Cruise altitude for electric airplanes.
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Pattern, that's simply nonsense. It takes energy to pressurize the aircraft - regardless of the fuel source - but the lower the altitude the higher the drag and the more thrust required. The reason we normally cruise at 30k and above is simple - the reduction in drag means less fuel (energy) is required to fly a given distance, overwhelming the relatively small amount of extra fuel (energy) needed to warm and pressurize the aircraft. That is simple physics - going to electric propulsion doesn't change the physics.
In fact, the plane may well carry high pressure air tanks that can be filled with ground power and serve as a backup air supply or even backup power source since it would already be there... but maybe not if its too hard to make the air compressors dual purpose: high volume low pressure for cabin air, high pressure low volume for tank air.
Anyway, with modern turbojet planes is it is much easier and fuel efficient to fly M .8 at FL 32+ than 12k. Drag being a drag with still be true no matter the propulsive force... in fact, electrics should have an advantage considering they can make their full power at altitude versus SL minus the any cooling capacity loss. Combustion engines lose much more power, but the reduction in drag more than offsets this.
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Pattern, that's simply nonsense. It takes energy to pressurize the aircraft - regardless of the fuel source - but the lower the altitude the higher the drag and the more thrust required. The reason we normally cruise at 30k and above is simple - the reduction in drag means less fuel (energy) is required to fly a given distance, overwhelming the relatively small amount of extra fuel (energy) needed to warm and pressurize the aircraft. That is simple physics - going to electric propulsion doesn't change the physics.
In fact, the plane may well carry high pressure air tanks that can be filled with ground power and serve as a backup air supply or even backup power source since it would already be there... but maybe not if its too hard to make the air compressors dual purpose: high volume low pressure for cabin air, high pressure low volume for tank air.
Anyway, with modern turbojet planes is it is much easier and fuel efficient to fly M .8 at FL 32+ than 12k. Drag being a drag with still be true no matter the propulsive force... in fact, electrics should have an advantage considering they can make their full power at altitude versus SL minus the any cooling capacity loss. Combustion engines lose much more power, but the reduction in drag more than offsets this. The main stumbling block for electrics now is the ability to carry enough juice for flights lasting more than an hour. I somehow doubt that battery tech will magically achieve a 2x energy density improvement in any time less than a couple of decades.
However, for those missions of an hour or less, like short regional flights or training flights, I think electrics will be great.
The wizards of aerodynamics and engine design work together to make all these requirements fit together in the most efficient way possible.
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As reply to Lord Lucan, post 4.
Recovering energy???
Yet another conceptual mistake, such as you find everywhere in the green madness of todays world!
A car driver that approaches a red traffic light at 50 mph and then brakes to stop the car is wasting the kinetic energy that is in the car - he should have started coasting early enough to come to a stop right at the traffic light without any braking. Because this method is impractical in normal traffic, hey, an electric car can use the motor as a generator to convert the kinetic energy back to stored electric power in the battery.
An airplane that descends from cruise level to landing does use the coast technique already, the engines are already just idling, it cannot be done more efficiently. If you want to “brake” by using the propellor to drive the e-motor as a generator, your aircraft will have more drag, thus descend more steeply than the idle glide path. You will have to expend (=waste) energy either before starting descent, by staying level longer, or by flying level at the bottom of the descent.
There is no such thing as a free lunch!
Recovering energy???
Yet another conceptual mistake, such as you find everywhere in the green madness of todays world!
A car driver that approaches a red traffic light at 50 mph and then brakes to stop the car is wasting the kinetic energy that is in the car - he should have started coasting early enough to come to a stop right at the traffic light without any braking. Because this method is impractical in normal traffic, hey, an electric car can use the motor as a generator to convert the kinetic energy back to stored electric power in the battery.
An airplane that descends from cruise level to landing does use the coast technique already, the engines are already just idling, it cannot be done more efficiently. If you want to “brake” by using the propellor to drive the e-motor as a generator, your aircraft will have more drag, thus descend more steeply than the idle glide path. You will have to expend (=waste) energy either before starting descent, by staying level longer, or by flying level at the bottom of the descent.
