Is electric propulsion worth it?

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Sockmonkey

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The issue with that is "power is power". The ICE is still doing all the work - literally, in the exact meaning of the word - of driving the aircraft. And now it has to produce extra power to overcome the losses in the genset, power transmission system, and electric motor.

Let's say your generator is 90% efficient (pulling these numbers out of thin air), your transmission lines are 95% efficient, your motor controller is 85% efficient, and your electric motor is 90% efficient. And let's say you want 100hp (or Watts) of power at the prop.

Your ICE will need to produce: 100/(0.9*0.95*0.85*0.9) = 153 horsepower into the generator to get 100 hp out at the propshaft. Using a genset and remote electric motor makes the ICE engine have to be bigger to account for the losses in the system. It doesn't allow it to be smaller.
Two important factors.
A: The ICE can always run at it's optimum speed for maximum efficiency.
B: The ICE only needs to be big enough for the final output at the prop to be max cruise speed. The short bursts of extra power needed during takeoff and climb.can be supplied by capacitors or a small battery pack.
That's not to say this setup is automatically better, since there are tweaks to improve a straight ICE setup as well. It's just not as dismal as it might look at first glance and can certainly match some standard ICE layouts.
 

danmoser

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... short bursts of extra power needed during takeoff and climb.can be supplied by capacitors or a small battery pack...
Possible in theory, but today's technology is problematic in achieving that.
A practical quantity of the best current-day supercapacitors are only good for a few seconds of burst power in this scenario.
And current-day Lithium-based batteries should not be discharged that quickly... you get short battery lifetimes at best, and cell overheating with a nasty fire or explosion at worst...
It's much better to have a larger capacity battery pack that is discharged slowly .. say over 15-45 minutes, depending on your specific battery cell internal resistance ..
Most will want to avoid the complicating nightmare of adding a gasoline ICE, generator, power supply, charger, and battery management system to their electric aircraft.
 

Highplains

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The top of the line "Thunderpower" LiPo batteries are rated at 70 C discharge rate, which means that you would empty the cell in under 1 minute. They also have a "burst current" at double this rate. The RC experiences with this technology are all over the map with battery life. However the control line aerobatics guys that fly the exact same pattern (about 5-6 minutes) get hundreds of flight out of a battery pack. They only use 75-80% of it's capacity on each flight. A deeper discharge is what kills LiPo cells.
 

proppastie

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The top of the line "Thunderpower" LiPo batteries are rated at 70 C discharge rate, which means that you would empty the cell in under 1 minute. They also have a "burst current" at double this rate. The RC experiences with this technology are all over the map with battery life. However the control line aerobatics guys that fly the exact same pattern (about 5-6 minutes) get hundreds of flight out of a battery pack. They only use 75-80% of it's capacity on each flight. A deeper discharge is what kills LiPo cells.
Ok let get specific, say I want a 5 min aux power launch with one of those 5-10 lb electric engines putting out 16 hp (1 kilowatt =1.34102209 hp) 12KW. How many RC batteries for 75-80% power, and how much will that weigh?
 

Highplains

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Well the number of batteries depends on the operating voltage of the motor. But I had looked at a 20 hp booster for 3 minutes and came up with a system weight of about 30 lbs. So for 5 minutes (easier on the batteries) I would expect about 20 lbs. of battery.

These numbers improve every year. While storage density changes only 1 or 2% each year, the power density improves 5-10% each year.
 

danmoser

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True.. battery technology gets better continually.. there are LiPo RC batteries now claimed to have 90C discharge ratings.
However, the longevity of these types batteries at high discharge rates is dicey and inconsistent, as any experienced RC pilot will tell you..
Generally speaking, slower discharge rates are safer and have longer battery life, as does preventing the pack from getting too deeply discharged before recharging.
 

proppastie

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Well the number of batteries depends on the operating voltage of the motor. But I had looked at a 20 hp booster for 3 minutes and came up with a system weight of about 30 lbs. So for 5 minutes (easier on the batteries) I would expect about 20 lbs. of battery.

These numbers improve every year. While storage density changes only 1 or 2% each year, the power density improves 5-10% each year.
Thanks much. Would sure be lots easier to start and restart than a Gas Giant Scale model engine. However some development required, control, prop hub, shock mounts, etc. unless there Are Giant scale Electric motors set up for aircraft? Off the shelf, 10-20 KW. with prop hub, shock mounts and controller etc. ????
 

BBerson

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I attended a talk by a lithium battery manufacturer. He said for good life the batteries are intended to be discharged at around one C. The actual life also depends on the batch of chemicals. Avoiding contamination is hard for them to control.
You just can't trust any claims for battery life.
It is best to try one and cycle it and see what you get before buying a hundred.
Even that is no guarantee, because each batch is unique.
 

henryk

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True.. battery technology gets better continually.. there are LiPo RC batteries now claimed to have 90C discharge ratings.
However, the longevity of these types batteries at high discharge rates is dicey and inconsistent, as any experienced RC pilot will tell you..
Generally speaking, slower discharge rates are safer and have longer battery life, as does preventing the pack from getting too deeply discharged before recharging.
=russian inventer works with 2 complets of batterys=1 is discharged,2-nd is loaded
in this time=much longer life time\up to 8 years\,much longer distance to drive...

https://www.youtube.com/watch?v=25ceCK4GBus

=+unipolar motor,puls with controlled!
 

DangerZone

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Whether electric propulsion is "worth it" or not really depends on what "it" is.
According to this:
Cost of Power from Batteries and Other Sources - Battery University
..the cost of power to recharge the battery is about 1/5 the cost of current technology Lithium-chemistry battery replacement, on a per hour of use time basis.
This is almost a wash with gasoline-ICE engines on life-cycle cost per flight hour basis today.
So the cost of battery recharging power is very low..
And rapid advancements in battery technology are continually lowering their cost and extending their useful lifetime.

