Discussion:
Electric Aircraft Motors: Ducted Fans vs. Propellers
(too old to reply)
David E. Powell
2019-07-24 17:45:48 UTC
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With the issue of electric aircraft approaching practicality at a higher degree than ever, based on new engine and battery technologies, will the electric ducted fan drive or propeller drive be the most likely way to go?

Of course, it is possible that we will see both.

With ducted fans, model aircraft makers seem to have found use for them in recent years:

https://www.horizonhobby.com/category/airplanes/airplane-accessories/ducted-fan-units

<https://www.horizonhobby.com/category/airplanes/airplane-accessories/ducted-fan-units>

Meanwhile, the electric propeller drivetrain concept has been making news in Science publications since at least the early 1980s:

https://en.wikipedia.org/wiki/MacCready_Solar_Challenger

<https://en.wikipedia.org/wiki/MacCready_Solar_Challenger>

The electric light plane concept, aiming for some of the same market as the Tesla Automobile or Volkswagen Electric van, is certainly doable. Could a ducted fan craft, either of Business Jet size or a Jetliner size, be practicable? I would think that the difference between a conventionally powered aircraft on long flights would be a factor - Namely, the conventionally powered aircraft will use fuel over the course of a flight and thus become lighter in weight. This helps with fuel economy as well as range.

Also, I tend to think of the classic Jet, Turbojet or turbofan when it comes to Ducted Fans. How much power could one get from driving one electrically? Burning aviation kerosene generates a lot of power and sets a heck of a benchmark.

There are a lot of hoops to clear to make either of these concepts work commercially. Can they do it? With one or both?

In military terms, an ability to "plug in anywhere" could give a flexibility similar to the ability of some military vehicles to operate on several types of petroleum based fuels: Jet fuel, Kerosene, Gasoline, etc.

Any thoughts, folks? This could be a fun thread.
ZZyXX
2019-07-24 20:04:21 UTC
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Post by David E. Powell
I would think that the difference between a conventionally powered aircraft on long flights would be a factor - Namely, the conventionally powered aircraft will use fuel over the course of a flight and thus become lighter in weight. This helps with fuel economy as well as range.
doesn't the extra weight on take-off consume more fuel...an electric
plane would have an almost constant energy curve over a flight duration
which could make some planning aspects easier.
Jim Wilkins
2019-07-24 22:01:12 UTC
Permalink
Post by ZZyXX
Post by David E. Powell
I would think that the difference between a conventionally powered
aircraft on long flights would be a factor - Namely, the
conventionally powered aircraft will use fuel over the course of a
flight and thus become lighter in weight. This helps with fuel
economy as well as range.
doesn't the extra weight on take-off consume more fuel...an electric
plane would have an almost constant energy curve over a flight
duration which could make some planning aspects easier.
Petroleum fuel contains ~100 times as much energy per kilogram as
Lithium batteries.
https://en.wikipedia.org/wiki/Energy_density

"lower heating value" means energy isn't recovered by condensing any
water in the exhaust from steam to liquid. See Hydrogen for the
difference between lower and higher heating values.
Daryl
2019-07-25 20:47:37 UTC
Permalink
Post by Jim Wilkins
Post by ZZyXX
Post by David E. Powell
I would think that the difference between a conventionally powered
aircraft on long flights would be a factor - Namely, the
conventionally powered aircraft will use fuel over the course of a
flight and thus become lighter in weight. This helps with fuel
economy as well as range.
doesn't the extra weight on take-off consume more fuel...an electric
plane would have an almost constant energy curve over a flight
duration which could make some planning aspects easier.
Petroleum fuel contains ~100 times as much energy per kilogram as
Lithium batteries.
https://en.wikipedia.org/wiki/Energy_density
"lower heating value" means energy isn't recovered by condensing any
water in the exhaust from steam to liquid. See Hydrogen for the
difference between lower and higher heating values.
Yes, you are correct. But the Electric Motor is many times more
efficient than the gas engine at all power curves but the ideal power
curve of the gas engine. For instance, a 90 hp electric car can perform
equally well against a 250 hp gas car because the electric motor does
not have to spool up to get the HP and Torque. The electric develops it
at a very low rpm (somewhere just above 1 rpm). You can play with the
Pitch to make up for the difference in power and stretch the run time of
the batteries.

They are also waiting on the new Maxwell Solid States that are due to
come into full production by 2025. It already works. Tesla just Merged
with Maxwell (another name for bought) and Maxwell now has the funds to
go ahead with the production. 5 times the weight reduction of the
Lithiums, 5 times the power output, able to recharge over 100,000 times
before replacement. The Lithium will only make up to about 2000
recharges before it starts to degrade. Some lithiums start degrading as
early as 800.

The Solid State Battery and Rare Earth brushless motors are decades away
from affecting long, over water flights but they will have a profound
affect in sport, training and short hauls. The Short Hauls will be
affected immediately starting in 2025 when the batteries are introduced.
The Planes are already under production waiting for the batteries.



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