There is no such thing as a free lunch!
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As reply to Lord Lucan, post 4.
Recovering energy???
Yet another conceptual mistake, such as you find everywhere in the green madness of todays world!
A car driver that approaches a red traffic light at 50 mph and then brakes to stop the car is wasting the kinetic energy that is in the car - he should have started coasting early enough to come to a stop right at the traffic light without any braking. Because this method is impractical in normal traffic, hey, an electric car can use the motor as a generator to convert the kinetic energy back to stored electric power in the battery....!
Recovering energy???
Yet another conceptual mistake, such as you find everywhere in the green madness of todays world!
A car driver that approaches a red traffic light at 50 mph and then brakes to stop the car is wasting the kinetic energy that is in the car - he should have started coasting early enough to come to a stop right at the traffic light without any braking. Because this method is impractical in normal traffic, hey, an electric car can use the motor as a generator to convert the kinetic energy back to stored electric power in the battery....!
https://auto.howstuffworks.com/auto-...ve-braking.htm
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Hi David1300,
did you see the following part of the text that you quoted?
Quote
hey, an electric car can use the motor as a generator to convert the kinetic energy back to stored electric power in the battery.
Unquote
The folly is in people just blindly projecting that sort of ‘technique’ onto aviation.
did you see the following part of the text that you quoted?
Quote
hey, an electric car can use the motor as a generator to convert the kinetic energy back to stored electric power in the battery.
Unquote
The folly is in people just blindly projecting that sort of ‘technique’ onto aviation.
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I do agree to a large part with you, however, why not think speedbrakes differently? Simply wasting energy into sound/vibrations is not very efficient either. Especially when the planes do become much more aerodynamically efficient and therefore glide too well for ATC prescribed profiles.
Well, you gonna be waiting an awful long time before anyone comes up with an aeroplane that can manage any sort of credibly useful performance to compare with conventionally fueled ones.
Even longer for airline size and performance, barring a revolutionary and to-date unanticipated breakthrough in battery technology or realisation of fuel cells.
It's a simple matter of energy density - how much energy can be stored in the space available. Currently batteries lag two orders of magnitude behind fossil fuels in this.
LiIon batteries currently stand in the range of .4 to .8 MJ/Kg. Jet A1 is 48. That's one hundred times more.
Certainly some necessarily small future aerodynamic and weight effciencies will narrow the gap slightly (small because those sciences are pretty much at peak already)
Batteries got some catching up to do!
Even longer for airline size and performance, barring a revolutionary and to-date unanticipated breakthrough in battery technology or realisation of fuel cells.
It's a simple matter of energy density - how much energy can be stored in the space available. Currently batteries lag two orders of magnitude behind fossil fuels in this.
LiIon batteries currently stand in the range of .4 to .8 MJ/Kg. Jet A1 is 48. That's one hundred times more.
Certainly some necessarily small future aerodynamic and weight effciencies will narrow the gap slightly (small because those sciences are pretty much at peak already)
Batteries got some catching up to do!
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Well, you gonna be waiting an awful long time before anyone comes up with an aeroplane that can manage any sort of credibly useful performance to compare with conventionally fueled ones.
Even longer for airline size and performance, barring a revolutionary and to-date unanticipated breakthrough in battery technology or realisation of fuel cells.
It's a simple matter of energy density - how much energy can be stored in the space available. Currently batteries lag two orders of magnitude behind fossil fuels in this.
LiIon batteries currently stand in the range of .4 to .8 MJ/Kg. Jet A1 is 48. That's one hundred times more.
Certainly some necessarily small future aerodynamic and weight effciencies will narrow the gap slightly (small because those sciences are pretty much at peak already)
Batteries got some catching up to do!