It has already been worth it for RC planes.
It is now worth it for motorgliders and ultralights.
It will soon be worth it for LSAs and other light aircraft.
It may never be worth it for commercial airliners.
You are right about the first three statements. However, the last one might very soon be challenged.

Many electric aircraft use electric power for takeoff/landing and a short range flight. If a longer flight is needed, range extenders are used. The latest developments in aviation show electric motors are replacing hydraulic cylinders in aircraft and many military equipment. They are lighter, more reliable, have a faster response time and more energy efficient. The same goes for commercial airliners, for short flight and commercial trips the savings in electric propulsion would be enormous.

The down side of elecrric propulsion would be that such commercial aircraft should be built from scratch to use the elctric advantage to a maximum potential. Thus, every electric commercial that we could build today would necessarily be a hybrid system, the same way the airplanes are built today: they use jet fule turbine, hydralic and electric propulsion depending on what they want the system to achieve. So the future commercial aircraft will have the same but will usemore electric power and save more of the jet fuel for long range flights. And this is exactly where the electric propulsion will make sense, in short commercial trips around the EU, USA, China, Japan and those countries where normous jet fuel savings could be made.

A couple of years ago I played with the design of a short range commercial jet liner, the idea was to save fuel and reduce noise. The only design that had a calculated saving of fuel up to 8% was a canard wih a radical design which allowed slower approach and landing speeds and electric motors/brake regenerators in the wheel hubs for taxiing and braking. As most people know, these are the heavy segments of jet liners, so by cutting the amount of jet fuel needed for taxiing after landing and the weight reduction of the disc brakes, the fuel saving were even higher. Eventually, by installing a dual hybrid system (electric/jet fuel) the savings went sky high, the consumption was drastically reduced and for short 30 minute trips the aircraft would save up to 50% on jet fuel. Plus, the redundancy went up, if the jet fuel turbine segment of the engine would have to be shut down there was still the electric motor to turn the turbine fan which produces most of the propulsion. However, this would require changing/improving the existing jet engines and that is simply beyond my field of airplane building interest.

It is just a matter of time, but commercal aicraft will fly electric in the near future. With the advancement of battery technology, the commercial airplanes might fly electric sooner than many of us think possible.
 
M

Manticore

From edav

"It was also proven that the compressed air from a high pressure Bauer compressor running on 5 hp (3730 watts) whose power was supplied from the 40 kW generator could almost out run the engine pumping the tanks full equally as fast."

= Perpetual Motion

Scam or delusion?
 

BJC

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From edav

"It was also proven that the compressed air from a high pressure Bauer compressor running on 5 hp (3730 watts) whose power was supplied from the 40 kW generator could almost out run the engine pumping the tanks full equally as fast."

= Perpetual Motion

Scam or delusion?
The only thing keeping him from mass producing an engine with an efficiency over 100% is the US oil industry. They arrived in their black helicopters in the middle of the night and ...
 

proppastie

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40 kW generator
40,000 Watts? and how big is that generator, and how much fuel does it use? (I did not read the site, so ignore if a stupid response)(I glanced at it, he has done a lot of work making that web page.)
 

DangerZone

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From edav

"It was also proven that the compressed air from a high pressure Bauer compressor running on 5 hp (3730 watts) whose power was supplied from the 40 kW generator could almost out run the engine pumping the tanks full equally as fast."

= Perpetual Motion

Scam or delusion?
Ignorance or lack of physics knowledge?

'Available power for a considerate amount of time' would refer to energy, and energy is expressed in kWh (kiloWatt-hours). Power expressed in kW is a rate of doing work (expressed in Joules or Nm - Newton-meters), and when talking about rotating electric motors there's a very important factor called moment or torque (also in Nm). Since it is clear the writer(s) of these pages have managed to mix these somehow, it does not surprise there are errors in their calculus.

Another example:
"A key part of this package is the axial flux (AF) electric motor technology with an extended torque radius. Use of Axial Flux motor technology lets us again multiply this electrical force to our advantage. These electric motors can produce up to 2 kW for every kg of weight. So a 150 horsepower motor (112 kW) will weigh 11.3 kg instead of 227 kg currently purchased off the shelf today."
An electric motor has high torque from zero rpm, unlike the ICE machines. We can design an electric motor to have a desired torque, rpm and power adjusted for a specific work. Torque is usually a line when usable torque is calculated in a well designed electric motor, not a radius. ICE machines have a torque and power curve, electric motors can be designed to have a flat line from 0rpm to 3000rpm. And yes, an electric motor can be designed to have less than 12kg and have an output of 112kW of power, it all depends on how much money you have and how much power you wanna spend. In conclusion, spending energy and producing a powerfull motor is EASY, as easy as spending money. However, making money or energy is a completely different thing. Or to be specific, spending money/energy and getting the most out of it, that is what efficiency is all about.

Most of these real flying projects they refer to were 'kept in secret' because they were shameful, they have shown that some people invested money/energy into projects without efficiency. Wrong calculations, unreal figures, missed parameters, these were the causes of their dead-end fate. I doubt they were meant to scam, more probably they dragged people with money into their delusions, and everyone learned the hard way.

In other words, electric propulsion is real, more efficient than an ICE engine and if well designed can pass the turbine level efficiencies of 92%. A well designed electric motor can have an efficiency of 92% to 95% efficiency which is quite good. Thus the future is in better turbine and electric motor design, cause 1% can be a lot of improvement if large amounts of energy are spent.
 
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