) field coils
and, when driving a propeller, isn't much affected by the load its
working against. Its one reason electric brushless motors are popular
with the RC and CL aerobatic crowd - the nearly constant RPM causes
airspeed on uplines and downlines to be more constant than it ever was
with IC engines.



--
Dan, 5J

You mean that a glider hs a higher mass after releasing from tow because you added potential energy??