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Electric aeroplanes...

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Electric aeroplanes...

Old 15th Feb 2018, 18:34
  #21 (permalink)  
 
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I always thought electric propulsion, assuming enough power was available, would be good for aerobatic flight. Short duration with time on the ground in between sequences. No problems of inverted fuel or oil systems.

Alternative is this Part 103 home built example.

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Old 15th Feb 2018, 19:03
  #22 (permalink)  
 
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I don't believe this "It will never happen" notion.
I do subscribe to, "We don't know what we don't know".
If someone had suggested 100 years ago that you could cut grass efficiently with a piece of plastic string, they would have been laughed at.
If someone were to tell the gunnery officer on HMS Victory that one day you could put an explosive shell into a target 600 miles away to within a yard, what would he have said?
Battery technology is making leaps and bounds in the motor industry and it won't be too long before power density--weight--size will fit aviation.
Suppose the entire wing of an A380 could be one battery weighing the same, and rechargeable in seconds by a man made bolt of lightning, taking 5/10 hours to discharge at cruise, then what?
Who can say with certainty "it can't be done".
Not today it can't, but-------
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Old 16th Feb 2018, 01:46
  #23 (permalink)  
 
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I do subscribe to, "We don't know what we don't know".
I agree with you that electric and/or hybrid aircraft will become widespread but I disagree that we don't know what we don't know, at least in broad terms.

Batteries of various types have been around for a long while; the main issues with them are longevity and energy density. There are physical limitations on the energy density of the Lithium Ion cells that are currently used to power aircraft and they'll never compete outside the training/microlight/powered glider markets. There are chemistries such as Lithium-Air that could be practical in terms of energy density for longer range aircraft but thus far they've been hard to develop. Ditto for fuel cells. Will they become practical? Maybe. But the basics of electrochemistry are well understood and there are hard limits on what the technologies will be able to achieve.

Last edited by abgd; 16th Feb 2018 at 04:40.
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Old 16th Feb 2018, 03:17
  #24 (permalink)  
 
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I am also highly sceptical when someone says, "it can never be done,"

I am the proud possessor of a pile of 'Flight' magazines from 1912 to 1918. In one of the articles a professor of medicine from Birmingham University (England) states that it is physically impossible for a human to fly at more than 250 miles an hour as his chest will cave in.

Unless you are dealing with a law of thermodynamics, the future can be anything the human imagination can conceive.

At Freidrischhaven this year there will be a good selection of electric motors and aeroplanes, many more than even five years ago. It is happening now.
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Old 16th Feb 2018, 09:51
  #25 (permalink)  
 
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Problems to be solved...

- Energy density
- Crashworthiness of any battery technology used.
- Best practice in power system management
- Pilot training and qualification
- Ground infrastructure for charging, battery swappover, etc.
- Design practices

I don't see any of that as insoluble, it's just that the solutions seem likely at the moment to primarily favour small, short duration training aeroplanes. That seems unlikely to be the permanent position and touring light aeroplanes and regional airliners may just happen in my lifetime, if not necessarily in my flying career.

However, I'm quite happy to also say that some things I'm regularly reading are complete cobblers. I am getting to the point of wanting to shout abuse at the authors every time I read of yet another "flying taxi" project offering an electric, autonomous flying car that will be delivered within 5 years, operate from outside people's houses and cost a fraction of the price of a new Cessna 172 - having been developed invariably by teams with little or no aircraft design, flight test and certification experience. There is just so much snake oil there that the people who are peddling this rubbish should be facing public ritual humiliation, not having their fanciful artists impressions spread all over the internet.