Even longer for airline size and performance, barring a revolutionary and to-date unanticipated breakthrough in battery technology or realisation of fuel cells.
It's a simple matter of energy density - how much energy can be stored in the space available. Currently batteries lag two orders of magnitude behind fossil fuels in this.
LiIon batteries currently stand in the range of .4 to .8 MJ/Kg. Jet A1 is 48. That's one hundred times more.
Certainly some necessarily small future aerodynamic and weight effciencies will narrow the gap slightly (small because those sciences are pretty much at peak already)
Batteries got some catching up to do!
On the car side however, it is already very close. As those engines are rarely if ever used at their optimal point of specific fuel usage, they have an average efficiency of around 17% for gasoline cars and around 20% for diesel ones. On the other hand, a 100kWh battery, the largest size currently available for cars, has only the energy that around 11 litre of gasoline have. So yes, in that application electrification is much more sensible currently.
There is also the possibility that the battery packs could be quite small in large airliners.
Telephones use to be fixed to the wall and get its power from that plug, we then had cordless phones that had a battery in the handset and would charge in a cradle at the end of the call. Years later we had "mobile phones" that had a battery pack the size of a brick, these eventually became very small and truly mobile and you plug the charger in once or so a day. Phones then became smart (and bigger again) and use more power again needing plugging into the charge a couple of times a day. From a few years ago many phones do not need to be "plugged" in to charge simply place them on a charging pad.
So it seems a new system will be required for large airliners, as the current battery and fuel cell technologies will not work.
But if we can charge during flight we might only need enough battery storage equivalent to that of the current twin engine ETOPS range.
So if there is a big breakthrough in wireless energy transfer, then heated/cooled pressurised airliners can certainly be a reality.
Will it be mini lightning strikes at set locations like in Back to the Future along flight paths or a more steady continuous charge from lasers tracking the flight from space? I do not have any idea, but I don't expect that a electric powered aircraft will carry "batteries" with the capacity for the entire flight.
As for the height, similar to now I expect.
Wireless Energy Transfer
Telephones use to be fixed to the wall and get its power from that plug, we then had cordless phones that had a battery in the handset and would charge in a cradle at the end of the call. Years later we had "mobile phones" that had a battery pack the size of a brick, these eventually became very small and truly mobile and you plug the charger in once or so a day. Phones then became smart (and bigger again) and use more power again needing plugging into the charge a couple of times a day. From a few years ago many phones do not need to be "plugged" in to charge simply place them on a charging pad.
So it seems a new system will be required for large airliners, as the current battery and fuel cell technologies will not work.
But if we can charge during flight we might only need enough battery storage equivalent to that of the current twin engine ETOPS range.
So if there is a big breakthrough in wireless energy transfer, then heated/cooled pressurised airliners can certainly be a reality.
Will it be mini lightning strikes at set locations like in Back to the Future along flight paths or a more steady continuous charge from lasers tracking the flight from space? I do not have any idea, but I don't expect that a electric powered aircraft will carry "batteries" with the capacity for the entire flight.
As for the height, similar to now I expect.
Wireless Energy Transfer
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The reality of battery power required, storage and recharging comparing a phone, computer or car is not even in the same world in comparison to a 121 jet.
A Tesla battery will take a 3,000 pound car a couple hundred miles or so. To take a hundred thousand pound aircraft to 30,000 feet and a few hours of flight or more requires a huge (heavy) amount of battery power/weight.
Also the ability to recharge or relace the cells for a rather quick turnaround is required. The fact that fuel burn and weight loss makes an aircraft more economic over time is lost on battery powered aircraft as well.
A Tesla battery will take a 3,000 pound car a couple hundred miles or so. To take a hundred thousand pound aircraft to 30,000 feet and a few hours of flight or more requires a huge (heavy) amount of battery power/weight.
Also the ability to recharge or relace the cells for a rather quick turnaround is required. The fact that fuel burn and weight loss makes an aircraft more economic over time is lost on battery powered aircraft as well.
