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Dingbatt
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  #2805173 1-Nov-2021 10:53
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By large are you talking Dash8, A320, A350 or A380?





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Technofreak

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  #2805179 1-Nov-2021 10:59
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RobDickinson:

 

Sigh 2035?

We're currently at about 250wh/kg energy density for batteries

Large commercial aircraft should be doable with 400wh/kg

 

 

 

We should reach that at about 2028 or so.

 

 

I think you're dreaming. 400 wh/kg is about 1/29th the energy per kg of JetA1.

 

400 wh/kg is 1.4 MJ/kg

 

JetA1 is 42.8 MJ/kg

 

Even with the thermodynamic benefits of an electric engine 400 wh/kg isn't going to cut the mustard.





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RobDickinson
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  #2805196 1-Nov-2021 11:24
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"Others suggest a shortcut of sorts. “Electric propulsion permits new design architectures,” says Venkat Viswanathan, a battery scientist at Carnegie Mellon University. “Future electric aircraft will look nothing like the aircraft of today, and they will be able to fly with much less energy—as little as 400 watt-hours/kg—thanks to distributed motors and reduced drag. We’ll redesign aircraft around electric motors.” Faster said than done. Because aircraft development times are measured in decades, it’s unlikely the planes Viswanathan imagines will arrive before those 1,000 watt-hours/kg batteries."

https://www.wired.com/2017/05/electric-airplanes-2/


 

"Trainers (Pipistrel’s Velis Ectro, Bye Aerospace’s eFlyers) and some small retrofitted aircraft have been successfully demonstrated using today’s batteries, with around 250-270 Watt-hours per kilogram (Wh/kg) of specific energy. Many industry leaders suggest an energy density around 350 or 400 Wh/kg is necessary for the industry to really emerge."

 

https://www.aviationtoday.com/2020/09/08/batteries-behind-electric-aircraft-revolution/



I'm just going on what the industry is talking about, if you factor in the 'normal' 7% per year energy density increase on our current 250wh/kg cells you get about 650wh/kg by 2035




Technofreak

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  #2805213 1-Nov-2021 11:53
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When you get to about 5000 wh/kg then you're getting to where BEV aircraft are properly viable and are not just toys like the likes of Pipstrel are right now. Even 650kw/kg is practically useless from an economic/useful aircraft point of view.

 

Sure you have to start somewhere but right now there are a lot of optimists promising the earth and chasing rainbows.

 

I see them rabbiting on about improved drag and distributed motors. Aircraft now are already very drag efficient. I don't see the magnitudes of efficiency gains being achieved that are needed to make wh/kg figures of 400 to 600 work.

 

In reality useful BEV aircraft are a very long way into the future with current technology.





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RobDickinson
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  #2805223 1-Nov-2021 11:58
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I think I will believe the experts over a forum user sorry.


MadEngineer
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  #2805229 1-Nov-2021 12:11
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You have to look at who those “experts” are. Of course a battery expert is going to say how good their product is. I’m sure those solar roadways guys are experts at their BS too.




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Technofreak

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  #2805231 1-Nov-2021 12:23
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RobDickinson:

 

I think I will believe the experts over a forum user sorry.

 

 

Which experts are these?

 

Venkat Viswanathan, a battery scientist at Carnegie Mellon University telling us all about aerodynamics. Really? 

 

Richard Wang of Cuborg, as lithium battery manufacturer telling us how aviation operates? This statement from the Aviation Today article shows how naive Richard Wang is about the realities of aviation.

 

“Cargo-driven applications are going to be relatively early in terms of adoption,” Wang speculated. “The other most promising area is these small, two-seater and four-seater retrofitted fixed-wing aircraft, using an existing airframe and swapping out the propulsion system. We see those customer segments picking up very quickly, and then the Uber Elevate air taxi model is more ambitious and will take a little longer to build out the full ecosystem.”

 

Cargo might be relatively easy but it's not happening in a hurry Two and four seat aircraft are generally privately owned. The cost of retro fitting any power system will be prohibitive to those owners. Even at prices that aren't prohibitive the cost benefits will not be there. These owners don't fly enough to amortise the costs of conversion. It won't happen.

 

Aviation experts? I don't think so.

 

I might be a forum user but then.....? You don't know what expertise I have.

 

 





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Dingbatt
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  #2805312 1-Nov-2021 13:04
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RobDickinson:

 

I think I will believe the experts over a forum user sorry.