G
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Old 16th Feb 2018, 11:03
  #26 (permalink)  
 
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I would agree that, currently, the technology favours the light end short duration stuff.
But taking that list of problems to be solved.
Energy density.
Would make the personal single/two seat VTOL device possible using current drone technology.
What is this story about Toshiba developing a battery giving cars a duration of 200 miles, recharged in 6mins? True or krap?
Would this be possible with a row of 240volt sockets at the local pumps?
Crashworthieness.
I watched something recently where a battery was hit with a hammer, smashed in half and still delivered power. Whether that was practical or a set up I don't know.
What is the crashworthieness of a can of Avgas by comparison?
The rest, training, etc will follow as reqd.
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Old 16th Feb 2018, 12:06
  #27 (permalink)  
 
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As I said Crash - they're all solvable problems, just not overnight, and not necessarily in a way that permits a straight swap with the technologies we're flying at the moment, or at the same scale.

For example - a major issue may be unattended charging - if you rummage around YouTube you can find plenty of examples of people who seem to be determined to blow batteries up, and the most exciting seem to be where they've deliberately overcharged them. That's solvable too - but is a problem that just doesn't exist at-all with present technologies.

Another for-example. Train a new PPL on an all-electric, then they want to go and fly a Piper or Cessna conventional product. What differences training will then need in a new aeroplane that has a fuel system instead of an electrical system, can change CG position with fuel/energy state, and requires familiarity with a mixture control and carb heat. Again, all solvable - but does need to be solved.

G

Last edited by Genghis the Engineer; 16th Feb 2018 at 12:23.
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Old 16th Feb 2018, 12:56
  #28 (permalink)  
 
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I think we (private flying pilots) will be the first to use battery powered airplanes regularly. Some are in the market already, and two seat planes with about 1 hour endurance are getting close to where a training aircraft needs to be. If performances were doubled to around 2 hours things start to get interesting for flight schools. Service and maintenance costs are very low, except for batteries but that is a quite predictable write-off with time.

Conversion to piston or turbine should not be more challenging than conversion between piston and turbine today. Regarding things like carb-heat, I was actually shocked to meet pilots at my current club that had never flown a plane with carb heat, only new 172SP's with injection engines, so there we have a challenge already today.
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Old 16th Feb 2018, 20:12
  #29 (permalink)  
 
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What is this story about Toshiba developing a battery giving cars a duration of 200 miles, recharged in 6mins? True or krap?
Would this be possible with a row of 240volt sockets at the local pumps?
Scratching head... Many unknowns... bit of assumption here and there.

Drive 200 miles ~ 320 km at (assume, on the optimistic side) 3 l/100 km => burn 10 litres of petrol. There's 13 kWh in a kg of petrol so one litre holds 13 x 0.8 (density) ~ 10,4 kWh. So those 10 litres burned are equivalent to 100 kWh or a bit more. To charge 100 kWh in one hour takes 100 kW power (and that's assuming a 100% efficient charge process) - to do so in 6 minutes = 1/10th of an hour requires 1 Megawatt. Not something to take from a 230V~ socket or you would need VERY solid cables. And a power plant VERY near by.

Someone please check my maths? It is getting late. The 13,0 kWh/litre is from en.wikipedia

I was actually shocked to meet pilots at my current club that had never flown a plane with carb heat
To each their own To me it is shocking that there are pilots who do fly with such paleo-primitive technology.
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Old 16th Feb 2018, 21:05
  #30 (permalink)  
 
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I see where you're coming from there Jan, but I think you're missing a fundamental difference in efficiency. An electric powerplant on an aeroplane is around 70-80% efficient, whilst piston engine powerplant is around 15% efficient. So you only need to store for an electric system about 1/5th of the total energy you do in a fuel tank. I'm guessing that there's a similar difference on cars.

The other side of that - and the fundamental problem for electric flight is that the energy storage density of petrol is about 46 MJ/kg, whilst for the very best Li-Ion batteries it's about 0.9 MJ/kg.

So you need 1/5th of the energy (thus allowing sensibleish charging times and very low energy costs) but because energy storage density is about 1/50th - you need 10 times the mass to store energy to do the same amount of work.