The reality of battery power required, storage and recharging comparing a phone, computer or car is not even in the same world in comparison to a 121 jet.
A Tesla battery will take a 3,000 pound car a couple hundred miles or so. To take a hundred thousand pound aircraft to 30,000 feet and a few hours of flight or more requires a huge (heavy) amount of battery power/weight.
Also the ability to recharge or relace the cells for a rather quick turnaround is required. The fact that fuel burn and weight loss makes an aircraft more economic over time is lost on battery powered aircraft as well.
A Tesla battery will take a 3,000 pound car a couple hundred miles or so. To take a hundred thousand pound aircraft to 30,000 feet and a few hours of flight or more requires a huge (heavy) amount of battery power/weight.
Also the ability to recharge or relace the cells for a rather quick turnaround is required. The fact that fuel burn and weight loss makes an aircraft more economic over time is lost on battery powered aircraft as well.
Although Tesla had the idea of wireless transfer of power on a large magnitude 100ish years ago - he never thought of supplying 10 GW (Many, many, many houses) base load solar power from space 36,000 km away.
A) they will be different batteries than that of now.
B) the take off (launch) of aircraft may be very different - zero power consumed till after take off, dodgem cars or catapult launch or some new thing.
C) The ability to recharge or replace the cells may not be required - they may just be the emergency back up.
D) If your batteries/cells are only back up and are lighter than current fuel burnt to carry such reserve & its weight, fuel then becomes the economic problem to be carried prior to take off in comparison.
F) the phone was a tech advancement example not a power consumption one.
The Japanese a number of years ago now transferred wireless power, enough to boil a kettle with accuracy over 55 meters. That I assume charges a few phones.
https://link.springer.com/article/10...309-018-0139-7
Bend alot: I quite agree that there can be shortsightness. But that cuts both ways. One has to be longsighted enough to see the problems and solve them ahead of time.
A) Will there be new batteries? Very probably. Will they mean compressing more and more joules into smaller and smaller packages? Yep. Three numbers to keep in mind: 7-8-7. Cellphone and laptop batteries have already started small on-board fires, and then there is UPS 6 - brought down by autoignition of a cargo pallet of 81,000 lithium batteries. https://en.wikipedia.org/wiki/UPS_Airlines_Flight_6
B) Good idea - in principle. But - voltage-carrying taxiways? "Third rails" alongside? Overhead wires? We'll assume linear accelerators can be tuned to be less violent than carrier launches.
How much power will "beamed power" beams have to transmit to hold up x-many kilos of aircraft, and x-many kilos of passengers? At what point do they become thousands of directed-energy weapons criss-crossing the skies? https://en.wikipedia.org/wiki/Directed-energy_weapon
Good (longsighted) engineering is not just having a bright idea - it is poking all the holes in that idea yourself, and then figuring out how to plug them.
A) Will there be new batteries? Very probably. Will they mean compressing more and more joules into smaller and smaller packages? Yep. Three numbers to keep in mind: 7-8-7. Cellphone and laptop batteries have already started small on-board fires, and then there is UPS 6 - brought down by autoignition of a cargo pallet of 81,000 lithium batteries. https://en.wikipedia.org/wiki/UPS_Airlines_Flight_6
B) Good idea - in principle. But - voltage-carrying taxiways? "Third rails" alongside? Overhead wires? We'll assume linear accelerators can be tuned to be less violent than carrier launches.
How much power will "beamed power" beams have to transmit to hold up x-many kilos of aircraft, and x-many kilos of passengers? At what point do they become thousands of directed-energy weapons criss-crossing the skies? https://en.wikipedia.org/wiki/Directed-energy_weapon
Good (longsighted) engineering is not just having a bright idea - it is poking all the holes in that idea yourself, and then figuring out how to plug them.
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Dear All
I am skeptical.
But here in Norway we love all electrical , considering we get all our Hydro as they say in Canada, from hydro- electric generators.
And God knows we have enough rain to fill the magazines.