 

 

Yes. You’ll always be able to find an ‘expert’ to back up your own point of view.

 

Pretty dangerous assumption to make about forum users when it isn’t a requirement to post what your credentials are.





“We’ve arranged a society based on science and technology, in which nobody understands anything about science technology. Carl Sagan 1996


RobDickinson
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  #2805325 1-Nov-2021 13:28
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And until it happens its schodingers aircraft. I dont care that some people say its not possible, change was never done by people saying you cant do it.  


Technofreak

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  #2805384 1-Nov-2021 14:03
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RobDickinson:

 

And until it happens its schodingers aircraft. I dont care that some people say its not possible, change was never done by people saying you cant do it.  

 

 

There's a difference between can't or not possible and not possible at present.

 

No one has said it couldn't be done however simple physics and maths show it is not possible to make an effective commercial BEV aircraft with current technology.

 

I believe you said that by 2028 we should have 400wh/kg batteries and "Large commercial aircraft should be doable with 400wh/kg". I was able to show that 400 wh/kg wasn't viable just by making a comparison to the energy density of Jet A1. 

 

Without a quantum change in battery technology BEV commercial aircraft are just pie in the sky right now. Will it happen? Probably. When? Who knows? Could another energy source be used instead? Quite probably.





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Rikkitic
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  #2805400 1-Nov-2021 14:39
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I am not an engineer, not even close. But I have an imagination. The argument against space travel used to be that no rocket could carry enough fuel to overcome the weight of that fuel. Until someone thought of multi-stage rockets. 

 

Electric planes will be impractical until someone thinks of a way around the limitations. For example, what about solar-powered microwave generators in orbit sending tight beams of energy down to aircraft and other users? I am not an engineer so I can't calculate all the reasons why this would never work, but someone who knows more might think of something out of the box that actually does. For example, what about metallic hydrogen as a fuel? Not electric, just a lot of power in a small tank. I just stumbled across this while reading about something else. I'm sure there are all kinds of other things out there that no-one has thought pf yet.

 

 





Plesse igmore amd axxept applogies in adbance fir anu typos

 


 


tdgeek
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  #2805410 1-Nov-2021 14:54
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Rikkitic:

 

I am not an engineer, not even close. But I have an imagination. The argument against space travel used to be that no rocket could carry enough fuel to overcome the weight of that fuel. Until someone thought of multi-stage rockets. 

 

Electric planes will be impractical until someone thinks of a way around the limitations. For example, what about solar-powered microwave generators in orbit sending tight beams of energy down to aircraft and other users? I am not an engineer so I can't calculate all the reasons why this would never work, but someone who knows more might think of something out of the box that actually does. For example, what about metallic hydrogen as a fuel? Not electric, just a lot of power in a small tank. I just stumbled across this while reading about something else. I'm sure there are all kinds of other things out there that no-one has thought pf yet.

 

 

 

 

Its all quite fascinating. The Saturn 5 rocket was a controlled bomb fuel tank with a teeny capsule on top, one massive fuel tank. Electric power is awesome, but some things are way too hard right now, so focus on todays capability while development will open more doors as time goes by


Dingbatt
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  #2805426 1-Nov-2021 15:11
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Rikkitic:

 

I am not an engineer, not even close. But I have an imagination.

 



 

And thankfully there are people around like Elon Musk who has the imagination and drive (and wealth) to get things moving. He is able to collect some very talented people around him. But even they are constrained by physics, chemistry and available material technologies. It’s a shame some of the other tech oligarchs aren’t as focused on improving the future for those beyond their shareholders.





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RobDickinson
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  #2805576 1-Nov-2021 17:03
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There is nothing in physics that says we cant have large scale electric aircraft. 

I'm sure if Airbus dont do it then someone else, possibly tesla, will. 

It sounds like Airbus is considering being the next nokia.


Batman
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  #2805646 1-Nov-2021 17:51
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I'd rather fly Airbus knowing I'll get across the ocean than get stuck in Tesla waiting for a technician to visit. It's ok in town when the AA will come and get me home, but I ain't waiting on the Atlantic!

 

Maybe it'll do domestic flights but I'm not sure I'm game enough to fly the first few years. Others can test it out for me ...





Involuntary autocorrect in operation on mobile device. Apologies in advance.


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