On a car, that's bearable within reasonable limits. But the 70L = 50kg of fuel you'd need for an hours flying plus sensible reserves in a PA28 requires around 500kg of batteries. The 450kg difference is all of your available payload, and then some.

G
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Old 16th Feb 2018, 22:31
  #31 (permalink)  
 
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I used A123 batteries in my electric helicopter a decade ago. They're still going strong and you could charge them in 8 minutes. They were unfussy and the combination of batteries/motor gave a better power to weight ratio than an IC engine. It was only in energy density that they fell short.

The obvious solution to the fast-charge problem is to have a large battery on slow charge from the mains. If you take somebody for an hour's lesson then charge in 10 minutes from the ground-based battery then you will only need a 17kW mains supply - assuming you need 1/5 the energy of petrol for an equivalent flight. Expensive, but probably cheaper and easier than trying to swap batteries in and out of the aircraft which is the other solution that has been proposed.
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Old 17th Feb 2018, 05:55
  #32 (permalink)  
 
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The electric motor is a lot lighter for the same HP output as an IC engine, making up for some of the weight penalty of the batteries. Plus, it runs efficiently at very low RPM, making more efficient and lower noise propellers possible.
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Old 17th Feb 2018, 06:43
  #33 (permalink)  
 
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@GtE: thanks, there had to be a flaw somewhere. Still, if only 20% is required of what I calculated, it still takes a 200kW power source to recharge in 6 minutes - only slightly less unrealistic. And @abgb, "only" a 17kW power supply? How many m2 of solar panels does that take? Or a 40+ amp cable from a 400V outlet? Or would you produce those 17kW from a diesel generator ? And mind you, that is only for one aircraft. If, on a sunny weekend day, your field wants four planes in the training circuit than you'll need four of those 17 kW power sources, too.

On a more general note, I agree that the evolution is not to be reversed - but I remain highly cautious, there's too many tell-tales around, and the technology does need time to ripen.

Last edited by Jan Olieslagers; 17th Feb 2018 at 06:57.
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Old 17th Feb 2018, 08:35
  #34 (permalink)  
 
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There is an electric motor fitted to a glider that seems to have some advantages over the lawnmower engines that are currently used when a glider runs out of lift but these have had problems with battery fires so there is currently an AD to fit a fire detection system.

The Question Of do I use the parachute or do I try to land the glider after a fire warning is the current hot topic in gliding clubhouses when the weather prevents flying.
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Old 17th Feb 2018, 11:30
  #35 (permalink)  
 
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Even Elon Musk hasn't been bold enough to promote electric passenger flying and the likely reason is the Laws of Physics. Here on planet earth we have things like gravity and wind resistance to cope with and a vehicle is never going to sustain long periods of motion from battery power alone, particularly at high speed.
To do that will need an entirely new and yet unknown power source,
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Old 17th Feb 2018, 14:34
  #36 (permalink)  
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Kryptonite...
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Old 17th Feb 2018, 17:22
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... or nuclear fusion, said to be 99% ready for operation 50 years ago. O no, wait, it still is at 99% - reminds one of an aircraft homebuild project...
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Old 21st Feb 2018, 02:40
  #38 (permalink)  
 
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Another take on electric aircraft here.

Fairly light on detail but it it looks as if they've got it working in real life. There appears to be some serious work that's gone into it by an experienced team, and they have real backing, so it's not a 'vapourcraft'

Whether the predictions will come true is another matter, nevertheless good luck to them!

FP.
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Old 21st Feb 2018, 07:06
  #39 (permalink)  
 
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OK, it has flown so the engineering must be sound enough, I guess, but to my eye that Lilium thing just looks so unbalanced...but perhaps to a millennial it just looks cool.
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Old 21st Feb 2018, 07:09
  #40 (permalink)  
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I would suggest that in the 'future' (now!) how it looks is almost as important as how it flies for commercial success!
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