Anyway
Avinor ,the State owned airport owner ( 95% of the public airports) have declared that they support and will aim to have some of the shorthaul TP traffic over on EL operated planes within a short time ( 7- 10 years , I forget).
This has then taken the form of the CEO ,Cpt Falck Pettersen putt putting around in his private EL twoseater , charming any journalist and politician in sight.
I love it!
I think it is some years ahead, but let think Prius!
Been around for ages!
Problems getting it up? Think JATO bottles C130! Or equivalent.What do I know!
I just know that once the need is, there is a way!
After all we had wood fired cars during the war!
Just to stick to what I do know.
My 737 has 7800kg of fuel in the wings AND two wopping big engines that are ca 2500ks each, never to mention all the plumbing and doohickkys that a jet engine needs!
Simply taking a CFM 56-27k with 70% bypass and stuffing in a EL motor with no core thrust gives you close to a 22k derated on. And I am sure that a somewhat more elegant model would take 5 minutes for an Engineer to dream up. Doubtfully done in A and B cafeteria!
So for starter we have ca 10 tons of SALT battery fixed in the wing which gets, say 1 hrs plus IFR reserve.
I am starting to think this is possible.
Helmet On
I am skeptical.
But here in Norway we love all electrical , considering we get all our Hydro as they say in Canada, from hydro- electric generators.
And God knows we have enough rain to fill the magazines.
Anyway
Avinor ,the State owned airport owner ( 95% of the public airports) have declared that they support and will aim to have some of the shorthaul TP traffic over on EL operated planes within a short time ( 7- 10 years , I forget).
This has then taken the form of the CEO ,Cpt Falck Pettersen putt putting around in his private EL twoseater , charming any journalist and politician in sight.
I love it!
I think it is some years ahead, but let think Prius!
Been around for ages!
Problems getting it up? Think JATO bottles C130! Or equivalent.What do I know!
I just know that once the need is, there is a way!
After all we had wood fired cars during the war!
Just to stick to what I do know.
My 737 has 7800kg of fuel in the wings AND two wopping big engines that are ca 2500ks each, never to mention all the plumbing and doohickkys that a jet engine needs!
Simply taking a CFM 56-27k with 70% bypass and stuffing in a EL motor with no core thrust gives you close to a 22k derated on. And I am sure that a somewhat more elegant model would take 5 minutes for an Engineer to dream up. Doubtfully done in A and B cafeteria!
So for starter we have ca 10 tons of SALT battery fixed in the wing which gets, say 1 hrs plus IFR reserve.
I am starting to think this is possible.
Helmet On
Bend alot: I quite agree that there can be shortsightness. But that cuts both ways. One has to be longsighted enough to see the problems and solve them ahead of time.
A) Will there be new batteries? Very probably. Will they mean compressing more and more joules into smaller and smaller packages? Yep. Three numbers to keep in mind: 7-8-7. Cellphone and laptop batteries have already started small on-board fires, and then there is UPS 6 - brought down by autoignition of a cargo pallet of 81,000 lithium batteries. https://en.wikipedia.org/wiki/UPS_Airlines_Flight_6
B) Good idea - in principle. But - voltage-carrying taxiways? "Third rails" alongside? Overhead wires? We'll assume linear accelerators can be tuned to be less violent than carrier launches.
How much power will "beamed power" beams have to transmit to hold up x-many kilos of aircraft, and x-many kilos of passengers? At what point do they become thousands of directed-energy weapons criss-crossing the skies? https://en.wikipedia.org/wiki/Directed-energy_weapon
Good (longsighted) engineering is not just having a bright idea - it is poking all the holes in that idea yourself, and then figuring out how to plug them.
