Primarily for general aviation discussion, but other aviation topics are also welcome.
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By davef77
#1662639
A couple of other thoughts to throw in the mix...

Electric aeroplanes are not really here yet, but they are coming. If you are buying one today you are certainly in the “early adopter” category and so happy to compromise.

Battery tech has been slow to develop, compared to electronics, but is moving. There are technologies that are understood that can deliver at sensible energy densities. The problem is producing these at scale, economically. It is engineering, not science that is the barrier. This means that it is possible and is likely to happen (given the commercial incentives).

Possibles that I have read about... Lithium Air batteries and Graphene super-capacitors. The later charge more quickly than refueling with petrol! There are some other Lithium based battery options too that significantly outperform current generation batteries.

There is massive investment in solving this problem, not driven by aviation but other sectors. E.g. automotive, renewable energy generation (storage) and consumer electronics.

As for ducted fan vs prop vs jet. My understanding is that ducted fans are significantly more efficient than conventional props. I think that the reason why we don’t fly with them is complexity and engine cooling.

There are several big advatages to electric power. Notably simplicity and reduced need for cooling. So ducted fans probably make more sense.

Does anyone know if that reasoning is correct?

IMO Jets will win, only if we can stop them producing CO2 not because of energy density in the long term.
User avatar
By Sir Morley Steven
#1662643
Re the Dyson idea would it not be possible to develop the Venturi tech he uses for his fans?
Then you would have an electric jet engine that couldn’t be damaged by bird strikes.
I expect you couldn’t get anywhere near the thrust required though.
User avatar
By davef77
#1662650
Sir Morley Steven wrote:Re the Dyson idea would it not be possible to develop the Venturi tech he uses for his fans?
Then you would have an electric jet engine that couldn’t be damaged by bird strikes.
I expect you couldn’t get anywhere near the thrust required though.


Some ducted fans do that kind of thing. Still very different to a jet though. In a jet the engine is driven, as a by-product, by the thrust it produces.

The “blow” of the jet pushes the plane AND turns the engine.

(You probably know all this already, sorry, just being a pedant :thumright: )
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By Genghis the Engineer
#1662662
davef77 wrote:A couple of other thoughts to throw in the mix...

Electric aeroplanes are not really here yet, but they are coming. If you are buying one today you are certainly in the “early adopter” category and so happy to compromise.

Battery tech has been slow to develop, compared to electronics, but is moving. There are technologies that are understood that can deliver at sensible energy densities. The problem is producing these at scale, economically. It is engineering, not science that is the barrier. This means that it is possible and is likely to happen (given the commercial incentives).

Agreed.

Possibles that I have read about... Lithium Air batteries and Graphene super-capacitors. The later charge more quickly than refueling with petrol! There are some other Lithium based battery options too that significantly outperform current generation batteries.

Significantly is a few tens of percent - we need a factor four improvement to break even with fuelled aeroplanes. I'm not doubting that'll happen - just not yet. But that we can see that in the distance, makes now absolutely the right time to be starting to develop all of the other technologies behind electric aircraft - control systems, flight test techniques, certification basis, thermal control, motor cooling, crashworthiness, monitoring of battery life remaining ... All solveable problems, just not solved, well enough, yet.


There is massive investment in solving this problem, not driven by aviation but other sectors. E.g. automotive, renewable energy generation (storage) and consumer electronics.

In solving one part of the problem (battery energy density and cost) yes - but not the whole problem as it appears to an aeronautical engineer. We have to solve a lot ourselves.

As for ducted fan vs prop vs jet. My understanding is that ducted fans are significantly more efficient than conventional props. I think that the reason why we don’t fly with them is complexity and engine cooling.

No, not really true. Ducted fans are more efficient when measured static - so you can expect shorter take-offs, but in flight actually they offer no real performance advantage whilst being significantly heavier. I've flown the Optica - a 1300kg aeroplane, with a 240hp engine, that cruises around 90kts. There are many conventionally configured aeroplanes that will beat that performance into a cocked hat.


There are several big advatages to electric power. Notably simplicity and reduced need for cooling. So ducted fans probably make more sense.

There are, but not the advantages that you think. The biggest is efficiency - a batter/motor/prop combo is about 65% efficient compared to around 17% for a piston/prop combo - so about four times as efficient. That's why we only need batteries to be about a quarter the energy density of fuel and not match it. And then when we're using that more efficient system - with electricity from the grid the energy cost savings will be massive, along with the fact that the carbon footprint of grid electricity, per MJ, is about a third that of burning fuel.

Cost wise, an electric aeroplane will need about 1/4 of the energy of a fuelled aeroplane, and grid electricity costs around 1/4 per MJ what the same amount of energy as fuel costs. So we're looking at~ 1/16th of the energy costs. Operating an aeroplane presently is usually about 50% energy costs and about 50% everything else, so a saving of 40+% in aircraft running costs, eventually, seems quite possible.

There is a need for cooling - the low weight high power electric motors that'll need to be used for electric aeroplanes are built with cooling systems and need them - otherwise they'll overheat and seize up pretty much as fast as an uncooled piston engine.

There's also a need for battery monitoring, motor control systems, parallel electrical systems, battery thermal control...

Again, all of these are solvable problems, and there are good reasons to solve them - but the summary is that no, electrical propulsion won't be simpler than the present solutions, nor can we avoid cooling.


Does anyone know if that reasoning is correct?[/quote[
Some of it.

IMO Jets will win, only if we can stop them producing CO2 not because of energy density in the long term.

The ultimate solution will probably be price related, but w.r.t. CO2, the solution in turbine aircraft will be two fold...

(1) A move towards hybrid technologies. This will exploit both the high energy density of liquid hydrocarbon fuels, and the high efficiency of electric propulsion.

(2) The use of biofuels - this is difficult and will at least in the short term be in small percentages of perhaps 10%. The two complementary difficulties here are relatively limited supply, and that it is unacceptable to mankind to jeapordise food security for anything, even reducing carbon emissions. Subsidiary to this, there are other industries that can quite probably achieve better carbon emission reductions than aviation can, cheaper, by using biofuels in different ways (particularly the use of fermentation ethanol - not safely useable in the air but fine in many industrial and surface transportation roles).



(Yes, I have thought about this quite a lot 8) )

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User avatar
By kanga
#1663010
Sooty25 wrote:Not electric, but an example of ducted fan tech in GA
..

https://www.flyer.co.uk/czechs-debut-microlight-fighter-at-aero/


Gloucestershire technology was, of course, there first :)

https://www.airteamimages.com/britten-n ... 42511.html