A) Will there be new batteries? Very probably. Will they mean compressing more and more joules into smaller and smaller packages? Yep. Three numbers to keep in mind: 7-8-7. Cellphone and laptop batteries have already started small on-board fires, and then there is UPS 6 - brought down by autoignition of a cargo pallet of 81,000 lithium batteries. https://en.wikipedia.org/wiki/UPS_Airlines_Flight_6
B) Good idea - in principle. But - voltage-carrying taxiways? "Third rails" alongside? Overhead wires? We'll assume linear accelerators can be tuned to be less violent than carrier launches.
How much power will "beamed power" beams have to transmit to hold up x-many kilos of aircraft, and x-many kilos of passengers? At what point do they become thousands of directed-energy weapons criss-crossing the skies? https://en.wikipedia.org/wiki/Directed-energy_weapon
Good (longsighted) engineering is not just having a bright idea - it is poking all the holes in that idea yourself, and then figuring out how to plug them.
B) Maglev or something new.
The thrust required for a set speed to overcome the drag is what is needed to be known, once that is sorted the wings will hopefully hold up x kilos of aircraft and passengers - in a similar way to a conventional aircraft.
I would rather to let the scientists currently working on the "idea" to continue as I am not very good with plugs and they seem better funded than me.
Dear All
I am skeptical.
But here in Norway we love all electrical , considering we get all our Hydro as they say in Canada, from hydro- electric generators.
And God knows we have enough rain to fill the magazines.
Anyway
Avinor ,the State owned airport owner ( 95% of the public airports) have declared that they support and will aim to have some of the shorthaul TP traffic over on EL operated planes within a short time ( 7- 10 years , I forget).
This has then taken the form of the CEO ,Cpt Falck Pettersen putt putting around in his private EL twoseater , charming any journalist and politician in sight.
I love it!
I think it is some years ahead, but let think Prius!
Been around for ages!
Problems getting it up? Think JATO bottles C130! Or equivalent.What do I know!
I just know that once the need is, there is a way!
After all we had wood fired cars during the war!
Just to stick to what I do know.
My 737 has 7800kg of fuel in the wings AND two wopping big engines that are ca 2500ks each, never to mention all the plumbing and doohickkys that a jet engine needs!
Simply taking a CFM 56-27k with 70% bypass and stuffing in a EL motor with no core thrust gives you close to a 22k derated on. And I am sure that a somewhat more elegant model would take 5 minutes for an Engineer to dream up. Doubtfully done in A and B cafeteria!
So for starter we have ca 10 tons of SALT battery fixed in the wing which gets, say 1 hrs plus IFR reserve.
I am starting to think this is possible.
Helmet On
I am skeptical.
But here in Norway we love all electrical , considering we get all our Hydro as they say in Canada, from hydro- electric generators.
And God knows we have enough rain to fill the magazines.
Anyway
Avinor ,the State owned airport owner ( 95% of the public airports) have declared that they support and will aim to have some of the shorthaul TP traffic over on EL operated planes within a short time ( 7- 10 years , I forget).
This has then taken the form of the CEO ,Cpt Falck Pettersen putt putting around in his private EL twoseater , charming any journalist and politician in sight.
I love it!
I think it is some years ahead, but let think Prius!
Been around for ages!
Problems getting it up? Think JATO bottles C130! Or equivalent.What do I know!
I just know that once the need is, there is a way!
After all we had wood fired cars during the war!
Just to stick to what I do know.
My 737 has 7800kg of fuel in the wings AND two wopping big engines that are ca 2500ks each, never to mention all the plumbing and doohickkys that a jet engine needs!
Simply taking a CFM 56-27k with 70% bypass and stuffing in a EL motor with no core thrust gives you close to a 22k derated on. And I am sure that a somewhat more elegant model would take 5 minutes for an Engineer to dream up. Doubtfully done in A and B cafeteria!
So for starter we have ca 10 tons of SALT battery fixed in the wing which gets, say 1 hrs plus IFR reserve.
I am starting to think this is possible.
Helmet On
Engines are around 2,000 kg but extras will be around the 2,500 kg mark.
Less cowling structure to contain a fan blade than a high energy turbine blade would reduce the 2,500 kg mark a vast amount.
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the lower the altitude the higher the drag and the more thrust required. The reason we normally cruise at 30k and above is simple - the reduction in drag means less fuel (energy) is required to fly a given distance...That is simple physics
It is when you consider efficiency of the propulsion system that fuel, as opposed to tiime, may be saved by operating higher. The piston engine works most efficiently with a wide open throttle. Therefore best range for a piston is found at the critical altitude where the torque required for range speed can only just be achieved with a wide open throttle. Meanwhile, for a turbine the best TSFC occurs at about 85% RPM and at the tropopause so that is where you want thrust available to equal thrust required for the cruise.
Clearly, if you go to an electric motor then air density does not affect the motor output. However air density will still impact on the thrust available from the prop. Therefore it seems to me that for public transport, electric aircraft will be limited to the 20-30k altitudes unless ducted fans raise the ceiling.
The simple physics do not support the statement. Max L/D gives range speed at fixed angle of attack, drag, and therefore thrust required, regardless of altitude because as density decreases you have to speed up to get the lift back. End result is lift and drag back to where they started. As TAS is higher, power required is also now higher. Nonetheless you get there in a shorter time proportional to the extra power. Therefore, in terms of drag, you require the same energy at all altitudes. But you save time if at high altitude, which is reason enough to do it.
It is when you consider efficiency of the propulsion system that fuel, as opposed to tiime, may be saved by operating higher. The piston engine works most efficiently with a wide open throttle. Therefore best range for a piston is found at the critical altitude where the torque required for range speed can only just be achieved with a wide open throttle. Meanwhile, for a turbine the best TSFC occurs at about 85% RPM and at the tropopause so that is where you want thrust available to equal thrust required for the cruise.
Clearly, if you go to an electric motor then air density does not affect the motor output. However air density will still impact on the thrust available from the prop. Therefore it seems to me that for public transport, electric aircraft will be limited to the 20-30k altitudes unless ducted fans raise the ceiling.
It is when you consider efficiency of the propulsion system that fuel, as opposed to tiime, may be saved by operating higher. The piston engine works most efficiently with a wide open throttle. Therefore best range for a piston is found at the critical altitude where the torque required for range speed can only just be achieved with a wide open throttle. Meanwhile, for a turbine the best TSFC occurs at about 85% RPM and at the tropopause so that is where you want thrust available to equal thrust required for the cruise.
Clearly, if you go to an electric motor then air density does not affect the motor output. However air density will still impact on the thrust available from the prop. Therefore it seems to me that for public transport, electric aircraft will be limited to the 20-30k altitudes unless ducted fans raise the ceiling.
I will not buy into the rest of your statement other to say "I do not agree" WOT well I will be.
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My bet will be initially a hybrid design, with all engines operating for high drag regimes and in flight shutdown once at cruise condition. We may see a single donk providing generator output for 2 electric propulsion units. This design would lend itself to a return to 3 engines or twin electric, single turbo propulsion, which could also provide pressurisation and heating via heat recovery. The benefits are a much higher propulsive efficiency over jet thrust, operation at design point, heat recovery put to purpose for what would be otherwise wasted energy plus a greater contingency. You could even shut down the propulsion unit and run off of batteries whilst holding! The dawn of geared turbofans lends itself towards this, albeit with much higher gear ratios. The important tech is the ability to handle the enormous torque required to be used to generate electricity for 2 electric propulsion units.
I think all electric is a pipe dream. Too much power required for the likes of pressurisation, heating and ovens to go all electric. We are struggling to get past 100WHr/KG with sulphur battery technology at present so I think hybrid has to be the most likely commercially usable solution. We will still get a significant reduction in CO2 usage.
I think all electric is a pipe dream. Too much power required for the likes of pressurisation, heating and ovens to go all electric. We are struggling to get past 100WHr/KG with sulphur battery technology at present so I think hybrid has to be the most likely commercially usable solution. We will still get a significant reduction in CO2 usage.